Temporal Anti-Aliasing for Real-Time Froxel-Based Volumetric Rendering - Advances in volumetric temporal anti-aliasing for real-time ren dering of participating media

Abstract

Froxel-based rendering is widely used in modern graphics pipelines to render participating media such as fog and atmospheric lighting. Due to the low resolution of the froxel grid, required for real-time rendering feasibility, these techniques suffer from temporal instability, including flickering, shimmering and ghosting artifacts. Existing temporal accumulation methods that use an exponential moving average provide stable images in static scenes but perform poorly under dynamic volumetric lighting conditions. This thesis investigates how temporal anti-aliasing techniques originally developed for surface-based rendering can be extended into froxel space for volumetric rendering of participating media. Several history validation, blending, jittering, filtering, and spatial reconstruction methods were implemented and evaluated in Godot and Frostbite. The methods were compared quantitatively against a supersampled volumetric ground truth and qualitatively in dynamic lighting conditions. The results show that variance clipping applied directly to volumetric froxel data, together with heuristic anti-flicker techniques, greatly reduces ghosting artifacts while introducing only a small amount of flickering. By considering the six nearest froxels when computing current-frame local variance estimates, the best trade-off between temporal stability, spatial accuracy and performance cost is achieved. Depth only low-discrepancy jittering and weighting samples based on their distance to the froxel center further helps reduce flickering artifacts. The proposed volumetric TAA algorithm was successfully implemented in Frostbite, showing clear visual improvements and acceptable runtime performance on modern console hardware.