Description of the Application Group Extension

Implementation for the X11 Sample Server

Kaleb KEITHLEY

   FUJITSU Limited.

   X Version 11, Release 7.7

   Version 1.0

   Copyright © 1996 X Consortium

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   The following document explains the server side of the
   Application Group Extension.
     __________________________________________________________

   Table of Contents

   AppGroup Server Public Functions
   AppGroup Server Private APIs
   Known Problems in this release.

   To understand this document and the accompanying source code,
   you should know the C language, should be familiar with X
   server internals, and should also have a general knowledge of
   the X Window System.

AppGroup Server Public Functions

   The AppGroup extension adds seven new functions that are called
   from elsewhere in the server. They are: XagExtensionInit,
   XagDefaultColormap, XagRootVisual, XagLeader,
   XagIsControlledRoot, XagConnectionInfo,
   XagCallClientStateChange.

   XagExtensionInit is the extension initialization function
   called from InitExtension in mi/miinitext.c. Note that an new
   resource type, RT_APPGROUP, is created, specifying the
   destructor function XagAppGroupFree.

   XagDefaultColormap returns the colormap ID that was specified
   in the creation of the AppGroup. Any time CopyFromParent is
   specified for a top-level window's colormap, i.e. in a
   CreateWindow or ChangeWindowAttributes request, this function
   is called to see if there is an AppGroup specific colormap to
   use. If there is one, its ID is returned, otherwise None is
   returned.

   XagRootVisual returns the visual ID that was specified in the
   creation of the Appgroup. Like XagDefaultColormap, when
   CopyFromParent is specified for a top-level window's visual in
   a CreateWindow request, this function is called to see if there
   is an AppGroup specific visual to use. If there is one, its ID
   is returned, otherwise 0 (zero) is returned.

   XagLeader returns the ClientPtr of the client that is the
   AppGroup Leader. Normally when an application maps or
   configures a top-level window a MapRequest or ConfigureRequest
   event is delivered to the client, e.g. a window manager, that
   has selected SubstructureRedirect on the root window. However,
   when the application is part of an AppGroup, the MapRequest and
   ConfigureRequest events are delivered to the AppGroup Leader
   instead.

   XagIsControlledRoot returns a boolean: True if the window is a
   top-level window of a client in an AppGroup, False otherwise.
   In a combined server, i.e. one that provides both UI and
   printing, the application may create and map windows on the
   "printing" screens; thus it becomes necessary to discriminate
   between the AppGroup's root window and other root windows. If
   an AppGroup member creates and maps a [top-level] window then
   the window's parent [the root window] is tested to determine
   whether to send MapRequest or ConfigureRequest events to the
   AppGroup Leader to to some other client.

   In the trivial case XagIsControlledRoot returns True if the
   parent window has no parent itself, i.e. it is a root window.
   In the case where the application is embedded, indicated by the
   singleScreen attribute being True, the parent's drawable ID is
   compared to the AppGroup's root window ID, and if it is the
   same, True is returned. If neither case is true, then False is
   returned.

   XagConnectionInfo returns an abreviated version of the
   connection setup information. When an embedded AppGroup is
   created the server returns only the information about the [UI]
   screen that the application is embedded within in the
   connection setup in order to prevent the application from
   creating windows on other screens; thus attempting to guarantee
   that any window that should be embedded can be reparented into
   the AppGroup Leader's window hierarchy.

   XagCallClientStateChange is called to invoke the extension's
   client state change callback additional times as necessary --
   currently only once, after the auth data becomes available
   between ClientStateInitial and ClientStateConnected. Client
   state change callbacks were introduced in the Record extension,
   which specifies when the callbacks are invoked. Unfortunately
   the points at which they are called are not necessarily the
   best as far as the AppGroup Extension is concerned. Adding an
   additional state and calling all the callbacks works too,
   however this seemed unnecessary overkill.

AppGroup Server Private APIs

   The AppGroup extension adds the following functions which are
   private to the extension: ProcXagDispatch and SProcXagDispatch,
   ProcXagQueryVersion and SProcXagQueryVersion, ProcXagCreate and
   SProcXagCreate, ProcXagDestroy and SProcXagDestroy, ProcGetAttr
   and SProcGetAttr, ProcXagQuery and SProcXagQuery,
   ProcXagCreateAssoc and SProcXagCreateAssoc, ProcXagDestroyAssoc
   and SProcXagDestroyAssoc, XagResetProc, and XagAppGroupFree.

   The ProcXagDispatch, SProcXagDispatch, and XagResetProc
   functions should be familiar to anyone familiar with X server
   internals and I won't elaborate on them here. Similarly the
   wrapper functions: SProcXagQueryVersion, SProcXagCreate,
   SProcXagDestroy, SProcXagGetAttr, SProcXagQuery,
   SProcXagCreateAssoc, and SProcXagDestroyAssoc, as wrappers
   which handle swapping integer data into the host's byte order
   will not be explained in any detail.

   ProcXagQueryVersion returns the major and minor versions of the
   AppGroup extension supported by the server.

   ProcXagCreate creates an AppGroup. A new record in a linked
   list of AppGroups is allocated and initialized. The attributes
   from the request are validated and copied to the AppGroup
   record. If necessary an abbreviated version of the connection
   setup information is compiled and also stored in the AppGroup
   record. The first time an AppGroup is created a
   client-state-change callback is registered and a reference
   count is incremented.

   ProcXagDestroy destroys an AppGroup an AppGroup by calling
   FreeResource specifying the AppGroup ID. This will result in
   the destructor function XagAppGroupFree being called. The
   reference count is decremented and when it reaches zero the
   client-state-change callback is deleted.

   ProcXagGetAttr returns the AppGroup Attributes to the
   requesting client.

   ProcXagQuery returns the AppGroup ID of an arbitrary resource
   to the requesting client.

   ProcXagCreateAssoc creates an association between an X window
   ID and system-specific data. In native X this functionality is
   unnecessary but for various personal computers, e.g. Macintosh,
   OS/2, and MS-Windows it is necessary to associate an X window
   ID with the system's native window identifier so that when the
   AppGroup Leader issues a ReparentWindow request the personal
   computer X server can lookup the system-specific window ID and
   make the necessary function call(s) with it.

   ProcXagDestroyAssoc destroys the association created with
   ProcXagCreateAssoc.

   XagResetProc removes the client-state-change callback, sets the
   reference count to zero, and frees all the AppGroup records in
   the linked list by calling XagAppGroupFree.

   XagAppGroupFree calls CloseDownClient for each client in an
   AppGroup if the AppGroup has a leader, unlinks the AppGroup
   record from the linked list, frees allocated memory referenced
   by the record, and finally frees the record itself.

Known Problems in this release.

   In a combined UI/Print server the connection setup returned to
   an embedded application will not have information about the
   print screens.

   The LBX proxy caches connection setup information and will
   return incorrect connection setup information to an embedded
   client.
