Evaluating and Sampling Glinty NDFs in Constant Time

Pauli Kemppinen, LoÏs Paulin, Théo Thonat, Jean-Marc Thiery, Jaakko Lehtinen & Tamy Boubekeur

ACM Transactions on Graphics (Proc. SIGGRAPH Asia 2025)

From left to right: our glittery version of the a microfacet BRDF with a Trowbridge-Reitz (GGX) normal distribution, a Beckmann variant showing per-facet color (red/yellow) control, an anisotropic variant and an image-based lighting setup illustrating the support of importance sampling.

Abstract

Geometric features between the micro and macro scales produce an expressive family of visual effects grouped under the term 'glints'. Efficiently rendering these effects amounts to finding the highlights caused by the geometry under each pixel. To allow for fast rendering, we represent our faceted geometry as a 4D point process on an implicit multiscale grid, designed to efficiently find the facets most likely to cause a highlight. The facets' normals are generated to match a given micro-facet normal distribution such as Trowbridge-Reitz (GGX) or Beckmann, to which our model converges under increasing surface area. Our method is simple to implement, memory-and-precomputation-free, allows for importance sampling and covers a wide range of different appearances such as anisotropic as well as individually colored particles. We provide a base implementation as a standalone fragment shader.

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Bibtex

@article{KPT:2025:Glinty, 
  title = {Evaluating and Sampling Glinty NDFs in Constant Time}, 
  author = {Pauli Kemppinen, LoÏs Paulin, Théo Thonat, Jean-Marc Thiery, Jaakko Lehtinen and Tamy Boubekeur}, 
  year = {2025}, 
  journal = {ACM Transactions on Graphics (Proc. SIGGRAPH Asia 2025)},
  volume = {44},
  number = {6},
  articleno = {255},
}