Datasheet

Functional Description
R
Datasheet 183
5.4.2.5 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.
5.4.2.6 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.
5.4.2.7 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 the Intel 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.
5.4.2.8 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.
5.4.2.9 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.