Datasheet

Functional Description
R
Datasheet 185
• 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 to 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 OGL (Rev.1.1) allow support for all these filtering modes.
5.4.2.13 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 a 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.
Flexible vertex format support allows multi-texturing because it makes it possible to pass more
than one texture in the vertex structure.
5.4.2.14 Cubic Environment Mapping
Environment maps allow applications to render scenes with complex lighting and reflections
while significantly decreasing processor 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.