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authorMike Gabriel <mike.gabriel@das-netzwerkteam.de>2015-02-02 15:02:49 +0100
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- 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);
-