          Definition of the Porting Layer for the X v11 Sample Server

   Copyright * 1994 X Consortium, Inc., 2004 X.org Foundation, Inc.

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the
   ``Software''), to deal in the Software without restriction, including
   without limitation the rights to use, copy, modify, merge, publish,
   distribute, sublicense, and/or sell copies of the Software, and to permit
   persons to whom the Software is furnished to do so, subject to the
   following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
   NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   DEALINGS IN THE SOFTWARE.

   LK201 and DEC are trademarks of Digital Equipment Corporation. Macintosh
   and Apple are trademarks of Apple Computer, Inc. PostScript is a trademark
   of Adobe Systems, Inc. Ethernet is a trademark of Xerox Corporation. X
   Window System is a trademark of the X.org Foundation, Inc. Cray is a
   trademark of Cray Research, Inc.

                     Abstract
                     The following document explains the
                     structure of the X Window System
                     display server and the interfaces
                     among the larger pieces. It is
                     intended as a reference for
                     programmers who are implementing an X
                     Display Server on their workstation
                     hardware. It is included with the X
                     Window System source tape, along with
                     the document "Strategies for Porting
                     the X v11 Sample Server." The order
                     in which you should read these
                     documents is:

                      1. Read the first section of the
                         "Strategies for Porting" document
                         (Overview of Porting Process).

                      2. Skim over this document (the
                         Definition document).

                      3. Skim over the remainder of the
                         Strategies document.

                      4. Start planning and working,
                         referring to the Strategies and
                         Definition documents.

                     You may also want to look at the
                     following documents:

                       * "The X Window System" for an
                         overview of X.

                       * "Xlib - C Language X Interface"
                         for a view of what the client
                         programmer sees.

                       * "X Window System Protocol" for a
                         terse description of the byte
                         stream protocol between the
                         client and server.

                     To understand this document and the
                     accompanying source code, you should
                     know the C language. You should be
                     familiar with 2D graphics and
                     windowing concepts such as clipping,
                     bitmaps, fonts, etc. You should have
                     a general knowledge of the X Window
                     System. To implement the server code
                     on your hardware, you need to know a
                     lot about your hardware, its graphic
                     display device(s), and (possibly) its
                     networking and multitasking
                     facilities. This document depends a
                     lot on the source code, so you should
                     have a listing of the code handy.

                     Some source in the distribution is
                     directly compilable on your machine.
                     Some of it will require modification.
                     Other parts may have to be completely
                     written from scratch. The
                     distribution also includes source for
                     a sample implementation of a display
                     server which runs on a very wide
                     variety of color and monochrome
                     displays on Linux and *BSD which you
                     will find useful for implementing any
                     type of X server.

                     Note to the 2004 edition: at this
                     time this document must be considered
                     incomplete. In particular, the new
                     Render extension is still lacking
                     good documentation, and has become
                     vital to high performance X
                     implementations. A new "fb" portable
                     frame buffer graphics library
                     (replacing "cfb") is used by most
                     implementations to implement software
                     rendering for most operations.
                     Accelerating only a few of the old
                     "core" graphics functions is now
                     needed, as performance in software is
                     "good enough" for most operations.
                     Modern applications and desktop
                     environments are now much more
                     sensitive to good implementation of
                     the Render extension than in most
                     operations of the old X graphics
                     model. The shadow frame buffer
                     implementation is also very useful in
                     many circumstances, and also needs
                     documentation. We hope to rectify
                     these shortcomings in our
                     documentation in the future. Help
                     would be greatly appreciated.

            -------------------------------------------------------

   Table of Contents

   [1]The X Window System

   [2]Overview of the Server

   [3]DIX Layer

   [4]OS Layer

   [5]DDX Layer

   [6]Summary of Routines

The X Window System

    The X Window System, or simply "X," is a windowing system that provides
   high-performance, high-level, device-independent graphics.

    X is a windowing system designed for bitmapped graphic displays. The
   display can have a simple, monochrome display or it can have a color
   display with up to 32 bits per pixel with a special graphics processor
   doing the work. (In this document, monochrome means a black and white
   display with one bit per pixel. Even though the usual meaning of
   monochrome is more general, this special case is so common that we decided
   to reserve the word for this purpose.) In practice, monochrome displays
   are now almost unheard of, with 4 bit gray scale displays being the low
   end.

    X is designed for a networking environment where users can run
   applications on machines other than their own workstations. Sometimes, the
   connection is over an Ethernet network with a protocol such as TCP/IP;
   but, any "reliable" byte stream is allowable. A high-bandwidth byte stream
   is preferable; RS-232 at 9600 baud would be slow without compression
   techniques.

    X by itself allows great freedom of design. For instance, it does not
   include any user interface standard. Its intent is to "provide mechanism,
   not policy." By making it general, it can be the foundation for a wide
   variety of interactive software.

    For a more detailed overview, see the document "The X Window System." For
   details on the byte stream protocol, see "X Window System protocol."

   --------------------------------------------------------------------------

Overview of the Server

    The display server manages windows and simple graphics requests for the
   user on behalf of different client applications. The client applications
   can be running on any machine on the network. The server mainly does three
   things:

     * Responds to protocol requests from existing clients (mostly graphic
       and text drawing commands)

     * Sends device input (keystrokes and mouse actions) and other events to
       existing clients

     * Maintains client connections

    The server code is organized into four major pieces:

     * Device Independent (DIX) layer - code shared among all implementations

     * Operating System (OS) layer - code that is different for each
       operating system but is shared among all graphic devices for this
       operating system

     * Device Dependent (DDX) layer - code that is (potentially) different
       for each combination of operating system and graphic device

     * Extension Interface - a standard way to add features to the X server

    The "porting layer" consists of the OS and DDX layers; these are actually
   parallel and neither one is on top of the other. The DIX layer is intended
   to be portable without change to target systems and is not detailed here,
   although several routines in DIX that are called by DDX are documented.
   Extensions incorporate new functionality into the server; and require
   additional functionality over a simple DDX.

    The following sections outline the functions of the layers. Section 3
   briefly tells what you need to know about the DIX layer. The OS layer is
   explained in Section 4. Section 5 gives the theory of operation and
   procedural interface for the DDX layer. Section 6 describes the functions
   which exist for the extension writer.

   --------------------------------------------------------------------------

DIX Layer

    The DIX layer is the machine and device independent part of X. The source
   should be common to all operating systems and devices. The port process
   should not include changes to this part, therefore internal interfaces to
   DIX modules are not discussed, except for public interfaces to the DDX and
   the OS layers. The functions described in this section are available for
   extension writers to use.

    In the process of getting your server to work, if you think that DIX must
   be modified for purposes other than bug fixes, you may be doing something
   wrong. Keep looking for a more compatible solution. When the next release
   of the X server code is available, you should be able to just drop in the
   new DIX code and compile it. If you change DIX, you will have to remember
   what changes you made and will have to change the new sources before you
   can update to the new version.

    The heart of the DIX code is a loop called the dispatch loop. Each time
   the processor goes around the loop, it sends off accumulated input events
   from the input devices to the clients, and it processes requests from the
   clients. This loop is the most organized way for the server to process the
   asynchronous requests that it needs to process. Most of these operations
   are performed by OS and DDX routines that you must supply.

   --------------------------------------------------------------------------

  Server Resource System

    X resources are C structs inside the server. Client applications create
   and manipulate these objects according to the rules of the X byte stream
   protocol. Client applications refer to resources with resource IDs, which
   are 32-bit integers that are sent over the network. Within the server, of
   course, they are just C structs, and we refer to them by pointers.

   --------------------------------------------------------------------------

    Pre-Defined Resource Types

    The DDX layer has several kinds of resources:

     * Window

     * Pixmap

     * Screen

     * Device

     * Colormap

     * Font

     * Cursor

     * Graphics Contexts

    The type names of the more important server structs usually end in "Rec,"
   such as "DeviceRec;" the pointer types usually end in "Ptr," such as
   "DevicePtr."

    The structs and important defined constants are declared in .h files that
   have names that suggest the name of the object. For instance, there are
   two .h files for windows, window.h and windowstr.h. window.h defines only
   what needs to be defined in order to use windows without peeking inside of
   them; windowstr.h defines the structs with all of their components in
   great detail for those who need it.

    Three kinds of fields are in these structs:

     * Attribute fields - struct fields that contain values like normal
       structs

     * Pointers to procedures, or structures of procedures, that operate on
       the object

     * A private field (or two) used by your DDX code to keep private data
       (probably a pointer to another data structure), or an array of private
       fields, which is sized as the server initializes.

    DIX calls through the struct's procedure pointers to do its tasks. These
   procedures are set either directly or indirectly by DDX procedures. Most
   of the procedures described in the remainder of this document are accessed
   through one of these structs. For example, the procedure to create a
   pixmap is attached to a ScreenRec and might be called by using the
   expression



     (* pScreen->CreatePixmap)(pScreen, width, height, depth).

    All procedure pointers must be set to some routine unless noted
   otherwise; a null pointer will have unfortunate consequences.

    Procedure routines will be indicated in the documentation by this
   convention:

     void pScreen->MyScreenRoutine(arg, arg, ...)

   as opposed to a free routine, not in a data structure:

     void MyFreeRoutine(arg, arg, ...)

    The attribute fields are mostly set by DIX; DDX should not modify them
   unless noted otherwise.

   --------------------------------------------------------------------------

    Creating Resources and Resource Types

    These functions should also be called from your extensionInitProc to
   allocate all of the various resource classes and types required for the
   extension. Each time the server resets, these types must be reallocated as
   the old allocations will have been discarded. Resource types are integer
   values starting at 1. Get a resource type by calling

         RESTYPE CreateNewResourceType(deleteFunc)

   deleteFunc will be called to destroy all resources with this type.

    Resource classes are masks starting at 1 << 31 which can be or'ed with
   any resource type to provide attributes for the type. To allocate a new
   class bit, call

         RESTYPE CreateNewResourceClass()

    There are two ways of looking up resources, by type or by class. Classes
   are non-exclusive subsets of the space of all resources, so you can lookup
   the union of multiple classes. (RC_ANY is the union of all classes).

    Note that the appropriate class bits must be or'ed into the value
   returned by CreateNewResourceType when calling resource lookup functions.

    If you need to create a ``private'' resource ID for internal use, you can
   call FakeClientID.

             XID FakeClientID(client)
                 int client;

   This allocates from ID space reserved for the server.

    To associate a resource value with an ID, use AddResource.

             Bool AddResource(id, type, value)
                 XID id;
                 RESTYPE type;
                 pointer value;

   The type should be the full type of the resource, including any class
   bits. If AddResource fails to allocate memory to store the resource, it
   will call the deleteFunc for the type, and then return False.

    To free a resource, use one of the following.

             void FreeResource(id, skipDeleteFuncType)
                 XID id;
                 RESTYPE skipDeleteFuncType;

             void FreeResourceByType(id, type, skipFree)
                 XID id;
                 RESTYPE type;
                 Bool    skipFree;

   FreeResource frees all resources matching the given id, regardless of
   type; the type's deleteFunc will be called on each matching resource,
   except that skipDeleteFuncType can be set to a single type for which the
   deleteFunc should not be called (otherwise pass RT_NONE).
   FreeResourceByType frees a specific resource matching a given id and type;
   if skipFree is true, then the deleteFunc is not called.

   --------------------------------------------------------------------------

    Looking Up Resources

    To look up a resource, use one of the following.

             pointer LookupIDByType(id, rtype)
                 XID id;
                 RESTYPE rtype;

             pointer LookupIDByClass(id, classes)
                 XID id;
                 RESTYPE classes;

   LookupIDByType finds a resource with the given id and exact type.
   LookupIDByClass finds a resource with the given id whose type is included
   in any one of the specified classes.

   --------------------------------------------------------------------------

  Callback Manager

    To satisfy a growing number of requests for the introduction of ad hoc
   notification style hooks in the server, a generic callback manager was
   introduced in R6. A callback list object can be introduced for each new
   hook that is desired, and other modules in the server can register
   interest in the new callback list. The following functions support these
   operations.

    Before getting bogged down in the interface details, an typical usage
   example should establish the framework. Let's look at the
   ClientStateCallback in dix/dispatch.c. The purpose of this particular
   callback is to notify intereseted parties when a client's state (initial,
   running, gone) changes. The callback is "created" in this case by simply
   declaring a variable:

             CallbackListPtr ClientStateCallback;

    Whenever the client's state changes, the following code appears, which
   notifies all intereseted parties of the change:

        if (ClientStateCallback) CallCallbacks(&ClientStateCallback, (pointer)client);

    Interested parties subscribe to the ClientStateCallback list by saying:

             AddCallback(&ClientStateCallback, func, data);

    When CallCallbacks is invoked on the list, func will be called thusly:

             (*func)(&ClientStateCallback, data, client)

    Now for the details.

             Bool CreateCallbackList(pcbl, cbfuncs)
                 CallbackListPtr  *pcbl;
                 CallbackFuncsPtr cbfuncs;

   CreateCallbackList creates a callback list. We envision that this function
   will be rarely used because the callback list is created automatically (if
   it doesn't already exist) when the first call to AddCallback is made on
   the list. The only reason to explicitly create the callback list with this
   function is if you want to override the implementation of some of the
   other operations on the list by passing your own cbfuncs. You also lose
   something by explicit creation: you introduce an order dependency during
   server startup because the list must be created before any modules
   subscribe to it. Returns TRUE if successful.



             Bool AddCallback(pcbl, callback, subscriber_data)
                 CallbackListPtr *pcbl;
                 CallbackProcPtr callback;
                 pointer         subscriber_data;


   Adds the (callback, subscriber_data) pair to the given callback list.
   Creates the callback list if it doesn't exist. Returns TRUE if successful.



             Bool DeleteCallback(pcbl, callback, subscriber_data)
                 CallbackListPtr *pcbl;
                 CallbackProcPtr callback;
                 pointer         subscriber_data;

   Removes the (callback, data) pair to the given callback list if present.
   Returns TRUE if (callback, data) was found.



             void CallCallbacks(pcbl, call_data)
                 CallbackListPtr    *pcbl;
                 pointer         call_data;

   For each callback currently registered on the given callback list, call it
   as follows:

             (*callback)(pcbl, subscriber_data, call_data);



             void DeleteCallbackList(pcbl)
                 CallbackListPtr    *pcbl;

   Destroys the given callback list.

   --------------------------------------------------------------------------

  Extension Interfaces

    This function should be called from your extensionInitProc which should
   be called by InitExtensions.

        ExtensionEntry *AddExtension(name, NumEvents,NumErrors,
                MainProc, SwappedMainProc, CloseDownProc, MinorOpcodeProc)

                char *name;  /*Null terminate string; case matters*/
                int NumEvents;
                int NumErrors;
                int (* MainProc)(ClientPtr);/*Called if client matches server order*/
                int (* SwappedMainProc)(ClientPtr);/*Called if client differs from server*/
                void (* CloseDownProc)(ExtensionEntry *);
                unsigned short (*MinorOpcodeProc)(ClientPtr);

   name is the name used by clients to refer to the extension. NumEvents is
   the number of event types used by the extension, NumErrors is the number
   of error codes needed by the extension. MainProc is called whenever a
   client accesses the major opcode assigned to the extension.
   SwappedMainProc is identical, except the client using the extension has
   reversed byte-sex. CloseDownProc is called at server reset time to
   deallocate any private storage used by the extension. MinorOpcodeProc is
   used by DIX to place the appropriate value into errors. The DIX routine
   StandardMinorOpcode can be used here which takes the minor opcode from the
   normal place in the request (i.e. just after the major opcode).

   --------------------------------------------------------------------------

  Macros and Other Helpers

    There are a number of macros in Xserver/include/dix.h which are useful to
   the extension writer. Ones of particular interest are: REQUEST,
   REQUEST_SIZE_MATCH, REQUEST_AT_LEAST_SIZE, REQUEST_FIXED_SIZE,
   LEGAL_NEW_RESOURCE, LOOKUP_DRAWABLE, VERIFY_GC, and
   VALIDATE_DRAWABLE_AND_GC. Useful byte swapping macros can be found in
   Xserver/include/misc.h: lswapl, lswaps, LengthRestB, LengthRestS,
   LengthRestL, SwapRestS, SwapRestL, swapl, swaps, cpswapl, and cpswaps.

   --------------------------------------------------------------------------

OS Layer

    This part of the source consists of a few routines that you have to
   rewrite for each operating system. These OS functions maintain the client
   connections and schedule work to be done for clients. They also provide an
   interface to font files, font name to file name translation, and low level
   memory management.

     void OsInit()

   OsInit initializes your OS code, performing whatever tasks need to be
   done. Frequently there is not much to be done. The sample server
   implementation is in Xserver/os/osinit.c.

   --------------------------------------------------------------------------

  Scheduling and Request Delivery

    The main dispatch loop in DIX creates the illusion of multitasking
   between different windows, while the server is itself but a single
   process. The dispatch loop breaks up the work for each client into small
   digestible parts. Some parts are requests from a client, such as
   individual graphic commands. Some parts are events delivered to the
   client, such as keystrokes from the user. The processing of events and
   requests for different clients can be interleaved with one another so true
   multitasking is not needed in the server.

    You must supply some of the pieces for proper scheduling between clients.

             int WaitForSomething(pClientReady)
                     int *pClientReady;

    WaitForSomething is the scheduler procedure you must write that will
   suspend your server process until something needs to be done. This call
   should make the server suspend until one or more of the following occurs:

     * There is an input event from the user or hardware (see
       SetInputCheck())

     * There are requests waiting from known clients, in which case you
       should return a count of clients stored in pClientReady

     * A new client tries to connect, in which case you should create the
       client and then continue waiting

    Before WaitForSomething() computes the masks to pass to select, poll or
   similar operating system interface, it needs to see if there is anything
   to do on the work queue; if so, it must call a DIX routine called
   ProcessWorkQueue.

             extern WorkQueuePtr     workQueue;

             if (workQueue)
                     ProcessWorkQueue ();

    If WaitForSomething() decides it is about to do something that might
   block (in the sample server, before it calls select() or poll) it must
   call a DIX routine called BlockHandler().

             void BlockHandler(pTimeout, pReadmask)
                     pointer pTimeout;
                     pointer pReadmask;

   The types of the arguments are for agreement between the OS and DDX
   implementations, but the pTimeout is a pointer to the information
   determining how long the block is allowed to last, and the pReadmask is a
   pointer to the information describing the descriptors that will be waited
   on.

    In the sample server, pTimeout is a struct timeval **, and pReadmask is
   the address of the select() mask for reading.

    The DIX BlockHandler() iterates through the Screens, for each one calling
   its BlockHandler. A BlockHandler is declared thus:

             void xxxBlockHandler(nscreen, pbdata, pptv, pReadmask)
                     int nscreen;
                     pointer pbdata;
                     struct timeval ** pptv;
                     pointer pReadmask;

   The arguments are the index of the Screen, the blockData field of the
   Screen, and the arguments to the DIX BlockHandler().

    Immediately after WaitForSomething returns from the block, even if it
   didn't actually block, it must call the DIX routine WakeupHandler().

             void WakeupHandler(result, pReadmask)
                     int result;
                     pointer pReadmask;

   Once again, the types are not specified by DIX. The result is the success
   indicator for the thing that (may have) blocked, and the pReadmask is a
   mask of the descriptors that came active. In the sample server, result is
   the result from select() (or equivalent operating system function), and
   pReadmask is the address of the select() mask for reading.

    The DIX WakeupHandler() calls each Screen's WakeupHandler. A
   WakeupHandler is declared thus:

             void xxxWakeupHandler(nscreen, pbdata, err, pReadmask)
                     int nscreen;
                     pointer pbdata;
                     unsigned long result;
                     pointer pReadmask;

   The arguments are the index of the Screen, the blockData field of the
   Screen, and the arguments to the DIX WakeupHandler().

    In addition to the per-screen BlockHandlers, any module may register
   block and wakeup handlers (only together) using:

        Bool RegisterBlockAndWakeupHandlers (blockHandler, wakeupHandler, blockData)
                BlockHandlerProcPtr    blockHandler;
                WakeupHandlerProcPtr   wakeupHandler;
                pointer blockData;

   A FALSE return code indicates that the registration failed for lack of
   memory. To remove a registered Block handler at other than server reset
   time (when they are all removed automatically), use:

           RemoveBlockAndWakeupHandlers (blockHandler, wakeupHandler, blockData)
                   BlockHandlerProcPtr   blockHandler;
                   WakeupHandlerProcPtr  wakeupHandler;
                   pointer blockData;

   All three arguments must match the values passed to
   RegisterBlockAndWakeupHandlers.

    These registered block handlers are called after the per-screen handlers:

             void (*BlockHandler) (blockData, pptv, pReadmask)
                     pointer blockData;
                     OSTimePtr pptv;
                     pointer pReadmask;

    Sometimes block handlers need to adjust the time in a OSTimePtr
   structure, which on UNIX family systems is generally represented by a
   struct timeval consisting of seconds and microseconds in 32 bit values. As
   a convenience to reduce error prone struct timeval computations which
   require modulus arithmetic and correct overflow behavior in the face of
   millisecond wrapping throrugh 32 bits,

        void AdjustWaitForDelay(pointer /*waitTime*, unsigned long /* newdelay */)

   has been provided.

    Any wakeup handlers registered with RegisterBlockAndWakeupHandlers will
   be called before the Screen handlers:

             void (*WakeupHandler) (blockData, err, pReadmask)
                     pointer blockData;
                     int err;
                     pointer pReadmask;

    The WaitForSomething on the sample server also has a built in screen
   saver that darkens the screen if no input happens for a period of time.
   The sample server implementation is in Xserver/os/WaitFor.c.

    Note that WaitForSomething() may be called when you already have several
   outstanding things (events, requests, or new clients) queued up. For
   instance, your server may have just done a large graphics request, and it
   may have been a long time since WaitForSomething() was last called. If
   many clients have lots of requests queued up, DIX will only service some
   of them for a given client before going on to the next client (see
   isItTimeToYield, below). Therefore, WaitForSomething() will have to report
   that these same clients still have requests queued up the next time
   around.

    An implementation should return information on as many outstanding things
   as it can. For instance, if your implementation always checks for client
   data first and does not report any input events until there is no client
   data left, your mouse and keyboard might get locked out by an application
   that constantly barrages the server with graphics drawing requests.
   Therefore, as a general rule, input devices should always have priority
   over graphics devices.

    A list of indexes (client->index) for clients with data ready to be read
   or processed should be returned in pClientReady, and the count of indexes
   returned as the result value of the call. These are not clients that have
   full requests ready, but any clients who have any data ready to be read or
   processed. The DIX dispatcher will process requests from each client in
   turn by calling ReadRequestFromClient(), below.

    WaitForSomething() must create new clients as they are requested (by
   whatever mechanism at the transport level). A new client is created by
   calling the DIX routine:

             ClientPtr NextAvailableClient(ospriv)
                     pointer ospriv;

   This routine returns NULL if a new client cannot be allocated (e.g.
   maximum number of clients reached). The ospriv argument will be stored
   into the OS private field (pClient->osPrivate), to store OS private
   information about the client. In the sample server, the osPrivate field
   contains the number of the socket for this client. See also "New Client
   Connections." NextAvailableClient() will call InsertFakeRequest(), so you
   must be prepared for this.

    If there are outstanding input events, you should make sure that the two
   SetInputCheck() locations are unequal. The DIX dispatcher will call your
   implementation of ProcessInputEvents() until the SetInputCheck() locations
   are equal.

    The sample server contains an implementation of WaitForSomething(). The
   following two routines indicate to WaitForSomething() what devices should
   be waited for. fd is an OS dependent type; in the sample server it is an
   open file descriptor.

             int AddEnabledDevice(fd)
                     int fd;

             int RemoveEnabledDevice(fd)
                     int fd;

   These two routines are usually called by DDX from the initialize cases of
   the Input Procedures that are stored in the DeviceRec (the routine passed
   to AddInputDevice()). The sample server implementation of AddEnabledDevice
   and RemoveEnabledDevice are in Xserver/os/connection.c.

   --------------------------------------------------------------------------

    Timer Facilities

    Similarly, the X server or an extension may need to wait for some
   timeout. Early X releases implemented this functionality using block and
   wakeup handlers, but this has been rewritten to use a general timer
   facilty, and the internal screen saver facilties reimplemented to use
   Timers. These functions are TimerInit, TimerForce, TimerSet, TimerCheck,
   TimerCancel, and TimerFree, as defined in Xserver/include/os.h. A callback
   function will be called when the timer fires, along with the current time,
   and a user provided argument.

             typedef struct _OsTimerRec *OsTimerPtr;

             typedef CARD32 (*OsTimerCallback)(
                     OsTimerPtr /* timer */,
                     CARD32 /* time */,
                     pointer /* arg */);

              OsTimerPtr TimerSet( OsTimerPtr /* timer */,
                     int /* flags */,
                     CARD32 /* millis */,
                     OsTimerCallback /* func */,
                     pointer /* arg */);

    TimerSet returns a pointer to a timer structure and sets a timer to the
   specified time with the specified argument. The flags can be TimerAbsolute
   and TimerForceOld. The TimerSetOld flag controls whether if the timer is
   reset and the timer is pending, the whether the callback function will get
   called. The TimerAbsolute flag sets the callback time to an absolute time
   in the future rather than a time relative to when TimerSet is called.
   TimerFree should be called to free the memory allocated for the timer
   entry.

             void TimerInit(void)

             Bool TimerForce(OsTimerPtr /* pTimer */)

             void TimerCheck(void);

             void TimerCancel(OsTimerPtr /* pTimer */)

             void TimerFree(OSTimerPtr /* pTimer */)

    TimerInit frees any exisiting timer entries. TimerForce forces a call to
   the timer's callback function and returns true if the timer entry existed,
   else it returns false and does not call the callback function. TimerCancel
   will cancel the specified timer. TimerFree calls TimerCancel and frees the
   specified timer. Calling TimerCheck will force the server to see if any
   timer callbacks should be called.

   --------------------------------------------------------------------------

  New Client Connections

    The process whereby a new client-server connection starts up is very
   dependent upon what your byte stream mechanism. This section describes
   byte stream initiation using examples from the TCP/IP implementation on
   the sample server.

    The first thing that happens is a client initiates a connection with the
   server. How a client knows to do this depends upon your network facilities
   and the Xlib implementation. In a typical scenario, a user named Fred on
   his X workstation is logged onto a Cray supercomputer running a command
   shell in an X window. Fred can type shell commands and have the Cray
   respond as though the X server were a dumb terminal. Fred types in a
   command to run an X client application that was linked with Xlib. Xlib
   looks at the shell environment variable DISPLAY, which has the value
   "fredsbittube:0.0." The host name of Fred's workstation is "fredsbittube,"
   and the 0s are for multiple screens and multiple X server processes.
   (Precisely what happens on your system depends upon how X and Xlib are
   implemented.)

    The client application calls a TCP routine on the Cray to open a TCP
   connection for X to communicate with the network node "fredsbittube." The
   TCP software on the Cray does this by looking up the TCP address of
   "fredsbittube" and sending an open request to TCP port 6000 on
   fredsbittube.

    All X servers on TCP listen for new clients on port 6000 by default; this
   is known as a "well-known port" in IP terminology.

    The server receives this request from its port 6000 and checks where it
   came from to see if it is on the server's list of "trustworthy" hosts to
   talk to. Then, it opens another port for communications with the client.
   This is the byte stream that all X communications will go over.

    Actually, it is a bit more complicated than that. Each X server process
   running on the host machine is called a "display." Each display can have
   more than one screen that it manages. "corporatehydra:3.2" represents
   screen 2 on display 3 on the multi-screened network node corporatehydra.
   The open request would be sent on well-known port number 6003.

    Once the byte stream is set up, what goes on does not depend very much
   upon whether or not it is TCP. The client sends an xConnClientPrefix
   struct (see Xproto.h) that has the version numbers for the version of Xlib
   it is running, some byte-ordering information, and two character strings
   used for authorization. If the server does not like the authorization
   strings or the version numbers do not match within the rules, or if
   anything else is wrong, it sends a failure response with a reason string.

    If the information never comes, or comes much too slowly, the connection
   should be broken off. You must implement the connection timeout. The
   sample server implements this by keeping a timestamp for each
   still-connecting client and, each time just before it attempts to accept
   new connections, it closes any connection that are too old. The connection
   timeout can be set from the command line.

    You must implement whatever authorization schemes you want to support.
   The sample server on the distribution tape supports a simple authorization
   scheme. The only interface seen by DIX is:

            char *
            ClientAuthorized(client, proto_n, auth_proto, string_n, auth_string)
                ClientPtr client;
                unsigned int proto_n;
                char *auth_proto;
                unsigned int string_n;
                char *auth_string;

   DIX will only call this once per client, once it has read the full initial
   connection data from the client. If the connection should be accepted
   ClientAuthorized() should return NULL, and otherwise should return an
   error message string.

    Accepting new connections happens internally to WaitForSomething().
   WaitForSomething() must call the DIX routine NextAvailableClient() to
   create a client object. Processing of the initial connection data will be
   handled by DIX. Your OS layer must be able to map from a client to
   whatever information your OS code needs to communicate on the given byte
   stream to the client. DIX uses this ClientPtr to refer to the client from
   now on. The sample server uses the osPrivate field in the ClientPtr to
   store the file descriptor for the socket, the input and output buffers,
   and authorization information.

    To initialize the methods you choose to allow clients to connect to your
   server, main() calls the routine

             void CreateWellKnownSockets()

   This routine is called only once, and not called when the server is reset.
   To recreate any sockets during server resets, the following routine is
   called from the main loop:

             void ResetWellKnownSockets()

   Sample implementations of both of these routines are found in
   Xserver/os/connection.c.

    For more details, see the section called "Connection Setup" in the X
   protocol specification.

   --------------------------------------------------------------------------

  Reading Data from Clients

    Requests from the client are read in as a byte stream by the OS layer.
   They may be in the form of several blocks of bytes delivered in sequence;
   requests may be broken up over block boundaries or there may be many
   requests per block. Each request carries with it length information. It is
   the responsibility of the following routine to break it up into request
   blocks.

             int ReadRequestFromClient(who)
                     ClientPtr who;

    You must write the routine ReadRequestFromClient() to get one request
   from the byte stream belonging to client "who." You must swap the third
   and fourth bytes (the second 16-bit word) according to the byte-swap rules
   of the protocol to determine the length of the request. This length is
   measured in 32-bit words, not in bytes. Therefore, the theoretical maximum
   request is 256K. (However, the maximum length allowed is dependent upon
   the server's input buffer. This size is sent to the client upon
   connection. The maximum size is the constant MAX_REQUEST_SIZE in
   Xserver/include/os.h) The rest of the request you return is assumed NOT to
   be correctly swapped for internal use, because that is the responsibility
   of DIX.

    The 'who' argument is the ClientPtr returned from WaitForSomething. The
   return value indicating status should be set to the (positive) byte count
   if the read is successful, 0 if the read was blocked, or a negative error
   code if an error happened.

    You must then store a pointer to the bytes of the request in the client
   request buffer field; who->requestBuffer. This can simply be a pointer
   into your buffer; DIX may modify it in place but will not otherwise cause
   damage. Of course, the request must be contiguous; you must shuffle it
   around in your buffers if not.

    The sample server implementation is in Xserver/os/io.c.

   --------------------------------------------------------------------------

    Inserting Data for Clients

    DIX can insert data into the client stream, and can cause a "replay" of
   the current request.

             Bool InsertFakeRequest(client, data, count)
                 ClientPtr client;
                 char *data;
                 int count;

             int ResetCurrentRequest(client)
                 ClientPtr client;

    InsertFakeRequest() must insert the specified number of bytes of data
   into the head of the input buffer for the client. This may be a complete
   request, or it might be a partial request. For example,
   NextAvailableCient() will insert a partial request in order to read the
   initial connection data sent by the client. The routine returns FALSE if
   memory could not be allocated. ResetCurrentRequest() should "back up" the
   input buffer so that the currently executing request will be reexecuted.
   DIX may have altered some values (e.g. the overall request length), so you
   must recheck to see if you still have a complete request.
   ResetCurrentRequest() should always cause a yield (isItTimeToYield).

   --------------------------------------------------------------------------

  Sending Events, Errors And Replies To Clients



             int WriteToClient(who, n, buf)
                     ClientPtr who;
                     int n;
                     char *buf;

   WriteToClient should write n bytes starting at buf to the ClientPtr "who".
   It returns the number of bytes written, but for simplicity, the number
   returned must be either the same value as the number requested, or -1,
   signaling an error. The sample server implementation is in
   Xserver/os/io.c.



          void SendErrorToClient(client, majorCode, minorCode, resId, errorCode)
              ClientPtr client;
              unsigned int majorCode;
              unsigned int minorCode;
              XID resId;
              int errorCode;

   SendErrorToClient can be used to send errors back to clients, although in
   most cases your request function should simply return the error code,
   having set client->errorValue to the appropriate error value to return to
   the client, and DIX will call this function with the correct opcodes for
   you.



             void FlushAllOutput()

             void FlushIfCriticalOutputPending()

             void SetCriticalOutputPending()

   These three routines may be implemented to support buffered or delayed
   writes to clients, but at the very least, the stubs must exist.
   FlushAllOutput() unconditionally flushes all output to clients;
   FlushIfCriticalOutputPending() flushes output only if
   SetCriticalOutputPending() has be called since the last time output was
   flushed. The sample server implementation is in Xserver/os/io.c and
   actually ignores requests to flush output on a per-client basis if it
   knows that there are requests in that client's input queue.

   --------------------------------------------------------------------------

  Font Support

    In the sample server, fonts are encoded in disk files or fetched from the
   font server. For disk fonts, there is one file per font, with a file name
   like "fixed.pcf". Font server fonts are read over the network using the X
   Font Server Protocol. The disk directories containing disk fonts and the
   names of the font servers are listed together in the current "font path."

    In principle, you can put all your fonts in ROM or in RAM in your server.
   You can put them all in one library file on disk. You could generate them
   on the fly from stroke descriptions. By placing the appropriate code in
   the Font Library, you will automatically export fonts in that format both
   through the X server and the Font server.

    With the incorporation of font-server based fonts and the Speedo donation
   from Bitstream, the font interfaces have been moved into a separate
   library, now called the Font Library (../fonts/lib). These routines are
   shared between the X server and the Font server, so instead of this
   document specifying what you must implement, simply refer to the font
   library interface specification for the details. All of the interface code
   to the Font library is contained in dix/dixfonts.c

   --------------------------------------------------------------------------

  Memory Management

    Memory management is based on functions in the C runtime library.
   Xalloc(), Xrealloc(), and Xfree() work just like malloc(), realloc(), and
   free(), except that you can pass a null pointer to Xrealloc() to have it
   allocate anew or pass a null pointer to Xfree() and nothing will happen.
   The versions in the sample server also do some checking that is useful for
   debugging. Consult a C runtime library reference manual for more details.

    The macros ALLOCATE_LOCAL and DEALLOCATE_LOCAL are provided in
   Xserver/include/os.h. These are useful if your compiler supports alloca()
   (or some method of allocating memory from the stack); and are defined
   appropriately on systems which support it.

    Treat memory allocation carefully in your implementation. Memory leaks
   can be very hard to find and are frustrating to a user. An X server could
   be running for days or weeks without being reset, just like a regular
   terminal. If you leak a few dozen k per day, that will add up and will
   cause problems for users that leave their workstations on.

   --------------------------------------------------------------------------

  Client Scheduling

    The X server has the ability to schedule clients much like an operating
   system would, suspending and restarting them without regard for the state
   of their input buffers. This functionality allows the X server to suspend
   one client and continue processing requests from other clients while
   waiting for a long-term network activity (like loading a font) before
   continuing with the first client.

             Bool isItTimeToYield;

   isItTimeToYield is a global variable you can set if you want to tell DIX
   to end the client's "time slice" and start paying attention to the next
   client. After the current request is finished, DIX will move to the next
   client.

    In the sample server, ReadRequestFromClient() sets isItTimeToYield after
   10 requests packets in a row are read from the same client.

    This scheduling algorithm can have a serious effect upon performance when
   two clients are drawing into their windows simultaneously. If it allows
   one client to run until its request queue is empty by ignoring
   isItTimeToYield, the client's queue may in fact never empty and other
   clients will be blocked out. On the other hand, if it switchs between
   different clients too quickly, performance may suffer due to too much
   switching between contexts. For example, if a graphics processor needs to
   be set up with drawing modes before drawing, and two different clients are
   drawing with different modes into two different windows, you may switch
   your graphics processor modes so often that performance is impacted.

    See the Strategies document for heuristics on setting isItTimeToYield.

    The following functions provide the ability to suspend request processing
   on a particular client, resuming it at some later time:

             int IgnoreClient (who)
                     ClientPtr who;

             int AttendClient (who)
                     ClientPtr who;

   Ignore client is responsible for pretending that the given client doesn't
   exist. WaitForSomething should not return this client as ready for reading
   and should not return if only this client is ready. AttendClient undoes
   whatever IgnoreClient did, setting it up for input again.

    Three functions support "process control" for X clients:

             Bool ClientSleep (client, function, closure)
                     ClientPtr       client;
                     Bool            (*function)();
                     pointer         closure;

   This suspends the current client (the calling routine is responsible for
   making its way back to Dispatch()). No more X requests will be processed
   for this client until ClientWakeup is called.

             Bool ClientSignal (client)
                     ClientPtr       client;

   This function causes a call to the (*function) parameter passed to
   ClientSleep to be queued on the work queue. This does not automatically
   "wakeup" the client, but the function called is free to do so by calling:

             ClientWakeup (client)
                     ClientPtr       client;

   This re-enables X request processing for the specified client.

   --------------------------------------------------------------------------

  Other OS Functions



             void
             ErrorF(char *f, ...)

             void
             FatalError(char *f, ...)

             void
             Error(str)
                 char *str;

   You should write these three routines to provide for diagnostic output
   from the dix and ddx layers, although implementing them to produce no
   output will not affect the correctness of your server. ErrorF() and
   FatalError() take a printf() type of format specification in the first
   argument and an implementation-dependent number of arguments following
   that. Normally, the formats passed to ErrorF() and FatalError() should be
   terminated with a newline. Error() provides an os interface for printing
   out the string passed as an argument followed by a meaningful explanation
   of the last system error. Normally the string does not contain a newline,
   and it is only called by the ddx layer. In the sample implementation,
   Error() uses the perror() function.

    After printing the message arguments, FatalError() must be implemented
   such that the server will call AbortDDX() to give the ddx layer a chance
   to reset the hardware, and then terminate the server; it must not return.

    The sample server implementation for these routines is in
   Xserver/os/util.c.

   --------------------------------------------------------------------------

  Idiom Support

    The DBE specification introduces the notion of idioms, which are groups
   of X requests which can be executed more efficiently when taken as a whole
   compared to being performed individually and sequentially. This following
   server internal support to allows DBE implementations, as well as other
   parts of the server, to do idiom processing.



           xReqPtr PeekNextRequest(xReqPtr req, ClientPtr client, Bool readmore)

   If req is NULL, the return value will be a pointer to the start of the
   complete request that follows the one currently being executed for the
   client. If req is not NULL, the function assumes that req is a pointer to
   a request in the client's request buffer, and the return value will be a
   pointer to the the start of the complete request that follows req. If the
   complete request is not available, the function returns NULL; pointers to
   partial requests will never be returned. If (and only if) readmore is
   TRUE, PeekNextRequest should try to read an additional request from the
   client if one is not already available in the client's request buffer. If
   PeekNextRequest reads more data into the request buffer, it should not
   move or change the existing data.



             void SkipRequests(xReqPtr req, ClientPtr client, int numskipped)

   The requests for the client up to and including the one specified by req
   will be skipped. numskipped must be the number of requests being skipped.
   Normal request processing will resume with the request that follows req.
   The caller must not have modified the contents of the request buffer in
   any way (e.g., by doing byte swapping in place).

    Additionally, two macros in os.h operate on the xReq pointer returned by
   PeekNextRequest:

             int ReqLen(xReqPtr req, ClientPtr client)

   The value of ReqLen is the request length in bytes of the given xReq.

             otherReqTypePtr CastxReq(xReq *req, otherReqTypePtr)

   The value of CastxReq is the conversion of the given request pointer to an
   otherReqTypePtr (which should be a pointer to a protocol structure type).
   Only those fields which come after the length field of otherReqType may be
   accessed via the returned pointer.

    Thus the first two fields of a request, reqType and data, can be accessed
   directly using the xReq * returned by PeekNextRequest. The next field, the
   length, can be accessed with ReqLen. Fields beyond that can be accessed
   with CastxReq. This complexity was necessary because of the reencoding of
   core protocol that can happen due to the BigRequests extension.

   --------------------------------------------------------------------------

DDX Layer

    This section describes the interface between DIX and DDX. While there may
   be an OS-dependent driver interface between DDX and the physical device,
   that interface is left to the DDX implementor and is not specified here.

    The DDX layer does most of its work through procedures that are pointed
   to by different structs. As previously described, the behavior of these
   resources is largely determined by these procedure pointers. Most of these
   routines are for graphic display on the screen or support functions
   thereof. The rest are for user input from input devices.

   --------------------------------------------------------------------------

  Input

    In this document "input" refers to input from the user, such as mouse,
   keyboard, and bar code readers. X input devices are of several types:
   keyboard, pointing device, and many others. The core server has support
   for extension devices as described by the X Input Extension document; the
   interfaces used by that extension are described elsewhere. The core
   devices are actually implemented as two collections of devices, the mouse
   is a ButtonDevice, a ValuatorDevice and a PtrFeedbackDevice while the
   keyboard is a KeyDevice, a FocusDevice and a KbdFeedbackDevice. Each part
   implements a portion of the functionality of the device. This abstraction
   is hidden from view for core devices by DIX.

    You, the DDX programmer, are responsible for some of the routines in this
   section. Others are DIX routines that you should call to do the things you
   need to do in these DDX routines. Pay attention to which is which.

   --------------------------------------------------------------------------

    Input Device Data Structures

    DIX keeps a global directory of devices in a central data structure
   called InputInfo. For each device there is a device structure called a
   DeviceRec. DIX can locate any DeviceRec through InputInfo. In addition, it
   has a special pointer to identify the main pointing device and a special
   pointer to identify the main keyboard.

    The DeviceRec (Xserver/include/input.h) is a device-independent structure
   that contains the state of an input device. A DevicePtr is simply a
   pointer to a DeviceRec.

    An xEvent describes an event the server reports to a client. Defined in
   Xproto.h, it is a huge struct of union of structs that have fields for all
   kinds of events. All of the variants overlap, so that the struct is
   actually very small in memory.

   --------------------------------------------------------------------------

    Processing Events

    The main DDX input interface is the following routine:

             void ProcessInputEvents()

   You must write this routine to deliver input events from the user. DIX
   calls it when input is pending (see next section), and possibly even when
   it is not. You should write it to get events from each device and deliver
   the events to DIX. To deliver the events to DIX, DDX should call the
   following routine:

             void DevicePtr->processInputProc(pEvent, device, count)
                         xEventPtr events;
                         DeviceIntPtr device;
                         int count;

   This is the "input proc" for the device, a DIX procedure. DIX will fill in
   this procedure pointer to one of its own routines by the time
   ProcessInputEvents() is called the first time. Call this input proc
   routine as many times as needed to deliver as many events as should be
   delivered. DIX will buffer them up and send them out as needed. Count is
   set to the number of event records which make up one atomic device event
   and is always 1 for the core devices (see the X Input Extension for
   descriptions of devices which may use count > 1).

    For example, your ProcessInputEvents() routine might check the mouse and
   the keyboard. If the keyboard had several keystrokes queued up, it could
   just call the keyboard's processInputProc as many times as needed to flush
   its internal queue.

    event is an xEvent struct you pass to the input proc. When the input proc
   returns, it is finished with the event rec, and you can fill in new values
   and call the input proc again with it.

    You should deliver the events in the same order that they were generated.

    For keyboard and pointing devices the xEvent variant should be
   keyButtonPointer. Fill in the following fields in the xEvent record:

     * type - is one of the following: KeyPress, KeyRelease, ButtonPress,
       ButtonRelease, or MotionNotify

     * detail - for KeyPress or KeyRelease fields, this should be the key
       number (not the ASCII code); otherwise unused

     * time - is the time that the event happened (32-bits, in milliseconds,
       arbitrary origin)

     * rootX - is the x coordinate of cursor

     * rootY - is the y coordinate of cursor

   The rest of the fields are filled in by DIX.

    The time stamp is maintained by your code in the DDX layer, and it is
   your responsibility to stamp all events correctly.

    The x and y coordinates of the pointing device and the time must be
   filled in for all event types including keyboard events.

    The pointing device must report all button press and release events. In
   addition, it should report a MotionNotify event every time it gets called
   if the pointing device has moved since the last notify. Intermediate
   pointing device moves are stored in a special GetMotionEvents buffer,
   because most client programs are not interested in them.

    There are quite a collection of sample implementations of this routine,
   one for each supported device.

   --------------------------------------------------------------------------

    Telling DIX When Input is Pending

    In the server's dispatch loop, DIX checks to see if there is any device
   input pending whenever WaitForSomething() returns. If the check says that
   input is pending, DIX calls the DDX routine ProcessInputEvents().

    This check for pending input must be very quick; a procedure call is too
   slow. The code that does the check is a hardwired IF statement in DIX code
   that simply compares the values pointed to by two pointers. If the values
   are different, then it assumes that input is pending and
   ProcessInputEvents() is called by DIX.

    You must pass pointers to DIX to tell it what values to compare. The
   following procedure is used to set these pointers:

             void SetInputCheck(p1, p2)
                     long *p1, *p2;

   You should call it sometime during initialization to indicate to DIX the
   correct locations to check. You should pay special attention to the size
   of what they actually point to, because the locations are assumed to be
   longs.

    These two pointers are initialized by DIX to point to arbitrary values
   that are different. In other words, if you forget to call this routine
   during initialization, the worst thing that will happen is that
   ProcessInputEvents will be called when there are no events to process.

    p1 and p2 might point at the head and tail of some shared memory queue.
   Another use would be to have one point at a constant 0, with the other
   pointing at some mask containing 1s for each input device that has
   something pending.

    The DDX layer of the sample server calls SetInputCheck() once when the
   server's private internal queue is initialized. It passes pointers to the
   queue's head and tail. See Xserver/mi/mieq.c.



             int TimeSinceLastInputEvent()

   DDX must time stamp all hardware input events. But DIX sometimes needs to
   know the time and the OS layer needs to know the time since the last
   hardware input event in order for the screen saver to work.
   TimeSinceLastInputEvent() returns the this time in milliseconds.

   --------------------------------------------------------------------------

    Controlling Input Devices

    You must write four routines to do various device-specific things with
   the keyboard and pointing device. They can have any name you wish because
   you pass the procedure pointers to DIX routines.



        int pInternalDevice->valuator->GetMotionProc(pdevice, coords, start, stop, pScreen)
                DeviceIntPtr pdevice;
                xTimecoord * coords;
                unsigned long start;
                unsigned long stop;
                ScreenPtr pScreen;

   You write this DDX routine to fill in coords with all the motion events
   that have times (32-bit count of milliseconds) between time start and time
   stop. It should return the number of motion events returned. If there is
   no motion events support, this routine should do nothing and return zero.
   The maximum number of coords to return is set in
   InitPointerDeviceStruct(), below.

    When the user drags the pointing device, the cursor position
   theoretically sweeps through an infinite number of points. Normally, a
   client that is concerned with points other than the starting and ending
   points will receive a pointer-move event only as often as the server
   generates them. (Move events do not queue up; each new one replaces the
   last in the queue.) A server, if desired, can implement a scheme to save
   these intermediate events in a motion buffer. A client application, like a
   paint program, may then request that these events be delivered to it
   through the GetMotionProc routine.



           void pInternalDevice->bell->BellProc(percent, pDevice, ctrl, unknown)
                   int percent;
                   DeviceIntPtr pDevice;
                   pointer ctrl;
                   int class;

   You need to write this routine to ring the bell on the keyboard. loud is a
   number from 0 to 100, with 100 being the loudest. Class is either
   BellFeedbackClass or KbdFeedbackClass (from XI.h).



             void pInternalDevice->somedevice->CtrlProc(device, ctrl)
                     DevicePtr device;
                     SomethingCtrl *ctrl;

   You write two versions of this procedure, one for the keyboard and one for
   the pointing device. DIX calls it to inform DDX when a client has
   requested changes in the current settings for the particular device. For a
   keyboard, this might be the repeat threshold and rate. For a pointing
   device, this might be a scaling factor (coarse or fine) for position
   reporting. See input.h for the ctrl structures.

   --------------------------------------------------------------------------

    Input Initialization

    Input initialization is a bit complicated. It all starts with
   InitInput(), a routine that you write to call AddInputDevice() twice (once
   for pointing device and once for keyboard.) You also want to call
   RegisterKeyboardDevice() and RegisterPointerDevice() on them.

    When you Add the devices, a routine you supply for each device gets
   called to initialize them. Your individual initialize routines must call
   InitKeyboardDeviceStruct() or InitPointerDeviceStruct(), depending upon
   which it is. In other words, you indicate twice that the keyboard is the
   keyboard and the pointer is the pointer.



             void InitInput(argc, argv)
                 int argc;
                 char **argv;

   InitInput is a DDX routine you must write to initialize the input
   subsystem in DDX. It must call AddInputDevice() for each device that might
   generate events. In addition, you must register the main keyboard and
   pointing devices by calling RegisterPointerDevice() and
   RegisterKeyboardDevice().



             DevicePtr AddInputDevice(deviceProc, autoStart)
                     DeviceProc deviceProc;
                     Bool autoStart;

   AddInputDevice is a DIX routine you call to create a device object.
   deviceProc is a DDX routine that is called by DIX to do various
   operations. AutoStart should be TRUE for devices that need to be turned on
   at initialization time with a special call, as opposed to waiting for some
   client application to turn them on. This routine returns NULL if
   sufficient memory cannot be allocated to install the device.

    Note also that except for the main keyboard and pointing device, an
   extension is needed to provide for a client interface to a device.



             void RegisterPointerDevice(device)
                     DevicePtr device;

   RegisterPointerDevice is a DIX routine that your DDX code calls that makes
   that device the main pointing device. This routine is called once upon
   initialization and cannot be called again.



             void RegisterKeyboardDevice(device)
                     DevicePtr device;

   RegisterKeyboardDevice makes the given device the main keyboard. This
   routine is called once upon initialization and cannot be called again.

    The following DIX procedures return the specified DevicePtr. They may or
   may not be useful to DDX implementors.



             DevicePtr LookupKeyboardDevice()

   LookupKeyboardDevice returns pointer for current main keyboard device.



             DevicePtr LookupPointerDevice()

   LookupPointerDevice returns pointer for current main pointing device.

    A DeviceProc (the kind passed to AddInputDevice()) in the following form:

             Bool pInternalDevice->DeviceProc(device, action);
                     DeviceIntPtr device;
                     int action;

   You must write a DeviceProc for each device. device points to the device
   record. action tells what action to take; it will be one of these defined
   constants (defined in input.h):

     *  DEVICE_INIT - At DEVICE_INIT time, the device should initialize
       itself by calling InitPointerDeviceStruct(),
       InitKeyboardDeviceStruct(), or a similar routine (see below) and
       "opening" the device if necessary. If you return a non-zero (i.e., !=
       Success) value from the DEVICE_INIT call, that device will be
       considered unavailable. If either the main keyboard or main pointing
       device cannot be initialized, the DIX code will refuse to continue
       booting up.

     *  DEVICE_ON - If the DeviceProc is called with DEVICE_ON, then it is
       allowed to start putting events into the client stream by calling
       through the ProcessInputProc in the device.

     *  DEVICE_OFF - If the DeviceProc is called with DEVICE_OFF, no further
       events from that device should be given to the DIX layer. The device
       will appear to be dead to the user.

     *  DEVICE_CLOSE - At DEVICE_CLOSE (terminate or reset) time, the device
       should be totally closed down.



             void InitPointerDeviceStruct(device, map, mapLength,
                             GetMotionEvents, ControlProc, numMotionEvents)
                     DevicePtr device;
                     CARD8 *map;
                     int mapLength;
                     ValuatorMotionProcPtr ControlProc;
                     PtrCtrlProcPtr GetMotionEvents;
                     int numMotionEvents;

   InitPointerDeviceStruct is a DIX routine you call at DEVICE_INIT time to
   declare some operating routines and data structures for a pointing device.
   map and mapLength are as described in the X Window System protocol
   specification. ControlProc and GetMotionEvents are DDX routines, see
   above.

    numMotionEvents is for the motion-buffer-size for the GetMotionEvents
   request. A typical length for a motion buffer would be 100 events. A
   server that does not implement this capability should set numMotionEvents
   to zero.



        void InitKeyboardDeviceStruct(device, pKeySyms, pModifiers, Bell, ControlProc)
                DevicePtr device;
                KeySymsPtr pKeySyms;
                CARD8 *pModifiers;
                BellProcPtr Bell;
                KbdCtrlProcPtr ControlProc;

   You call this DIX routine when a keyboard device is initialized and its
   device procedure is called with DEVICE_INIT. The formats of the keysyms
   and modifier maps are defined in Xserver/include/input.h. They describe
   the layout of keys on the keyboards, and the glyphs associated with them.
   ( See the next section for information on setting up the modifier map and
   the keysym map.) ControlProc and Bell are DDX routines, see above.

   --------------------------------------------------------------------------

    Keyboard Mapping and Keycodes

    When you send a keyboard event, you send a report that a given key has
   either been pressed or has been released. There must be a keycode for each
   key that identifies the key; the keycode-to-key mapping can be any mapping
   you desire, because you specify the mapping in a table you set up for DIX.
   However, you are restricted by the protocol specification to keycode
   values in the range 8 to 255 inclusive.

    The keycode mapping information that you set up consists of the
   following:

     *  A minimum and maximum keycode number

     *  An array of sets of keysyms for each key, that is of length
       maxkeycode - minkeycode + 1. Each element of this array is a list of
       codes for symbols that are on that key. There is no limit to the
       number of symbols that can be on a key.

   Once the map is set up, DIX keeps and maintains the client's changes to
   it.

    The X protocol defines standard names to indicate the symbol(s) printed
   on each keycap. (See X11/keysym.h)

    Legal modifier keys must generate both up and down transitions. When a
   client tries to change a modifier key (for instance, to make "A" the
   "Control" key), DIX calls the following routine, which should retuurn TRUE
   if the key can be used as a modifier on the given device:

             Bool LegalModifier(key, pDev)
                 unsigned int key;
                 DevicePtr pDev;

   --------------------------------------------------------------------------

  Screens

    Different computer graphics displays have different capabilities. Some
   are simple monochrome frame buffers that are just lying there in memory,
   waiting to be written into. Others are color displays with many bits per
   pixel using some color lookup table. Still others have high-speed graphic
   processors that prefer to do all of the work themselves, including
   maintaining their own high-level, graphic data structures.

   --------------------------------------------------------------------------

    Screen Hardware Requirements

    The only requirement on screens is that you be able to both read and
   write locations in the frame buffer. All screens must have a depth of 32
   or less (unless you use an X extension to allow a greater depth). All
   screens must fit into one of the classes listed in the section in this
   document on Visuals and Depths.

    X uses the pixel as its fundamental unit of distance on the screen.
   Therefore, most programs will measure everything in pixels.

    The sample server assumes square pixels. Serious WYSIWYG (what you see is
   what you get) applications for publishing and drawing programs will adjust
   for different screen resolutions automatically. Considerable work is
   involved in compensating for non-square pixels (a bit in the DDX code for
   the sample server but quite a bit in the client applications).

   --------------------------------------------------------------------------

    Data Structures

    X supports multiple screens that are connected to the same server.
   Therefore, all the per-screen information is bundled into one data
   structure of attributes and procedures, which is the ScreenRec (see
   Xserver/include/scrnintstr.h). The procedure entry points in a ScreenRec
   operate on regions, colormaps, cursors, and fonts, because these resources
   can differ in format from one screen to another.

    Windows are areas on the screen that can be drawn into by graphic
   routines. "Pixmaps" are off-screen graphic areas that can be drawn into.
   They are both considered drawables and are described in the section on
   Drawables. All graphic operations work on drawables, and operations are
   available to copy patches from one drawable to another.

    The pixel image data in all drawables is in a format that is private to
   DDX. In fact, each instance of a drawable is associated with a given
   screen. Presumably, the pixel image data for pixmaps is chosen to be
   conveniently understood by the hardware. All screens in a single server
   must be able to handle all pixmaps depths declared in the connection setup
   information.

    Pixmap images are transferred to the server in one of two ways: XYPixmap
   or ZPimap. XYPixmaps are a series of bitmaps, one for each bit plane of
   the image, using the bitmap padding rules from the connection setup.
   ZPixmaps are a series of bits, nibbles, bytes or words, one for each
   pixel, using the format rules (padding and so on) for the appropriate
   depth.

    All screens in a given server must agree on a set of pixmap image formats
   (PixmapFormat) to support (depth, number of bits per pixel, etc.).

    There is no color interpretation of bits in the pixmap. Pixmaps do not
   contain pixel values. The interpretation is made only when the bits are
   transferred onto the screen.

    The screenInfo structure (in scrnintstr.h) is a global data structure
   that has a pointer to an array of ScreenRecs, one for each screen on the
   server. (These constitute the one and only description of each screen in
   the server.) Each screen has an identifying index (0, 1, 2, ...). In
   addition, the screenInfo struct contains global server-wide details, such
   as the bit- and byte- order in all bit images, and the list of pixmap
   image formats that are supported. The X protocol insists that these must
   be the same for all screens on the server.

   --------------------------------------------------------------------------

    Output Initialization



             InitOutput(pScreenInfo, argc, argv)
                     ScreenInfo *pScreenInfo;
                     int argc;
                     char **argv;

   Upon initialization, your DDX routine InitOutput() is called by DIX. It is
   passed a pointer to screenInfo to initialize. It is also passed the argc
   and argv from main() for your server for the command-line arguments. These
   arguments may indicate what or how many screen device(s) to use or in what
   way to use them. For instance, your server command line may allow a "-D"
   flag followed by the name of the screen device to use.

    Your InitOutput() routine should initialize each screen you wish to use
   by calling AddScreen(), and then it should initialize the pixmap formats
   that you support by storing values directly into the screenInfo data
   structure. You should also set certain implementation-dependent numbers
   and procedures in your screenInfo, which determines the pixmap and
   scanline padding rules for all screens in the server.



             int AddScreen(scrInitProc, argc, argv)
                     Bool (*scrInitProc)();
                     int argc;
                     char **argv;

   You should call AddScreen(), a DIX procedure, in InitOutput() once for
   each screen to add it to the screenInfo database. The first argument is an
   initialization procedure for the screen that you supply. The second and
   third are the argc and argv from main(). It returns the screen number of
   the screen installed, or -1 if there is either insufficient memory to add
   the screen, or (*scrInitProc) returned FALSE.

    The scrInitProc should be of the following form:

             Bool scrInitProc(iScreen, pScreen, argc, argv)
                     int iScreen;
                     ScreenPtr pScreen;
                     int argc;
                     char **argv;

   iScreen is the index for this screen; 0 for the first one initialized, 1
   for the second, etc. pScreen is the pointer to the screen's new ScreenRec.
   argc and argv are as before. Your screen initialize procedure should
   return TRUE upon success or FALSE if the screen cannot be initialized (for
   instance, if the screen hardware does not exist on this machine).

    This procedure must determine what actual device it is supposed to
   initialize. If you have a different procedure for each screen, then it is
   no problem. If you have the same procedure for multiple screens, it may
   have trouble figuring out which screen to initialize each time around,
   especially if InitOutput() does not initialize all of the screens. It is
   probably easiest to have one procedure for each screen.

    The initialization procedure should fill in all the screen procedures for
   that screen (windowing functions, region functions, etc.) and certain
   screen attributes for that screen.

   --------------------------------------------------------------------------

    Region Routines in the ScreenRec

    A region is a dynamically allocated data structure that describes an
   irregularly shaped piece of real estate in XY pixel space. You can think
   of it as a set of pixels on the screen to be operated upon with set
   operations such as AND and OR.

    A region is frequently implemented as a list of rectangles or bitmaps
   that enclose the selected pixels. Region operators control the "clipping
   policy," or the operations that work on regions. (The sample server uses
   YX-banded rectangles. Unless you have something already implemented for
   your graphics system, you should keep that implementation.) The procedure
   pointers to the region operators are located in the ScreenRec data
   structure. The definition of a region can be found in the file
   Xserver/include/regionstr.h. The region code is found in
   Xserver/mi/miregion.c. DDX implementations using other region formats will
   need to supply different versions of the region operators.

    Since the list of rectangles is unbounded in size, part of the region
   data structure is usually a large, dynamically allocated chunk of memory.
   As your region operators calculate logical combinations of regions, these
   blocks may need to be reallocated by your region software. For instance,
   in the sample server, a RegionRec has some header information and a
   pointer to a dynamically allocated rectangle list. Periodically, the
   rectangle list needs to be expanded with Xrealloc(), whereupon the new
   pointer is remembered in the RegionRec.

    Most of the region operations come in two forms: a function pointer in
   the Screen structure, and a macro. The server can be compiled so that the
   macros make direct calls to the appropriate functions (instead of
   indirecting through a screen function pointer), or it can be compiled so
   that the macros are identical to the function pointer forms. Making direct
   calls is faster on many architectures.



             RegionPtr pScreen->RegionCreate( rect, size)
                     BoxPtr rect;
                     int size;

             macro: RegionPtr REGION_CREATE(pScreen, rect, size)

   RegionCreate creates a region that describes ONE rectangle. The caller can
   avoid unnecessary reallocation and copying by declaring the probable
   maximum number of rectangles that this region will need to describe
   itself. Your region routines, though, cannot fail just because the region
   grows beyond this size. The caller of this routine can pass almost
   anything as the size; the value is merely a good guess as to the maximum
   size until it is proven wrong by subsequent use. Your region procedures
   are then on their own in estimating how big the region will get. Your
   implementation might ignore size, if applicable.



             void pScreen->RegionInit (pRegion, rect, size)
                     RegionPtr       pRegion;
                     BoxPtr          rect;
                     int             size;

             macro: REGION_INIT(pScreen, pRegion, rect, size)

   Given an existing raw region structure (such as an local variable), this
   routine fills in the appropriate fields to make this region as usable as
   one returned from RegionCreate. This avoids the additional dynamic memory
   allocation overhead for the region structure itself.



             Bool pScreen->RegionCopy(dstrgn, srcrgn)
                     RegionPtr dstrgn, srcrgn;

             macro: Bool REGION_COPY(pScreen, dstrgn, srcrgn)

   RegionCopy copies the description of one region, srcrgn, to another
   already-created region, dstrgn; returning TRUE if the copy succeeded, and
   FALSE otherwise.



             void pScreen->RegionDestroy( pRegion)
                     RegionPtr pRegion;

             macro: REGION_DESTROY(pScreen, pRegion)

   RegionDestroy destroys a region and frees all allocated memory.



             void pScreen->RegionUninit (pRegion)
                     RegionPtr pRegion;

             macro: REGION_UNINIT(pScreen, pRegion)

   Frees everything except the region structure itself, useful when the
   region was originally passed to RegionInit instead of received from
   RegionCreate. When this call returns, pRegion must not be reused until it
   has been RegionInit'ed again.



            Bool pScreen->Intersect(newReg, reg1, reg2)
                    RegionPtr newReg, reg1, reg2;

            macro: Bool REGION_INTERSECT(pScreen, newReg, reg1, reg2)

            Bool  pScreen->Union(newReg, reg1, reg2)
                    RegionPtr newReg, reg1, reg2;

            macro: Bool REGION_UNION(pScreen, newReg, reg1, reg2)

            Bool  pScreen->Subtract(newReg, regMinuend, regSubtrahend)
                    RegionPtr newReg, regMinuend, regSubtrahend;

            macro: Bool REGION_UNION(pScreen, newReg, regMinuend, regSubtrahend)

            Bool pScreen->Inverse(newReg, pReg,  pBox)
                    RegionPtr newReg, pReg;
                    BoxPtr pBox;

            macro: Bool REGION_INVERSE(pScreen, newReg, pReg,  pBox)

   The above four calls all do basic logical operations on regions. They set
   the new region (which already exists) to describe the logical
   intersection, union, set difference, or inverse of the region(s) that were
   passed in. Your routines must be able to handle a situation where the
   newReg is the same region as one of the other region arguments.

    The subtract function removes the Subtrahend from the Minuend and puts
   the result in newReg.

    The inverse function returns a region that is the pBox minus the region
   passed in. (A true "inverse" would make a region that extends to infinity
   in all directions but has holes in the middle.) It is undefined for
   situations where the region extends beyond the box.

    Each routine must return the value TRUE for success.



             void pScreen->RegionReset(pRegion, pBox)
                     RegionPtr pRegion;
                     BoxPtr pBox;

             macro: REGION_RESET(pScreen, pRegion, pBox)

   RegionReset sets the region to describe one rectangle and reallocates it
   to a size of one rectangle, if applicable.



             void  pScreen->TranslateRegion(pRegion, x, y)
                     RegionPtr pRegion;
                     int x, y;

             macro: REGION_TRANSLATE(pScreen, pRegion, x, y)

   TranslateRegion simply moves a region +x in the x direction and +y in the
   y direction.



             int  pScreen->RectIn(pRegion, pBox)
                     RegionPtr pRegion;
                     BoxPtr pBox;

             macro: int RECT_IN_REGION(pScreen, pRegion, pBox)

   RectIn returns one of the defined constants rgnIN, rgnOUT, or rgnPART,
   depending upon whether the box is entirely inside the region, entirely
   outside of the region, or partly in and partly out of the region. These
   constants are defined in Xserver/include/region.h.



             Bool pScreen->PointInRegion(pRegion, x, y, pBox)
                     RegionPtr pRegion;
                     int x, y;
                     BoxPtr pBox;

             macro: Bool POINT_IN_REGION(pScreen, pRegion, x, y, pBox)

   PointInRegion returns true if the point x, y is in the region. In
   addition, it fills the rectangle pBox with coordinates of a rectangle that
   is entirely inside of pRegion and encloses the point. In the mi
   implementation, it is the largest such rectangle. (Due to the sample
   server implementation, this comes cheaply.)

    This routine used by DIX when tracking the pointing device and deciding
   whether to report mouse events or change the cursor. For instance, DIX
   needs to change the cursor when it moves from one window to another. Due
   to overlapping windows, the shape to check may be irregular. A
   PointInRegion() call for every pointing device movement may be too
   expensive. The pBox is a kind of wake-up box; DIX need not call
   PointInRegion() again until the cursor wanders outside of the returned
   box.



             Bool pScreen->RegionNotEmpty(pRegion)
                     RegionPtr pRegion;

             macro: Bool REGION_NOTEMPTY(pScreen, pRegion)

   RegionNotEmpty is a boolean function that returns true or false depending
   upon whether the region encloses any pixels.



             void pScreen->RegionEmpty(pRegion)
                     RegionPtr pRegion;

             macro: REGION_EMPTY(pScreen, pRegion)

   RegionEmpty sets the region to be empty.



             BoxPtr pScreen->RegionExtents(pRegion)
                     RegionPtr pRegion;

             macro: REGION_EXTENTS(pScreen, pRegion)

   RegionExtents returns a rectangle that is the smallest possible superset
   of the entire region. The caller will not modify this rectangle, so it can
   be the one in your region struct.



             Bool pScreen->RegionAppend (pDstRgn, pRegion)
                     RegionPtr pDstRgn;
                     RegionPtr pRegion;

             macro: Bool REGION_APPEND(pScreen, pDstRgn, pRegion)

             Bool pScreen->RegionValidate (pRegion, pOverlap)
                     RegionPtr pRegion;
                     Bool *pOverlap;

             macro: Bool REGION_VALIDATE(pScreen, pRegion, pOverlap)

   These functions provide an optimization for clip list generation and must
   be used in conjunction. The combined effect is to produce the union of a
   collection of regions, by using RegionAppend several times, and finally
   calling RegionValidate which takes the intermediate representation (which
   needn't be a valid region) and produces the desired union. pOverlap is set
   to TRUE if any of the original regions overlap; FALSE otherwise.



             RegionPtr pScreen->BitmapToRegion (pPixmap)
                     PixmapPtr pPixmap;

             macro: RegionPtr BITMAP_TO_REGION(pScreen, pPixmap)

   Given a depth-1 pixmap, this routine must create a valid region which
   includes all the areas of the pixmap filled with 1's and excludes the
   areas filled with 0's. This routine returns NULL if out of memory.



             RegionPtr pScreen->RectsToRegion (nrects, pRects, ordering)
                     int nrects;
                     xRectangle *pRects;
                     int ordering;

             macro: RegionPtr RECTS_TO_REGION(pScreen, nrects, pRects, ordering)

   Given a client-supplied list of rectangles, produces a region which
   includes the union of all the rectangles. Ordering may be used as a hint
   which describes how the rectangles are sorted. As the hint is provided by
   a client, it must not be required to be correct, but the results when it
   is not correct are not defined (core dump is not an option here).



           void pScreen->SendGraphicsExpose(client,pRegion,drawable,major,minor)
                   ClientPtr client;
                   RegionPtr pRegion;
                   XID drawable;
                   int major;
                   int minor;

   SendGraphicsExpose dispatches a list of GraphicsExposure events which span
   the region to the specified client. If the region is empty, or a NULL
   pointer, a NoExpose event is sent instead.

   --------------------------------------------------------------------------

    Cursor Routines for a Screen

    A cursor is the visual form tied to the pointing device. The default
   cursor is an "X" shape, but the cursor can have any shape. When a client
   creates a window, it declares what shape the cursor will be when it strays
   into that window on the screen.

    For each possible shape the cursor assumes, there is a CursorRec data
   structure. This data structure contains a pointer to a CursorBits data
   structure which contains a bitmap for the image of the cursor and a bitmap
   for a mask behind the cursor, in addition, the CursorRec data structure
   contains foreground and background colors for the cursor. The CursorBits
   data structure is shared among multiple CursorRec structures which use the
   same font and glyph to describe both source and mask. The cursor image is
   applied to the screen by applying the mask first, clearing 1 bits in its
   form to the background color, and then overwriting on the source image, in
   the foreground color. (One bits of the source image that fall on top of
   zero bits of the mask image are undefined.) This way, a cursor can have
   transparent parts, and opaque parts in two colors. X allows any cursor
   size, but some hardware cursor schemes allow a maximum of N pixels by M
   pixels. Therefore, you are allowed to transform the cursor to a smaller
   size, but be sure to include the hot-spot.

    CursorBits in Xserver/include/cursorstr.h is a device-independent
   structure containing a device-independent representation of the bits for
   the source and mask. (This is possible because the bitmap representation
   is the same for all screens.)

    When a cursor is created, it is "realized" for each screen. At
   realization time, each screen has the chance to convert the bits into some
   other representation that may be more convenient (for instance, putting
   the cursor into off-screen memory) and set up its device-private area in
   either the CursorRec data structure or CursorBits data structure as
   appropriate to possibly point to whatever data structures are needed. It
   is more memory-conservative to share realizations by using the CursorBits
   private field, but this makes the assumption that the realization is
   independent of the colors used (which is typically true). For instance,
   the following are the device private entries for a particular screen and
   cursor:

             pCursor->devPriv[pScreen->myNum]
             pCursor->bits->devPriv[pScreen->myNum]

   This is done because the change from one cursor shape to another must be
   fast and responsive; the cursor image should be able to flutter as fast as
   the user moves it across the screen.

    You must implement the following routines for your hardware:

             Bool pScreen->RealizeCursor( pScr, pCurs)
                     ScreenPtr pScr;
                     CursorPtr pCurs;

             Bool pScreen->UnrealizeCursor( pScr, pCurs)
                     ScreenPtr pScr;
                     CursorPtr pCurs;

    RealizeCursor and UnrealizeCursor should realize (allocate and calculate
   all data needed) and unrealize (free the dynamically allocated data) a
   given cursor when DIX needs them. They are called whenever a
   device-independent cursor is created or destroyed. The source and mask
   bits pointed to by fields in pCurs are undefined for bits beyond the right
   edge of the cursor. This is so because the bits are in Bitmap format,
   which may have pad bits on the right edge. You should inhibit
   UnrealizeCursor() if the cursor is currently in use; this happens when the
   system is reset.



             Bool pScreen->DisplayCursor( pScr, pCurs)
                     ScreenPtr pScr;
                     CursorPtr pCurs;

   DisplayCursor should change the cursor on the given screen to the one
   passed in. It is called by DIX when the user moves the pointing device
   into a different window with a different cursor. The hotspot in the cursor
   should be aligned with the current cursor position.



             void pScreen->RecolorCursor( pScr, pCurs, displayed)
                     ScreenPtr pScr;
                     CursorPtr pCurs;
                     Bool displayed;

   RecolorCursor notifies DDX that the colors in pCurs have changed and
   indicates whether this is the cursor currently being displayed. If it is,
   the cursor hardware state may have to be updated. Whether displayed or
   not, state created at RealizeCursor time may have to be updated. A generic
   version, miRecolorCursor, may be used that does an unrealize, a realize,
   and possibly a display (in micursor.c); however this constrains
   UnrealizeCursor and RealizeCursor to always return TRUE as no error
   indication is returned here.



             void pScreen->ConstrainCursor( pScr, pBox)
                     ScreenPtr pScr;
                     BoxPtr pBox;

   ConstrainCursor should cause the cursor to restrict its motion to the
   rectangle pBox. DIX code is capable of enforcing this constraint by
   forcefully moving the cursor if it strays out of the rectangle, but
   ConstrainCursor offers a way to send a hint to the driver or hardware if
   such support is available. This can prevent the cursor from wandering out
   of the box, then jumping back, as DIX forces it back.



             void pScreen->PointerNonInterestBox( pScr, pBox)
                     ScreenPtr pScr;
                     BoxPtr pBox;

   PointerNonInterestBox is DIX's way of telling the pointing device code not
   to report motion events while the cursor is inside a given rectangle on
   the given screen. It is optional and, if not implemented, it should do
   nothing. This routine is called only when the client has declared that it
   is not interested in motion events in a given window. The rectangle you
   get may be a subset of that window. It saves DIX code the time required to
   discard uninteresting mouse motion events. This is only a hint, which may
   speed performance. Nothing in DIX currently calls PointerNonInterestBox.



             void pScreen->CursorLimits( pScr, pCurs, pHotBox, pTopLeftBox)
                     ScreenPtr pScr;
                     CursorPtr pCurs;
                     BoxPtr pHotBox;
                     BoxPtr pTopLeftBox;     /* return value */

   CursorLimits should calculate the box that the cursor hot spot is
   physically capable of moving within, as a function of the screen pScr, the
   device-independent cursor pCurs, and a box that DIX hypothetically would
   want the hot spot confined within, pHotBox. This routine is for informing
   DIX only; it alters no state within DDX.



             Bool pScreen->SetCursorPosition( pScr, newx, newy, generateEvent)
                     ScreenPtr pScr;
                     int newx;
                     int newy;
                     Bool generateEvent;

   SetCursorPosition should artificially move the cursor as though the user
   had jerked the pointing device very quickly. This is called in response to
   the WarpPointer request from the client, and at other times. If
   generateEvent is True, the device should decide whether or not to call
   ProcessInputEvents() and then it must call DevicePtr->processInputProc.
   Its effects are, of course, limited in value for absolute pointing devices
   such as a tablet.



             void NewCurrentScreen(newScreen, x, y)
                 ScreenPtr newScreen;
                 int x,y;

   If your ddx provides some mechanism for the user to magically move the
   pointer between multiple screens, you need to inform DIX when this occurs.
   You should call NewCurrentScreen to accomplish this, specifying the new
   screen and the new x and y coordinates of the pointer on that screen.

   --------------------------------------------------------------------------

    Visuals, Depths and Pixmap Formats for Screens

    The "depth" of a image is the number of bits that are used per pixel to
   display it.

    The "bits per pixel" of a pixmap image that is sent over the client byte
   stream is a number that is either 4, 8, 16, 24 or 32. It is the number of
   bits used per pixel in Z format. For instance, a pixmap image that has a
   depth of six is best sent in Z format as 8 bits per pixel.

    A "pixmap image format" or a "pixmap format" is a description of the
   format of a pixmap image as it is sent over the byte stream. For each
   depth available on a server, there is one and only one pixmap format. This
   pixmap image format gives the bits per pixel and the scanline padding
   unit. (For instance, are pixel rows padded to bytes, 16-bit words, or
   32-bit words?)

    For each screen, you must decide upon what depth(s) it supports. You
   should only count the number of bits used for the actual image. Some
   displays store additional bits to indicate what window this pixel is in,
   how close this object is to a viewer, transparency, and other data; do not
   count these bits.

    A "display class" tells whether the display is monochrome or color,
   whether there is a lookup table, and how the lookup table works.

    A "visual" is a combination of depth, display class, and a description of
   how the pixel values result in a color on the screen. Each visual has a
   set of masks and offsets that are used to separate a pixel value into its
   red, green, and blue components and a count of the number of colormap
   entries. Some of these fields are only meaningful when the class dictates
   so. Each visual also has a screen ID telling which screen it is usable on.
   Note that the depth does not imply the number of map_entries; for
   instance, a display can have 8 bits per pixel but only 254 colormap
   entries for use by applications (the other two being reserved by hardware
   for the cursor).

    Each visual is identified by a 32-bit visual ID which the client uses to
   choose what visual is desired on a given window. Clients can be using more
   than one visual on the same screen at the same time.

    The class of a display describes how this translation takes place. There
   are three ways to do the translation.

     *  Pseudo - The pixel value, as a whole, is looked up in a table of
       length map_entries to determine the color to display.

     *  True - The pixel value is broken up into red, green, and blue fields,
       each of which are looked up in separate red, green, and blue lookup
       tables, each of length map_entries.

     *  Gray - The pixel value is looked up in a table of length map_entries
       to determine a gray level to display.

    In addition, the lookup table can be static (resulting colors are fixed
   for each pixel value) or dynamic (lookup entries are under control of the
   client program). This leads to a total of six classes:

     *  Static Gray - The pixel value (of however many bits) determines
       directly the level of gray that the pixel assumes.

     *  Gray Scale - The pixel value is fed through a lookup table to arrive
       at the level of gray to display for the given pixel.

     *  Static Color - The pixel value is fed through a fixed lookup table
       that yields the color to display for that pixel.

     *  PseudoColor - The whole pixel value is fed through a programmable
       lookup table that has one color (including red, green, and blue
       intensities) for each possible pixel value, and that color is
       displayed.

     *  True Color - Each pixel value consists of one or more bits that
       directly determine each primary color intensity after being fed
       through a fixed table.

     *  Direct Color - Each pixel value consists of one or more bits for each
       primary color. Each primary color value is individually looked up in a
       table for that primary color, yielding an intensity for that primary
       color. For each pixel, the red value is looked up in the red table,
       the green value in the green table, and the blue value in the blue
       table.

    Here are some examples:

     *  A simple monochrome 1 bit per pixel display is Static Gray.

     *  A display that has 2 bits per pixel for a choice between the colors
       of black, white, green and violet is Static Color.

     *  A display that has three bits per pixel, where each bit turns on or
       off one of the red, green or blue guns, is in the True Color class.

     *  If you take the last example and scramble the correspondence between
       pixel values and colors it becomes a Static Color display.

    A display has 8 bits per pixel. The 8 bits select one entry out of 256
   entries in a lookup table, each entry consisting of 24 bits (8bits each
   for red, green, and blue). The display can show any 256 of 16 million
   colors on the screen at once. This is a pseudocolor display. The client
   application gets to fill the lookup table in this class of display.

    Imagine the same hardware from the last example. Your server software
   allows the user, on the command line that starts up the server program, to
   fill the lookup table to his liking once and for all. From then on, the
   server software would not change the lookup table until it exits. For
   instance, the default might be a lookup table with a reasonable sample of
   colors from throughout the color space. But the user could specify that
   the table be filled with 256 steps of gray scale because he knew ahead of
   time he would be manipulating a lot of black-and-white scanned photographs
   and not very many color things. Clients would be presented with this
   unchangeable lookup table. Although the hardware qualifies as a
   PseudoColor display, the facade presented to the X client is that this is
   a Static Color display.

    You have to decide what kind of display you have or want to pretend you
   have. When you initialize the screen(s), this class value must be set in
   the VisualRec data structure along with other display characteristics like
   the depth and other numbers.

    The allowable DepthRec's and VisualRec's are pointed to by fields in the
   ScreenRec. These are set up when InitOutput() is called; you should
   Xalloc() appropriate blocks or use static variables initialized to the
   correct values.

   --------------------------------------------------------------------------

    Colormaps for Screens

    A colormap is a device-independent mapping between pixel values and
   colors displayed on the screen.

    Different windows on the same screen can have different colormaps at the
   same time. At any given time, the most recently installed colormap(s) will
   be in use in the server so that its (their) windows' colors will be
   guaranteed to be correct. Other windows may be off-color. Although this
   may seem to be chaotic, in practice most clients use the default colormap
   for the screen.

    The default colormap for a screen is initialized when the screen is
   initialized. It always remains in existence and is not owned by any
   regular client. It is owned by client 0 (the server itself). Many clients
   will simply use this default colormap for their drawing. Depending upon
   the class of the screen, the entries in this colormap may be modifiable by
   client applications.

   --------------------------------------------------------------------------

    Colormap Routines

    You need to implement the following routines to handle the
   device-dependent aspects of color maps. You will end up placing pointers
   to these procedures in your ScreenRec data structure(s). The sample server
   implementations of many of these routines are in both cfbcmap.c and
   mfbcmap.c; since mfb does not do very much with color, the cfb versions
   are typically more useful prototypes.



             Bool pScreen->CreateColormap(pColormap)
                     ColormapPtr pColormap;

   This routine is called by the DIX CreateColormap routine after it has
   allocated all the data for the new colormap and just before it returns to
   the dispatcher. It is the DDX layer's chance to initialize the colormap,
   particularly if it is a static map. See the following section for more
   details on initializing colormaps. The routine returns FALSE if creation
   failed, such as due to memory limitations. Notice that the colormap has a
   devPriv field from which you can hang any colormap specific storage you
   need. Since each colormap might need special information, we attached the
   field to the colormap and not the visual.



             void pScreen->DestroyColormap(pColormap)
                     ColormapPtr pColormap;

   This routine is called by the DIX FreeColormap routine after it has
   uninstalled the colormap and notified all interested parties, and before
   it has freed any of the colormap storage. It is the DDX layer's chance to
   free any data it added to the colormap.



             void pScreen->InstallColormap(pColormap)
                     ColormapPtr pColormap;

   InstallColormap should fill a lookup table on the screen with which the
   colormap is associated with the colors in pColormap. If there is only one
   hardware lookup table for the screen, then all colors on the screen may
   change simultaneously.

    In the more general case of multiple hardware lookup tables, this may
   cause some other colormap to be uninstalled, meaning that windows that
   subscribed to the colormap that was uninstalled may end up being
   off-color. See the note, below, about uninstalling maps.



             void pScreen->UninstallColormap(pColormap)
                     ColormapPtr pColormap;

   UninstallColormap should remove pColormap from screen pColormap->pScreen.
   Some other map, such as the default map if possible, should be installed
   in place of pColormap if applicable. If pColormap is the default map, do
   nothing. If any client has requested ColormapNotify events, the DDX layer
   must notify the client. (The routine WalkTree() is be used to find such
   windows. The DIX routines TellNoMap(), TellNewMap() and TellGainedMap()
   are provided to be used as the procedure parameter to WalkTree. These
   procedures are in Xserver/dix/colormap.c.)



             int pScreen->ListInstalledColormaps(pScreen, pCmapList)
                     ScreenPtr pScreen;
                     XID *pCmapList;

   ListInstalledColormaps fills the pCMapList in with the resource ids of the
   installed maps and returns a count of installed maps. pCmapList will point
   to an array of size MaxInstalledMaps that was allocated by the caller.



             void pScreen->StoreColors (pmap, ndef, pdefs)
                     ColormapPtr pmap;
                     int ndef;
                     xColorItem *pdefs;

   StoreColors changes some of the entries in the colormap pmap. The number
   of entries to change are ndef, and pdefs points to the information
   describing what to change. Note that partial changes of entries in the
   colormap are allowed. Only the colors indicated in the flags field of each
   xColorItem need to be changed. However, all three color fields will be
   sent with the proper value for the benefit of screens that may not be able
   to set part of a colormap value. If the screen is a static class, this
   routine does nothing. The structure of colormap entries is nontrivial; see
   colormapst.h and the definition of xColorItem in Xproto.h for more
   details.



             void pScreen->ResolveColor(pRed, pGreen, pBlue, pVisual)
                     unsigned short *pRed, *pGreen, *pBlue;
                     VisualPtr pVisual;

   Given a requested color, ResolveColor returns the nearest color that this
   hardware is capable of displaying on this visual. In other words, this
   rounds off each value, in place, to the number of bits per primary color
   that your screen can use. Remember that each screen has one of these
   routines. The level of roundoff should be what you would expect from the
   value you put in the bits_per_rgb field of the pVisual.

    Each value is an unsigned value ranging from 0 to 65535. The bits least
   likely to be used are the lowest ones.

    For example, if you had a pseudocolor display with any number of bits per
   pixel that had a lookup table supplying 6 bits for each color gun (a total
   of 256K different colors), you would round off each value to 6 bits.
   Please don't simply truncate these values to the upper 6 bits, scale the
   result so that the maximum value seen by the client will be 65535 for each
   primary. This makes color values more portable between different depth
   displays (a 6-bit truncated white will not look white on an 8-bit
   display).

   --------------------------------------------------------------------------

      Initializing a Colormap

    When a client requests a new colormap and when the server creates the
   default colormap, the procedure CreateColormap in the DIX layer is
   invoked. That procedure allocates memory for the colormap and related
   storage such as the lists of which client owns which pixels. It then sets
   a bit, BeingCreated, in the flags field of the ColormapRec and calls the
   DDX layer's CreateColormap routine. This is your chance to initialize the
   colormap. If the colormap is static, which you can tell by looking at the
   class field, you will want to fill in each color cell to match the
   hardwares notion of the color for that pixel. If the colormap is the
   default for the screen, which you can tell by looking at the IsDefault bit
   in the flags field, you should allocate BlackPixel and WhitePixel to match
   the values you set in the pScreen structure. (Of course, you picked those
   values to begin with.)

    You can also wait and use AllocColor() to allocate blackPixel and
   whitePixel after the default colormap has been created. If the default
   colormap is static and you initialized it in pScreen->CreateColormap, then
   use can use AllocColor afterwards to choose pixel values with the closest
   rgb values to those desired for blackPixel and whitePixel. If the default
   colormap is dynamic and uninitialized, then the rgb values you request
   will be obeyed, and AllocColor will again choose pixel values for you.
   These pixel values can then be stored into the screen.

    There are two ways to fill in the colormap. The simplest way is to use
   the DIX function AllocColor.

     int AllocColor (pmap, pred, pgreen, pblue, pPix, client)
         ColormapPtr         pmap;
         unsigned short      *pred, *pgreen, *pblue;
         Pixel               *pPix;
         int                 client;

   This takes three pointers to 16 bit color values and a pointer to a
   suggested pixel value. The pixel value is either an index into one
   colormap or a combination of three indices depending on the type of pmap.
   If your colormap starts out empty, and you don't deliberately pick the
   same value twice, you will always get your suggested pixel. The truly
   nervous could check that the value returned in *pPix is the one AllocColor
   was called with. If you don't care which pixel is used, or would like them
   sequentially allocated from entry 0, set *pPix to 0. This will find the
   first free pixel and use that.

    AllocColor will take care of all the bookkeeping and will call
   StoreColors to get the colormap rgb values initialized. The hardware
   colormap will be changed whenever this colormap is installed.

    If for some reason AllocColor doesn't do what you want, you can do your
   own bookkeeping and call StoreColors yourself. This is much more difficult
   and shouldn't be necessary for most devices.

   --------------------------------------------------------------------------

    Fonts for Screens

    A font is a set of bitmaps that depict the symbols in a character set.
   Each font is for only one typeface in a given size, in other words, just
   one bitmap for each character. Parallel fonts may be available in a
   variety of sizes and variations, including "bold" and "italic." X supports
   fonts for 8-bit and 16-bit character codes (for oriental languages that
   have more than 256 characters in the font). Glyphs are bitmaps for
   individual characters.

    The source comes with some useful font files in an ASCII, plain-text
   format that should be comprehensible on a wide variety of operating
   systems. The text format, referred to as BDF, is a slight extension of the
   current Adobe 2.1 Bitmap Distribution Format (Adobe Systems, Inc.).

    A short paper in PostScript format is included with the sample server
   that defines BDF. It includes helpful pictures, which is why it is done in
   PostScript and is not included in this document.

    Your implementation should include some sort of font compiler to read
   these files and generate binary files that are directly usable by your
   server implementation. The sample server comes with the source for a font
   compiler.

    It is important the font properties contained in the BDF files are
   preserved across any font compilation. In particular, copyright
   information cannot be casually tossed aside without legal ramifications.
   Other properties will be important to some sophisticated applications.

    All clients get font information from the server. Therefore, your server
   can support any fonts it wants to. It should probably support at least the
   fonts supplied with the X11 tape. In principle, you can convert fonts from
   other sources or dream up your own fonts for use on your server.

   --------------------------------------------------------------------------

      Portable Compiled Format

    A font compiler is supplied with the sample server. It has compile-time
   switches to convert the BDF files into a portable binary form, called
   Portable Compiled Format or PCF. This allows for an arbitrary data format
   inside the file, and by describing the details of the format in the header
   of the file, any PCF file can be read by any PCF reading client. By
   selecting the format which matches the required internal format for your
   renderer, the PCF reader can avoid reformatting the data each time it is
   read in. The font compiler should be quite portable.

    The fonts included with the tape are stored in fonts/bdf. The font
   compiler is found in fonts/tools/bdftopcf.

   --------------------------------------------------------------------------

      Font Realization

    Each screen configured into the server has an opportunity at font-load
   time to "realize" a font into some internal format if necessary. This
   happens every time the font is loaded into memory.

    A font (FontRec in Xserver/include/dixfontstr.h) is a device-independent
   structure containing a device-independent representation of the font. When
   a font is created, it is "realized" for each screen. At this point, the
   screen has the chance to convert the font into some other format. The DDX
   layer can also put information in the devPrivate storage.



             Bool pScreen->RealizeFont(pScr, pFont)
                     ScreenPtr pScr;
                     FontPtr pFont;

             Bool pScreen->UnrealizeFont(pScr, pFont)
                     ScreenPtr pScr;
                     FontPtr pFont;

   RealizeFont and UnrealizeFont should calculate and allocate these extra
   data structures and dispose of them when no longer needed. These are
   called in response to OpenFont and CloseFont requests from the client. The
   sample server implementation is in mfbfont.c (which does very little).

   --------------------------------------------------------------------------

    Other Screen Routines

    You must supply several other screen-specific routines for your X server
   implementation. Some of these are described in other sections:

     *  GetImage() is described in the Drawing Primitives section.

     *  GetSpans() is described in the Pixblit routine section.

     *  Several window and pixmap manipulation procedures are described in
       the Window section under Drawables.

     *  The CreateGC() routine is described under Graphics Contexts.



             void pScreen->QueryBestSize(kind, pWidth, pHeight)
                     int kind;
                     unsigned short *pWidth, *pHeight;
                     ScreenPtr pScreen;

   QueryBestSize() returns the best sizes for cursors, tiles, and stipples in
   response to client requests. kind is one of the defined constants
   CursorShape, TileShape, or StippleShape (defined in X.h). For CursorShape,
   return the maximum width and height for cursors that you can handle. For
   TileShape and StippleShape, start with the suggested values in pWidth and
   pHeight and modify them in place to be optimal values that are greater
   than or equal to the suggested values. The sample server implementation is
   in Xserver/mfb/mfbmisc.c.



             pScreen->SourceValidate(pDrawable, x, y, width, height)
                     DrawablePtr pDrawable;
                     int x, y, width, height;

   SourceValidate should be called by CopyArea/CopyPlane primitives when the
   source drawable is not the same as the destination, and the SourceValidate
   function pointer in the screen is non-null. If you know that you will
   never need SourceValidate, you can avoid this check. Currently,
   SourceValidate is used by the mi software cursor code to remove the cursor
   from the screen when the source rectangle overlaps the cursor position.
   x,y,width,height describe the source rectangle (source relative, that is)
   for the copy operation.



             Bool pScreen->SaveScreen(pScreen, on)
                     ScreenPtr pScreen;
                     int on;

   SaveScreen() is used for Screen Saver support (see WaitForSomething()).
   pScreen is the screen to save.



             Bool pScreen->CloseScreen(pScreen)
                 ScreenPtr pScreen;

   When the server is reset, it calls this routine for each screen.



             Bool pScreen->CreateScreenResources(pScreen)
                 ScreenPtr pScreen;

   If this routine is not NULL, it will be called once per screen per server
   initialization/reset after all modules have had a chance to register their
   devPrivates on all structures that support them (see the section on
   devPrivates below). If you need to create any resources that have dynamic
   devPrivates as part of your screen initialization, you should do so in
   this function instead of in the screen init function passed to AddScreen
   to guarantee that the resources have a complete set of devPrivates. This
   routine returns TRUE if successful.

   --------------------------------------------------------------------------

  Drawables

    A drawable is a descriptor of a surface that graphics are drawn into,
   either a window on the screen or a pixmap in memory.

    Each drawable has a type, class, ScreenPtr for the screen it is
   associated with, depth, position, size, and serial number. The type is one
   of the defined constants DRAWABLE_PIXMAP, DRAWABLE_WINDOW and
   UNDRAWABLE_WINDOW. (An undrawable window is used for window class
   InputOnly.) The serial number is guaranteed to be unique across drawables,
   and is used in determining the validity of the clipping information in a
   GC. The screen selects the set of procedures used to manipulate and draw
   into the drawable. Position is used (currently) only by windows; pixmaps
   must set these fields to 0,0 as this reduces the amount of conditional
   code executed throughout the mi code. Size indicates the actual
   client-specified size of the drawable. There are, in fact, no other fields
   that a window drawable and pixmap drawable have in common besides those
   mentioned here.

    Both PixmapRecs and WindowRecs are structs that start with a drawable and
   continue on with more fields. Pixmaps have devPrivate pointers which
   usually point to the pixmap data but could conceivably be used for
   anything that DDX wants. Both windows and pixmaps have an array of
   devPrivates unions, one entry of which will probably be used for DDX
   specific data. Entries in this array are allocated using
   Allocate{Window|Pixmap}PrivateIndex() (see Wrappers and devPrivates
   below). This is done because different graphics hardware has different
   requirements for management; if the graphics is always handled by a
   processor with an independent address space, there is no point having a
   pointer to the bit image itself.

    The definition of a drawable and a pixmap can be found in the file
   Xserver/include/pixmapstr.h. The definition of a window can be found in
   the file Xserver/include/windowstr.h.

   --------------------------------------------------------------------------

    Pixmaps

    A pixmap is a three-dimensional array of bits stored somewhere offscreen,
   rather than in the visible portion of the screen's display frame buffer.
   It can be used as a source or destination in graphics operations. There is
   no implied interpretation of the pixel values in a pixmap, because it has
   no associated visual or colormap. There is only a depth that indicates the
   number of significant bits per pixel. Also, there is no implied physical
   size for each pixel; all graphic units are in numbers of pixels.
   Therefore, a pixmap alone does not constitute a complete image; it
   represents only a rectangular array of pixel values.

    Note that the pixmap data structure is reference-counted.

    The server implementation is free to put the pixmap data anywhere it sees
   fit, according to its graphics hardware setup. Many implementations will
   simply have the data dynamically allocated in the server's address space.
   More sophisticated implementations may put the data in undisplayed
   framebuffer storage.

    In addition to dynamic devPrivates (see the section on devPrivates
   below), the pixmap data structure has two fields that are private to the
   device. Although you can use them for anything you want, they have
   intended purposes. devKind is intended to be a device specific indication
   of the pixmap location (host memory, off-screen, etc.). In the sample
   server, since all pixmaps are in memory, devKind stores the width of the
   pixmap in bitmap scanline units. devPrivate is probably a pointer to the
   bits in the pixmap.

    A bitmap is a pixmap that is one bit deep.



             PixmapPtr pScreen->CreatePixmap(pScreen, width, height, depth)
                     ScreenPtr pScreen;
                     int width, height, depth;

   This ScreenRec procedure must create a pixmap of the size requested. It
   must allocate a PixmapRec and fill in all of the fields. The reference
   count field must be set to 1. If width or height are zero, no space should
   be allocated for the pixmap data, and if the implementation is using the
   devPrivate field as a pointer to the pixmap data, it should be set to
   NULL. If successful, it returns a pointer to the new pixmap; if not, it
   returns NULL. See Xserver/mfb/mfbpixmap.c for the sample server
   implementation.



             Bool pScreen->DestroyPixmap(pPixmap)
                     PixmapPtr pPixmap;

   This ScreenRec procedure must "destroy" a pixmap. It should decrement the
   reference count and, if zero, it must deallocate the PixmapRec and all
   attached devPrivate blocks. If successful, it returns TRUE. See
   Xserver/mfb/mfbpixmap.c for the sample server implementation.



        Bool
        pScreen->ModifyPixmapHeader(pPixmap, width, height, depth, bitsPerPixel, devKind, pPixData)
                PixmapPtr   pPixmap;
                int         width;
                int         height;
                int         depth;
                int         bitsPerPixel;
                int         devKind;
                pointer     pPixData;

   This routine takes a pixmap header (the PixmapRec plus all the dynamic
   devPrivates) and initializes the fields of the PixmapRec to the parameters
   of the same name. pPixmap must have been created via pScreen->CreatePixmap
   with a zero width or height to avoid allocating space for the pixmap data.
   pPixData is assumed to be the pixmap data; it will be stored in an
   implementation-dependent place (usually pPixmap->devPrivate.ptr). This
   routine returns TRUE if successful. See Xserver/mi/miscrinit.c for the
   sample server implementation.



        PixmapPtr
        GetScratchPixmapHeader(pScreen, width, height, depth, bitsPerPixel, devKind, pPixData)
                ScreenPtr   pScreen;
                int         width;
                int         height;
                int         depth;
                int         bitsPerPixel;
                int         devKind;
                pointer     pPixData;

        void FreeScratchPixmapHeader(pPixmap)
                PixmapPtr pPixmap;

   DDX should use these two DIX routines when it has a buffer of raw image
   data that it wants to manipulate as a pixmap temporarily, usually so that
   some other part of the server can be leveraged to perform some operation
   on the data. The data should be passed in pPixData, and will be stored in
   an implementation-dependent place (usually pPixmap->devPrivate.ptr). The
   other fields go into the corresponding PixmapRec fields. If successful,
   GetScratchPixmapHeader returns a valid PixmapPtr which can be used
   anywhere the server expects a pixmap, else it returns NULL. The pixmap
   should be released when no longer needed (usually within the same function
   that allocated it) with FreeScratchPixmapHeader.

   --------------------------------------------------------------------------

    Windows

    A window is a visible, or potentially visible, rectangle on the screen.
   DIX windowing functions maintain an internal n-ary tree data structure,
   which represents the current relationships of the mapped windows. Windows
   that are contained in another window are children of that window and are
   clipped to the boundaries of the parent. The root window in the tree is
   the window for the entire screen. Sibling windows constitute a
   doubly-linked list; the parent window has a pointer to the head and tail
   of this list. Each child also has a pointer to its parent.

    The border of a window is drawn by a DDX procedure when DIX requests that
   it be drawn. The contents of the window is drawn by the client through
   requests to the server.

    Window painting is orchestrated through an expose event system. When a
   region is exposed, DIX generates an expose event, telling the client to
   repaint the window and passing the region that is the minimal area needed
   to be repainted.

    As a favor to clients, the server may retain the output to the hidden
   parts of windows in off-screen memory; this is called "backing store".
   When a part of such a window becomes exposed, it can quickly move pixels
   into place instead of triggering an expose event and waiting for a client
   on the other end of the network to respond. Even if the network response
   is insignificant, the time to intelligently paint a section of a window is
   usually more than the time to just copy already-painted sections. At best,
   the repainting involves blanking out the area to a background color, which
   will take about the same amount of time. In this way, backing store can
   dramatically increase the performance of window moves.

    On the other hand, backing store can be quite complex, because all
   graphics drawn to hidden areas must be intercepted and redirected to the
   off-screen window sections. Not only can this be complicated for the
   server programmer, but it can also impact window painting performance. The
   backing store implementation can choose, at any time, to forget pieces of
   backing that are written into, relying instead upon expose events to
   repaint for simplicity.

    In X, the decision to use the backing-store scheme is made by you, the
   server implementor. X provides hooks for implementing backing store,
   therefore the decision to use this strategy can be made on the fly. For
   example, you may use backing store only for certain windows that the user
   requests or you may use backing store until memory runs out, at which time
   you start dropping pieces of backing as needed to make more room.

    When a window operation is requested by the client, such as a window
   being created or moved, a new state is computed. During this transition,
   DIX informs DDX what rectangles in what windows are about to become
   obscured and what rectangles in what windows have become exposed. This
   provides a hook for the implementation of backing store. If DDX is unable
   to restore exposed regions, DIX generates expose events to the client. It
   is then the client's responsibility to paint the window parts that were
   exposed but not restored.

    If a window is resized, pixels sometimes need to be moved, depending upon
   the application. The client can request "Gravity" so that certain blocks
   of the window are moved as a result of a resize. For instance, if the
   window has controls or other items that always hang on the edge of the
   window, and that edge is moved as a result of the resize, then those
   pixels should be moved to avoid having the client repaint it. If the
   client needs to repaint it anyway, such an operation takes time, so it is
   desirable for the server to approximate the appearance of the window as
   best it can while waiting for the client to do it perfectly. Gravity is
   used for that, also.

    The window has several fields used in drawing operations:

     *  clipList - This region, in conjunction with the client clip region in
       the gc, is used to clip output. clipList has the window's children
       subtracted from it, in addition to pieces of sibling windows that
       overlap this window. To get the list with the children included
       (subwindow-mode is IncludeInferiors), the routine
       NotClippedByChildren(pWin) returns the unclipped region.

     *  borderClip is the region used by CopyWindow and includes the area of
       the window, its children, and the border, but with the overlapping
       areas of sibling children removed.

   Most of the other fields are for DIX use only.

   --------------------------------------------------------------------------

      Window Procedures in the ScreenRec

    You should implement all of the following procedures and store pointers
   to them in the screen record.

    The device-independent portion of the server "owns" the window tree.
   However, clever hardware might want to know the relationship of mapped
   windows. There are pointers to procedures in the ScreenRec data structure
   that are called to give the hardware a chance to update its internal
   state. These are helpers and hints to DDX only; they do not change the
   window tree, which is only changed by DIX.



             Bool pScreen->CreateWindow(pWin)
                     WindowPtr pWin;

   This routine is a hook for when DIX creates a window. It should fill in
   the "Window Procedures in the WindowRec" below and also allocate the
   devPrivate block for it.

    See Xserver/mfb/mfbwindow.c for the sample server implementation.



             Bool pScreen->DestroyWindow(pWin);
                     WindowPtr pWin;

   This routine is a hook for when DIX destroys a window. It should
   deallocate the devPrivate block for it and any other blocks that need to
   be freed, besides doing other cleanup actions.

    See Xserver/mfb/mfbwindow.c for the sample server implementation.



             Bool pScreen->PositionWindow(pWin, x, y);
                     WindowPtr pWin;
                     int x, y;

   This routine is a hook for when DIX moves or resizes a window. It should
   do whatever private operations need to be done when a window is moved or
   resized. For instance, if DDX keeps a pixmap tile used for drawing the
   background or border, and it keeps the tile rotated such that it is
   longword aligned to longword locations in the frame buffer, then you
   should rotate your tiles here. The actual graphics involved in moving the
   pixels on the screen and drawing the border are handled by CopyWindow(),
   below.

    See Xserver/mfb/mfbwindow.c for the sample server implementation.



             Bool pScreen->RealizeWindow(pWin);
                     WindowPtr pWin;

             Bool  pScreen->UnrealizeWindow(pWin);
                     WindowPtr pWin;

   These routines are hooks for when DIX maps (makes visible) and unmaps
   (makes invisible) a window. It should do whatever private operations need
   to be done when these happen, such as allocating or deallocating
   structures that are only needed for visible windows. RealizeWindow does
   NOT draw the window border, background or contents; UnrealizeWindow does
   NOT erase the window or generate exposure events for underlying windows;
   this is taken care of by DIX. DIX does, however, call
   PaintWindowBackground() and PaintWindowBorder() to perform some of these.



             Bool pScreen->ChangeWindowAttributes(pWin, vmask)
                     WindowPtr pWin;
                     unsigned long vmask;

   ChangeWindowAttributes is called whenever DIX changes window attributes,
   such as the size, front-to-back ordering, title, or anything of lesser
   severity that affects the window itself. The sample server implements this
   routine. It computes accelerators for quickly putting up background and
   border tiles. (See description of the set of routines stored in the
   WindowRec.)



             int pScreen->ValidateTree(pParent,  pChild, kind)
                     WindowPtr pParent, pChild;
                     VTKind kind;

   ValidateTree calculates the clipping region for the parent window and all
   of its children. This routine must be provided. The sample server has a
   machine-independent version in Xserver/mi/mivaltree.c. This is a very
   difficult routine to replace.



             void pScreen->PostValidateTree(pParent,  pChild, kind)
                     WindowPtr pParent, pChild;
                     VTKind kind;

   If this routine is not NULL, DIX calls it shortly after calling
   ValidateTree, passing it the same arguments. This is useful for managing
   multi-layered framebuffers. The sample server sets this to NULL.



             void pScreen->WindowExposures(pWin, pRegion, pBSRegion)
                     WindowPtr pWin;
                     RegionPtr pRegion;
                     RegionPtr pBSRegion;

   The WindowExposures() routine paints the border and generates exposure
   events for the window. pRegion is an unoccluded region of the window, and
   pBSRegion is an occluded region that has backing store. Since exposure
   events include a rectangle describing what was exposed, this routine may
   have to send back a series of exposure events, one for each rectangle of
   the region. The count field in the expose event is a hint to the client as
   to the number of regions that are after this one. This routine must be
   provided. The sample server has a machine-independent version in
   Xserver/mi/miexpose.c.



             void pScreen->ClipNotify (pWin, dx, dy)
                     WindowPtr pWin;
                     int dx, dy;

   Whenever the cliplist for a window is changed, this function is called to
   perform whatever hardware manipulations might be necessary. When called,
   the clip list and border clip regions in the window are set to the new
   values. dx,dy are the distance that the window has been moved (if at all).

   --------------------------------------------------------------------------

      Window Painting Procedures

    In addition to the procedures listed above, there are four routines which
   manipulate the actual window image directly. In the sample server, mi
   implementations will work for most purposes and mfb/cfb routines speed up
   situations, such as solid backgrounds/borders or tiles that are 8, 16 or
   32 pixels square.

    These three routines are used for systems that implement a backing-store
   scheme for it to know when to stash away areas of pixels and to restore or
   reposition them.



           void pScreen->ClearToBackground(pWin, x, y, w, h, generateExposures);
                   WindowPtr pWin;
                   int x, y, w, h;
                   Bool generateExposures;

   This routine is called on a window in response to a ClearToBackground
   request from the client. This request has two different but related
   functions, depending upon generateExposures.

    If generateExposures is true, the client is declaring that the given
   rectangle on the window is incorrectly painted and needs to be repainted.
   The sample server implementation calculates the exposure region and hands
   it to the DIX procedure HandleExposures(), which calls the
   WindowExposures() routine, below, for the window and all of its child
   windows.

    If generateExposures is false, the client is trying to simply erase part
   of the window to the background fill style. ClearToBackground should write
   the background color or tile to the rectangle in question (probably using
   PaintWindowBackground). If w or h is zero, it clears all the way to the
   right or lower edge of the window.

    The sample server implementation is in Xserver/mi/miwindow.c.



             void pScreen->PaintWindowBackground(pWin, region, kind)
                     WindowPtr pWin;
                     RegionPtr region;
                     int kind;       /* must be PW_BACKGROUND */

             void pScreen->PaintWindowBorder(pWin, region, kind)
                     WindowPtr pWin;
                     RegionPtr region;
                     int kind;       /* must be PW_BORDER */

   These two routines are for painting pieces of the window background or
   border. They both actually paint the area designated by region. The kind
   parameter is a defined constant that is always PW_BACKGROUND or PW_BORDER,
   as shown. Therefore, you can use the same routine for both. The defined
   constant tells the routine whether to use the window's border fill style
   or its background fill style to paint the given region. Both fill styles
   consist of a union which holds a tile pointer and a pixel value, along
   with a separate variable which indicates which entry is valid. For
   PW_BORDER, borderIsPixel != 0 indicates that the border PixUnion contains
   a pixel value, else a tile. For PW_BACKGROUND there are four values,
   contained in backgroundState; None, ParentRelative, BackgroundPixmap and
   BackgroundPixel. None indicates that the region should be left unfilled,
   while ParentRelative indicates that the background of the parent is
   inherited (see the Protocol document for the exact semantics).



             void pScreen->CopyWindow(pWin, oldpt, oldRegion);
                     WindowPtr pWin;
                     DDXPointRec oldpt;
                     RegionPtr oldRegion;

   CopyWindow is called when a window is moved, and graphically moves to
   pixels of a window on the screen. It should not change any other state
   within DDX (see PositionWindow(), above).

    oldpt is the old location of the upper-left corner. oldRegion is the old
   region it is coming from. The new location and new region is stored in the
   WindowRec. oldRegion might modified in place by this routine (the sample
   implementation does this).

    CopyArea could be used, except that this operation has more
   complications. First of all, you do not want to copy a rectangle onto a
   rectangle. The original window may be obscured by other windows, and the
   new window location may be similarly obscured. Second, some hardware
   supports multiple windows with multiple depths, and your routine needs to
   take care of that.

    The pixels in oldRegion (with reference point oldpt) are copied to the
   window's new region (pWin->borderClip). pWin->borderClip is gotten
   directly from the window, rather than passing it as a parameter.

    The sample server implementation is in Xserver/mfb/mfbwindow.c.

   --------------------------------------------------------------------------

      Screen Operations for Backing Store

    Each ScreenRec has six functions which provide the backing store
   interface. For screens not supporting backing store, these pointers may be
   nul. Servers that implement some backing store scheme must fill in the
   procedure pointers for the procedures below, and must maintain the
   backStorage field in each window struct. The sample implementation is in
   mi/mibstore.c.



             void pScreen->SaveDoomedAreas(pWin, pRegion, dx, dy)
                     WindowPtr pWin;
                     RegionPtr pRegion;
                     int dx, dy;

   This routine saves the newly obscured region, pRegion, in backing store.
   dx, dy indicate how far the window is being moved, useful as the obscured
   region is relative to the window as it will appear in the new location,
   rather then relative to the bits as the are on the screen when the
   function is invoked.



             RegionPtr pScreen->RestoreAreas(pWin, pRegion)
                     WindowPtr pWin;
                     RegionPtr pRegion;

   This looks at the exposed region of the window, pRegion, and tries to
   restore to the screen the parts that have been saved. It removes the
   restored parts from the backing storage (because they are now on the
   screen) and subtracts the areas from the exposed region. The returned
   region is the area of the window which should have expose events generated
   for and can be either a new region, pWin->exposed, or NULL. The region
   left in pRegion is set to the area of the window which should be painted
   with the window background.



        RegionPtr pScreen->TranslateBackingStore(pWin, dx, dy, oldClip, oldx, oldy)
                WindowPtr pWin;
                int dx, dy;
                RegionPtr oldClip;
                int oldx, oldy;

   This is called when the window is moved or resized so that the backing
   store can be translated if necessary. oldClip is the old cliplist for the
   window, which is used to save doomed areas if the window is moved
   underneath its parent as a result of bitgravity. The returned region
   represents occluded areas of the window for which the backing store
   contents are invalid.



        void pScreen->ExposeCopy(pSrc, pDst, pGC, prgnExposed, srcx, srcy, dstx, dsty, plane)
                WindowPtr pSrc;
                DrawablePtr pDst;
                GCPtr pGC;
                RegionPtr prgnExposed;
                int srcx;
                int srcy;
                int dstx;
                int dsty;
                unsigned long plane;

   Copies a region from the backing store of pSrc to pDs.



        RegionPtr pScreen->ClearBackingStore(pWindow, x, y, w, h, generateExposures)
                WindowPtr pWindow;
                int x;
                int y;
                int w;
                int h;
                Bool generateExposures;

   Clear the given area of the backing pixmap with the background of the
   window. If generateExposures is TRUE, generate exposure events for the
   area. Note that if the area has any part outside the saved portions of the
   window, we do not allow the count in the expose events to be 0, since
   there will be more expose events to come.



             void pScreen->DrawGuarantee(pWindow, pGC, guarantee)
                     WindowPtr pWindow;
                     GCPtr pGC;
                     int guarantee;

   This informs the backing store layer that you are about to validate a gc
   with a window, and that subsequent output to the window is (or is not)
   guaranteed to be already clipped to the visible regions of the window.

   --------------------------------------------------------------------------

      Screen Operations for Multi-Layered Framebuffers

    The following screen functions are useful if you have a framebuffer with
   multiple sets of independent bit planes, e.g. overlays or underlays in
   addition to the "main" planes. If you have a simple single-layer
   framebuffer, you should probably use the mi versions of these routines in
   mi/miwindow.c. This can be easily accomplished by calling miScreenInit.



         void pScreen->MarkWindow(pWin)
             WindowPtr pWin;

   This formerly dix function MarkWindow has moved to ddx and is accessed via
   this screen function. This function should store something, usually a
   pointer to a device-dependent structure, in pWin->valdata so that
   ValidateTree has the information it needs to validate the window.



         Bool pScreen->MarkOverlappedWindows(parent, firstChild, ppLayerWin)
             WindowPtr parent;
             WindowPtr firstChild;
             WindowPtr * ppLayerWin;

   This formerly dix function MarkWindow has moved to ddx and is accessed via
   this screen function. In the process, it has grown another parameter:
   ppLayerWin, which is filled in with a pointer to the window at which save
   under marking and ValidateTree should begin. In the single-layered
   framebuffer case, pLayerWin == pWin.



         Bool pScreen->ChangeSaveUnder(pLayerWin, firstChild)
             WindowPtr pLayerWin;
             WindowPtr firstChild;

   The dix functions ChangeSaveUnder and CheckSaveUnder have moved to ddx and
   are accessed via this screen function. pLayerWin should be the window
   returned in the ppLayerWin parameter of MarkOverlappedWindows. The
   function may turn on backing store for windows that might be covered, and
   may partially turn off backing store for windows. It returns TRUE if
   PostChangeSaveUnder needs to be called to finish turning off backing
   store.



         void pScreen->PostChangeSaveUnder(pLayerWin, firstChild)
             WindowPtr pLayerWin;
             WindowPtr firstChild;

   The dix function DoChangeSaveUnder has moved to ddx and is accessed via
   this screen function. This function completes the job of turning off
   backing store that was started by ChangeSaveUnder.



         void pScreen->MoveWindow(pWin, x, y, pSib, kind)
             WindowPtr pWin;
             int x;
             int y;
             WindowPtr pSib;
             VTKind kind;

   The formerly dix function MoveWindow has moved to ddx and is accessed via
   this screen function. The new position of the window is given by x,y. kind
   is VTMove if the window is only moving, or VTOther if the border is also
   changing.



         void pScreen->ResizeWindow(pWin, x, y, w, h, pSib)
             WindowPtr pWin;
             int x;
             int y;
             unsigned int w;
             unsigned int h;
             WindowPtr pSib;

   The formerly dix function SlideAndSizeWindow has moved to ddx and is
   accessed via this screen function. The new position is given by x,y. The
   new size is given by w,h.



         WindowPtr pScreen->GetLayerWindow(pWin)
             WindowPtr pWin

   This is a new function which returns a child of the layer parent of pWin.



         void pScreen->HandleExposures(pWin)
             WindowPtr pWin;

   The formerly dix function HandleExposures has moved to ddx and is accessed
   via this screen function. This function is called after ValidateTree and
   uses the information contained in valdata to send exposures to windows.



         void pScreen->ReparentWindow(pWin, pPriorParent)
             WindowPtr pWin;
             WindowPtr pPriorParent;

   This function will be called when a window is reparented. At the time of
   the call, pWin will already be spliced into its new position in the window
   tree, and pPriorParent is its previous parent. This function can be NULL.



         void pScreen->SetShape(pWin)
             WindowPtr pWin;

   The formerly dix function SetShape has moved to ddx and is accessed via
   this screen function. The window's new shape will have already been stored
   in the window when this function is called.



         void pScreen->ChangeBorderWidth(pWin, width)
             WindowPtr pWin;
             unsigned int width;

   The formerly dix function ChangeBorderWidth has moved to ddx and is
   accessed via this screen function. The new border width is given by width.



         void pScreen->MarkUnrealizedWindow(pChild, pWin, fromConfigure)
             WindowPtr pChild;
             WindowPtr pWin;
             Bool fromConfigure;

   This function is called for windows that are being unrealized as part of
   an UnrealizeTree. pChild is the window being unrealized, pWin is an
   ancestor, and the fromConfigure value is simply propogated from
   UnrealizeTree.

   --------------------------------------------------------------------------

  Graphics Contexts and Validation

    This graphics context (GC) contains state variables such as foreground
   and background pixel value (color), the current line style and width, the
   current tile or stipple for pattern generation, the current font for text
   generation, and other similar attributes.

    In many graphics systems, the equivalent of the graphics context and the
   drawable are combined as one entity. The main distinction between the two
   kinds of status is that a drawable describes a writing surface and the
   writings that may have already been done on it, whereas a graphics context
   describes the drawing process. A drawable is like a chalkboard. A GC is
   like a piece of chalk.

    Unlike many similar systems, there is no "current pen location." Every
   graphic operation is accompanied by the coordinates where it is to happen.

    The GC also includes two vectors of procedure pointers, the first operate
   on the GC itself and are called GC funcs. The second, called GC ops,
   contains the functions that carry out the fundamental graphic operations
   such as drawing lines, polygons, arcs, text, and copying bitmaps. The DDX
   graphic software can, if it wants to be smart, change these two vectors of
   procedure pointers to take advantage of hardware/firmware in the server
   machine, which can do a better job under certain circumstances. To reduce
   the amount of memory consumed by each GC, it is wise to create a few
   "boilerplate" GC ops vectors which can be shared by every GC which matches
   the constraints for that set. Also, it is usually reasonable to have every
   GC created by a particular module to share a common set of GC funcs.
   Samples of this sort of sharing can be seen in cfb/cfbgc.c and
   mfb/mfbgc.c.

    The DDX software is notified any time the client (or DIX) uses a changed
   GC. For instance, if the hardware has special support for drawing
   fixed-width fonts, DDX can intercept changes to the current font in a GC
   just before drawing is done. It can plug into either a fixed-width
   procedure that makes the hardware draw characters, or a variable-width
   procedure that carefully lays out glyphs by hand in software, depending
   upon the new font that is selected.

    A definition of these structures can be found in the file
   Xserver/include/gcstruct.h.

    Also included in each GC is an array of devPrivates which portions of the
   DDX can use for any reason. Entries in this array are allocated with
   AllocateGCPrivateIndex() (see Wrappers and Privates below).

    The DIX routines available for manipulating GCs are CreateGC, ChangeGC,
   CopyGC, SetClipRects, SetDashes, and FreeGC.


             GCPtr CreateGC(pDrawable, mask, pval, pStatus)
                 DrawablePtr pDrawable;
                 BITS32 mask;
                 XID *pval;
                 int *pStatus;

             int ChangeGC(pGC, mask, pval)
                 GCPtr pGC;
                 BITS32 mask;
                 XID *pval;

             int CopyGC(pgcSrc, pgcDst, mask)
                 GCPtr pgcSrc;
                 GCPtr pgcDst;
                 BITS32 mask;

             int SetClipRects(pGC, xOrigin, yOrigin, nrects, prects, ordering)
                 GCPtr pGC;
                 int xOrigin, yOrigin;
                 int nrects;
                 xRectangle *prects;
                 int ordering;

             SetDashes(pGC, offset, ndash, pdash)
                 GCPtr pGC;
                 unsigned offset;
                 unsigned ndash;
                 unsigned char *pdash;

             int FreeGC(pGC, gid)
                 GCPtr pGC;
                 GContext gid;

    As a convenience, each Screen structure contains an array of GCs that are
   preallocated, one at each depth the screen supports. These are
   particularly useful in the mi code. Two DIX routines must be used to get
   these GCs:

             GCPtr GetScratchGC(depth, pScreen)
                 int depth;
                 ScreenPtr pScreen;

             FreeScratchGC(pGC)
                 GCPtr pGC;

   Always use these two routines, don't try to extract the scratch GC
   yourself -- someone else might be using it, so a new one must be created
   on the fly.

    If you need a GC for a very long time, say until the server is restarted,
   you should not take one from the pool used by GetScratchGC, but should get
   your own using CreateGC or CreateScratchGC. This leaves the ones in the
   pool free for routines that only need it for a little while and don't want
   to pay a heavy cost to get it.

             GCPtr CreateScratchGC(pScreen, depth)
                 ScreenPtr pScreen;
                 int depth;

   NULL is returned if the GC cannot be created. The GC returned can be freed
   with FreeScratchGC.

   --------------------------------------------------------------------------

    Details of Operation

    At screen initialization, a screen must supply a GC creation procedure.
   At GC creation, the screen must fill in GC funcs and GC ops vectors
   (Xserver/include/gcstruct.h). For any particular GC, the func vector must
   remain constant, while the op vector may vary. This invariant is to ensure
   that Wrappers work correctly.

    When a client request is processed that results in a change to the GC,
   the device-independent state of the GC is updated. This includes a record
   of the state that changed. Then the ChangeGC GC func is called. This is
   useful for graphics subsystems that are able to process state changes in
   parallel with the server CPU. DDX may opt not to take any action at
   GC-modify time. This is more efficient if multiple GC-modify requests
   occur between draws using a given GC.

    Validation occurs at the first draw operation that specifies the GC after
   that GC was modified. DIX calls then the ValidateGC GC func. DDX should
   then update its internal state. DDX internal state may be stored as one or
   more of the following: 1) device private block on the GC; 2) hardware
   state; 3) changes to the GC ops.

    The GC contains a serial number, which is loaded with a number fetched
   from the window that was drawn into the last time the GC was used. The
   serial number in the drawable is changed when the drawable's clipList or
   absCorner changes. Thus, by comparing the GC serial number with the
   drawable serial number, DIX can force a validate if the drawable has been
   changed since the last time it was used with this GC.

    In addition, the drawable serial number is always guaranteed to have the
   most significant bit set to 0. Thus, the DDX layer can set the most
   significant bit of the serial number to 1 in a GC to force a validate the
   next time the GC is used. DIX also uses this technique to indicate that a
   change has been made to the GC by way of a SetGC, a SetDashes or a SetClip
   request.

   --------------------------------------------------------------------------

    GC Handling Routines

    The ScreenRec data structure has a pointer for CreateGC().

             Bool pScreen->CreateGC(pGC)
                     GCPtr pGC;

   This routine must fill in the fields of a dynamically allocated GC that is
   passed in. It does NOT allocate the GC record itself or fill in the
   defaults; DIX does that.

    This must fill in both the GC funcs and ops; none of the drawing
   functions will be called before the GC has been validated, but the others
   (dealing with allocating of clip regions, changing and destroying the GC,
   etc.) might be.

    The GC funcs vector contains pointers to 7 routines and a devPrivate
   field:

             pGC->funcs->ChangeGC(pGC, changes)
                     GCPtr pGC;
                     unsigned long changes;

   This GC func is called immediately after a field in the GC is changed.
   changes is a bit mask indicating the changed fields of the GC in this
   request.

    The ChangeGC routine is useful if you have a system where state-changes
   to the GC can be swallowed immediately by your graphics system, and a
   validate is not necessary.



             pGC->funcs->ValidateGC(pGC, changes, pDraw)
                     GCPtr pGC;
                     unsigned long changes;
                     DrawablePtr pDraw;

   ValidateGC is called by DIX just before the GC will be used when one of
   many possible changes to the GC or the graphics system has happened. It
   can modify a devPrivates field of the GC or its contents, change the op
   vector, or change hardware according to the values in the GC. It may not
   change the device-independent portion of the GC itself.

    In almost all cases, your ValidateGC() procedure should take the regions
   that drawing needs to be clipped to and combine them into a composite clip
   region, which you keep a pointer to in the private part of the GC. In this
   way, your drawing primitive routines (and whatever is below them) can
   easily determine what to clip and where. You should combine the regions
   clientClip (the region that the client desires to clip output to) and the
   region returned by NotClippedByChildren(), in DIX. An example is in
   Xserver/mfb/mfbgc.c.

    Some kinds of extension software may cause this routine to be called more
   than originally intended; you should not rely on algorithms that will
   break under such circumstances.

    See the Strategies document for more information on creatively using this
   routine.



             pGC->funcs->CopyGC(pGCSrc, mask, pGCDst)
                     GCPtr pGCSrc;
                     unsigned long mask;
                     GCPtr pGCDst;

   This routine is called by DIX when a GC is being copied to another GC.
   This is for situations where dynamically allocated chunks of memory are
   hanging off a GC devPrivates field which need to be transferred to the
   destination GC.



             pGC->funcs->DestroyGC(pGC)
                     GCPtr pGC;

   This routine is called before the GC is destroyed for the entity
   interested in this GC to clean up after itself. This routine is
   responsible for freeing any auxiliary storage allocated.

   --------------------------------------------------------------------------

    GC Clip Region Routines

    The GC clientClip field requires three procedures to manage it. These
   procedures are in the GC funcs vector. The underlying principle is that
   dix knows nothing about the internals of the clipping information, (except
   when it has come from the client), and so calls ddX whenever it needs to
   copy, set, or destroy such information. It could have been possible for
   dix not to allow ddX to touch the field in the GC, and require it to keep
   its own copy in devPriv, but since clip masks can be very large, this
   seems like a bad idea. Thus, the server allows ddX to do whatever it wants
   to the clientClip field of the GC, but requires it to do all manipulation
   itself.



             void pGC->funcs->ChangeClip(pGC, type, pValue, nrects)
                     GCPtr pGC;
                     int type;
                     char *pValue;
                     int nrects;

   This routine is called whenever the client changes the client clip region.
   The pGC points to the GC involved, the type tells what form the region has
   been sent in. If type is CT_NONE, then there is no client clip. If type is
   CT_UNSORTED, CT_YBANDED or CT_YXBANDED, then pValue pointer to a list of
   rectangles, nrects long. If type is CT_REGION, then pValue pointer to a
   RegionRec from the mi region code. If type is CT_PIXMAP pValue is a
   pointer to a pixmap. (The defines for CT_NONE, etc. are in
   Xserver/include/gc.h.) This routine is responsible for incrementing any
   necessary reference counts (e.g. for a pixmap clip mask) for the new
   clipmask and freeing anything that used to be in the GC's clipMask field.
   The lists of rectangles passed in can be freed with Xfree(), the regions
   can be destroyed with the RegionDestroy field in the screen, and pixmaps
   can be destroyed by calling the screen's DestroyPixmap function. DIX and
   MI code expect what they pass in to this to be freed or otherwise
   inaccessible, and will never look inside what's been put in the GC. This
   is a good place to be wary of storage leaks.

    In the sample server, this routine transforms either the bitmap or the
   rectangle list into a region, so that future routines will have a more
   predictable starting point to work from. (The validate routine must take
   this client clip region and merge it with other regions to arrive at a
   composite clip region before any drawing is done.)



             void pGC->funcs->DestroyClip(pGC)
                     GCPtr pGC;

   This routine is called whenever the client clip region must be destroyed.
   The pGC points to the GC involved. This call should set the clipType field
   of the GC to CT_NONE. In the sample server, the pointer to the client clip
   region is set to NULL by this routine after destroying the region, so that
   other software (including ChangeClip() above) will recognize that there is
   no client clip region.



             void pGC->funcs->CopyClip(pgcDst, pgcSrc)
                     GCPtr pgcDst, pgcSrc;

   This routine makes a copy of the clipMask and clipType from pgcSrc into
   pgcDst. It is responsible for destroying any previous clipMask in pgcDst.
   The clip mask in the source can be the same as the clip mask in the dst
   (clients do the strangest things), so care must be taken when destroying
   things. This call is required because dix does not know how to copy the
   clip mask from pgcSrc.

   --------------------------------------------------------------------------

  Drawing Primitives

    The X protocol (rules for the byte stream that goes between client and
   server) does all graphics using primitive operations, which are called
   Drawing Primitives. These include line drawing, area filling, arcs, and
   text drawing. Your implementation must supply 16 routines to perform these
   on your hardware. (The number 16 is arbitrary.)

    More specifically, 16 procedure pointers are in each GC op vector. At any
   given time, ALL of them MUST point to a valid procedure that attempts to
   do the operation assigned, although the procedure pointers may change and
   may point to different procedures to carry out the same operation. A
   simple server will leave them all pointing to the same 16 routines, while
   a more optimized implementation will switch each from one procedure to
   another, depending upon what is most optimal for the current GC and
   drawable.

    The sample server contains a considerable chunk of code called the mi
   (machine independent) routines, which serve as drawing primitive routines.
   Many server implementations will be able to use these as-is, because they
   work for arbitrary depths. They make no assumptions about the formats of
   pixmaps and frame buffers, since they call a set of routines known as the
   "Pixblit Routines" (see next section). They do assume that the way to draw
   is through these low-level routines that apply pixel values rows at a
   time. If your hardware or firmware gives more performance when things are
   done differently, you will want to take this fact into account and rewrite
   some or all of the drawing primitives to fit your needs.

   --------------------------------------------------------------------------

    GC Components

    This section describes the fields in the GC that affect each drawing
   primitive. The only primitive that is not affected is GetImage, which does
   not use a GC because its destination is a protocol-style bit image. Since
   each drawing primitive mirrors exactly the X protocol request of the same
   name, you should refer to the X protocol specification document for more
   details.

    ALL of these routines MUST CLIP to the appropriate regions in the
   drawable. Since there are many regions to clip to simultaneously, your
   ValidateGC routine should combine these into a unified clip region to
   which your drawing routines can quickly refer. This is exactly what the
   cfb and mfb routines supplied with the sample server do. The mi
   implementation passes responsibility for clipping while drawing down to
   the Pixblit routines.

    Also, all of them must adhere to the current plane mask. The plane mask
   has one bit for every bit plane in the drawable; only planes with 1 bits
   in the mask are affected by any drawing operation.

    All functions except for ImageText calls must obey the alu function. This
   is usually Copy, but could be any of the allowable 16 raster-ops.

    All of the functions, except for CopyArea, might use the current
   foreground and background pixel values. Each pixel value is 32 bits. These
   correspond to foreground and background colors, but you have to run them
   through the colormap to find out what color the pixel values represent. Do
   not worry about the color, just apply the pixel value.

    The routines that draw lines (PolyLine, PolySegment, PolyRect, and
   PolyArc) use the line width, line style, cap style, and join style. Line
   width is in pixels. The line style specifies whether it is solid or
   dashed, and what kind of dash. The cap style specifies whether Rounded,
   Butt, etc. The join style specifies whether joins between joined lines are
   Miter, Round or Beveled. When lines cross as part of the same polyline,
   they are assumed to be drawn once. (See the X protocol specification for
   more details.)

    Zero-width lines are NOT meant to be really zero width; this is the
   client's way of telling you that you can optimize line drawing with little
   regard to the end caps and joins. They are called "thin" lines and are
   meant to be one pixel wide. These are frequently done in hardware or in a
   streamlined assembly language routine.

    Lines with widths greater than zero, though, must all be drawn with the
   same algorithm, because client software assumes that every jag on every
   line at an angle will come at the same place. Two lines that should have
   one pixel in the space between them (because of their distance apart and
   their widths) should have such a one-pixel line of space between them if
   drawn, regardless of angle.

    The solid area fill routines (FillPolygon, PolyFillRect, PolyFillArc) all
   use the fill rule, which specifies subtle interpretations of what points
   are inside and what are outside of a given polygon. The PolyFillArc
   routine also uses the arc mode, which specifies whether to fill pie
   segments or single-edge slices of an ellipse.

    The line drawing, area fill, and PolyText routines must all apply the
   correct "fill style." This can be either a solid foreground color, a
   transparent stipple, an opaque stipple, or a tile. Stipples are bitmaps
   where the 1 bits represent that the foreground color is written, and 0
   bits represent that either the pixel is left alone (transparent) or that
   the background color is written (opaque). A tile is a pixmap of the full
   depth of the GC that is applied in its full glory to all areas. The
   stipple and tile patterns can be any rectangular size, although some
   implementations will be faster for certain sizes such as 8x8 or 32x32. The
   mi implementation passes this responsibility down to the Pixblit routines.

    See the X protocol document for full details. The description of the
   CreateGC request has a very good, detailed description of these
   attributes.

   --------------------------------------------------------------------------

    The Primitives

    The Drawing Primitives are as follows:

        RegionPtr pGC->ops->CopyArea(src, dst, pGC, srcx, srcy, w, h, dstx, dsty)
                DrawablePtr dst, src;
                GCPtr pGC;
                int srcx, srcy, w, h, dstx, dsty;

   CopyArea copies a rectangle of pixels from one drawable to another of the
   same depth. To effect scrolling, this must be able to copy from any
   drawable to itself, overlapped. No squeezing or stretching is done because
   the source and destination are the same size. However, everything is still
   clipped to the clip regions of the destination drawable.

    If pGC->graphicsExposures is True, any portions of the destination which
   were not valid in the source (either occluded by covering windows, or
   outside the bounds of the drawable) should be collected together and
   returned as a region (if this resultant region is empty, NULL can be
   returned instead). Furthermore, the invalid bits of the source are not
   copied to the destination and (when the destination is a window) are
   filled with the background tile. The sample routine miHandleExposures
   generates the appropriate return value and fills the invalid area using
   pScreen->PaintWindowBackground.

    For instance, imagine a window that is partially obscured by other
   windows in front of it. As text is scrolled on your window, the pixels
   that are scrolled out from under obscuring windows will not be available
   on the screen to copy to the right places, and so an exposure event must
   be sent for the client to correctly repaint them. Of course, if you
   implement some sort of backing store, you could do this without resorting
   to exposure events.

    An example implementation is mfbCopyArea() in Xserver/mfb/mfbbitblt.c.



        RegionPtr pGC->ops->CopyPlane(src, dst, pGC, srcx, srcy, w, h, dstx, dsty, plane)
                DrawablePtr dst, src;
                GCPtr pGC;
                int srcx, srcy, w, h, dstx, dsty;
                unsigned long plane;

   CopyPlane must copy one plane of a rectangle from the source drawable onto
   the destination drawable. Because this routine only copies one bit out of
   each pixel, it can copy between drawables of different depths. This is the
   only way of copying between drawables of different depths, except for
   copying bitmaps to pixmaps and applying foreground and background colors
   to it. All other conditions of CopyArea apply to CopyPlane too.

    An example implementation is mfbCopyPlane() in Xserver/mfb/mfbbitblt.c.



             void pGC->ops->PolyPoint(dst, pGC, mode, n, pPoint)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int mode;
                     int n;
                     DDXPointPtr pPoint;

   PolyPoint draws a set of one-pixel dots (foreground color) at the
   locations given in the array. mode is one of the defined constants Origin
   (absolute coordinates) or Previous (each coordinate is relative to the
   last). Note that this does not use the background color or any tiles or
   stipples.

    Example implementations are mfbPolyPoint() in Xserver/mfb/mfbpolypnt.c
   and miPolyPoint in Xserver/mi/mipolypnt.c.



             void pGC->ops->Polylines(dst, pGC, mode, n, pPoint)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int mode;
                     int n;
                     DDXPointPtr pPoint;

   Similar to PolyPoint, Polylines draws lines between the locations given in
   the array. Zero-width lines are NOT meant to be really zero width; this is
   the client's way of telling you that you can maximally optimize line
   drawing with little regard to the end caps and joins. mode is one of the
   defined constants Previous or Origin, depending upon whether the points
   are each relative to the last or are absolute.

    Example implementations are miWideLine() and miWideDash() in
   mi/miwideline.c and miZeroLine() in mi/mizerline.c.



             void pGC->ops->PolySegment(dst, pGC, n, pPoint)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int n;
                     xSegment *pSegments;

   PolySegments draws unconnected lines between pairs of points in the array;
   the array must be of even size; no interconnecting lines are drawn.

    An example implementation is miPolySegment() in mipolyseg.c.



             void pGC->ops->PolyRectangle(dst, pGC, n, pRect)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int n;
                     xRectangle *pRect;

   PolyRectangle draws outlines of rectangles for each rectangle in the
   array.

    An example implementation is miPolyRectangle() in
   Xserver/mi/mipolyrect.c.



             void pGC->ops->PolyArc(dst, pGC, n, pArc)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int n;
                     xArc*pArc;

   PolyArc draws connected conic arcs according to the descriptions in the
   array. See the protocol specification for more details.

    Example implementations are miZeroPolyArc in Xserver/mi/mizerarc. and
   miPolyArc() in Xserver/mi/miarc.c.



             void pGC->ops->FillPolygon(dst, pGC, shape, mode, count, pPoint)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int shape;
                     int mode;
                     int count;
                     DDXPointPtr pPoint;

   FillPolygon fills a polygon specified by the points in the array with the
   appropriate fill style. If necessary, an extra border line is assumed
   between the starting and ending lines. The shape can be used as a hint to
   optimize filling; it indicates whether it is convex (all interior angles
   less than 180), nonconvex (some interior angles greater than 180 but
   border does not cross itself), or complex (border crosses itself). You can
   choose appropriate algorithms or hardware based upon mode. mode is one of
   the defined constants Previous or Origin, depending upon whether the
   points are each relative to the last or are absolute.

    An example implementation is miFillPolygon() in Xserver/mi/mipoly.c.



             void pGC->ops->PolyFillRect(dst, pGC, n, pRect)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int n;
                     xRectangle *pRect;

   PolyFillRect fills multiple rectangles.

    Example implementations are mfbPolyFillRect() in Xserver/mfb/mfbfillrct.c
   and miPolyFillRect() in Xserver/mi/mifillrct.c.



             void pGC->ops->PolyFillArc(dst, pGC, n, pArc)
                     DrawablePtr dst;
                     GCPtr pGC;
                     int n;
                     xArc *pArc;

   PolyFillArc fills a shape for each arc in the list that is bounded by the
   arc and one or two line segments with the current fill style.

    An example implementation is miPolyFillArc() in Xserver/mi/mifillarc.c.



        void pGC->ops->PutImage(dst, pGC, depth, x, y, w, h, leftPad, format, pBinImage)
                DrawablePtr dst;
                GCPtr pGC;
                int x, y, w, h;
                int format;
                char *pBinImage;

   PutImage copies a pixmap image into the drawable. The pixmap image must be
   in X protocol format (either Bitmap, XYPixmap, or ZPixmap), and format
   tells the format. (See the X protocol specification for details on these
   formats). You must be able to accept all three formats, because the client
   gets to decide which format to send. Either the drawable and the pixmap
   image have the same depth, or the source pixmap image must be a Bitmap. If
   a Bitmap, the foreground and background colors will be applied to the
   destination.

    An example implementation is miPutImage() in Xserver/mfb/mibitblt.c.



           void pScreen->GetImage(src, x, y, w, h, format, planeMask, pBinImage)
                    DrawablePtr src;
                    int x, y, w, h;
                    unsigned int format;
                    unsigned long planeMask;
                    char *pBinImage;

   GetImage copies the bits from the source drawable into the destination
   pointer. The bits are written into the buffer according to the
   server-defined pixmap padding rules. pBinImage is guaranteed to be big
   enough to hold all the bits that must be written.

    This routine does not correspond exactly to the X protocol GetImage
   request, since DIX has to break the reply up into buffers of a size
   requested by the transport layer. If format is ZPixmap, the bits are
   written in the ZFormat for the depth of the drawable; if there is a 0 bit
   in the planeMask for a particular plane, all pixels must have the bit in
   that plane equal to 0. If format is XYPixmap, planemask is guaranteed to
   have a single bit set; the bits should be written in Bitmap format, which
   is the format for a single plane of an XYPixmap.

    An example implementation is miGetImage() in Xserver/mi/mibitblt.c.

             void pGC->ops->ImageText8(pDraw, pGC, x, y, count, chars)
                     DrawablePtr pDraw;
                     GCPtr pGC;
                     int x, y;
                     int count;
                     char *chars;

   ImageText8 draws text. The text is drawn in the foreground color; the
   background color fills the remainder of the character rectangles. The
   coordinates specify the baseline and start of the text.

    An example implementation is miImageText8() in Xserver/mi/mipolytext.c.



             int pGC->ops->PolyText8(pDraw, pGC, x, y, count, chars)
                     DrawablePtr pDraw;
                     GCPtr pGC;
                     int x, y;
                     int count;
                     char *chars;

   PolyText8 works like ImageText8, except it draws with the current fill
   style for special effects such as shaded text. See the X protocol
   specification for more details.

    An example implementation is miPolyText8() in Xserver/mi/mipolytext.c.



             int pGC->ops->PolyText16(pDraw, pGC, x, y, count, chars)
                     DrawablePtr pDraw;
                     GCPtr pGC;
                     int x, y;
                     int count;
                     unsigned short *chars;

             void pGC->ops->ImageText16(pDraw, pGC, x, y, count, chars)
                     DrawablePtr pDraw;
                     GCPtr pGC;
                     int x, y;
                     int count;
                     unsigned short *chars;

   These two routines are the same as the "8" versions, except that they are
   for 16-bit character codes (useful for oriental writing systems).

    The primary difference is in the way the character information is looked
   up. The 8-bit and the 16-bit versions obviously have different kinds of
   character values to look up; the main goal of the lookup is to provide a
   pointer to the CharInfo structs for the characters to draw and to pass
   these pointers to the Glyph routines. Given a CharInfo struct, lower-level
   software can draw the glyph desired with little concern for other
   characteristics of the font.

    16-bit character fonts have a row-and-column scheme, where the 2bytes of
   the character code constitute the row and column in a square matrix of
   CharInfo structs. Each font has row and column minimum and maximum values;
   the CharInfo structures form a two-dimensional matrix.

    Example implementations are miPolyText16() and miImageText16() in
   Xserver/mi/mipolytext.c.

    See the X protocol specification for more details on these graphic
   operations.

    There is a hook in the GC ops, called LineHelper, that used to be used in
   the sample implementation by the code for wide lines. It no longer servers
   any purpose in the sample servers, but still exists, #ifdef'ed by
   NEED_LINEHELPER, in case someone needs it.

   --------------------------------------------------------------------------

  Pixblit Procedures

    The Drawing Primitive functions must be defined for your server. One
   possible way to do this is to use the mi routines from the sample server.
   If you choose to use the mi routines (even part of them!) you must
   implement these Pixblit routines. These routines read and write pixel
   values and deal directly with the image data.

    The Pixblit routines for the sample server are part of the "mfb" routines
   (for Monochrome Frame Buffer), and "cfb" routines (for Color Frame
   Buffer). As with the mi routines, the mfb and cfb routines are portable
   but are not as portable as the mi routines.

    The mfb routines only work for monochrome frame buffers, the simplest
   type of display. Furthermore, they only work for screens that organize
   their bits in rows of pixels on the screen. (See the Strategies document
   for more details on porting mfb.) The cfb routines work for packed-pixel
   displays from 2 to 32 bits in depth, although they have a bit of code
   which has been tuned to run on 8-bit (1 pixel per byte) displays.

    In other words, if you have a "normal" frame buffer type display, you can
   probably use either the mfb or cfb code, and the mi code. If you have a
   stranger hardware, you will have to supply your own Pixblit routines, but
   you can use the mi routines on top of them. If you have better ways of
   doing some of the Drawing Primitive functions, then you may want to supply
   some of your own Drawing Primitive routines. (Even people who write their
   own Drawing Primitives save at least some of the mi code for certain
   special cases that their hardware or library or fancy algorithm does not
   handle.)

    The client, DIX, and the machine-independent routines do not carry the
   final responsibility of clipping. They all depend upon the Pixblit
   routines to do their clipping for them. The rule is, if you touch the
   frame buffer, you clip.

    (The higher level routines may decide to clip at a high level, but this
   is only for increased performance and cannot substitute for bottom-level
   clipping. For instance, the mi routines, DIX, or the client may decide to
   check all character strings to be drawn and chop off all characters that
   would not be displayed. If so, it must retain the character on the edge
   that is partly displayed so that the Pixblit routines can clip off
   precisely at the right place.)

    To make this easier, all of the reasons to clip can be combined into one
   region in your ValidateGC procedure. You take this composite clip region
   with you into the Pixblit routines. (The sample server does this.)

    Also, FillSpans() has to apply tile and stipple patterns. The patterns
   are all aligned to the window origin so that when two people write patches
   that are contiguous, they will merge nicely. (Really, they are aligned to
   the patOrg point in the GC. This defaults to (0, 0) but can be set by the
   client to anything.)

    However, the mi routines can translate (relocate) the points from
   window-relative to screen-relative if desired. If you set the miTranslate
   field in the GC (set it in the CreateGC or ValidateGC routine), then the
   mi output routines will translate all coordinates. If it is false, then
   the coordinates will be passed window-relative. Screens with no hardware
   translation will probably set miTranslate to TRUE, so that geometry (e.g.
   polygons, rectangles) can be translated, rather than having the resulting
   list of scanlines translated; this is good because the list vertices in a
   drawing request will generally be much smaller than the list of scanlines
   it produces. Similarly, hardware that does translation can set miTranslate
   to FALSE, and avoid the extra addition per vertex, which can be (but is
   not always) important for getting the highest possible performance.
   (Contrast the behavior of GetSpans, which is not expected to be called as
   often, and so has different constraints.) The miTranslate field is
   settable in each GC, if , for example, you are mixing several kinds of
   destinations (offscreen pixmaps, main memory pixmaps, backing store, and
   windows), all of which have different requirements, on one screen.

    As with other drawing routines, there are fields in the GC to direct
   higher code to the correct routine to execute for each function. In this
   way, you can optimize for special cases, for example, drawing solids
   versus drawing stipples.

    The Pixblit routines are broken up into three sets. The Span routines
   simply fill in rows of pixels. The Glyph routines fill in character
   glyphs. The PushPixels routine is a three-input bitblt for more
   sophisticated image creation.

    It turns out that the Glyph and PushPixels routines actually have a
   machine-independent implementation that depends upon the Span routines. If
   you are really pressed for time, you can use these versions, although they
   are quite slow.

   --------------------------------------------------------------------------

    Span Routines

    For these routines, all graphic operations have been reduced to "spans."
   A span is a horizontal row of pixels. If you can design these routines
   which write into and read from rows of pixels at a time, you can use the
   mi routines.

    Each routine takes a destination drawable to draw into, a GC to use while
   drawing, the number of spans to do, and two pointers to arrays that
   indicate the list of starting points and the list of widths of spans.



            void pGC->ops->FillSpans(dst, pGC, nSpans, pPoints, pWidths, sorted)
                    DrawablePtr dst;
                    GCPtr pGC;
                    int nSpans;
                    DDXPointPtr pPoints;
                    int *pWidths;
                    int sorted;

   FillSpans should fill horizontal rows of pixels with the appropriate
   patterns, stipples, etc., based on the values in the GC. The starting
   points are in the array at pPoints; the widths are in pWidths. If sorted
   is true, the scan lines are in increasing y order, in which case you may
   be able to make assumptions and optimizations.

    GC components: alu, clipOrg, clientClip, and fillStyle.

    GC mode-dependent components: fgPixel (for fillStyle Solid); tile, patOrg
   (for fillStyle Tile); stipple, patOrg, fgPixel (for fillStyle Stipple);
   and stipple, patOrg, fgPixel and bgPixel (for fillStyle OpaqueStipple).



        void pGC->ops->SetSpans(pDrawable, pGC, pSrc, ppt, pWidths, nSpans, sorted)
                DrawablePtr pDrawable;
                GCPtr pGC;
                char *pSrc;
                DDXPointPtr pPoints;
                int *pWidths;
                int nSpans;
                int sorted;

   For each span, this routine should copy pWidths bits from pSrc to
   pDrawable at pPoints using the raster-op from the GC. If sorted is true,
   the scan lines are in increasing y order. The pixels in pSrc are padded
   according to the screen's padding rules. These can be used to support
   interesting extension libraries, for example, shaded primitives. It does
   not use the tile and stipple.

    GC components: alu, clipOrg, and clientClip

    The above functions are expected to handle all modifiers in the current
   GC. Therefore, it is expedient to have different routines to quickly
   handle common special cases and reload the procedure pointers at validate
   time, as with the other output functions.



             void pScreen->GetSpans(pDrawable, wMax, pPoints, pWidths, nSpans)
                     DrawablePtr pDrawable;
                     int wMax;
                     DDXPointPtr pPoints;
                     int *pWidths;
                     int nSpans;
                     char *pDst;

   For each span, GetSpans gets bits from the drawable starting at pPoints
   and continuing for pWidths bits. Each scanline returned will be
   server-scanline padded. The routine can return NULL if memory cannot be
   allocated to hold the result.

    GetSpans never translates -- for a window, the coordinates are already
   screen-relative. Consider the case of hardware that doesn't do
   translation: the mi code that calls ddX will translate each shape
   (rectangle, polygon,. etc.) before scan-converting it, which requires many
   fewer additions that having GetSpans translate each span does. Conversely,
   consider hardware that does translate: it can set its translation point to
   (0, 0) and get each span, and the only penalty is the small number of
   additions required to translate each shape being scan-converted by the
   calling code. Contrast the behavior of FillSpans and SetSpans (discussed
   above under miTranslate), which are expected to be used more often.

    Thus, the penalty to hardware that does hardware translation is
   negligible, and code that wants to call GetSpans() is greatly simplified,
   both for extensions and the machine-independent core implementation.

   --------------------------------------------------------------------------

      Glyph Routines

    The Glyph routines draw individual character glyphs for text drawing
   requests.

    You have a choice in implementing these routines. You can use the mi
   versions; they depend ultimately upon the span routines. Although text
   drawing will work, it will be very slow.



        void pGC->ops->PolyGlyphBlt(pDrawable, pGC, x, y, nglyph, ppci, pglyphBase)
                DrawablePtr pDrawable;
                GCPtr pGC;
                int x , y;
                unsigned int nglyph;
                CharInfoRec **ppci;             /* array of character info */
                pointer unused;                 /* unused since R5 */

   GC components: alu, clipOrg, clientClip, font, and fillStyle.

    GC mode-dependent components: fgPixel (for fillStyle Solid); tile, patOrg
   (for fillStyle Tile); stipple, patOrg, fgPixel (for fillStyle Stipple);
   and stipple, patOrg, fgPixel and bgPixel (for fillStyle OpaqueStipple).



        void pGC->ops->ImageGlyphBlt(pDrawable, pGC, x, y, nglyph, ppci, pglyphBase)
                DrawablePtr pDrawable;
                GCPtr pGC;
                int x , y;
                unsigned int nglyph;
                CharInfoRec **ppci;     /* array of character info */
                pointer unused;         /* unused since R5 */

   GC components: clipOrg, clientClip, font, fgPixel, bgPixel

    These routines must copy the glyphs defined by the bitmaps in pglyphBase
   and the font metrics in ppci to the DrawablePtr, pDrawable. The poly
   routine follows all fill, stipple, and tile rules. The image routine
   simply blasts the glyph onto the glyph's rectangle, in foreground and
   background colors.

    More precisely, the Image routine fills the character rectangle with the
   background color, and then the glyph is applied in the foreground color.
   The glyph can extend outside of the character rectangle. ImageGlyph() is
   used for terminal emulators and informal text purposes such as button
   labels.

    The exact specification for the Poly routine is that the glyph is painted
   with the current fill style. The character rectangle is irrelevant for
   this operation. PolyText, at a higher level, includes facilities for font
   changes within strings and such; it is to be used for WYSIWYG word
   processing and similar systems.

    Both of these routines must clip themselves to the overall clipping
   region.

    Example implementations in mi are miPolyGlyphBlt() and miImageGlyphBlt()
   in Xserver/mi/miglblt.c.

   --------------------------------------------------------------------------

      PushPixels routine

    The PushPixels routine writes the current fill style onto the drawable in
   a certain shape defined by a bitmap. PushPixels is equivalent to using a
   second stipple. You can thing of it as pushing the fillStyle through a
   stencil. PushPixels is not used by any of the mi rendering code, but is
   used by the mi software cursor code.

       Suppose the stencil is: 00111100 and the stipple is: 10101010
     PushPixels result: 00101000

    You have a choice in implementing this routine. You can use the mi
   version which depends ultimately upon FillSpans(). Although it will work,
   it will be slow.



          void pGC->ops->PushPixels(pGC, pBitMap, pDrawable, dx, dy, xOrg, yOrg)
                  GCPtr pGC;
                  PixmapPtr pBitMap;
                  DrawablePtr pDrawable;
                  int dx, dy, xOrg, yOrg;

   GC components: alu, clipOrg, clientClip, and fillStyle.

    GC mode-dependent components: fgPixel (for fillStyle Solid); tile, patOrg
   (for fillStyle Tile); stipple, patOrg, fgPixel (for fillStyle Stipple);
   and stipple, patOrg, fgPixel and bgPixel (for fillStyle OpaqueStipple).

    PushPixels applys the foreground color, tile, or stipple from the pGC
   through a stencil onto pDrawable. pBitMap points to a stencil (of which we
   use an area dx wide by dy high), which is oriented over the drawable at
   xOrg, yOrg. Where there is a 1 bit in the bitmap, the destination is set
   according to the current fill style. Where there is a 0 bit in the bitmap,
   the destination is left the way it is.

    This routine must clip to the overall clipping region.

    An Example implementation is miPushPixels() in Xserver/mi/mipushpxl.c.

   --------------------------------------------------------------------------

  Shutdown Procedures



             void AbortDDX()
             void ddxGiveUp()

   Some hardware may require special work to be done before the server exits
   so that it is not left in an intermediate state. As explained in the OS
   layer, FatalError() will call AbortDDX() just before terminating the
   server. In addition, ddxGiveUp() will be called just before terminating
   the server on a "clean" death. What AbortDDX() and ddxGiveUP do is left
   unspecified, only that stubs must exist in the ddx layer. It is up to
   local implementors as to what they should accomplish before termination.

   --------------------------------------------------------------------------

    Command Line Procedures



             int ddxProcessArgument(argc, argv, i)
                 int argc;
                 char *argv[];
                 int i;

             void
             ddxUseMsg()

   You should write these routines to deal with device-dependent command line
   arguments. The routine ddxProcessArgument() is called with the command
   line, and the current index into argv; you should return zero if the
   argument is not a device-dependent one, and otherwise return a count of
   the number of elements of argv that are part of this one argument. For a
   typical option (e.g., "-realtime"), you should return the value one. This
   routine gets called before checks are made against device-independent
   arguments, so it is possible to peek at all arguments or to override
   device-independent argument processing. You can document the
   device-dependent arguments in ddxUseMsg(), which will be called from
   UseMsg() after printing out the device-independent arguments.

   --------------------------------------------------------------------------

  Wrappers and devPrivates

    Two new extensibility concepts have been developed for release 4,
   Wrappers and devPrivates. These replace the R3 GCInterest queues, which
   were not a general enough mechanism for many extensions and only provided
   hooks into a single data structure.

   --------------------------------------------------------------------------

    devPrivates

    devPrivates are arrays of values attached to various data structures
   (Screens, GCs, Windows, and Pixmaps currently). These arrays are sized
   dynamically at server startup (and reset) time as various modules allocate
   portions of them. They can be used for any purpose; each array entry is
   actually a union, DevUnion, of common useful types (pointer, long and
   unsigned long). devPrivates must be allocated on startup and whenever the
   server resets. To make this easier, the global variable "serverGeneration"
   is incremented each time devPrivates should be allocated, but before the
   initialization process begins, typical usage would be:

     static int privateGeneration = 0;

             if (privateGeneration != serverGeneration)
             {
                     allocate devPrivates here.

                     privateGeneration = serverGeneration;
             }

   --------------------------------------------------------------------------

      Screen devPrivates

    An index into every screen devPrivates array is allocated with

             int AllocateScreenPrivateIndex()

   This call can occur at any time, each existing devPrivates array is
   resized to accommodate the new entry. This routine returns -1 indicating
   an allocation failure. Otherwise, the return value can be used to index
   the array of devPrivates on any screen:

        private = (PrivatePointer) pScreen->devPrivates[screenPrivateIndex].ptr;

   The pointer in each screen is not initialized by
   AllocateScreenPrivateIndex().

   --------------------------------------------------------------------------

      Window devPrivates

    An index into every window devPrivates array is allocated with

             int AllocateWindowPrivateIndex ()

   AllocateWindowPrivateIndex() never returns an error. This call must be
   associated with a call which causes a chunk of memory to be automatically
   allocated and attached to the devPrivate entry on every screen which the
   module will need to use the index:

             Bool AllocateWindowPrivate (pScreen, index, amount)
                     ScreenPtr pScreen;
                     int index;
                     unsigned amount;

    If this space is not always needed for every object, use 0 as the amount.
   In this case, the pointer field of the entry in the devPrivates array is
   initialized to NULL. This call exists so that DIX may preallocate all of
   the space required for an object with one call; this reduces memory
   fragmentation considerably. AllocateWindowPrivate returns FALSE on
   allocation failure. Both of these calls must occur before any window
   structures are allocated; the server is careful to avoid window creation
   until all modules are initialized, but do not call this after
   initialization. A typical allocation sequence for WindowPrivates would be:

         privateInitialize (pScreen)
             ScreenPtr pScreen;
         {
             if (privateGeneration != serverGeneration)
             {
                 windowPrivateIndex = AllocateWindowPrivateIndex();
                 privateGeneration = serverGeneration;
             }

             return (AllocateWindowPrivate(pScreen, windowPrivateIndex,
                                           sizeof(windowPrivateStructure)));
         }

   --------------------------------------------------------------------------

      GC and Pixmap devPrivates

    The calls for GCs and Pixmaps mirror the Window calls exactly; they have
   the same requirements and limitations:

             int AllocateGCPrivateIndex ()

             Bool AllocateGCPrivate (pScreen, index, amount)
                     ScreenPtr pScreen;
                     int index;
                     unsigned amount;

             int AllocatePixmapPrivateIndex ()

             Bool AllocatePixmapPrivate (pScreen, index, amount)
                     ScreenPtr pScreen;
                     int index;
                     unsigned amount;

   --------------------------------------------------------------------------

    Wrappers

    Wrappers are not a body of code, nor an interface spec. They are,
   instead, a technique for hooking a new module into an existing calling
   sequence. There are limitations on other portions of the server
   implementation which make using wrappers possible; limits on when specific
   fields of data structures may be modified. They are intended as a
   replacement for GCInterest queues, which were not general enough to
   support existing modules; in particular software cursors and backing store
   both needed more control over the activity. The general mechanism for
   using wrappers is:

privateWrapperFunction (object, ...)
        ObjectPtr       object;
{
        pre-wrapped-function-stuff ...

        object->functionVector = (void *) object->devPrivates[privateIndex].ptr;
        (*object->functionVector) (object, ...);
        /*
         * this next line is occasionally required by the rules governing
         * wrapper functions.  Always using it will not cause problems.
         * Not using it when necessary can cause severe troubles.
         */
        object->devPrivates[privateIndex].ptr = (pointer) object->functionVector;
        object->functionVector = privateWrapperFunction;

        post-wrapped-function-stuff ...
}

privateInitialize (object)
        ObjectPtr       object;
{
        object->devPrivates[privateIndex].ptr = (pointer) object->functionVector;
        object->functionVector = privateWrapperFunction;
}

    Thus the privateWrapperFunction provides hooks for performing work both
   before and after the wrapped function has been called; the process of
   resetting the functionVector is called "unwrapping" while the process of
   fetching the wrapped function and replacing it with the wrapping function
   is called "wrapping". It should be clear that GCInterest queues could be
   emulated using wrappers. In general, any function vectors contained in
   objects can be wrapped, but only vectors in GCs and Screens have been
   tested.

    Wrapping screen functions is quite easy; each vector is individually
   wrapped. Screen functions are not supposed to change after initialization,
   so rewrapping is technically not necessary, but causes no problems.

    Wrapping GC functions is a bit more complicated. GC's have two tables of
   function vectors, one hanging from gc->ops and the other from gc->funcs,
   which should be initially wrapped from a CreateGC wrapper. Wrappers should
   modify only table pointers, not the contents of the tables, as they may be
   shared by more than one GC (and, in the case of funcs, are probably shared
   by all gcs). Your func wrappers may change the GC funcs or ops pointers,
   and op wrappers may change the GC op pointers but not the funcs.

    Thus, the rule for GC wrappings is: wrap the funcs from CreateGC and, in
   each func wrapper, unwrap the ops and funcs, call down, and re-wrap. In
   each op wrapper, unwrap the ops, call down, and rewrap afterwards. Note
   that in re-wrapping you must save out the pointer you're replacing again.
   This way the chain will be maintained when wrappers adjust the funcs/ops
   tables they use.

   --------------------------------------------------------------------------

  Work Queue

    To queue work for execution when all clients are in a stable state (i.e.
   just before calling select() in WaitForSomething), call:

             Bool QueueWorkProc(function,client,closure)
                     Bool            (*function)();
                     ClientPtr       client;
                     pointer         closure;

    When the server is about to suspend itself, the given function will be
   executed:

             (*function) (client, closure)

    Neither client nor closure are actually used inside the work queue
   routines.

   --------------------------------------------------------------------------

Summary of Routines

    This is a summary of the routines discussed in this document. The
   procedure names are in alphabetical order. The Struct is the structure it
   is attached to; if blank, this procedure is not attached to a struct and
   must be named as shown. The sample server provides implementations in the
   following categories. Notice that many of the graphics routines have both
   mi and mfb implementations.



     * dix portable to all systems; do not attempt to rewrite (Xserver/dix)

     * os routine provided in Xserver/os or Xserver/include/os.h

     * ddx frame buffer dependent (examples in Xserver/mfb,Xserver/cfb)

     * mi routine provided in Xserver/mi

     * hd hardware dependent (examples in many Xserver/hw directories)

     * none not implemented in sample implementation

   Table 1. Server Routines (Page 1)

   +-----------------------------------------------+
   |          Procedure           | Port | Struct  |
   |------------------------------+------+---------|
   | ALLOCATE_LOCAL               | os   |         |
   |------------------------------+------+---------|
   | AbortDDX                     | hd   |         |
   |------------------------------+------+---------|
   | AddCallback                  | dix  |         |
   |------------------------------+------+---------|
   | AddEnabledDevice             | os   |         |
   |------------------------------+------+---------|
   | AddInputDevice               | dix  |         |
   |------------------------------+------+---------|
   | AddScreen                    | dix  |         |
   |------------------------------+------+---------|
   | AdjustWaitForDelay           | os   |         |
   |------------------------------+------+---------|
   | Bell                         | hd   | Device  |
   |------------------------------+------+---------|
   | ChangeClip                   | mi   | GC func |
   |------------------------------+------+---------|
   | ChangeGC                     |      | GC func |
   |------------------------------+------+---------|
   | ChangeWindowAttributes       | ddx  | Screen  |
   |------------------------------+------+---------|
   | ClearToBackground            | ddx  | Window  |
   |------------------------------+------+---------|
   | ClientAuthorized             | os   |         |
   |------------------------------+------+---------|
   | ClientSignal                 | dix  |         |
   |------------------------------+------+---------|
   | ClientSleep                  | dix  |         |
   |------------------------------+------+---------|
   | ClientWakeup                 | dix  |         |
   |------------------------------+------+---------|
   | ClipNotify                   | ddx  | Screen  |
   |------------------------------+------+---------|
   | CloseScreen                  | hd   |         |
   |------------------------------+------+---------|
   | ConstrainCursor              | hd   | Screen  |
   |------------------------------+------+---------|
   | CopyArea                     | mi   | GC op   |
   |------------------------------+------+---------|
   | CopyGCDest                   | ddx  | GC func |
   |------------------------------+------+---------|
   | CopyGCSource                 | none | GC func |
   |------------------------------+------+---------|
   | CopyPlane                    | mi   | GC op   |
   |------------------------------+------+---------|
   | CopyWindow                   | ddx  | Window  |
   |------------------------------+------+---------|
   | CreateGC                     | ddx  | Screen  |
   |------------------------------+------+---------|
   | CreateCallbackList           | dix  |         |
   |------------------------------+------+---------|
   | CreatePixmap                 | ddx  | Screen  |
   |------------------------------+------+---------|
   | CreateScreenResources        | ddx  | Screen  |
   |------------------------------+------+---------|
   | CreateWellKnowSockets        | os   |         |
   |------------------------------+------+---------|
   | CreateWindow                 | ddx  | Screen  |
   |------------------------------+------+---------|
   | CursorLimits                 | hd   | Screen  |
   |------------------------------+------+---------|
   | DEALLOCATE_LOCAL             | os   |         |
   |------------------------------+------+---------|
   | DeleteCallback               | dix  |         |
   |------------------------------+------+---------|
   | DeleteCallbackList           | dix  |         |
   |------------------------------+------+---------|
   | DestroyClip                  | ddx  | GC func |
   |------------------------------+------+---------|
   | DestroyGC                    | ddx  | GC func |
   |------------------------------+------+---------|
   | DestroyPixmap                | ddx  | Screen  |
   |------------------------------+------+---------|
   | DestroyWindow                | ddx  | Screen  |
   |------------------------------+------+---------|
   | DisplayCursor                | hd   | Screen  |
   |------------------------------+------+---------|
   | Error                        | os   |         |
   |------------------------------+------+---------|
   | ErrorF                       | os   |         |
   |------------------------------+------+---------|
   | FatalError                   | os   |         |
   |------------------------------+------+---------|
   | FillPolygon                  | mi   | GC op   |
   |------------------------------+------+---------|
   | FillSpans                    | ddx  | GC op   |
   |------------------------------+------+---------|
   | FlushAllOutput               | os   |         |
   |------------------------------+------+---------|
   | FlushIfCriticalOutputPending | os   |         |
   |------------------------------+------+---------|
   | FreeScratchPixmapHeader      | dix  |         |
   |------------------------------+------+---------|
   | GetImage                     | mi   | Screen  |
   |------------------------------+------+---------|
   | GetMotionEvents              | hd   | Device  |
   |------------------------------+------+---------|
   | GetScratchPixmapHeader       | dix  |         |
   |------------------------------+------+---------|
   | GetSpans                     | ddx  | Screen  |
   |------------------------------+------+---------|
   | GetStaticColormap            | ddx  | Screen  |
   +-----------------------------------------------+

   Table 2. Server Routines (Page 2)

   +------------------------------------------+
   |        Procedure         | Port | Struct |
   |--------------------------+------+--------|
   | ImageGlyphBlt            | mi   | GC op  |
   |--------------------------+------+--------|
   | ImageText16              | mi   | GC op  |
   |--------------------------+------+--------|
   | ImageText8               | mi   | GC op  |
   |--------------------------+------+--------|
   | InitInput                | hd   |        |
   |--------------------------+------+--------|
   | InitKeyboardDeviceStruct | dix  |        |
   |--------------------------+------+--------|
   | InitOutput               | hd   |        |
   |--------------------------+------+--------|
   | InitPointerDeviceStruct  | dix  |        |
   |--------------------------+------+--------|
   | InsertFakeRequest        | os   |        |
   |--------------------------+------+--------|
   | InstallColormap          | ddx  | Screen |
   |--------------------------+------+--------|
   | Intersect                | mi   | Screen |
   |--------------------------+------+--------|
   | Inverse                  | mi   | Screen |
   |--------------------------+------+--------|
   | LegalModifier            | hd   |        |
   |--------------------------+------+--------|
   | LineHelper               | mi   | GC op  |
   |--------------------------+------+--------|
   | ListInstalledColormaps   | ddx  | Screen |
   |--------------------------+------+--------|
   | LookupKeyboardDevice     | dix  |        |
   |--------------------------+------+--------|
   | LookupPointerDevice      | dix  |        |
   |--------------------------+------+--------|
   | ModifyPixmapheader       | mi   | Screen |
   |--------------------------+------+--------|
   | NextAvailableClient      | dix  |        |
   |--------------------------+------+--------|
   | OsInit                   | os   |        |
   |--------------------------+------+--------|
   | PaintWindowBackground    | mi   | Window |
   |--------------------------+------+--------|
   | PaintWindowBorder        | mi   | Window |
   |--------------------------+------+--------|
   | PointerNonInterestBox    | hd   | Screen |
   |--------------------------+------+--------|
   | PointInRegion            | mi   | Screen |
   |--------------------------+------+--------|
   | PolyArc                  | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyFillArc              | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyFillRect             | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyGlyphBlt             | mi   | GC op  |
   |--------------------------+------+--------|
   | Polylines                | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyPoint                | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyRectangle            | mi   | GC op  |
   |--------------------------+------+--------|
   | PolySegment              | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyText16               | mi   | GC op  |
   |--------------------------+------+--------|
   | PolyText8                | mi   | GC op  |
   |--------------------------+------+--------|
   | PositionWindow           | ddx  | Screen |
   |--------------------------+------+--------|
   | ProcessInputEvents       | hd   |        |
   |--------------------------+------+--------|
   | PushPixels               | mi   | GC op  |
   |--------------------------+------+--------|
   | PutImage                 | mi   | GC op  |
   |--------------------------+------+--------|
   | QueryBestSize            | hd   | Screen |
   |--------------------------+------+--------|
   | ReadRequestFromClient    | os   |        |
   |--------------------------+------+--------|
   | RealizeCursor            | hd   | Screen |
   |--------------------------+------+--------|
   | RealizeFont              | ddx  | Screen |
   |--------------------------+------+--------|
   | RealizeWindow            | ddx  | Screen |
   |--------------------------+------+--------|
   | RecolorCursor            | hd   | Screen |
   |--------------------------+------+--------|
   | RectIn                   | mi   | Screen |
   |--------------------------+------+--------|
   | RegionCopy               | mi   | Screen |
   |--------------------------+------+--------|
   | RegionCreate             | mi   | Screen |
   |--------------------------+------+--------|
   | RegionDestroy            | mi   | Screen |
   |--------------------------+------+--------|
   | RegionEmpty              | mi   | Screen |
   |--------------------------+------+--------|
   | RegionExtents            | mi   | Screen |
   |--------------------------+------+--------|
   | RegionNotEmpty           | mi   | Screen |
   |--------------------------+------+--------|
   | RegionReset              | mi   | Screen |
   |--------------------------+------+--------|
   | ResolveColor             | ddx  | Screen |
   +------------------------------------------+

   Table 3. Server Routines (Page 3)

   +------------------------------------------------+
   |        Procedure         | Port |    Struct    |
   |--------------------------+------+--------------|
   | RegisterKeyboardDevice   | dix  |              |
   |--------------------------+------+--------------|
   | RegisterPointerDevice    | dix  |              |
   |--------------------------+------+--------------|
   | RemoveEnabledDevice      | os   |              |
   |--------------------------+------+--------------|
   | ResetCurrentRequest      | os   |              |
   |--------------------------+------+--------------|
   | RestoreAreas             | none | BackingStore |
   |--------------------------+------+--------------|
   | SaveDoomedAreas          | none | BackingStore |
   |--------------------------+------+--------------|
   | SaveScreen               | ddx  | Screen       |
   |--------------------------+------+--------------|
   | SetCriticalOutputPending | os   |              |
   |--------------------------+------+--------------|
   | SetCursorPosition        | hd   | Screen       |
   |--------------------------+------+--------------|
   | SetInputCheck            | dix  |              |
   |--------------------------+------+--------------|
   | SetSpans                 | ddx  | GC op        |
   |--------------------------+------+--------------|
   | StoreColors              | ddx  | Screen       |
   |--------------------------+------+--------------|
   | Subtract                 | mi   | Screen       |
   |--------------------------+------+--------------|
   | TimerCancel              | os   |              |
   |--------------------------+------+--------------|
   | TimerCheck               | os   |              |
   |--------------------------+------+--------------|
   | TimerForce               | os   |              |
   |--------------------------+------+--------------|
   | TimerFree                | os   |              |
   |--------------------------+------+--------------|
   | TimerInit                | os   |              |
   |--------------------------+------+--------------|
   | TimerSet                 | os   |              |
   |--------------------------+------+--------------|
   | TimeSinceLastInputEvent  | hd   |              |
   |--------------------------+------+--------------|
   | TranslateBackingStore    | none | BackingStore |
   |--------------------------+------+--------------|
   | TranslateRegion          | mi   | Screen       |
   |--------------------------+------+--------------|
   | UninstallColormap        | ddx  | Screen       |
   |--------------------------+------+--------------|
   | Union                    | mi   | Screen       |
   |--------------------------+------+--------------|
   | UnrealizeCursor          | hd   | Screen       |
   |--------------------------+------+--------------|
   | UnrealizeFont            | ddx  | Screen       |
   |--------------------------+------+--------------|
   | UnrealizeWindow          | ddx  | Screen       |
   |--------------------------+------+--------------|
   | ValidateGC               | ddx  | GC func      |
   |--------------------------+------+--------------|
   | ValidateTree             | mi   | Screen       |
   |--------------------------+------+--------------|
   | WaitForSomething         | os   |              |
   |--------------------------+------+--------------|
   | WindowExposures          | mi   | Window       |
   |--------------------------+------+--------------|
   | WriteToClient            | os   |              |
   |--------------------------+------+--------------|
   | Xalloc                   | os   |              |
   |--------------------------+------+--------------|
   | Xfree                    | os   |              |
   |--------------------------+------+--------------|
   | Xrealloc                 | os   |              |
   +------------------------------------------------+

References

   Visible links
   1. file:///tmp/html-R10689#AEN107
   2. file:///tmp/html-R10689#AEN114
   3. file:///tmp/html-R10689#AEN136
   4. file:///tmp/html-R10689#AEN249
   5. file:///tmp/html-R10689#AEN414
   6. file:///tmp/html-R10689#AEN1213
