910GL datasheet(239/426 Pages) INTEL

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Functional Description

Datasheet

239

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

texels. Textures need not be square. Included in the texture processor is a texture cache, which

provides efficient MIP-mapping.

The GMCH supports 7 types of texture filtering:

• Nearest (aka Point Filtering): Texel with coordinates nearest to the desired pixel is used.

(This is used if only one LOD is present).

• Linear (aka Bilinear Filtering): A weighted average of a 2x2 area of texels surrounding the

desired pixel is used. (This is used if only one LOD is present).

• Nearest MIP Nearest (aka Point Filtering): This is used if many LODs are present. The

nearest LOD is chosen and the texel with coordinates nearest to the desired pixel is used.

• Linear MIP Nearest (Bilinear MIP Mapping): This is used if many LODs are present. The

nearest LOD is chosen and a weighted average of a 2x2 area of texels surrounding the

desired pixel is used (four texels). This is also referred to as Bilinear MIP Mapping.

• Nearest MIP Linear (Point MIP Mapping): This is used if many LODs are present. Two

appropriate LODs are selected and within each LOD the texel with coordinates nearest to the

desired pixel is selected. The Final texture value is generated by linear interpolation between

the two texels selected from each of the MIP Maps.

• Linear MIP Linear (Trilinear MIP Mapping): This is used if many LODs are present. Two

appropriate LODs are selected and a weighted average of a 2x2 area of texels surrounding the

desired pixel in each MIP Map is generated (four texels per MIP Map). The Final texture

value is generated by linear interpolation between the two texels generated for each of the

MIP Maps. Trilinear MIP Mapping is used minimize the visibility of LOD transitions across

the polygon.

• Anisotropic MIP Nearest (Anisotropic Filtering): This is used if many LODs are present. The

nearest LOD-1 level will be determined for each of four sub-samples for the desired pixel.

These four sub-samples are then bilinear filtered and averaged together.

Both D3D (DirectX 6.0 and later) and OpenGL (Revision 1.1) allow support for all these filtering

modes.

12.6.3.7

Multiple Texture Composition

The GMCH also performs multiple texture composition. This allows the combination of two or

greater MIP Maps to produce a new one with new LODs and texture attributes in a single or

iterated pass. Flexible vertex format support allows multitexturing because it makes it possible to

pass more than one texture in the vertex structure.

12.6.3.8

Bi-Cubic Filter (4x4 Programmable Texture Filter)

A bi-cubic texture filter can be selected instead of the bilinear filter. The implementation is of a

4x4 separable filter with loadable coefficients. A 4x4 filter can be used for providing high-quality

up/ down scaling of 2D or 3D rendered images.

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