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Intel
82865G/82865GV GMCH Datasheet
Functional Description
6. 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.
7. 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 (Revision1.1) 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. Flexible vertex format support allows multitexturing because it makes it possible to
pass more than one texture in the vertex structure.
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 rendered 2D or 3D rendered images.
Cubic Environment Mapping
Environment maps allow applications to render scenes with complex lighting and reflections while
significantly decreasing the processor load. There are several methods to generate environment
maps (e.g., spherical, circular, and cubic). The GMCH supports cubic reflection mapping over
spherical and circular since it is the best choice to provide real-time environment mapping for
complex lighting and reflections.
Cubic Mapping requires a texture map for each of the 6 cube faces. These can be generated by
pointing a camera with a 90-degree field-of-view in the appropriate direction. Per-vertex vectors
(normal, reflection or refraction) are interpolated across the polygon and the intersection of these
vectors with the cube texture faces is calculated. Texel values are then read from the intersection
point on the appropriate face and filtered accordingly.
5.4.1.5
Raster Engine
The Raster Engine is where the color data (e.g., fogging, specular RGB, texture map blending, etc.)
is processed. The final color of the pixel is calculated and the RGBA value combined with the
corresponding components resulting from the Texture Engine. These textured pixels are modified
by the specular and fog parameters. These specular highlighted, fogged, textured pixels are color
blended with the existing values in the frame buffer. In parallel, stencil, alpha, and depth buffer
tests are conducted that will determine whether the Frame and Depth Buffers will be updated with
the new pixel values.