Selectable mode smoothing texture filter for computer graphics

Abstract

A graphics system including a selectable mode smoothing filter for improved texture mapping. An x, y pixel coordinate is mapped into a u, v texture map. The mapped u, v coordinate includes integer and fractional portions. Depending on the location of the coordinate relative to the four nearest texels, which are represented as integers, one of several texture mapping schemes are used to either select or calculate the texel value to be used to render the pixel at the x, y screen location. The three texture mapping schemes include point sampling in which the nearest texel from the texture map is selected, two-texel averaging in which the closest two texels are combined in a weighted average, and four-texel averaging in which the closest four texels are combined in a weighted average. Scale factors in the range of 0 to 1 are computed for averaging texel values together. By including the complete range of 0 to 1, the scale factors permit greater control over the averaging process and accordingly, images with high spatial frequency content are not distorted as much as in previous graphics systems. By providing a selectable filter than can perform point sampling or two or four-texel averaging, the speed benefit of point sampling can be approached as well as the superior quality of two and four-texel averaging.