RG82855GMESL72L Datasheet, PDF (144/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Functional Description
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6.4.2.10
6.4.2.11
6.4.2.12
6.4.2.13
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.
Microsoft 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.
Texture Chromakey
Chromakey is a method for removing a specific color or range of colors from a texture map
before it is applied to an object. For nearest texture filter modes, removing a color simply makes
those portions of the object transparent (the previous contents of the back buffer show through).
For linear texture filtering modes, the texture filter is modified if only the non-nearest neighbor
texels match the key (range).
Chromakeying can be performed for both paletted and non-paletted textures, and removes texels
that fall within a specified color range. The Chromakey mode refers to testing the ARGB or YUV
components to see if they fall between high and low state variable values. If the color of a texel
contribution is in this range and chromakey is enabled, then this contribution is removed from the
resulting pixel color.
Anti-Aliasing
Aliasing is one of the artifacts that degrade image quality. In its simplest manifestation, aliasing
causes the jagged staircase effects on sloped lines and polygon edges. Another artifact is the
moiré patterns, which occur as a result of the fact that there is very small number of pixels
available on screen to contain the data of a high-resolution texture map.
Full scene anti-aliasing uses super-sampling, which means that the image is rendered internally at
a higher resolution than it is displayed on screen. The GMCH renders internally at 1600x1200,
reads the image as a texture, and finally down-samples (via a Bilinear filter) to the screen
resolution of 640x480 and 800x600. Full scene anti-aliasing removes jaggies at the edges.
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Datasheet