Xu, KeweiLucas, SimonRibardière, MickaelBringier, BenjaminBarla, PascalMasia, BelenThies, Justus2026-04-172026-04-172026Computer Graphics Forum, Volume 45, Issue 2, e70387, 20261467-8659https://diglib.eg.org/handle/10.1111/cgf70387https://doi.org/10.1111/cgf.70387We introduce a discrete polydisperse micrograin BSDF model for the rendering of porous surface materials composed of microscopic elements of different size, shape and reflectance distributed on a bulk medium. Our approach generalizes the anisotropic monodisperse micrograin model. We first reformulate it in a non-axis-aligned configuration, allowing for the later combination of different micrograin types elongated in arbitrary directions. We then extend the monodisperse model to the polydisperse case, deriving its three key components: (i) a general filling factor that controls the mix between micrograins and the bulk medium; (ii) an exact normal distribution function for surfaces composed of polydisperse micrograin distributions; and (iii) the corresponding fully-correlated shadowing and masking term. This results in an analytical single-scattering BSDF for discrete polydisperse surface materials, validated over ground truth simulations, for which we also derive a dedicated importance sampling procedure. Our model supports varying heights and anisotropy orientations of different micrograin types as input, giving additional control to simulate phenomena like retro-reflection from mixed materials, color mixture depending on lighting and observation directions, multiple directions of anisotropy, etc.CC-BY-4.0CCS Concepts: Computing methodologies → Reflectance modeling10.1111/cgf.7038713 pages