RG82855GMESL72L Datasheet, PDF (146/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Functional Description
R
6.4.2.16
6.4.2.17
Flexible vertex format support allows multi-texturing because it makes it possible to pass more
than one texture in the vertex structure.
Cubic Environment Mapping
Environment maps allow applications to render scenes with complex lighting and reflections
while significantly decreasing CPU load. There are several methods to generate environment
maps such as 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 supports 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 are calculated. Texel values are then read from the intersection
point on the appropriate face and filtered accordingly.
Bump Mapping
The GMCH only supports embossed and dot product bump mapping, not environment bump
mapping.
6.4.3
6.4.3.1
6.4.3.2
Raster Engine
The Raster engine is where the color data such as fogging, specular RGB, texture map blending,
etc. is processed. The final color of the pixel is calculated and the RGB 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 which will determine whether the Frame and Depth buffers will be updated
with the new pixel values.
Texture Map Blending
Multiple textures can be blended together in an iterative process and applied to a primitive. The
GMCH allows up to four distinct or shared texture coordinates and texture maps to be specified
onto the same polygon. Also, the GMCH supports a texture coordinate set to access multiple
texture maps. State variables in multiple textures are bound to texture coordinates, texture map or
texture blending.
Combining Intrinsic and Specular Color Components
The GMCH allows an independently specified and interpolated specular RGB attribute to be
added to the post-texture blended pixel color. This feature provides a full RGB specular highlight
to be applied to a textured surface, permitting a high quality reflective colored lighting effect not
available in devices which apply texture after the lighting components have been combined. If the
specular-add state variable is disabled, only the resultant colors from the map blending are used.
If this state variable is enabled, the specular RGB color is added to the RGB values from the
output of the map blending.
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Datasheet