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<article id="appgroup">

<articleinfo>
   <title>Description of the Application Group Extension</title>
   <subtitle>Implementation for the X11 Sample Server</subtitle>
   <authorgroup>
      <author>
         <firstname>Kaleb </firstname><surname>KEITHLEY</surname>
         <affiliation><orgname>FUJITSU Limited.</orgname></affiliation>
      </author>
   </authorgroup>
   <releaseinfo>X Version 11, Release &fullrelvers;</releaseinfo>
   <releaseinfo>Version 1.0</releaseinfo>
   <copyright><year>1996</year><holder>X Consortium</holder></copyright>

<legalnotice>
<para>
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:
</para>

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

<para>
THE SOFTWARE IS PROVIDED &ldquo;AS IS&rdquo;, 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.
</para>

<para>
Except as contained in this notice, the name of the X Consortium shall
not be used in advertising or otherwise to promote the sale, use or
other dealings in this Software without prior written authorization
from the X Consortium.
</para>
<para>X Window System is a trademark of The Open Group.</para>
</legalnotice>

<legalnotice>
<para>WindowsNT is a trademark of Microsoft, Inc.</para>
<para>Macintosh and Apple are trademarks of Apple Computer, Inc.</para>
</legalnotice>

<abstract>
<para>
The following document explains the server side of the Application
Group Extension.
</para>
</abstract>

</articleinfo>

<para>
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.
</para>

<sect1 id="AppGroup_Server_Public_Functions">
<title>AppGroup Server Public Functions</title>
<para>
The AppGroup extension adds seven new functions that are called
from elsewhere in the server. They are: XagExtensionInit,
XagDefaultColormap, XagRootVisual, XagLeader, XagIsControlledRoot,
XagConnectionInfo, XagCallClientStateChange.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
XagConnectionInfo returns an abbreviated 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.
</para>
<para>
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.
</para>
</sect1>

<sect1 id="AppGroup_Server_Private_APIs">
<title>AppGroup Server Private APIs</title>
<para>
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.
</para>
<para>
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.
</para>
<para>
ProcXagQueryVersion returns the major and minor versions of the
AppGroup extension supported by the server.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
ProcXagGetAttr returns the AppGroup Attributes to the requesting
client.
</para>
<para>
ProcXagQuery returns the AppGroup ID of an arbitrary resource to
the requesting client.
</para>
<para>
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.
</para>
<para>
ProcXagDestroyAssoc destroys the association created with
ProcXagCreateAssoc.
</para>
<para>
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.
</para>
<para>
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.
</para>
</sect1>

<sect1 id='Known_Problems_in_this_release'>
<title>Known Problems in this release.</title>
<para>
In a combined UI/Print server the connection setup returned to an
embedded application will not have information about the print
screens.
</para>
<para>
The LBX proxy caches connection setup information and will return
incorrect connection setup information to an embedded client.
</para>
</sect1>
</article>
