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Edit File: fixesproto.txt

The XFIXES Extension Version 5.0 Document Revision 1 2010-11-15 Keith Packard keithp@keithp.com 1. Introduction X applications have often needed to work around various shortcomings in the core X window system. This extension is designed to provide the minimal server-side support necessary to eliminate problems caused by these workarounds. 2. Acknowledgements This extension is a direct result of requests made by application developers, in particular, + Owen Taylor for describing the issues raised with the XEMBED mechanisms and SaveSet processing and his initial extension to handle this issue, and for pointer barriers + Bill Haneman for the design for cursor image tracking. + Havoc Pennington + Fredrik Höglund for cursor names + Deron Johnson for cursor visibility 3. Basic Premise Requests in this extension may seem to wander all over the map of X server capabilities, but they are tied by a simple rule -- resolving issues raised by application interaction with core protocol mechanisms that cannot be adequately worked around on the client side of the wire. 4. Extension initialization The client must negotiate the version of the extension before executing extension requests. Behavior of the server is undefined otherwise. 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 new requests, minor version changes introduce only adjustments to existing requests or backward compatible changes. It is the clients responsibility to ensure that the server supports a version which is compatible with its expectations. ************* XFIXES VERSION 1 OR BETTER *********** 5. Save Set processing changes Embedding one application within another provides a way of unifying disparate documents and views within a single framework. From the X protocol perspective, this appears similar to nested window managers; the embedding application "manages" the embedded windows much as a window manager does for top-level windows. To protect the embedded application from embedding application failure, it is reasonable to use the core SaveSet mechanism so that embedding application failure causes embedded windows to be preserved instead of destroyed. The core save set mechanism defines the target for each save set member window as the nearest enclosing window not owned by the terminating client. For embedding applications, this nearest window is usually the window manager frame. The problem here is that the window manager will not generally expect to receive and correctly manage new windows appearing within that window by the save set mechanism, and will instead destroy the frame window in response to the client window destruction. This causes the embedded window to be destroyed. An easy fix for this problem is to change the target of the save set member to a window which won't be affected by the underlying window destruction. XFIXES chooses the root window as the target. Having embedded windows suddenly appear at the top level can confuse users, so XFIXES also lets the client select whether the window should end up unmapped after the save set processing instead of unconditionally making them be mapped. 5.1 Requests ChangeSaveSet window: Window mode: { Insert, Delete } target: { Nearest, Root } map: { Map, Unmap } ChangeSaveSet is an extension of the core protocol ChangeSaveSet request. As in that request, mode specifies whether the indicated window is inserted or deleted from the save-set. Target specifies whether the window is reparented to the nearest non-client window as in the core protocol, or reparented to the root window. Map specifies whether the window is mapped as in the core protocol or unmapped. 6. Selection Tracking Applications wishing to monitor the contents of current selections must poll for selection changes. XFIXES improves this by providing an event delivered whenever the selection ownership changes. 6.1 Types SELECTIONEVENT { SetSelectionOwner, SelectionWindowDestroy, SelectionClientClose } 6.1 Events SelectionNotify subtype: SELECTIONEVENT window: Window owner: Window selection: Atom timestamp: Timestamp selection-timestamp: Timestamp 6.2 Requests SelectSelectionInput window: Window selection: Atom event-mask: SETofSELECTIONEVENT Selects for events to be delivered to window when various causes of ownership of selection occur. Subtype indicates the cause of the selection ownership change. Owner is set to the current selection owner, or None. Timestamp indicates the time the event was generated while selection-timestamp indicates the timestamp used to own the selection. 7. Cursor Image Monitoring Mirroring the screen contents is easily done with the core protocol or VNC addons, except for the current cursor image. There is no way using the core protocol to discover which cursor image is currently displayed. The cursor image often contains significant semantic content about the user interface. XFIXES provides a simple mechanism to discover when the cursor image changes and to fetch the current cursor image. As the current cursor may or may not have any XID associated with it, there is no stable name available. Instead, XFIXES returns only the image of the current cursor and provides a way to identify cursor images to avoid refetching the image each time it changes to a previously seen cursor. 7.1 Types CURSOREVENT { DisplayCursor } 7.2 Events CursorNotify subtype: CURSOREVENT window: Window cursor-serial: CARD32 timestamp: Timestamp name: Atom (Version 2 only) 7.3 Requests SelectCursorInput window: Window event-mask: SETofCURSOREVENT This request directs cursor change events to the named window. Events will be delivered irrespective of the screen on which they occur. Subtype indicates the cause of the cursor image change (there is only one subtype at present). Cursor-serial is a number assigned to the cursor image which identifies the image. Cursors with different serial numbers may have different images. Timestamp is the time of the cursor change. Servers supporting the X Input Extension Version 2.0 or higher only notify the clients of cursor change events for the ClientPointer, not of any other master pointer (see Section 4.4. in the XI2 protocol specificiation). GetCursorImage -> x: INT16 y: INT16 width: CARD16 height: CARD16 x-hot: CARD16 y-hot: CARD16 cursor-serial: CARD32 cursor-image: LISTofCARD32 GetCursorImage returns the image of the current cursor. X and y are the current cursor position. Width and height are the size of the cursor image. X-hot and y-hot mark the hotspot within the cursor image. Cursor-serial provides the number assigned to this cursor image, this same serial number will be reported in a CursorNotify event if this cursor image is redisplayed in the future. The cursor image itself is returned as a single image at 32 bits per pixel with 8 bits of alpha in the most significant 8 bits of the pixel followed by 8 bits each of red, green and finally 8 bits of blue in the least significant 8 bits. The color components are pre-multiplied with the alpha component. ************* XFIXES VERSION 2 OR BETTER *********** 8. Region Objects The core protocol doesn't expose regions as a primitive object and this makes many operations more complicated than they really need to be. Adding region objects simplifies expose handling, the Shape extension and other operations. These operations are also designed to support a separate extension, the X Damage Extension. 8.1 Types Region: XID WINDOW_REGION_KIND: { Bounding, Clip } 8.2 Errors Region The specified region is invalid 8.3 Requests CreateRegion region: REGION rects: LISTofRECTANGLE Creates a region initialized to the specified list of rectangles. The rectangles may be specified in any order, their union becomes the region. The core protocol allows applications to specify an order for the rectangles, but it turns out to be just as hard to verify the rectangles are actually in that order as it is to simply ignore the ordering information and union them together. Hence, this request dispenses with the ordering information. Errors: IDChoice CreateRegionFromBitmap region: REGION bitmap: PIXMAP Creates a region initialized to the set of 'one' pixels in bitmap (which must be depth 1, else Match error). Errors: Pixmap, IDChoice, Match CreateRegionFromWindow window: Window kind: WINDOW_REGION_KIND region: Region Creates a region initialized to the specified window region. See the Shape extension for the definition of Bounding and Clip regions. Errors: Window, IDChoice, Value CreateRegionFromGC gc: GContext region: Region Creates a region initialized from the clip list of the specified GContext. Errors: GContext, IDChoice CreateRegionFromPicture picture: Picture region: Region Creates a region initialized from the clip list of the specified Picture. Errors: Picture, IDChoice DestroyRegion region: Region Destroys the specified region. Errors: Region SetRegion region: Region rects: LISTofRECTANGLE This replaces the current contents of region with the region formed by the union of rects. CopyRegion source: Region destination: Region This replaces the contents of destination with the contents of source. UnionRegion IntersectRegion SubtractRegion source1: Region source2: Region destination: Region Combines source1 and source2, placing the result in destination. Destination may be the same as either source1 or source2. Errors: Region, Value InvertRegion source: Region bounds: RECTANGLE destination: Region The source region is subtracted from the region specified by bounds. The result is placed in destination, replacing its contents. Errors: Region TranslateRegion region: Region dx, dy: INT16 The region is translated by dx, dy in place. Errors: Region RegionExtents source: Region destination: Region The extents of the source region are placed in the destination FetchRegion region: Region -> extents: RECTANGLE rectangles: LISTofRECTANGLE The region is returned as a list of rectangles in YX-banded order. Errors: Region SetGCClipRegion gc: GCONTEXT clip-x-origin, clip-y-origin: INT16 region: Region or None This request changes clip-mask in gc to the specified region and sets the clip origin. Output will be clipped to remain contained within the region. The clip origin is interpreted relative to the origin of whatever destination drawable is specified in a graphics request. The region is interpreted relative to the clip origin. Future changes to region have no effect on the gc clip-mask. Errors: GContext, Region SetWindowShapeRegion dest: Window destKind: SHAPE_KIND xOff, yOff: INT16 region: Region or None This request sets the specified (by destKind) Shape extension region of the window to region, offset by xOff and yOff. Future changes to region have no effect on the window shape. Errors: Window, Value, Region SetPictureClipRegion picture: Picture clip-x-origin, clip-y-origin: INT16 region: Region or None This request changes clip-mask in picture to the specified region and sets the clip origin. Input and output will be clipped to remain contained within the region. The clip origin is interpreted relative to the origin of the drawable associated with picture. The region is interpreted relative to the clip origin. Future changes to region have no effect on the picture clip-mask. Errors: Picture, Region 9. Cursor Names Attaching names to cursors permits some abstract semantic content to be associated with specific cursor images. Reflecting those names back to applications allows that semantic content to be related to the user through non-visual means. 9.1 Events CursorNotify subtype: CURSOREVENT window: Window cursor-serial: CARD32 timestamp: Timestamp name: Atom or None In Version 2 of the XFIXES protocol, this event adds the atom of any name associated with the current cursor (else None). 9.2 Requests SetCursorName cursor: CURSOR name: LISTofCARD8 This request interns name as an atom and sets that atom as the name of cursor. Errors: Cursor GetCursorName cursor: CURSOR -> atom: ATOM or None name: LISTofCARD8 This request returns the name and atom of cursor. If no name is set, atom is None and name is empty. Errors: Cursor GetCursorImageAndName -> x: INT16 y: INT16 width: CARD16 height: CARD16 x-hot: CARD16 y-hot: CARD16 cursor-serial: CARD32 cursor-atom: ATOM cursor-image: LISTofCARD32 cursor-name: LISTofCARD8 This is similar to GetCursorImage except for including both the atom and name of the current cursor. ChangeCursor source, destination: CURSOR This request replaces all references to the destination with a reference to source. Any existing uses of the destination cursor object will now show the source cursor image. ChangeCursorByName src: CURSOR name: LISTofCARD8 This request replaces the contents of all cursors with the specified name with the src cursor. ************* XFIXES VERSION 3 OR BETTER *********** 10. Region Expansion This update provides another operation on the region objects defined in Section 8 of this document. 10.1 Requests ExpandRegion source: REGION destination: REGION left, right, top, bottom: CARD16 Creates destination region containing the area specified by expanding each rectangle in the source region by the specified number of pixels to the left, right, top and bottom. ************* XFIXES VERSION 4 OR BETTER *********** 11. Cursor Visibility Composite managers may want to render the cursor themselves instead of relying on the X server sprite drawing, this provides a way for them to do so without getting a double cursor image. 11.1 Requests HideCursor window: WINDOW A client sends this request to indicate that it wants the cursor image to be hidden (i.e. to not be displayed) when the sprite is on the same screen as the specified window. The sprite will be hidden if one or more clients have called HideCursor and not ShowCursor. Note that even though cursor hiding causes the cursor image to be invisible, CursorNotify events will still be sent normally, as if the cursor image were visible. When a client with outstanding cursor hiding requests terminates its connection these requests will be deleted. Servers supporting the X Input Extension Version 2.0 or higher hide all visible cursors in response to a HideCursor request. If a master pointer is created while the cursors are hidden, this master pointer's cursor will be hidden as well. ShowCursor window: WINDOW A client sends this request to indicate that it wants the cursor image to be displayed when the sprite is on the same screen as the specified window. The sprite will be hidden if one or more clients have called HideCursor and not ShowCursor. If the client has made no outstanding HideCursor requests a BadMatch error is generated. Servers supporting the X Input Extension Version 2.0 or higher show all visible cursors in response to a ShowCursor request. ************* XFIXES VERSION 5 OR BETTER *********** 12. Pointer Barriers Compositing managers and desktop environments may have UI elements in particular screen locations such that for a single-headed display they correspond to easy targets according to Fitt's Law, for example, the top left corner. For a multi-headed environment these corners should still be semi-impermeable. Pointer barriers allow the application to define additional constraint on cursor motion so that these areas behave as expected even in the face of multiple displays. Absolute positioning devices like touchscreens do not obey pointer barriers. There's no advantage to target acquisition to do so, since on a touchscreen all points are in some sense equally large, whereas for a relative positioning device the edges and corners are infinitely large. WarpPointer and similar requests do not obey pointer barriers, for essentially the same reason. 12.1 Types BARRIER: XID BarrierDirections BarrierPositiveX: 1 << 0 BarrierPositiveY: 1 << 1 BarrierNegativeX: 1 << 2 BarrierNegativeY: 1 << 3 12.2 Errors Barrier 12.3 Requests CreatePointerBarrier barrier: BARRIER window: Window x1, y2, x2, y2: INT16 directions: CARD32 devices: LISTofDEVICEID Creates a pointer barrier along the line specified by the given coordinates on the screen associated with the given window. The barrier has no spatial extent; it is simply a line along the left or top edge of the specified pixels. Barrier coordinates are in screen space. The coordinates must be axis aligned, either x1 == x2, or y1 == y2, but not both. The varying coordinates may be specified in any order. For x1 == x2, either y1 > y2 or y1 < y2 is valid. If the coordinates are not valid BadValue is generated. Motion is allowed through the barrier in the directions specified: setting the BarrierPositiveX bit allows travel through the barrier in the positive X direction, etc. Nonsensical values (forbidding Y axis travel through a vertical barrier, for example) and excess set bits are ignored. If the server supports the X Input Extension version 2 or higher, the devices element names a set of master device to apply the barrier to. If XIAllDevices or XIAllMasterDevices are given, the barrier applies to all master devices. If a slave device is named, BadDevice is generated; this does not apply to slave devices named implicitly by XIAllDevices. Naming a device multiple times is legal, and is treated as though it were named only once. If a device is removed, the barrier continues to apply to the remaining devices, but will not apply to any future device with the same ID as the removed device. Nothing special happens when all matching devices are removed; barriers must be explicitly destroyed. Errors: IDChoice, Window, Value, Device DestroyPointerBarrier barrier: BARRIER Destroys the named barrier. Errors: Barrier 99. Future compatibility This extension is not expected to remain fixed. Future changes will strive to remain compatible if at all possible. The X server will always support version 1 of the extension protocol if requested by a client. Additions to the protocol will always by marked by minor version number changes so that applications will be able to detect what requests are supported.