Vertex-based anisotropic texturing

Abstract

MIP mapping is a common method used by graphics hardware to avoid texture aliasing. In many situations, MIP mapping over-blurs in one direction to prevent aliasing in another. Anisotropic texturing reduces this blurring by allowing differing degrees of filtering in different directions, but is not as common in hardware due to the implementation complexity of current techniques. We present a new algorithm that enables anisotropic texturing on any current MIP map graphics hardware supporting MIP level biasing, available in OpenGL 1.2 or through the GL_EXT_texture_lod_bias or GL_SGIX_texture_lod_bias OpenGL extensions. The new algorithm computes anisotropic filter footprint parameters per vertex. It constructs the anisotropic filter out of several MIP map texturing passes or multi-texture lookups. Each lookup uses MIP level bias and perturbed texture coordinates to place one probe used to construct the more complex filter profile.