The SGGX microflake distribution

Abstract

Figure 1: Top-left: rendering a voxelized forest at decreasing levels of detail (left to right). Bottom-right: visualization of the voxel structure at the matching resolutions. We use the SGGX microflake distribution to represent volumetric anisotropic materials. Our representation supports downscaling and interpolation, resulting in smooth and antialiased renderings at multiple scales. AbstractWe introduce the Symmetric GGX (SGGX) distribution to represent spatially-varying properties of anisotropic microflake participating media. Our key theoretical insight is to represent a microflake distribution by the projected area of the microflakes. We use the projected area to parameterize the shape of an ellipsoid, from which we recover a distribution of normals. The representation based on the projected area allows for robust linear interpolation and prefiltering, and thanks to its geometric interpretation, we derive closed form expressions for all operations used in the microflake framework.We also incorporate microflakes with diffuse reflectance in our theoretical framework. This allows us to model the appearance of rough diffuse materials in addition to rough specular materials. Finally, we use the idea of sampling the distribution of visible normals to design a perfect importance sampling technique for our SGGX microflake phase functions. It is analytic, deterministic, simple to implement, and one order of magnitude faster than previous work.

Downsampling scattering parameters for rendering anisotropic media

“…This generalized framework collapses to the standard isotropic case (1) when D is set to uniform [Jakob et al 2010]. In addition, it has been shown to be capable of closely capturing the appearance of complex materials such as fabrics and fur [Jakob et al 2010;Zhao et al 2011;Zhao et al 2012;Heitz et al 2015].…”

“…Jakob et al [2010] later relaxed this assumption by modeling anisotropic media with structured micro-geometries. [Heitz et al 2015] has recently proposed a new anisotropic phase function offering fast evaluation and easy (linear) interpolation. We build our framework upon this state-of-the-art representation.…”

“…largely lacking for light scattering parameters [Chandrasekhar 1960;Jakob et al 2010]. Recently, Heitz et al [2015] proposed a new phase function formulation which offers easy (trilinear) prefiltering and is a valuable first-step toward this direction. However, linear downsampling is generally insufficient when handling scattering parameters including spatially varying densities and albedo values.…”

“…Recently, Heitz et al [2015] introduced a SGGX-based representation for the micro-flake normal distribution:…”

“…. , S n with one SGGX function with the matrixS, Heitz et al [2015] demonstrated that using the arithmetic average of those matrices, namely setting…”