“Feline: fast elliptical lines for anisotropic texture mapping” by McCormack, Perry, Farkas and Jouppi

Texture mapping using trilinearly filtered mip-mapped data is efficient and looks much better than point-sampled or bilinearly filtered data. But trilinear filtering represents the projection of a pixel filter footprint from screen space into texture space as a square, when in reality the footprint may be long and narrow. Consequently, trilinear filtering severely blurs images on surfaces angled obliquely away from the viewer. This paper describes a new texture filtering technique called Feline (for Fast Elliptical Lines). Like other recent hardware anisotropic filtering algorithms, Feline uses an underlying space-invariant (isotropic) filter with mip-mapped data, and so can be built on top of an existing trilinear filtering engine. To texture a pixel, it uses this space-invariant filter at several points along a line in texture space, and combines the results. With a modest increase in implementation complexity over earlier techniques, Feline more accurately matches the desired projection of the pixel filter in texture space, resulting in images with fewer aliasing artifacts. Feline’s visual quality compares well against Elliptical Weighted Average, the best software anisotropic texture filtering algorithm known to date, but Feline requires much less setup computation and far fewer cycles for texel fetches. Finally, since it uses standard mip-maps, Feline requires minimal extensions to standard 3D interfaces like OpenGL.

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