225 lines
6.0 KiB
Plaintext
225 lines
6.0 KiB
Plaintext
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.\" Use -ms and macros.t
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.\" $Xorg: bigreq.ms,v 1.3 2000/08/17 19:42:30 cpqbld Exp $
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.\" $XdotOrg: xc/doc/specs/Xext/bigreq.ms,v 1.2 2004/04/23 18:42:18 eich Exp $
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.EH ''''
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.OH ''''
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.EF ''''
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.OF ''''
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.ps 10
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.nr PS 10
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\&
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.sp 8
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.ce 1
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\s+2\fBBig Requests Extension\fP\s-2
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.sp 3
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.ce 3
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Version 2.0
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X Consortium Standard
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X Version 11, Release 6.8
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.sp 6
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.ce 4
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Bob Scheifler
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.sp 6p
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X Consortium, Inc.
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.ps 9
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.nr PS 9
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.sp 8
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.LP
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Copyright \(co 1993, 1994 X Consortium
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.LP
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the ``Software''), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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.LP
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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.LP
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THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
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AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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.LP
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Except as contained in this notice, the name of the X Consortium shall not be
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used in advertising or otherwise to promote the sale, use or other dealings
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in this Software without prior written authorization from the X Consortium.
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.ps 10
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.nr PS 10
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.bp 1
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.EH ''Big Requests Extension''
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.OH ''Big Requests Extension''
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.EF ''\fB % \fP''
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.OF ''\fB % \fP''
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.NH 1
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Overview
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.LP
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This extension enables the use of protocol requests that exceed 262140
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bytes in length.
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.LP
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The core protocol restricts the maximum length of a protocol request
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to 262140 bytes, in that it uses a 16-bit length field specifying the
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number of 4-byte units in the request. This is a problem in the core
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protocol when joining large numbers of lines
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.Pn ( PolyLine )
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or arcs
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.Pn ( PolyArc ),
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since these requests cannot be broken up into smaller requests without
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disturbing the rendering of the join points. It is also much more of
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a problem for protocol extensions, such as the PEX extension
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for 3D graphics and the XIE extension for imaging, that need to send
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long data lists in output commands.
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.LP
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This extension defines a mechanism for extending the length field
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beyond 16 bits. If the normal 16-bit length field of the protocol
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request is zero, then an additional 32-bit field containing the actual
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length (in 4-byte units) is inserted into the request, immediately
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following the 16-bit length field.
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.LP
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For example, a normal
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.PN PolyLine
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encoding is:
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.LP
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.Ds 0
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.TA .2i .5i 1.5i 2.5i
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.ta .2i .5i 1.5i 2.5i
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.R
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.PN PolyLine
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1 65 opcode
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1 coordinate-mode
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0 Origin
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1 Previous
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2 3+n request length
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4 DRAWABLE drawable
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4 GCONTEXT gc
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4n LISTofPOINT points
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.De
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.LP
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An extended-length
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.PN PolyLine
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encoding is:
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.LP
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.Ds 0
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.TA .2i .5i 1.5i 2.5i
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.ta .2i .5i 1.5i 2.5i
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.R
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.PN PolyLine
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1 65 opcode
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1 coordinate-mode
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0 Origin
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1 Previous
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2 0 extended length flag
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4 4+n request length
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4 DRAWABLE drawable
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4 GCONTEXT gc
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4n LISTofPOINT points
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.De
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.LP
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Extended-length protocol encodings, once enabled, can be used on all
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protocol requests, including all extensions.
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.NH 1
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Requests
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.LP
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.PN "BigReqEnable"
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.LP
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=>
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.IP
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\fImaximum-request-length\fP\^: CARD32
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.IP
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This request enables extended-length protocol requests
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for the requesting client. It also returns the maximum length of a
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request, in 4-byte units, that can be used in extended-length protocol
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requests. This value will always be greater than the maximum-request-length
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returned in the connection setup information.
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.NH 1
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Events and Errors
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.LP
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No new events or errors are defined by this extension.
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.NH 1
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Encoding
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.LP
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Please refer to the X11 Protocol Encoding document as this document uses
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conventions established there.
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.LP
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The name of this extension is ``BIG-REQUESTS''.
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.LP
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.LP
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.Ds 0
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.TA .2i .5i 1.5i 2.5i
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.ta .2i .5i 1.5i 2.5i
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.R
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.PN BigReqEnable
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1 CARD8 opcode
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1 0 bigreq opcode
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2 1 request length
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.De
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.Ds 0
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.TA .2i .5i 1.5i 2.5i
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.ta .2i .5i 1.5i 2.5i
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.R
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=>
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1 1 Reply
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1 unused
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2 CARD16 sequence number
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4 0 length
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4 CARD32 maximum-request-length
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20 unused
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.De
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.NH 1
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C language binding
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.LP
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It is desirable for core Xlib, and other extensions,
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to use this extension internally when necessary.
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It is also desirable to make the use of this extension as transparent as
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possible to the X client. For example, if enabling of the extension were
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delayed until the first time it was needed, an application that used
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.PN XNextRequest
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to determine the sequence number of a request would no longer get the
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correct sequence number.
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As such,
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.PN XOpenDisplay
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will determine if the extension is supported by the server and, if it is,
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enable extended-length encodings.
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.LP
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The core Xlib functions
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.PN XDrawLines ,
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.PN XDrawArcs ,
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.PN XFillPolygon ,
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.PN XChangeProperty ,
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.PN XSetClipRectangles ,
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and
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.PN XSetRegion
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are required to use extended-length encodings when necessary, if supported
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by the server. Use of extended-length encodings in other core Xlib
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functions
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.Pn ( XDrawPoints ,
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.PN XDrawRectangles ,
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.PN XDrawSegments ,
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.PN XFillArcs ,
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.PN XFillRectangles ,
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.PN XPutImage )
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is permitted but not required; an Xlib implementation may choose to
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split the data across multiple smaller requests instead.
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.LP
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To permit clients to know what the maximum-request-length for extended-length
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encodings is, the following function is added to Xlib:
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.LP
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long
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.br
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XExtendedMaxRequestSize (display)
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.RS
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Display *display;
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.RE
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.IP
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Returns zero (0) if the specified display does not support this
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extension, otherwise returns the maximum-request-length (in 4-byte
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units) supported by the server through the extended-length encoding.
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.NH 1
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Acknowledgements
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.LP
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Clive Feather (IXI) originated the extended-length encoding used in this
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extension proposal.
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