Patent ID: 7450136

Claim:
A pixel processing apparatus, comprising: a pixel shader operative to shade pixels of primitives, said pixel shader performing at least one pixel shading operation in which each pixel of a selected primitive that is shaded requires filtering information, the filtering information using an estimate of texture coordinate derivatives based on differences in values with neighboring pixels within a group footprint of neighboring pixels about a pixel being shaded, each group footprint comprising a plurality of pixels; and said pixel processing apparatus having a mode of operation in which a shading process is organized to reduce the number of pixels in each said group footprint extending outside of the selected primitive that must be rendered for the sole purpose of generating estimates of texture coordinate derivatives for pixels having a pixel center interior to said selected primitive; the shading process having at least two different group footprint alignments of pixel centers of the group footprint, the shading process reducing the number of pixels exterior to the selected primitive that must be rendered for generating texture coordinate derivatives by comparing the number of exterior pixels required to calculate texture coordinate derivatives for each of said at least two different group footprint alignments and selecting an alignment that minimizes the number of pixels exterior to said selected primitive that must be rendered to generate filtering information.