Intel® 945G/945GZ/945GC/ 945P/945PL Express Chipset Family ...

Functional Description
10.5.4.6 Texture Map Filtering
The GMCH supports many texture mapping modes. 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. Textures need not be square. Included in the texture processor is a texture cache that
provides efficient MIP-mapping.
The GMCH supports 7 types of texture filtering:
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� 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 to 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 OGL (Revision 1.1) allow support for all these filtering modes.
10.5.4.7 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.