JG82855GMESL7VN Datasheet, PDF (143/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Functional Description
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3D Primitives and Data Formats Support
The 3D primitives rendered by the GMCH are points, lines, discrete triangles, line strips, triangle
strips, triangle fans, and polygons. In addition to this, the GMCH supports DirectX’s* Flexible
Vertex Format* (FVF), which enables the application to specify a variable length parameter list,
obviating the need for sending unused information to the hardware. Strips, Fans, and Indexed
Vertices as well as FVF improves delivered vertex rate to the setup engine significantly.
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 identifies 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 (anisotropic,
trilinear, 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.
Datasheet
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