JG82852GMSL7VP Datasheet, PDF (128/176 Pages) Intel Corporation – Intel® 852GM/852GMV Chipset Intel® 852GM/852GMV Chipset Hub (GMCH)

Functional Description
5.4.2.4.
5.4.2.5.
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Pixel Accurate Fast Scissoring and Clipping Operation
The GMCH supports clipping to a scissoring rectangle within the drawing window. The GMCH clipping
and scissoring in hardware reduce the need for software to process polygons, and thus improves
performance. During the setup stage, the GMCH clips polygons to the drawing window. The scissor
rectangle accelerates the clipping process by allowing the driver to clip to a bigger region than the
hardware renders to. The scissor rectangle is pixel accurate, and independent of line and point width.
The GMCH supports a single scissor box rectangle.
Backface Culling
As part of the setup, the GMCH can discard polygons from further processing, if they are either facing
away from or towards the user’s viewpoint. This operation, referred to as “Back Face Culling” is
accomplished based on the “clockwise” or “counter-clockwise” orientation of the vertices on a primitive.
This can be enabled or disabled by the driver.
Scan Converter
The Scan Converter takes the vertex and edge information is used to identify all pixels that are affected
by features being rendered. It works on a per-polygon basis, and one polygon may be entering the
pipeline while calculations finish on another.
Texture Engine
The GMCH allows an image pattern, or video to be placed on the surface of a 3D polygon. The texture
engine performs texture color or chromakey matching texture filtering (an-isotropic, tri-linear, and
bilinear), and YUV to RGB conversion.
As texture sizes increase beyond the bounds of graphics memory, executing textures from graphics
memory becomes impractical. Every rendering pass would require copying each and every texture in a
scene from System Memory to graphics memory, then using the texture, and finally overwriting the local
memory copy of the texture by copying the next texture into graphics memory. The GMCH, using
Intel’s Direct Memory Execution model, simplifies this process by rendering each scene using the
texture located in System Memory. The GMCH includes a cache controller to avoid frequent memory
fetches of recently used texture data.
Perspective Correct Texture Support
A textured polygon is generated by mapping a 2D texture pattern onto each pixel of the polygon. A
texture map is like wallpaper pasted onto the polygon. Since polygons are rendered in perspective, it is
important that texture be mapped in perspective as well. Without perspective correction, texture is
distorted when an object recedes into the distance. Perspective correction involves a compute-intensive
“per-pixel-divide” operation on each pixel. Perspective correction is necessary for realistic 3D graphics.
Texture Decompression
As the textures’ average size gets larger with higher color depth and multiple textures become the norm,
it becomes increasingly important to provide support for compressed textures.
DirectX* supports Texture Compression/Decompression to reduce the bandwidth required to deliver
textures. The GMCH supports several compressed texture formats (DirectX: DXT1, DXT2, DXT3,
DXT4, DXT5) and OpenGL FXT1 formats.
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Intel^® 852GM/852GMV Chipset GMCH Datasheet