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diff --git a/specs/multibuf.xml b/specs/multibuf.xml new file mode 100644 index 0000000..9e2b065 --- /dev/null +++ b/specs/multibuf.xml @@ -0,0 +1,1628 @@ +<?xml version="1.0" encoding="UTF-8" ?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" + "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" +[ +<!ENTITY % defs SYSTEM "defs.ent"> %defs; +]> + + +<!-- lifted from troff+ms+XMan by doclifter --> +<book id="multibuf"> + +<bookinfo> + <title>Extending X for Double-Buffering, Multi-Buffering, and Stereo</title> + <authorgroup> + <othercredit> + <firstname>Jeffrey</firstname><surname>Friedberg</surname> + </othercredit> + <othercredit> + <firstname>Larry</firstname><surname>Seiler</surname> + </othercredit> + <othercredit> + <firstname>Jeff</firstname><surname>Vroom</surname> + </othercredit> + </authorgroup> + <copyright><year>1989</year><holder>Digital Equipment Corporation</holder></copyright> + <releaseinfo>X Version 11, Release &fullrelvers;</releaseinfo> + <releaseinfo>Version 3.3</releaseinfo> + +<legalnotice> +<para> +Permission to use, copy, modify, and distribute this documentation for any +purpose and without fee is hereby granted, provided that the above copyright +notice and this permission notice appear in all copies. +Digital Equipment Corporation makes no representations +about the suitability for any purpose of the information in +this document. This documentation is provided "as is" +without express or implied warranty. This document +is subject to change. +</para> +</legalnotice> + +<legalnotice> +<para role="multiLicensing">Copyright © 1989, 1994 X Consortium</para> +<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 “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. +</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 OpenGroup.</para> + +</legalnotice> +</bookinfo> + +<preface><title>Warning</title> +<warning><para> +The <emphasis remap='I'>Multi-Buffering</emphasis> extension described here +was a draft standard of the X Consortium prior to Release 6.1. It has been +superseded by the Double Buffer +Extension (DBE). DBE is an X Consortium Standard as of Release 6.1. +</para></warning> +</preface> + +<chapter id='Introduction'> +<title>Introduction</title> + +<para> +Several proposals have been written that address some of the +issues surrounding the support of double-buffered, multi-buffered, +and stereo windows in the X Window System: +</para> + +<itemizedlist> + <listitem> + <para> +<emphasis remap='I'>Extending X for Double-Buffering,</emphasis> +Jeffrey Friedberg, Larry Seiler, Randi Rost. + </para> + </listitem> + <listitem> + <para> +<emphasis remap='I'>(Proposal for) Double-Buffering Extensions</emphasis>, +Jeff Vroom. + </para> + </listitem> + <listitem> + <para> +<emphasis remap='I'>An Extension to X.11 for Displays with Multiple Buffers,</emphasis> +David S.H. Rosenthal. + </para> + </listitem> + <listitem> + <para> +<emphasis remap='I'>A Multiple Buffering/Stereo Proposal</emphasis>, +Mark Patrick. + </para> + </listitem> +</itemizedlist> + +<para> +The authors of this proposal have tried to unify the above documents +to yield a proposal that incorporates support for double-buffering, +multi-buffering, and stereo in a way that is acceptable to all concerned. +</para> +</chapter> + +<chapter id='Goals'> +<title>Goals</title> + +<para> +Clients should be able to: +</para> + +<itemizedlist> + <listitem> + <para> +Associate multiple buffers with a window. + </para> + </listitem> + <listitem> + <para> +Paint in any buffer associated with a window. + </para> + </listitem> + <listitem> + <para> +Display any buffer associated with a window. + </para> + </listitem> + <listitem> + <para> +Display a series of buffers in a window in rapid succession +to achieve a <emphasis remap='I'>smooth</emphasis> animation. + </para> + </listitem> + <listitem> + <para> +Request simultaneous display of different buffers in different windows. + </para> + </listitem> +</itemizedlist> + +<para> +In addition, the extension should: +</para> + +<itemizedlist> + <listitem> + <para> +Allow existing X applications to run unchanged. + </para> + </listitem> + <listitem> + <para> +Support a range of implementation methods that can capitalize on +existing hardware features. + </para> + </listitem> +</itemizedlist> + +</chapter> + +<chapter id='Image_Buffers'> +<title>Image Buffers</title> + +<para> +Normal windows are created using the standard +<function>CreateWindow</function> request: +</para> + +<literallayout class="monospaced"> +CreateWindow + parent : WINDOW + w_id : WINDOW + depth : CARD8 + visual : VISUALID or CopyFromParent + x, y : INT16 + width, height : INT16 + border_width : INT16 + value_mask : BITMASK + value_list : LISTofVALUE +</literallayout> + +<para> +This request allocates a set of window attributes and +a buffer into which an image can be drawn. +The contents of this <emphasis remap='I'>image buffer</emphasis> will +be displayed when the window is mapped to the screen. +</para> + +<para> +To support double-buffering and multi-buffering, +we introduce the notion that additional image buffers can +be created and bound together to form groups. +The following rules will apply: +</para> + +<itemizedlist> + <listitem> + <para> +All image buffers in a group will have the same +visual type, depth, and geometry (ie: width and height). + </para> + </listitem> + <listitem> + <para> +Only one image buffer per group can be displayed +at a time. + </para> + </listitem> + <listitem> + <para> +Draw operations can occur to any image buffer at +any time. + </para> + </listitem> + <listitem> + <para> +Window management requests (<function>MapWindow</function>, <function>DestroyWindow</function>, +<function>ConfigureWindow</function>, etc...) +affect all image buffers associated with a window. + </para> + </listitem> + <listitem> + <para> +Appropriate resize and exposure events will be generated +for every image buffer that is affected by a window +management operation. + </para> + </listitem> +</itemizedlist> + +<para> +By allowing draw operations to occur on any image buffer at any time, +a client could, on a multi-threaded multi-processor server, +simultaneously build up images for display. +To support this, each buffer must have its own resource ID. +Since buffers are different than windows and pixmaps +(buffers are not hierarchical and pixmaps cannot be displayed) +a new resource, <function>Buffer</function>, is introduced. +Furthermore, a <function>Buffer</function> is also a <function>Drawable</function>, thus +draw operations may also be performed on buffers simply +by passing a buffer ID to the existing pixmap/window +interface. +</para> + +<para> +To allow existing X applications to work unchanged, we assume +a window ID passed in a draw request, for a multi-buffered +window, will be an <emphasis remap='I'>alias</emphasis> for the ID of the currently +displayed image buffer. Any draw requests (eq: <function>GetImage</function>) on +the window will be relative to the displayed image buffer. +</para> + +<para> +In window management requests, only a window ID will be +accepted. Requests like <function>QueryTree</function>, will continue to +return only window ID's. Most events will return +just the window ID. Some new events, described in a subsequent +section, will return a buffer ID. +</para> + +<para> +When a window has backing store the contents of the window +are saved off-screen. Likewise, when the contents of an image +buffer of a multi-buffer window is saved off-screen, it is +said to have backing store. This applies to all image buffers, +whether or not they are selected for display. +</para> + +<para> +In some multi-buffer implementations, undisplayed buffers might be +implemented using pixmaps. Since the contents of pixmaps exist +off-screen and are not affected by occlusion, these image buffers +in effect have backing store. +</para> + +<para> +On the other hand, both the displayed and undisplayed image buffers +might be implemented using a subset of the on-screen pixels. +In this case, unless the contents of an image buffer are saved +off-screen, these image buffers in effect do not have backing store. +</para> + +<para> +Output to any image buffer of an unmapped multi-buffered window +that does not have backing store is discarded. Output to any +image buffer of a mapped multi-buffer window will be performed; +however, portions of an image buffer may be occluded or clipped. +</para> + +<para> +When an unmapped multi-buffered window becomes mapped, the contents +of any image buffer buffer that did not have backing store is +tiled with the background and zero or more exposure events are +generated. If no background is defined for the window, then +the screen contents are not altered and the contents of any +undisplayed image buffers are undefined. If backing store was +maintained for an image buffer, then no exposure events are generated. +</para> +</chapter> + +<chapter id='New_Requests'> +<title>New Requests</title> + +<para> +The new request, <function>CreateImageBuffers</function>, creates a group of +image buffers and associates them with a normal X window: +</para> + +<literallayout class="monospaced"> +CreateImageBuffers + w_id : WINDOW + buffers : LISTofBUFFER + update_action : {Undefined,Background,Untouched,Copied} + update_hint : {Frequent,Intermittent,Static} + => + number_buffers : CARD16 + + (Errors: Window, IDChoice, Value) +</literallayout> + +<para> +One image buffer will be associated with each ID passed in +<emphasis remap='I'>buffers</emphasis>. +The first buffer of the list is referred to as buffer[0], the next +buffer[1], and so on. Each buffer will have the same visual type +and geometry as the window. +Buffer[0] will refer to the image buffer already associated +with the window ID and its contents will not be modified. +The displayed image buffer attribute is set to buffer[0]. +</para> + +<para> +Image buffers for the remaining ID's (buffer[1],...) are allocated. +If the window is mapped, or if these image buffers have backing +store, their contents will be tiled with the window background +(if no background is defined, the buffer contents are undefined), +and zero or more expose events will be generated for each of these +buffers. The contents of an image buffer is undefined when +the window is unmapped and the buffer does not have backing store. +</para> + +<para> +If the window already has a group of image buffers +associated with it (ie: from a previous <function>CreateImageBuffers</function> request) +the actions described for <function>DestroyImageBuffers</function> are performed first +(this will delete the association of the previous buffer ID's and +their buffers as well as de-allocate all buffers except for the +one already associated with the window ID). +</para> + +<para> +To allow a server implementation to efficiently allocate the +buffers, the total number of buffers required and +the update action (how they will behave during an update) +is specified "up front" in the request. +If the server cannot allocate all the buffers requested, the +total number of buffers actually allocated will be returned. +No <function>Alloc</function> errors will be generated \- buffer[0] can +always be associated with the existing displayed image buffer. +</para> + +<para> +For example, an application that wants to animate a short movie +loop may request 64 image buffers. The server may only be able to +support 16 image buffers of this type, size, and depth. +The application can then decide 16 buffers is sufficient and may +truncate the movie loop, or it may decide it really needs +64 and will free the buffers and complain to the user. +</para> + +<para> +One might be tempted to provide a request that inquires whether +<emphasis remap='I'>n</emphasis> +buffers of a particular type, size, and depth +<emphasis remap='I'>could</emphasis> be allocated. +But if the query is decoupled from the actual allocation, +another client could sneak in and take the buffers before the +original client has allocated them. +</para> + +<para> +While any buffer of a group can be selected for display, +some applications may display buffers in a predictable order +(ie: the movie loop application). The +<emphasis remap='I'>list order</emphasis> +(buffer[0], buffer[1], ...) will be used as a hint by the +server as to which buffer will be displayed next. +A client displaying buffers in this order may see a +performance improvement. +</para> + +<para> +<emphasis remap='I'>update_action</emphasis> indicates what should happen to a previously +displayed buffer when a different buffer becomes displayed. +Possible actions are: +</para> + +<variablelist> + <varlistentry> + <term>Undefined</term> + <listitem> + <para> +The contents of the buffer that was +last displayed will become undefined after the update. This +is the most efficient action since it allows the implementation +to trash the contents of the buffer if it needs to. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>Background</term> + <listitem> + <para> +The contents of the buffer that was +last displayed will be set to the background of the window after the update. +The background action allows devices to use a fast clear +capability during an update. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>Untouched</term> + <listitem> + <para> +The contents of the buffer that was +last displayed will be untouched after the update. Used +primarily when cycling through images that have already +been drawn. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>Copied</term> + <listitem> + <para> +The contents of the buffer that was +last displayed will become the same as those that are being +displayed after the update. This is useful when incrementally +adding to an image. + </para> + </listitem> + </varlistentry> +</variablelist> + + + +<para> +<emphasis remap='I'>update_hint</emphasis> indicates how often the client will +request a different buffer to be displayed. +This hint will allow smart server implementations to choose the +most efficient means to support a multi-buffered window based +on the current need of the application (dumb implementations +may choose to ignore this hint). Possible hints are: +</para> + +<variablelist> + <varlistentry> + <term>Frequent</term> + <listitem> + <para> +An animation or movie loop is +being attempted and the fastest, most efficient means for +multi-buffering should be employed. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>Intermittent</term> + <listitem> + <para> +The displayed image will be +changed every so often. This is common for images that are +displayed at a rate slower than a second. For example, a +clock that is updated only once a minute. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>Static</term> + <listitem> + <para> +The displayed image buffer will +not be changed any time soon. Typically set by an application +whenever there is a pause in the animation. + </para> + </listitem> + </varlistentry> +</variablelist> + +<para> +To display an image buffer the following request can be used: +</para> + +<literallayout class="monospaced"> +DisplayImageBuffers + buffers : LISTofBUFFER + min_delay : CARD16 + max_delay : CARD16 + + (Errors: Buffer, Match) +</literallayout> + +<para> +The image buffers listed will become displayed as simultaneously +as possible and the update action, bound at +<function>CreateImageBuffers</function> +time, will be performed. +</para> + +<para> +A list of buffers is specified to +allow the server to efficiently change the display of more than one +window at a time (ie: when a global screen swap method is used). +Attempting to simultaneously display +multiple image buffers from the same window is an error +(<function>Match</function>) since it violates the rule that only one +image buffer per group can be displayed at a time. +</para> + +<para> +If a specified buffer is already displayed, +any delays and update action will still be +performed for that buffer. In this instance, +only the update action of <emphasis remap='I'>Background</emphasis> +(and possibly +<emphasis remap='I'>Undefined</emphasis>) will have any affect on the +contents of the displayed buffer. These semantics allow +an animation application to successfully execute +even when there is only a single buffer available +for a window. +</para> +<para> +<!-- .LP --> +When a <function>DisplayImageBuffers</function> request is made to an unmapped +multi-buffered window, the effect of the update action depends +on whether the image buffers involved have backing store. +When the target of the update action is an image buffer that +does not have backing store, output is discarded. When the +target image buffer does have backing store, the update is performed; +however, when the source of the update is an image buffer does not +have backing store (as in the case of update action +<emphasis remap='I'>Copied</emphasis>), the +contents of target image buffer will become undefined. +</para> +<para> +<!-- .LP --> +<emphasis remap='I'>min_delay</emphasis> and +<emphasis remap='I'>max_delay</emphasis> put a bound on how long the +server should wait before processing the display request. +For each of the windows to be updated by this request, at least +<emphasis remap='I'>min_delay</emphasis> milli-seconds should elapse since +the last +time any of the windows were updated; conversely, no window +should have to wait more than <emphasis remap='I'>max_delay</emphasis> +milli-seconds before being updated. +</para> + +<para> +<emphasis remap='I'>min_delay</emphasis> allows an application to +<emphasis remap='I'>slow down</emphasis> an animation or movie loop so that +it appears +synchronized at a rate the server can support given the current load. +For example, a <emphasis remap='I'>min_delay</emphasis> of 100 indicates the +server should +wait at least 1/10 of a second since the last time any of the +windows were updated. A <emphasis remap='I'>min_delay</emphasis> of zero +indicates no waiting is necessary. +</para> + +<para> +<emphasis remap='I'>max_delay</emphasis> can be thought of as an additional +delay beyond <emphasis remap='I'>min_delay</emphasis> the server is allowed +to wait +to facilitate such things as efficient update of multiple windows. +If <emphasis remap='I'>max_delay</emphasis> would require an update before +<emphasis remap='I'>min_delay</emphasis> +is satisfied, then the server should process the display request as +soon as the <emphasis remap='I'>min_delay</emphasis> requirement is met. A +typical value for <emphasis remap='I'>max_delay</emphasis> is zero. +</para> + +<para> +To implement the above functionality, the time since the last +update by a <function>DisplayImageBuffers</function> request for each +multi-buffered +window needs to be saved as state by the server. +The server may delay execution of the <function>DisplayImageBuffers</function> +request until the appropriate time (e.g. by requeuing the +request after computing the timeout); +however, the entire request must be processed in one operation. +Request execution indivisibility must be maintained. When +a server is implemented with internal concurrency, the +extension must adhere to the same concurrency semantics +as those defined for the core protocol. +</para> + +<para> +To explicitly clear a rectangular area of an image buffer to +the window background, the following request can be used: +</para> + +<literallayout class="monospaced"> +ClearImageBufferArea + buffer : BUFFER + x, y : INT16 + w, h : CARD16 + exposures : BOOL + + (Errors: Buffer, Value) +</literallayout> + +<para> +Like the X <function>ClearArea</function> request, +<emphasis remap='I'>x</emphasis> and <emphasis remap='I'>y</emphasis> +are relative to +the window's origin and specify the upper-left corner of the rectangle. +If <emphasis remap='I'>width</emphasis> is zero, it is replaced with the +current window width +minus <emphasis remap='I'>x</emphasis>. If +<emphasis remap='I'>height</emphasis> is zero it is replaced with the current +window height minus <emphasis remap='I'>y</emphasis>. If the window has a +defined background tile, the rectangle is tiled with a plane mask of all ones, +a function of <emphasis remap='I'>Copy</emphasis>, and a subwindow-mode of +<emphasis remap='I'>ClipByChildren</emphasis>. +If the window has background <emphasis remap='I'>None</emphasis>, the +contents of the buffer +are not changed. In either case, if +<emphasis remap='I'>exposures</emphasis> is true, then one or +more exposure events are generated for regions of the rectangle that are +either visible or are being retained in backing store. +</para> + +<para> +<!-- .LP --> +The group of image buffers allocated by a +<function>CreateImageBuffers</function> +request can be destroyed with the following request: +</para> + +<literallayout class="monospaced"> +DestroyImageBuffers + w_id : WINDOW + + (Error: Window) +</literallayout> + +<para> +The association between the buffer ID's and their corresponding +image buffers are deleted. Any image buffers not selected for +display are de-allocated. If the window is not multi-buffered, +the request is ignored. +</para> + +</chapter> + +<chapter id='Attributes'> +<title>Attributes</title> + +<para> +The following attributes will be associated with each window that +is multi-buffered: +</para> + +<literallayout class="monospaced"> + displayed_buffer : CARD16 + update_action : {Undefined,Background,Untouched,Copied} + update_hint : {Frequent,Intermittent,Static} + window_mode : {Mono,Stereo} + buffers : LISTofBUFFER +</literallayout> + +<para> +<emphasis remap='I'>displayed_buffer</emphasis> is set to the +<emphasis remap='I'>index</emphasis> of the currently +displayed image buffer (for stereo windows, this will be +the index of the left buffer \- the index of the right buffer +is simply <emphasis remap='I'>index</emphasis>+1). +<emphasis remap='I'>window_mode</emphasis> indicates whether this window is +<emphasis remap='I'>Mono</emphasis> or <emphasis remap='I'>Stereo</emphasis>. +The ID for each buffer associated with the window is recorded +in the <emphasis remap='I'>buffers</emphasis> list. +The above attributes can be queried with the following request: +</para> + +<literallayout class="monospaced"> +GetMultiBufferAttributes + w_id : WINDOW + => + displayed_buffer : CARD16 + update_action : {Undefined,Background,Untouched,Copied} + update_hint : {Frequent,Intermittent,Static} + window_mode : {Mono,Stereo} + buffers : LISTofBUFFER + + (Errors: Window, Access, Value) +</literallayout> + +<para> +If the window is not multi-buffered, a <function>Access</function> error +will be generated. +The only multi-buffer attribute that can be explicitly set +is <emphasis remap='I'>update_hint</emphasis>. Rather than have a specific +request to set this attribute, a generic set request is provided to +allow for future expansion: +</para> + +<literallayout class="monospaced"> +SetMultiBufferAttributes + w_id : WINDOW + value_mask : BITMASK + value_list : LISTofVALUE + + (Errors: Window, Match, Value) +</literallayout> + +<para> +If the window is not multi-buffered, a <function>Match</function> error +will be generated. +The following attributes are maintained for each buffer of a +multi-buffered window: +</para> + +<literallayout class="monospaced"> + window : WINDOW + event_mask : SETofEVENT + index : CARD16 + side : {Mono,Left,Right} +</literallayout> + +<para> +<emphasis remap='I'>window</emphasis> indicates the window this buffer is +associated with. +<emphasis remap='I'>event_mask</emphasis> specifies which events, relevant to +buffers, will be sent back to the client via the associated buffer ID +(initially no events are selected). +<emphasis remap='I'>index</emphasis> is the list position (0, 1, ...) of the +buffer. +<emphasis remap='I'>side</emphasis> indicates whether this buffer is +associated with +the left side or right side of a stereo window. +For non-stereo windows, this attribute will be set to +<emphasis remap='I'>Mono</emphasis>. +These attributes can be queried with the following request: +</para> + +<literallayout class="monospaced"> +GetBufferAttributes + buffer : BUFFER + => + window : WINDOW + event_mask : SETofEVENT + index : CARD16 + side : {Mono,Left,Right} + + (Errors: Buffer, Value) +</literallayout> + +<para> +The only buffer attribute that can be explicitly set +is <emphasis remap='I'>event_mask</emphasis>. +The only events that are valid are +<function>Expose</function> and the new +<function>ClobberNotify</function> and <function>UpdateNotify</function> +event (see Events section below). <!-- xref --> +A <function>Value</function> error will be generated if an event not +selectable for a buffer is specified in an event mask. +Rather than have a specific request +to set this attribute, a generic set request is provided to +allow for future expansion: +</para> + +<literallayout class="monospaced"> +SetBufferAttributes + buffer : BUFFER + value_mask : BITMASK + value_list : LISTofVALUE + + (Errors: Buffer, Value) +</literallayout> + +<para> +Clients may want to query the server about basic multi-buffer +and stereo capability on a per screen basis. The following request +returns a large list of information +that would most likely be read once by Xlib for each screen, and used as a +data base for other Xlib queries: +</para> + +<literallayout class="monospaced"> +GetBufferInfo + root : WINDOW + => + info : LISTofSCREEN_INFO +</literallayout> + +<para> +Where <function>SCREEN_INFO</function> and +<function>BUFFER_INFO</function> are defined as: +</para> + +<literallayout class="monospaced"> + SCREEN_INFO : [ normal_info : LISTofBUFFER_INFO, + stereo_info : LISTofBUFFER_INFO ] + + BUFFER_INFO : [ visual : VISUALID, + max_buffers : CARD16, + depth : CARD8 ] +</literallayout> + +<para> +Information regarding multi-buffering of normal (mono) windows +is returned in the <emphasis remap='I'>normal_info</emphasis> list. +The <emphasis remap='I'>stereo_info</emphasis> +list contains information about stereo windows. +If the <emphasis remap='I'>stereo_info</emphasis> list is empty, stereo +windows are +not supported on the screen. If +<emphasis remap='I'>max_buffers</emphasis> is zero, +the maximum number of buffers for the depth and visual is +a function of the size of the created window and current +memory limitations. +</para> + +<para> +The following request returns the major and minor version numbers +of this extension: +</para> + +<literallayout class="monospaced"> +GetBufferVersion + => + major_number : CARD8 + minor_number : CARD8 +</literallayout> + +<para> +The version numbers are an escape hatch in case future revisions of +the protocol are necessary. In general, the major version would +increment for incompatible changes, and the minor version would +increment for small upward compatible changes. Barring changes, the +major version will be 1, and the minor version will be 1. +</para> +</chapter> + +<chapter id='Events'> +<title>Events</title> + +<para> +All events normally generated for single-buffered +windows are also generated for multi-buffered windows. +Most of these events (ie: <function>ConfigureNotify</function>) will +only be generated for the window and not for each buffer. +These events will return a window ID. +</para> + +<para> +<function>Expose</function> events will be generated for both the window +and any buffer affected. When this event is generated for +a buffer, the same event structure will be used +but a buffer ID is returned instead of a window ID. +Clients, when processing these events, will know whether an +ID returned in an event structure is for a window or a buffer +by comparing the returned ID to the ones returned when the +window and buffer were created. +</para> + +<para> +<function>GraphicsExposure</function> and +<function>NoExposure</function> are generated +using whatever ID is specified in the graphics operation. +If a window ID is specified, the event will contain the +window ID. If a buffer ID is specified, the event will +contain the buffer ID. +</para> +<para> +In some implementations, moving a window +over a multi-buffered window may cause one or more of its buffers +to get overwritten or become unwritable. To allow a +client drawing into one of these buffers the opportunity +to stop drawing until some portion of the buffer is +writable, the following event is added: +</para> + +<literallayout class="monospaced"> +ClobberNotify + buffer : BUFFER + state : {Unclobbered,PartiallyClobbered,FullyClobbered} +</literallayout> + +<para> +The <function>ClobberNotify</function> event is reported to clients selecting +<emphasis remap='I'>ClobberNotify</emphasis> on a buffer. When a buffer +that was fully +or partially clobbered becomes unclobbered, an event with +<emphasis remap='I'>Unclobbered</emphasis> +is generated. When a buffer that was unclobbered becomes +partially clobbered, an event with +<emphasis remap='I'>PartiallyClobbered</emphasis> +is generated. When a buffer that was unclobbered or +partially clobbered becomes fully clobbered, an event with +<emphasis remap='I'>FullyClobbered</emphasis> is generated. +</para> + +<para> +<function>ClobberNotify</function> events on a given buffer are +generated before any <function>Expose</function> events on that buffer, +but it is not required that all <function>ClobberNotify</function> +events on all buffers be generated before all +<function>Expose</function> events on all buffers. +</para> + +<para> +The ordering of <function>ClobberNotify</function> events with respect +to <function>VisibilityNotify</function> events is not constrained. +</para> + +<para> +If multiple buffers were used as an image FIFO between an image +server and the X display server, then the FIFO manager would like +to know when a buffer that was previously displayed, has been +undisplayed and updated, as the side effect of a +<function>DisplayImageBuffers</function> +request. This allows the FIFO manager to load up a future frame as +soon as a buffer becomes available. To support this, +the following event is added: +</para> + +<literallayout class="monospaced"> +UpdateNotify + buffer : BUFFER +</literallayout> + +<para> +The <function>UpdateNotify</function> event is reported to clients selecting +<emphasis remap='I'>UpdateNotify</emphasis> on a buffer. Whenever a buffer +becomes <emphasis remap='I'>updated</emphasis> +(e.g. its update action is performed as part of a +<function>DisplayImageBuffers</function> +request), an <function>UpdateNotify</function> event is generated. +</para> +</chapter> + +<chapter id='Errors'> +<title>Errors</title> + +<para> +The following error type has been added to support +this extension: +</para> + +<sect1 id='Buffer_2'> +<title>Buffer</title> +<para> +A value for a BUFFER argument does not name a defined BUFFER. +</para> +</sect1> + +<sect1 id='Double_Buffering_Normal_Windows'> +<title>Double-Buffering Normal Windows</title> + +<para> +The following pseudo-code fragment illustrates how to create and display +a double-buffered image: +</para> + +<literallayout class="monospaced"> +/* + * Create a normal window + */ +CreateWindow( W, ... ) + +/* + * Create two image buffers. Assume after display, buffer + * contents become "undefined". Assume we will "frequently" + * update the display. Abort if we don't get two buffers, + */ +n = CreateImageBuffers( W, [B0,B1], Undefined, Frequent ) +if (n != 2) <abort> + +/* + * Map window to the screen + */ +MapWindow( W ) + +/* + * Draw images using alternate buffers, display every + * 1/10 of a second. Note we draw B1 first so it will + * "pop" on the screen + */ +while animating +{ + <draw picture using B1> + DisplayImageBuffers( [B1], 100, 0 ) + + <draw picture using B0> + DisplayImageBuffers( [B0], 100, 0 ) +} + +/* + * Strip image buffers and leave window with + * contents of last displayed image buffer. + */ +DestroyImageBuffers( W ) +</literallayout> + +</sect1> + +<sect1 id='Multi_Buffering_Normal_Windows'> +<title>Multi-Buffering Normal Windows</title> + +<para> +Multi-buffered images are also supported by these requests. +The following pseudo-code fragment illustrates how to create a +a multi-buffered image and cycle through the images to +simulate a movie loop: +</para> + +<literallayout class="monospaced"> +/* + * Create a normal window + */ +CreateWindow( W, ... ) + +/* + * Create 'N' image buffers. Assume after display, buffer + * contents are "untouched". Assume we will "frequently" + * update the display. Abort if we don't get all the buffers. + */ +n = CreateImageBuffers( W, [B0,B1,...,B(N-1)], Untouched, Frequent ) +if (n != N) <abort> + +/* + * Map window to screen + */ +MapWindow( W ) + +/* + * Draw each frame of movie one per buffer + */ +foreach frame + <draw frame using B(i)> + +/* + * Cycle through frames, one frame every 1/10 of a second. + */ +while animating +{ + foreach frame + DisplayImageBuffers( [B(i)], 100, 0 ) +} +</literallayout> + +</sect1> + +<sect1 id='Stereo_Windows'> +<title>Stereo Windows</title> +<para> +<emphasis remap='I'>How</emphasis> stereo windows are supported on a server +is implementation +dependent. A server may contain specialized hardware that allows +left and right images to be toggled at field or frame rates. The +stereo affect may only be perceived with the aid of special +viewing glasses. The <emphasis remap='I'>display</emphasis> of a +stereo picture should +be independent of how often the contents of the picture are +<emphasis remap='I'>updated</emphasis> by an application. Double and +multi-buffering +of images should be possible regardless of whether the image +is displayed normally or in stereo. +</para> + +<para> +To achieve this goal, a simple extension to normal windows +is suggested. Stereo windows are just like normal windows +except the displayed image is made up of a left image +buffer and a right image buffer. To create a stereo window, +a client makes the following request: +</para> + +<literallayout class="monospaced"> +CreateStereoWindow + parent : WINDOW + w_id : WINDOW + left, right : BUFFER + depth : CARD8 + visual : VISUALID or CopyFromParent + x, y : INT16 + width, height : INT16 + border_width : INT16 + value_mask : BITMASK + value_list : LISTofVALUE + + (Errors: Alloc, Color, Cursor, Match, + Pixmap, Value, Window) +</literallayout> + +<para> +This request, modeled after the <function>CreateWindow</function> request, +adds just two new parameters: <emphasis remap='I'>left</emphasis> and +<emphasis remap='I'>right</emphasis>. +For stereo, it is essential that one can distinguish whether +a draw operation is to occur on the left image or right image. +While an internal mode could have been added to achieve this, +using two buffer ID's allows clients to simultaneously build up +the left and right components of a stereo image. These +ID's always refer to (are an alias for) the left and right +image buffers that are currently <emphasis remap='I'>displayed</emphasis>. +</para> + +<para> +Like normal windows, the window ID is used whenever a window +management operation is to be performed. Window queries would +also return this window ID (eg: <function>QueryTree</function>) as would most +events. Like the window ID, the left and right buffer ID's +each have their own event mask. They can be set and queried +using the <function>Set/GetBufferAttributes</function> requests. +</para> + +<para> +Using the window ID of a stereo window in a draw request +(eg: <function>GetImage</function>) results in pixels that are +<emphasis remap='I'>undefined</emphasis>. +Possible semantics are that both left and right images get +drawn, or just a single side is operated on (existing applications +will have to be re-written to explicitly use the left and right +buffer ID's in order to successfully create, fetch, and store +stereo images). +</para> + +<para> +Having an explicit <function>CreateStereoWindow</function> request is helpful +in that a server implementation will know from the onset whether +a stereo window is desired and can return appropriate status +to the client if it cannot support this functionality. +</para> + +<para> +Some hardware may support separate stereo and non-stereo modes, +perhaps with different vertical resolutions. For example, the +vertical resolution in stereo mode may be half that of non-stereo +mode. Selecting one mode or the other must be done through some +means outside of this extension (eg: by providing a separate +screen for each hardware display mode). The screen attributes +(ie: x/y resolution) for a screen that supports normal windows, +may differ from a screen that supports stereo windows; +however, all windows, regardless of type, displayed on the +same screen must have the same screen attributes +(ie: pixel aspect ratio). +</para> + +<para> +If a screen that supports stereo windows also supports +normal windows, then the images presented to the left and +right eyes for normal windows should be the same +(ie: have no stereo offset). +</para> + +</sect1> + +<sect1 id='Single_Buffered_Stereo_Windows'> +<title>Single-Buffered Stereo Windows</title> + +<para> +The following shows how to create and display a single-buffered +stereo image: +</para> +<literallayout class="monospaced"> +/* + * Create the stereo window, map it the screen, + * and draw the left and right images + */ +CreateStereoWindow( W, L, R, ... ) + +MapWindow( W ) + +<draw picture using L,R> +</literallayout> +</sect1> + +<sect1 id='Double_Buffering_Stereo_Windows'> +<title>Double-Buffering Stereo Windows</title> + +<para> +Additional image buffers may be added to a stereo window +to allow double or multi-buffering of stereo images. +Simply use the the <function>CreateImageBuffers</function> request. +Even numbered buffers (0,2,...) will be left buffers. +Odd numbered buffers (1,3,...) will be right buffers. +Displayable stereo images are formed by consecutive +left/right pairs of image buffers. For example, +(buffer[0],buffer[1]) form the first displayable +stereo image; (buffer[2],buffer[3]) the next; +and so on. +</para> + +<para> +The <function>CreateImageBuffers</function> request will only create +pairs of left and right image buffers for stereo windows. +By always pairing left and right image +buffers together, implementations might be able to +perform some type of optimization. If an odd number +of buffers is specified, a <function>Value</function> error is generated. +All the rules mentioned at the start of this proposal +still apply to the image buffers supported by a stereo window. +</para> + +<para> +To display a image buffer pair of a multi-buffered stereo image, +either the left buffer ID or right buffer ID may be specified in a +<function>DisplayImageBuffers</function> request, but not both. +</para> + +<para> +To double-buffer a stereo window: +</para> + +<literallayout class="monospaced"> +/* + * Create stereo window and map it to the screen + */ +CreateStereoWindow( W, L, R, ... ) + +/* + * Create two pairs of image buffers. Assume after display, + * buffer contents become "undefined". Assume we will "frequently" + * update the display. Abort if we did get all the buffers. + */ +n = CreateImageBuffers( W, [L0,R0,L1,R1], Undefined, Frequently ) +if (n != 4) <abort> + +/* + * Map window to the screen + */ +MapWindow( W ) + +/* + * Draw images using alternate buffers, + * display every 1/10 of a second. + */ +while animating +{ + <draw picture using L1,R1> + DisplayImageBuffers( [L1], 100, 0 ) + + <draw picture using L0,R0> + DisplayImageBuffers( [L0], 100, 0 ) +} +</literallayout> + +</sect1> + +<sect1 id='Multi_Buffering_Stereo_Windows'> +<title>Multi-Buffering Stereo Windows</title> + +<para> +To cycle through <emphasis remap='I'>N</emphasis> stereo images: +</para> + +<literallayout class="monospaced"> +/* + * Create stereo window + */ +CreateStereoWindow( W, L, R, ... ) + +/* + * Create N pairs of image buffers. Assume after display, + * buffer contents are "untouched". Assume we will "frequently" + * update the display. Abort if we don't get all the buffers. + */ +n = CreateImageBuffers( W, [L0,R0,...,L(N-1),R(N-1)], Untouched, Frequently ) +if (n != N*2) <abort> + +/* + * Map window to screen + */ +MapWindow( W ) + +/* + * Draw the left and right halves of each image + */ +foreach stereo image + <draw picture using L(i),R(i)> + +/* + * Cycle through images every 1/10 of a second + */ +while animating +{ + foreach stereo image + DisplayImageBuffers( [L(i)], 100, 0 ) +} +</literallayout> +</sect1> + +<sect1 id='Protocol_Encoding'> +<title>Protocol Encoding</title> + +<para> +The official name of this extension is "Multi-Buffering". +When this string passed to <function>QueryExtension</function> the +information returned should be interpreted as follows: +</para> + +<variablelist> + <varlistentry> + <term>major-opcode</term> + <listitem> + <para> +Specifies the major opcode of this extension. +The first byte of each extension request should +specify this value. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>first-event</term> + <listitem> + <para> +Specifies the code that will be returned when +<function>ClobberNotify</function> events are generated. + </para> + </listitem> + </varlistentry> + <varlistentry> + <term>first-error</term> + <listitem> + <para> +Specifies the code that will be returned when +<function>Buffer</function> errors are generated. + </para> + </listitem> + </varlistentry> +</variablelist> + +<para> +The following sections describe the protocol +encoding for this extension. +</para> +</sect1> +</chapter> + +<chapter id='TYPES'> +<title>TYPES</title> + +<literallayout class="monospaced"> +BUFFER_INFO + +4 VISUALID visual +2 CARD16 max-buffers +1 CARD8 depth +1 unused +</literallayout> + +<literallayout class="monospaced"> +SETofBUFFER_EVENT + + #x00008000 Exposure + #x02000000 ClobberNotify + #x04000000 UpdateNotify +</literallayout> + +</chapter> + +<chapter id='EVENTS_2'> +<title>EVENTS</title> + +<literallayout class="monospaced"> +<function>ClobberNotify</function> +1 see <emphasis remap='I'>first-event</emphasis> code +1 unused +2 CARD16 sequence number +4 BUFFER buffer +1 state + 0 Unclobbered + 1 PartiallyClobbered + 2 FullyClobbered +23 unused +</literallayout> + +<literallayout class="monospaced"> +<function>UpdateNotify</function> +1 <emphasis remap='I'>first-event</emphasis>+1 code +1 unused +2 CARD16 sequence number +4 BUFFER buffer +24 unused +</literallayout> + +</chapter> +<chapter id='ERRORS_2'> +<title>ERRORS</title> + +<literallayout class="monospaced"> +<function>Buffer</function> +1 0 Error +1 see <emphasis remap='I'>first-error</emphasis> code +2 CARD16 sequence number +4 CARD32 bad resource id +2 CARD16 minor-opcode +1 CARD8 major-opcode +21 unused +</literallayout> + +</chapter> + +<chapter id='Requests'> +<title>REQUESTS</title> + +<literallayout class="monospaced"> +<function>GetBufferVersion</function> +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 0 minor-opcode +2 1 request length +-> +1 1 Reply +1 unused +2 CARD16 sequencenumber +4 0 reply length +1 CARD8 majorversion number +1 CARD8 minorversion number +22 unused + + +<function>CreateImageBuffers</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 1 minor-opcode +2 3+n requestlength +4 WINDOW wid +1 update-action + 0 Undefined + 1 Background + 2 Untouched + 3 Copied +1 update-hint + 0 Frequent + 1 Intermittent + 2 Static +2 unused +4n LISTofBUFFER buffer-list +-> +1 1 Reply +1 unused +2 CARD16 sequencenumber +4 0 reply length +2 CARD16 number-buffers +22 unused + + +<function>DestroyImageBuffers</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 2 minor-opcode +2 2 request length +4 WINDOW wid + + +<function>DisplayImageBuffers</function> + + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +2 2+n requestlength +2 CARD16 min-delay +2 CARD16 max-delay +4n LISTofBUFFER buffer-list + + +<function>SetMultiBufferAttributes</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 4 minor-opcode +2 3+n requestlength +4 WINDOW wid +4 BITMASK value-mask (has n bits set to 1) + #x00000001 update-hint +4n LISTofVALUE value-list +VALUEs +1 update-hint + 0 Frequent + 1 Intermittent + 2 Static + + +<function>GetMultiBufferAttributes</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 5 minor-opcode +2 2 request length +4 WINDOW wid +® +1 1 Reply +1 unused +2 CARD16 sequencenumber +4 n reply length +2 CARD16 displayed-buffer +1 update-action + 0 Undefined + 1 Background + 2 Untouched + 3 Copied +1 update-hint + 0 Frequent + 1 Intermittent + 2 Static +1 window-mode + 0 Mono + 1 Stereo +19 unused +4n LISTofBUFFER buffer list + + +<function>SetBufferAttributes</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 6 minor-opcode +2 3+n requestlength +4 BUFFER buffer +4 BITMASK value-mask (has n bits set to 1) + #x00000001 event-mask +4n LISTofVALUE value-list +VALUEs +4 SETofBUFFER_EVENT event-mask + +<function>GetBufferAttributes</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 7 minor-opcode +2 2 request length +4 BUFFER buffer +-> +1 1 Reply +1 unused +2 CARD16 sequencenumber +4 0 reply length +4 WINDOW wid +4 SETofBUFFER_EVENT event-mask +2 CARD16 index + 1 side + 0 Mono + 1 Left + 2 Right +13 unused + +<function>GetBufferInfo</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 8 minor-opcode +2 2 request length +4 WINDOW root +® +1 1 Reply +1 unused +2 CARD16 sequencenumber +4 2(n+m) replylength +2 n number BUFFER_INFO in normal-info +2 m number BUFFER_INFO in stereo-info +20 unused +8n LISTofBUFFER_INFO normal-info +8m LISTofBUFFER_INFO stereo-info + +<function>CreateStereoWindow</function> + +1 see <emphasis remap='I'>major-opcode</emphasis> major-opcode +1 9 minor-opcode +2 11+n requestlength +3 unused +1 CARD8 depth +4 WINDOW wid +4 WINDOW parent +4 BUFFER left +4 BUFFER right +2 INT16 x +2 INT16 y +2 CARD16 width +2 CARD16 height +2 CARD16 border-width +2 class + 0 CopyFromParent + 1 InputOutput + 2 InputOnly +4 VISUALID visual + 0 CopyFromParent +4 BITMASK value-mask (has n bits set to 1) + encodings are the same + as for CreateWindow +4n LISTofVALUE value-list + encodings are the same + as for CreateWindow + + +<function>ClearImageBufferArea</function> + +1 see major-opcode major-opcode +1 10 minor-opcode +2 5 request length +4 WINDOW buffer +2 INT16 x +2 INT16 y +2 CARD16 width +2 CARD16 height +3 unused +1 BOOL exposures + +</literallayout> + +</chapter> +</book> |