845GL datasheet(122/193 Pages) INTEL

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Functional Description

122

Intel® 82845G/82845GL/82845GV GMCH Datasheet

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.

Texture Formats and Storage

The GMCH supports up to 32 bits of color for non-palettized textures.

Texture Decompression

DX Texture Compression reduces the bandwidth required to deliver textures. As the textures’

average sizes get larger with higher color depth and multiple textures become the norm, it becomes

increasingly important to provide a mechanism to compress textures. Texture decompression

formats supported include DXTn and FXT1.

Texture Chromakey

Chromakey describes a method of 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).

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 a very small number of pixels available on

screen to contain the data of a high resolution texture map. More subtle effects are observed in

animation, where very small primitives blink in and out of view.

Texture Map Filtering

Many texture mapping modes are supported. Perspective correct mapping is always performed. As

the map is fitted across the polygon, the map can be tiled, mirrored in either the U or V directions,

or mapped up to the end of the texture and no longer placed on the object (this is known as clamp

mode). The way a texture is combined with other object attributes is also definable.

The GMCH supports up to 12 Levels-of-Detail (LODs) ranging in size from 2048x2048 to 1x1

texels. (A texel is defined as a texture map element). Textures need not be square. Included in the

texture processor is a texture cache that provides efficient MIP-mapping.

845GL Datasheet(PDF) 122 Page - Intel Corporation