82815 GMCH
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Datasheet
4.8.9.
Hardware Cursor
The GMCH allows an unlimited number of cursor patterns to be stored in the display cache or system
memory. Two sets of registers contain the x and y position of the cursor relative to the upper left corner
of the display. The following four cursor modes are provided:
32x32 2 bpp AND/XOR 2-plane mode
64x64 2 bpp 3-color and transparency mode
64x64 2 bpp AND/XOR 2-plane mode
64x64 2 bpp 4-color mode
4.8.10.
Overlay Engine
The overlay engine provides a method of merging either video capture data (from an external PCI Video
Capture Adapter) or data delivered by the processor, with the graphics data on the screen. Supported data
formats include YUV 4:2:2, YUV 4:2:0, YUV 4:1:0, YUV 4:1:1, RGB15, and RGB16. The source data
can be mirrored horizontally or vertically or both. Overlay data comes from a buffer located in system
memory. Additionally, the overlay engine can be quadruple buffered to support flipping between
different overlay images. Data can either be transferred into the overlay buffer from the host or from an
external PCI adapter (e.g., DVD hardware or video capture hardware). Buffer swaps can be done by the
host and internally synchronized with the display VBLANK.
The GMCH can accept line widths up to 720 pixels. In addition, overlay source and destination
chromakeying are also supported. Overlay source/destination chromakeying enables blending of the
overlay with the underlying graphics background. Destination color/chroma keying can be used to handle
occluded portions of the overlay window on a pixel-by-pixel basis which is actually an underlay. Source
color/chroma keying is used to handle transparency based on the overlay window on a pixel-by-pixel
basis. This is used when “blue screening” an image in order to overlay the image on a new background
later.
To compensate for overlay color intensity loss due to the non-linear response between display devices,
the overlay engine supports independent gamma correction. In addition, the brightness, saturation, and
contrast of the overlay may be independently varied.