A discrete microfacet model for transparent glints rendering

Many real-life materials have sparkling appearances. Some small flakes on the surface of an object can make a considerable contribution by reflecting or refracting light at a particular angle, eventually causing a sparkling appearance. Most existing approaches have focused on the glinty effects on reflective surfaces. However, transparent glint rendering has not been well studied, even though there are many natural phenomena (e.g., frost) in the real world. Recent studies have proposed the simulation of transparent glints under specific constraints (e.g., limited to the Beckmann distribution and V-groove shadowing-masking function). In this study, we propose a more general transparent glint model by performing a four-dimensional hierarchical search to count the particles located in the pixel footprint and cone around the refracted ray. Our method can produce transparent glint appearances for arbitrary normal distribution functions (e.g., GGX or Beckmann) and converge to a smooth microfacet model with a large particle count.