Graphics texture mapping

Sampling a texture using anisotropic filtering, comprising: for a sampling position in the texture having coordinates x and y, determining the square root of the coefficient F for an ellipse defined by the equation Ax2 + Bxy + Cy2 = F, the ellipse corresponding to the projection of the sampling position on to the surface to which the texture is applied, and using the square root of F to determine a number of positions to sample the texture along an anisotropy direction; taking the samples and using them to determine an output sampled texture value for the sampling position. Also disclosed: using mipmaps to represent the texture at different levels of detail and using a log2 operation on the square root of F to determine the level of detail at which to sample the texture. Also disclosed: selecting between two different levels of detail. Also disclosed is determining an anisotropy direction by: determining X and Y components of a vector corresponding to the major axis of the elliptical projection of the sampling position and normalising them to provide X and Y components for a corresponding unit vector; using the unit vector components to determine the anisotropy direction.