1. A computer graphics method, comprising: receiving or generating texture space gradient values for one or more primitives based on a non-orthonormal grid of sample points in a screen space with a texture unit of a graphics processing unit; and applying a transformation to the texture space gradient values with the texture unit, wherein the transformation is configured to generate corresponding ortho-normal texture space gradient values corrected for the non-orthonormality of the sample points in screen space with the texture unit.