Kenta Eto
ABSTRACT
Sampling according to a visible normal distribution function (VNDF) is often used to sample rays scattered by glossy surfaces, such as the Smith–GGX microfacet model. However, for rough reflections, existing VNDF sampling methods can generate undesirable reflection vectors occluded by the surface. Since these occluded reflection vectors must be rejected, VNDF sampling is inefficient for rough reflections. This paper introduces an unbiased method to reduce the number of rejected samples for Smith–GGX VNDF sampling. Our method limits the sampling range for a state-of-the-art VNDF sampling method that uses a spherical cap-based sampling range. By using our method, we can reduce the variance for highly rough and low-anisotropy surfaces. Since our method only modifies the spherical cap range in the existing sampling routine, it is simple and easy to implement.
Supplemental Material
Available for Download
- Brent Burley. 2012. Physically-Based Shading at Disney. In SIGGRAPH ’12 Course: Practical Physically-based Shading in Film and Game Production. 10:1–10:7. https://doi.org/10.1145/2343483.2343493Google Scholar
Digital Library
- Jonathan Dupuy and Anis Benyoub. 2023. Sampling Visible GGX Normals with Spherical Caps. Comput. Graph. Forum (2023). https://doi.org/10.1111/cgf.14867Google ScholarCross Ref
- Eric Heitz. 2018. Sampling the GGX Distribution of Visible Normals. JCGT 7, 4 (2018), 1–13. https://jcgt.org/published/0007/04/01/Google Scholar
- Eric Heitz and Eugene d’Eon. 2014. Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals. Comput. Graph. Forum 33, 4 (2014), 103–112. https://doi.org/10.1111/cgf.12417Google ScholarDigital Library
- Yusuke Tokuyoshi. 2021. Unbiased VNDF Sampling for Backfacing Shading Normals. In SIGGRAPH ’21 Talks. Article 8, 2 pages. https://doi.org/10.1145/3450623.3464655Google ScholarDigital Library
- Emmanuel Turquin. 2019. Practical Multiple Scattering Compensation for Microfacet Models. Technical Report. Industrial Light & Magic. https://blog.selfshadow.com/publications/turquin/ms_comp_final.pdfGoogle Scholar
- Bruce Walter, Stephen R. Marschner, Hongsong Li, and Kenneth E. Torrance. 2007. Microfacet Models for Refraction Through Rough Surfaces. In EGSR ’07. 195–206. https://doi.org/10.2312/EGWR/EGSR07/195-206Google ScholarCross Ref
Index Terms
- Bounded VNDF Sampling for Smith–GGX Reflections
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