Hemispherical Lighting Insights

Precomputed lighting is crucial in many interactive applications, which commonly encode global illumination in compact lightmaps or volumetric data structures. For precomputed lighting to interact with high-frequency geometric detail encoded in normal maps, each surface must be able to evaluate irradiance in any direction in its hemisphere, which requires that the precomputed lighting be represented using directional lighting models. We present two new highly compact hemispherical lighting models, each of which can be efficiently solved to and blended in an advancement over the commonly-used AHD model. We show how these models can be encoded to maintain exact reconstruction of irradiance in the vertex normal/local Z ("IrradZ"), providing a framework for solving to IrradZ models from spherical harmonics (SH) using hemispherical least-squares and correcting prior work where spherical methods have led to unnecessarily high error. Finally, we introduce an efficient method for hemisphere multiplies of quadratic SH and use it to inexpensively apply hemispherical or cone occlusion to volumetric lighting, mitigating light leakage for normal-mapped surfaces and significantly improving the appearance of runtime ambient occlusion.

Read the full paper HERE

View the accompanying ShaderToy HERE