RG82855GMESL72L Datasheet, PDF (145/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Functional Description
R
6.4.2.14
6.4.2.15
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.) Included in the texture processor is a texture
cache, which provides efficient MIP-mapping.
The GMCH supports seven types of texture filtering:
• Nearest (also known as Point filtering): Texel with coordinates nearest to the desired pixel is
used. (This is used if only one LOD is present.)
• Linear (also known as 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 (also known as 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 are
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 are 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 filter can be used when textured object
pixels map back to significantly non-square regions of the texture (e.g., when the texture is
scaled in one screen direction than the other screen direction).
• Both DirectX and OpenGL (Rev.1.1) allow support for all these filtering modes.
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. The setup engine supports up to four texture map coordinates in as single pass. The
GMCH allows up to two Bilinear MIP Maps or a single Trilinear MIP Map to be composited in a
single pass. Greater than two Bilinear MIP Maps or more than one Trilinear MIP Map would
require multiple passes. The actual blending or composition of the MIP Maps is done in the raster
engine. The texture engine provides the required texels including blending information.
Datasheet
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