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diff --git a/compositeproto.txt b/compositeproto.txt new file mode 100644 index 0000000..4b86621 --- /dev/null +++ b/compositeproto.txt @@ -0,0 +1,339 @@ + Composite Extension + Version 0.4 + 2007-7-3 + Keith Packard + keithp@keithp.com + Deron Johnson + deron.johnson@sun.com + +1. Introduction + +Many user interface operations would benefit from having pixel contents of +window hierarchies available without respect to sibling and antecedent +clipping. In addition, placing control over the composition of these pixel +contents into a final screen image in an external application will enable +a flexible system for dynamic application content presentation. + +2. Acknowledgements + +This small extension has been brewing for several years, contributors to +both early prototypes and the final design include: + + + Bill Haneman for motivating the ability to magnify occluded windows + with his work on accessibility + + + Carsten Haitzler for Enlightenment, the original eye-candy window + manager which demonstrated that clever hacks are an awfully + close substitute for changes in the underlying system. + + + Jim Gettys for key insights into the relationship between damage + events and per-window pixmap usage + + + Mike Harris and Owen Taylor for figuring out what to call it. + + + Deron Johnson for the Looking Glass implementation and + a prototype of the coordinate transformation mechanism. + + + Ryan Lortie for helping figure out reasonable parent clipping + semantics in the presense of manual redirected children. + +3. Architecture + +The composite extension provides three related mechanisms: + + 1. Per-hierarchy storage. The rendering of an entire hierarchy of windows + is redirected to off-screen storage. The pixels of that hierarchy + are available whenever it is viewable. Storage is automatically + reallocated when the top level window changes size. Contents beyond + the geometry of the top window are not preserved. + + 2. Automatic shadow update. When a hierarchy is rendered off-screen, + the X server provides an automatic mechanism for presenting those + contents within the parent window. The implementation is free to + make this update lag behind actual rendering operations by an + unspecified amount of time. This automatic update mechanism may + be disabled so that the parent window contents can be completely + determined by an external application. + + 3. External parent - child pointer coordinate transformation. + When a hierarchy is under manual compositing, the relationship + of coordinates within the parent to those in the child may + not be known within the X server. This mechanism provides + for redirection of these transformations through a client. + +Per-hierarchy storage may be created for individual windows or for all +children of a window. Manual shadow update may be selected by only a single +application for each window; manual update may also be selected on a +per-window basis or for each child of a window. Detecting when to update +may be done with the Damage extension. + +The off-screen storage includes the window contents, its borders and the +contents of all descendants. + +3.1 NameWindowPixmap + +Version 0.2 of the protocol introduces a mechanism for associating an XID +with the off-screen pixmap used to store these contents. This can be used +to hold onto window contents after the window is unmapped (and hence animate +it's disappearance), and also to access the border of the window, which is +not reachable through the Window ID itself. A new pixmap is created each +time the window is mapped or resized; as these events are nicely signalled +with existing events, no additional notification is needed. The old pixmap +will remain allocated as long as the Pixmap ID is left valid, it is +important that the client use the FreePixmap request when it is done with +the contents and to create a new name for the newly allocated pixmap. + +In automatic update mode, the X server is itself responsible for presenting +the child window contents within the parent. It seems reasonable, then, for +rendering to the parent window to be clipped so as not to interfere with any +child window content. In an environment with a mixure of manual and +automatic updating windows, rendering to the parent in the area nominally +occupied by a manual update window should be able to affect parent pixel +values in those areas, but such rendering should be clipped to automatic +update windows, and presumably to other manual update windows managed by +other applications. In any of these cases, it should be easy to ensure that +rendering has no effect on any non-redirected windows. + +Instead of attempting to define new clipping modes for rendering, the +Composite extension instead defines ClipByChildren rendering to the parent +to exclude regions occupied by redirected windows (either automatic or +manual). The CreateRegionFromBorderClip request can be used along with +IncludeInferiors clipping modes to restrict manual shadow updates to the +apporpriate region of the screen. Bracketing operations with +GrabServer/UngrabServer will permit atomic sequences that can update the +screen without artifact. As all of these operations are asynchronous, +network latency should not adversely affect update latency. + +3.2 Composite Overlay Window + +Version 0.3 of the protocol adds the Composite Overlay Window, which +provides compositing managers with a surface on which to draw without +interference. This window is always above normal windows and is always +below the screen saver window. It is an InputOutput window whose width +and height are the screen dimensions. Its visual is the root visual +and its border width is zero. Attempts to redirect it using the +composite extension are ignored. This window does not appear in the +reply of the QueryTree request. It is also an override redirect window. +These last two features make it invisible to window managers and other X11 +clients. The only way to access the XID of this window is via the +CompositeGetOverlayWindow request. Initially, the Composite Overlay +Window is unmapped. + +CompositeGetOverlayWindow returns the XID of the Composite Overlay +Window. If the window has not yet been mapped, it is mapped by this +request. When all clients who have called this request have terminated +their X11 connections the window is unmapped. + +Composite managers may render directly to the Composite Overlay +Window, or they may reparent other windows to be children of this +window and render to these. Multiple clients may render to the +Composite Overlay Window, create child windows of it, reshape it, and +redefine its input region, but the specific arbitration rules followed +by these clients is not defined by this specification; these policies +should be defined by the clients themselves. + +3.3 Clipping semantics redefined + +Version 0.4 of the protocol changes the semantics of clipping in the +presense of manual redirect children. In version 0.3, a parent was always +clipped to child windows, independent of the kind of redirection going on. +With version 0.4, the parent is no longer clipped to child windows which are +manually redirected. This means the parent can draw in the child region without using +IncludeInferiors mode, and (perhaps more importantly), it will receive +expose events in those regions caused by other actions. This new behaviour +is not selectable. + +4. Errors + +The composite extension does not define any new errors. + +5. Types + + UPDATETYPE { Automatic, Manual } + + CompositeCoordinate + child: Window + x, y: CARD16 + +7. Extension Initialization + +The client must negotiate the version of the extension before executing +extension requests. Otherwise, the server will return BadRequest for any +operations other than QueryVersion. + + QueryVersion + + client-major-version: CARD32 + client-minor-version: CARD32 + + -> + + major-version: CARD32 + minor-version: CARD32 + + The client sends the highest supported version to the server and + the server sends the highest version it supports, but no higher than + the requested version. Major versions changes can introduce + incompatibilities in existing functionality, minor version + changes introduce only backward compatible changes. It is + the client's responsibility to ensure that the server supports + a version which is compatible with its expectations. Servers + are encouraged to support multiple versions of the extension. + +8. Hierarchy Redirection + + RedirectWindow + + window: Window + update: UPDATETYPE + + errors: Window, Access, Match + + The hierarchy starting at 'window' is directed to off-screen + storage. 'update' specifies whether the contents are mirrored to + the parent window automatically or not. Only one client may specify + an update type of Manual, another attempt will result in an + Access error. When all clients enabling redirection terminate, + the redirection will automatically be disabled. + + The root window may not be redirected. Doing so results in a Match + error. + + RedirectSubwindows + + window: Window + update UPDATETYPE + + errors: Window, Access + + Hierarchies starting at all current and future children of window + will be redirected as in RedirectWindow. If update is Manual, + then painting of the window background during window manipulation + and ClearArea requests is inhibited. + + UnredirectWindow: + + window: Window + + errors: Window, Value + + Redirection of the specified window will be terminated. If + the specified window was not selected for redirection by the + current client, a 'Value' error results. + + UnredirectWindows: + + window: Window + + errors: Window, Value + + Redirection of all children of window will be terminated. If + the specified window was not selected for sub-redirection by the + current client, a 'Value' error results. + +9. Clip lists + + CreateRegionFromBorderClip + + region: Region + window: Window + + errors: Window, IDChoice + + This request creates a region containing the "usual" border clip + value; that is the area of the window clipped against siblings and + the parent. This region can be used to restrict rendering to + suitable areas while updating only a single window. The region + is copied at the moment the request is executed; future changes + to the window hierarchy will not be reflected in this region. + +10. Associating a Pixmap ID with the off-screen storage (0.2 and later) + + NameWindowPixmap + + window: Window + pixmap: Pixmap + + errors: Window, Match, IDChoice + + This request makes 'pixmap' a reference to the off-screen storage + for 'window'. This pixmap will remain allocated until freed, even + if 'window' is unmapped, reconfigured or destroyed. However, + 'window' will get a new pixmap allocated each time it is + mapped or resized, so this request will need to be reinvoked for + the client to continue to refer to the storage holding the current + window contents. Generates a 'Match' error if 'window' is not + redirected or is not visible. + +11. Composite Overlay Window (0.3 and later) + + CompositeGetOverlayWindow + + window: Window + + -> + + overlayWin: Window + + This request returns the XID of the Composite Overlay Window for + the screen specified by the argument 'window'. This request + indicates that the client wishes to use the Composite Overlay + Window of this screen. If this Composite Overlay Window has not + yet been mapped, it is mapped by this request. + + The Composite Overlay Window for a particular screen will be + unmapped when all clients who have invoked this request have + also invoked CompositeReleaseOverlayWindow for that screen. Also, + CompositeReleaseOverlayWindow for a screen will be implicitly + called when a client using the Composite Overlay Window on that + screen terminates its X11 connection. + + + CompositeReleaseOverlayWindow + + window: Window + + This request specifies that the client is no longer using the + Composite Overlay Window on the screen specified by the + argument 'window'. A screen's Composite Overlay Window is + unmapped when there are no longer any clients using it. + +12. External coordinate transformation (0.4 and later) + + RedirectCoordinate + + window: Window + redirect: BOOL + + errors: Window, Access + + If 'redirect' is TRUE, the requesting client is placed in charge of + coordinate transformations between 'window' and its children. If + 'redirect' is FALSE, any such redirection is disabled. Any + transformations needed by the server will be delivered to the + requesting client in TransformCoordinateNotify events and the + requesting client must reply with matching TransformCoordinate + requests for the server to continue with the operation. + + Generates an 'Access' error if another client has + redirected coordinates for 'window'. + + TransformCoordinate + + window: Window + serialNumber: CARD32 + x, y: INT16 + coordinates: LISTofCompositeCoordinate + + This provides the transformation data needed by the server for a + single TransformCoordinateNotify event. 'serialNumber' must match + the serial number delivered in the event. 'x' and 'y' represent the + coordinate from the event relative to the 'window'. 'coordinates' + represent the coordinate from the event relative to each child + listed. Any children not listed in 'coordinates' are given the + default transformation using the child window position within the + parent as a simple translation. + + The result of this is that any pointer data seen by means of + the protocol will appear to reflect the transformation + performed by this request. |