Normal mapping with low-frequency precomputed visibility

Normal mapping is a common technique used in video games, decoupling surface details stored at high spatial frequencies, which are often tiled or repeated, from lighting information that is both unique and stored at a lower sampling rate. This paper presents two techniques that couple normal maps on static geometry with soft shadows from smooth distant lighting in a more efficient manner compared with previous work. In the first technique, the visibility function is represented using low-order spherical harmonics, and the product of the Lambertian-clamped cosine function and the lighting environment is tabulated in textures. The second technique uses principal component analysis to compress the visibility function, decreasing the data size and increasing the performance. Finally, we also examine the efficiency of four common parameterizations for spherical harmonics.