Apparatus and method for geometry operations in a 3d-graphics pipeline

A system and method for performing tangent space lighting in a deferred shading graphics processor (DSGP) encompasses blocks of the DSGP that preprocess data and a Phong shader that executes only after all fragments have been preprocessed. A preprocessor block receives texture maps specified in a variety of formats and converts those texture maps to a common format for use by the Phong shader. The preprocessor blocks provide the Phong shader with interpolated surface basis vectors (vs, vt, n), a vector Tb that represents in tangen/object space the texture/bump data from the texture maps, light data, material data, eye coordinates and other information used by the Phong shader to perform the lighting and bump mapping computations. The data from the preprocessor is provided for each fragment for which lighting effects need to be computed. The Phong shader computes the color of a fragment using the information provided by the preprocessor. The Phong shader performs all lighting computations in eye space, which requires it first to transform bump data from tangent space to eye space. In one embodiment the Phong hardware does this by multiplying a matrix M whose columns comprise eye space basis vectors (bs, bt, n) derived from the surface basis vectors (vs, vt, n) and the vector Tb of bump map data. The eye space basis vectors are derived by the DSGP preprocessor so that the multiplication (MxTb) gives the perturbed surface normal N' in eye space, reflecting the bump effects. The perturbed surface normal N' is subsequently used in the lighting computations.