Techniques for anisotropic texture mapping using multiple space-invariant filtering operations per pixel

DETAILED DESCRIPTION The present invention relates to a method and a computer system for applying a texture image to an object when rendering the object on a display device.
The texture image is stored at varying levels of detail in a set of texture maps (a mip-map).
Each texture map in the mip-map is associated with one of the levels of detail.
In terms of the method, the invention projects a pixel filter onto one of the texture maps to define an elliptical footprint covering texture data in that texture map.
The footprint has a major axis and a minor axis.
The method determines sample points on a line in the footprint that closely approximates the major axis of the footprint.
Texture data are sampled at the sample points to determine a texture value for each sample point.
Each texel value contributes to a final texture value for modifying the pixel.
In one aspect of the invention, a weight is applied to each texture value to produce weighted texture values that are to be combined to produce the final texture value for modifying the pixel.
In another aspect, the length of the minor axis is used to determine a level of detail at which to sample texture data.
In one embodiment of the invention, a new level of detail is determined for each sample point.
In yet another aspect of the invention, the length of the minor axis is increased when texture data would be excluded from sampling or would be under-weighted.
Increasing the length of the minor axis increases the area covered by a space-invariant filter that is used to sample the texture data at the sample points.
In still another aspect of the invention, the length of the line is decreased when the sampling would include texture data beyond an end of the footprint.
In terms of the computer system, the invention includes a memory for storing the texture image at varying levels of detail in a set of texture maps.
Each texture map is associated with one of the levels of detail.
The system includes means for projecting a pixel onto one of the texture maps to define a footprint covering texture data in that texture map