A micrograin formalism for the rendering of porous materials
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2024-12-06
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Abstract
This thesis focuses on the impact of microscopic structures on material appearance, with a particular emphasis on porous materials. We first evaluated existing appearance models by conducting light transport simulations on sphere aggregates representing porous volumes. We found that none of the existing models accurately matched the simulations, with most errors arising from surface effects. This opened the path to the development of a specialized Bidirectional Scattering Distribution Function (BSDF) model for rendering porous layers, such as those found on surfaces covered with dust, rust, or dirt. Our model extends the Trowbridge-Reitz (GGX) distribution to handle pores between elliptical opaque micrograins and introduces a view- and light-dependent filling factor to blend porous and base layers. By adding height-normal and light-view correlations in the masking and shadowing terms, our model produces realistic effects seen in real world materials that were previously hardly obtainable like retro-reflection and height-color correlations. To improve the rendering efficiency of micrograin materials, we introduce an efficient importance sampling routine for visible Normal Distribution Functions (vNDF). Through numerical simulations, we validate the accuracy of our model. Finally, our work provides a comprehensive formalism for rendering porous layers and opens many perspectives of futur work.
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