All-Frequency Rendering of Dynamic, Spatially-Varying Reflectance

  • Baining Guo, Microsoft; John Snyder, Microsoft

We describe a technique for real-time rendering of dynamic,
spatially-varying BRDFs in static scenes with all-frequency shad-
ows from environmental and point lights. The 6D SVBRDF is rep-
resented with a general microfacet model and spherical lobes fit to
its 4D spatially-varying normal distribution function (SVNDF). A
sum of spherical Gaussians (SGs) provides an accurate approxima-
tion with a small number of lobes. Parametric BRDFs are fit on-
the-fly using simple analytic expressions; measured BRDFs are fit
as a preprocess using nonlinear optimization. Our BRDF represen-
tation is compact, allows detailed textures, is closed under products
and rotations, and supports reflectance of arbitrarily high specular-
ity. At run-time, SGs representing the NDF are warped to align the
half-angle vector to the lighting direction and multiplied by the mi-
crofacet shadowing and Fresnel factors. This yields the relevant 2D
view slice on-the-fly at each pixel, still represented in the SG basis.
We account for macro-scale shadowing using a new, nonlinear vis-
ibility representation based on spherical signed distance functions
(SSDFs). SSDFs allow per-pixel interpolation of high-frequency
visibility without ghosting and can be multiplied by the BRDF and
lighting efficiently on the GPU.

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