diff options
Diffstat (limited to 'miext/rootless/README.txt')
| -rw-r--r-- | miext/rootless/README.txt | 403 |
1 files changed, 403 insertions, 0 deletions
diff --git a/miext/rootless/README.txt b/miext/rootless/README.txt new file mode 100644 index 000000000..ffd17902f --- /dev/null +++ b/miext/rootless/README.txt @@ -0,0 +1,403 @@ + Generic Rootless Layer + Version 1.0 + July 13, 2004 + + Torrey T. Lyons + torrey@xfree86.org + + +Introduction + + The generic rootless layer allows an X server to be implemented +on top of another window server in a cooperative manner. This allows the +X11 windows and native windows of the underlying window server to +coexist on the same screen. The layer is called "rootless" because the root +window of the X server is generally not drawn. Instead, each top-level +child of the root window is represented as a separate on-screen window by +the underlying window server. The layer is referred to as "generic" +because it abstracts away the details of the underlying window system and +contains code that is useful for any rootless X server. The code for the +generic rootless layer is located in xc/programs/Xserver/miext/rootless. To +build a complete rootless X server requires a specific rootless +implementation, which provides functions that allow the generic rootless +layer to interact with the underlying window system. + + +Concepts + + In the context of a rootless X server the term window is used to +mean many fundamentally different things. For X11 a window is a DDX +resource that describes a visible, or potentially visible, rectangle on the +screen. A top-level window is a direct child of the root window. To avoid +confusion, an on-screen native window of the underlying window system +is referred to as a "frame". The generic rootless layer associates each +mapped top-level X11 window with a frame. An X11 window may be said +to be "framed" if it or its top-level parent is represented by a frame. + + The generic rootless layer models each frame as being backed at +all times by a backing buffer, which is periodically flushed to the screen. +If the underlying window system does not provide a backing buffer for +frames, this must be done by the rootless implementation. The generic +rootless layer model does not assume it always has access to the frames' +backing buffers. Any drawing to the buffer will be proceeded by a call to +the rootless implementation's StartDrawing() function and StopDrawing() +will be called when the drawing is concluded. The address of the frame's +backing buffer is returned by the StartDrawing() function and it can +change between successive calls. + + Because each frame is assumed to have a backing buffer, the +generic rootless layer will stop Expose events being generated when the +regions of visibility of a frame change on screen. This is similar to backing +store, but backing buffers are different in that they always store a copy of +the entire window contents, not just the obscured portions. The price paid +in increased memory consumption is made up by the greatly decreased +complexity in not having to track and record regions as they are obscured. + + +Rootless Implementation + + The specifics of the underlying window system are provided to the +generic rootless layer through rootless implementation functions, compile- +time options, and runtime parameters. The rootless implementation +functions are a list of functions that allow the generic rootless layer to +perform operations such as creating, destroying, moving, and resizing +frames. Some of the implementation functions are optional. A detailed +description of the rootless implementation functions is provided in +Appendix A. + + By design, a rootless implementation should only have to include +the rootless.h header file. The rootlessCommon.h file contains definitions +internal to the generic rootless layer. (If you find you need to use +rootlessCommon.h in your implementation, let the generic rootless layer +maintainers know. This could be an area where the generic rootless layer +should be generalized.) A rootless implementation should also modify +rootlessConfig.h to specify compile time options for its platform. + + The following compile-time options are defined in +rootlessConfig.h: + + o ROOTLESS_ACCEL: If true, use the optional rootless acceleration + functions where possible to a accelerate X11 drawing primitives. + If false, all drawing will be done with fb. + + o ROOTLESS_GLOBAL_COORDS: This option controls the way that frame + coordinates are passed to the rootless implementation. If false, + the coordinates are passed per screen relative to the origin of + the screen the frame is currently on. Some implementations may + prefer to work in a single global coordinate space that spans all + screens. If this option is true, the coordinates are passed after + adding the coordinates of the screen origin and an overall offset of + (rootlessGlobalOffsetX, rootlessGlobalOffsetY). + + o ROOTLESS_PROTECT_ALPHA: By default for a color bit depth of 24 and + 32 bits per pixel, fb will overwrite the "unused" 8 bits to optimize + drawing speed. If this is true, the alpha channel of frames is + protected and is not modified when drawing to them. The bits + containing the alpha channel are defined by the macro + RootlessAlphaMask(bpp), which should return a bit mask for + various bits per pixel. + + o ROOTLESS_REDISPLAY_DELAY: Time in milliseconds between updates to + the underlying window server. Most operations will be buffered until + this time has expired. + + o ROOTLESS_RESIZE_GRAVITY: If the underlying window system supports it, + some frame resizes can be optimized by relying on the frame contents + maintaining a particular gravity during the resize. In this way less + of the frame contents need to be preserved by the generic rootless + layer. If true, the generic rootless layer will pass gravity hints + during resizing and rely on the frame contents being preserved + accordingly. + + o ROOTLESS_TRACK_DAMAGE: The generic rootless layer draws to the + frames' backing buffers and periodically flushes the modified + regions to the underlying window server. If this option is true, + the generic rootless layer will track these damaged regions. + Currently it uses the miRegion code and will not simplify damaged + regions even when updating a bounding region would be more + efficient. Some window systems provide a more efficient way to + track damaged regions. If this option is false, the rootless + implementation function DamageRects() is called whenever a + backing buffer is modified and the rootless implementation is + expected to track the damaged regions itself. + + The following runtime options are defined in rootless.h: + + o rootlessGlobalOffsetX, rootlessGlobalOffsetY: These are only + used if ROOTLESS_GLOBAL_COORDS is true. They specify the global + offset that is applied to all screens when converting from + screen-local to global coordinates. + + o rootless_CopyBytes_threshold, rootless_FillBytes_threshold, + rootless_CompositePixels_threshold, rootless_CopyWindow_threshold: + The minimum number of bytes or pixels for which to use the rootless + implementation's respective acceleration function. The rootless + acceleration functions are all optional so these will only be used + if the respective acceleration function pointer is not NULL. + + +Accelerated Drawing + + The rootless implementation typically does not have direct access +to the hardware. Its access to the graphics hardware is generally through +the API of the underlying window system. This underlying API may not +overlap well with the X11 drawing primitives. The generic rootless layer +falls back to using fb for all its 2-D drawing. Providing optional rootless +implementation acceleration functions can accelerate some graphics +primitives and some window functions. Typically calling through to the +underlying window systems API will not speed up these operations for +small enough areas. The rootless_*_threshold runtime options allow the +rootless implementation to provide hints for when the acceleration +functions should be used instead of fb. + + +Alpha Channel Protection + + If the bits per pixel is greater then the color bit depth, the contents +of the extra bits are undefined by the X11 protocol. Some window systems +will use these extra bits as an alpha channel. The generic rootless layer can +be configured to protect these bits and make sure they are not modified by +other parts of the X server. To protect the alpha channel +ROOTLESS_PROTECT_ALPHA and RootlessAlphaMask(bpp) must be +set appropriately as described under the compile time options. This +ensures that the X11 graphics primitives do not overwrite the alpha +channel in an attempt to optimize drawing. In addition, the window +functions PaintWindow() and Composite() must be replaced by alpha +channel safe variants. These are provided in rootless/safeAlpha. + + +Credits + + The generic rootless layer was originally conceived and developed +by Greg Parker as part of the XDarwin X server on Mac OS X. John +Harper made later optimizations to this code but removed its generic +independence of the underlying window system. Torrey T. Lyons +reintroduced the generic abstractions and made the rootless code suitable +for use by other X servers. + + +Appendix A: Rootless Implementation Functions + + The rootless implementation functions are defined in rootless.h. It +is intended that rootless.h contains the complete interface that is needed by +rootless implementations. The definitions contained in rootlessCommon.h +are intended for internal use by the generic rootless layer and are more +likely to change. + + Most of these functions take a RootlessFrameID as a parameter. +The RootlessFrameID is an opaque object that is returned by the +implementation's CreateFrame() function. The generic rootless layer does +not use this frame id other than to pass it back to the rootless +implementation to indicate the frame to operate on. + +/* + * Create a new frame. + * The frame is created unmapped. + * + * pFrame RootlessWindowPtr for this frame should be completely + * initialized before calling except for pFrame->wid, which + * is set by this function. + * pScreen Screen on which to place the new frame + * newX, newY Position of the frame. These will be identical to pFrame-x, + * pFrame->y unless ROOTLESS_GLOBAL_COORDS is set. + * pNewShape Shape for the frame (in frame-local coordinates). NULL for + * unshaped frames. + */ +typedef Bool (*RootlessCreateFrameProc) + (RootlessWindowPtr pFrame, ScreenPtr pScreen, int newX, int newY, + RegionPtr pNewShape); + +/* + * Destroy a frame. + * Drawing is stopped and all updates are flushed before this is called. + * + * wid Frame id + */ +typedef void (*RootlessDestroyFrameProc) + (RootlessFrameID wid); + +/* + * Move a frame on screen. + * Drawing is stopped and all updates are flushed before this is called. + * + * wid Frame id + * pScreen Screen to move the new frame to + * newX, newY New position of the frame + */ +typedef void (*RootlessMoveFrameProc) + (RootlessFrameID wid, ScreenPtr pScreen, int newX, int newY); + +/* + * Resize and move a frame. + * Drawing is stopped and all updates are flushed before this is called. + * + * wid Frame id + * pScreen Screen to move the new frame to + * newX, newY New position of the frame + * newW, newH New size of the frame + * gravity Gravity for window contents (rl_gravity_enum). This is always + * RL_GRAVITY_NONE unless ROOTLESS_RESIZE_GRAVITY is set. + */ +typedef void (*RootlessResizeFrameProc) + (RootlessFrameID wid, ScreenPtr pScreen, + int newX, int newY, unsigned int newW, unsigned int newH, + unsigned int gravity); + +/* + * Change frame ordering (AKA stacking, layering). + * Drawing is stopped before this is called. Unmapped frames are mapped by + * setting their ordering. + * + * wid Frame id + * nextWid Frame id of frame that is now above this one or NULL if this + * frame is at the top. + */ +typedef void (*RootlessRestackFrameProc) + (RootlessFrameID wid, RootlessFrameID nextWid); + +/* + * Change frame's shape. + * Drawing is stopped before this is called. + * + * wid Frame id + * pNewShape New shape for the frame (in frame-local coordinates) + * or NULL if now unshaped. + */ +typedef void (*RootlessReshapeFrameProc) + (RootlessFrameID wid, RegionPtr pNewShape); + +/* + * Unmap a frame. + * + * wid Frame id + */ +typedef void (*RootlessUnmapFrameProc) + (RootlessFrameID wid); + +/* + * Start drawing to a frame. + * Prepare a frame for direct access to its backing buffer. + * + * wid Frame id + * pixelData Address of the backing buffer (returned) + * bytesPerRow Width in bytes of the backing buffer (returned) + */ +typedef void (*RootlessStartDrawingProc) + (RootlessFrameID wid, char **pixelData, int *bytesPerRow); + +/* + * Stop drawing to a frame. + * No drawing to the frame's backing buffer will occur until drawing + * is started again. + * + * wid Frame id + * flush Flush drawing updates for this frame to the screen. This + * will always be FALSE if ROOTLESS_TRACK_DAMAGE is set. + */ +typedef void (*RootlessStopDrawingProc) + (RootlessFrameID wid, Bool flush); + +/* + * Flush drawing updates to the screen. + * Drawing is stopped before this is called. + * + * wid Frame id + * pDamage Region containing all the changed pixels in frame-local + * coordinates. This is clipped to the window's clip. This + * will be NULL if ROOTLESS_TRACK_DAMAGE is not set. + */ +typedef void (*RootlessUpdateRegionProc) + (RootlessFrameID wid, RegionPtr pDamage); + +/* + * Mark damaged rectangles as requiring redisplay to screen. + * This will only be called if ROOTLESS_TRACK_DAMAGE is not set. + * + * wid Frame id + * nrects Number of damaged rectangles + * rects Array of damaged rectangles in frame-local coordinates + * shift_x, Vector to shift rectangles by + * shift_y + */ +typedef void (*RootlessDamageRectsProc) + (RootlessFrameID wid, int nrects, const BoxRec *rects, + int shift_x, int shift_y); + +/* + * Switch the window associated with a frame. (Optional) + * When a framed window is reparented, the frame is resized and set to + * use the new top-level parent. If defined this function will be called + * afterwards for implementation specific bookkeeping. + * + * pFrame Frame whose window has switched + * oldWin Previous window wrapped by this frame + */ +typedef void (*RootlessSwitchWindowProc) + (RootlessWindowPtr pFrame, WindowPtr oldWin); + +/* + * Copy bytes. (Optional) + * Source and destinate may overlap and the right thing should happen. + * + * width Bytes to copy per row + * height Number of rows + * src Source data + * srcRowBytes Width of source in bytes + * dst Destination data + * dstRowBytes Width of destination in bytes + */ +typedef void (*RootlessCopyBytesProc) + (unsigned int width, unsigned int height, + const void *src, unsigned int srcRowBytes, + void *dst, unsigned int dstRowBytes); + +/* + * Fill memory with 32-bit pattern. (Optional) + * + * width Bytes to fill per row + * height Number of rows + * value 32-bit pattern to fill with + * dst Destination data + * dstRowBytes Width of destination in bytes + */ +typedef void (*RootlessFillBytesProc) + (unsigned int width, unsigned int height, unsigned int value, + void *dst, unsigned int dstRowBytes); + +/* + * Composite pixels from source and mask to destination. (Optional) + * + * width, height Size of area to composite to in pizels + * function Composite function built with RL_COMPOSITE_FUNCTION + * src Source data + * srcRowBytes Width of source in bytes (Passing NULL means source + * is a single pixel. + * mask Mask data + * maskRowBytes Width of mask in bytes + * dst Destination data + * dstRowBytes Width of destination in bytes + * + * For src and dst, the first element of the array is the color data. If + * the second element is non-null it implies there is alpha data (which + * may be meshed or planar). Data without alpha is assumed to be opaque. + * + * An X11 error code is returned. + */ +typedef int (*RootlessCompositePixelsProc) + (unsigned int width, unsigned int height, unsigned int function, + void *src[2], unsigned int srcRowBytes[2], + void *mask, unsigned int maskRowBytes, + void *dst[2], unsigned int dstRowBytes[2]); + +/* + * Copy area in frame to another part of frame. (Optional) + * + * wid Frame id + * dstNrects Number of rectangles to copy + * dstRects Array of rectangles to copy + * dx, dy Number of pixels away to copy area + */ +typedef void (*RootlessCopyWindowProc) + (RootlessFrameID wid, int dstNrects, const BoxRec *dstRects, + int dx, int dy); + |