Volumetric Transparency with Per-Pixel Fragment Lists

TLDR: In this article, the authors describe the volumetric transparency method for rendering transparent objects that departs from classic alpha blending, and discuss per-pixel lists of surface fragments and evaluates illumination analytically between neighboring pairs.

Abstract: This chapter describes the volumetric transparency method for rendering transparent objects that departs from classic alpha blending. It discusses per-pixel lists of surface fragments and evaluates illumination analytically between neighboring pairs. The chapter discusses an algorithm for the case when the transparent objects are spheres. It suggests that executing a single iteration step of the intersection algorithm is sufficient to provide the required detail. The pixel shader traces linked lists reading fragments into a local array and sorts them according to their distance. The chapter shows how the approach can be extended to volumetric transparency, and even intersecting objects. Thus, volumetric transparency can be seen both as a relatively low-cost improvement to order-independent transparency and as a sophisticated approach to replace billboards in particle rendering. Thus, the method is geared at the most prevalent application of transparency: particle system rendering, where it avoids all popping and clipping artifacts characteristic of alpha-blended billboard clouds.