Microfacet theory for non-uniform heightfields

Eugene d'Eon Benedikt Bitterli Andrea Weidlich Tizian Zeltner

SIGGRAPH 2023 (Conference Track)

Our asymmetric blending operator creates two new microfacet BSDFs (center) using the same blended NDF (GGX with roughness 0.02 and 0.8) but with different roughness applied to different elevation ranges of the microsurface (as seen in the top row profiles). The result is that while the interior of the surface remains unchanged, the silhouettes of the asymmetric BSDFs are different. At grazing angles, the spheres in the middle-right column appear rougher (note the reflection of the checkerboard onto the conductive spheres) because the rougher component of the mixture protrudes outward. This behavior cannot be achieved through a simple linear blend of two single-NDF BSDFs (as seen on the left).

Abstract

We propose new methods for combining NDFs in microfacet theory, enabling a wider range of surface statistics. The new BSDFs that follow allow for independent adjustment of appearance at grazing angles, and can't be represented by linear blends of single-NDF BSDFs. We derive importance sampling for a symmetric operator that blends NDFs uniformly, and introduce a new asymmetric operator that supports NDF variation with elevation. We also extend Smith's model to support piecewise-constant NDF and material variations with elevation, and demonstrate accuracy via Monte Carlo simulations.

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BibTeX Reference


        @inproceedings{dEon2023NonuniformMicrofacets,
    author = {d'Eon, Eugene and Bitterli, Benedikt and Weidlich, Andrea and Zeltner, Tizian},
    title = {Microfacet theory for non-uniform heightfields},
    year = {2023},
    publisher = {Association for Computing Machinery},
    address = {New York, NY, USA},
    doi = {10.1145/3588432.3591486},
    booktitle = {SIGGRAPH 2023 Conference Papers},
    numpages = {10},
    location = {Los Angeles, CA, USA}
}