WebGPU Compute Shaders: Volumetric Raymarching
Rendering atmospheric haze, heterogenous nebula clouds, and realistic participating media in real-time requires calculating volumetric radiative transfer. WebGPU compute shaders parallelize numerical ray integration across GPU workgroups, evaluating Beer-Lambert light extinction and Henyey-Greenstein angular phase scattering at 60 FPS.
Radiative Transfer Equation & Phase Functions
How compute workgroups numerically sample optical depth and in-scattered radiance along primary camera rays:
The angular distribution of scattered photons within participating media is modeled via the Henyey-Greenstein phase function $P(\theta) = \frac{1}{4\pi} \frac{1 - g^2}{(1 + g^2 - 2g \cos\theta)^{3/2}}$. By adjusting asymmetry factor $g \in (-1, 1)$, shaders produce realistic forward solar glare and atmospheric backscattering.
Volumetric Rendering Paradigms Compared
| Volumetric Technique | Primary GPU Workload | Optical Accuracy | Browser Performance |
|---|---|---|---|
| WebGPU Compute Raymarching | Workgroup Parallel Numerical Integration | High (Heterogeneous Density & Shadows) | 60 FPS (Sub-sampled Jitter + TAA) |
| WebGL 2.0 Fragment Slicing | View-Aligned 3D Texture Quads | Moderate (Slicing Artifacts) | High Fill-Rate Overhead |
| Analytical Fog Shaders | Per-Vertex Distance Blend | Low (Homogeneous Approximation) | Ultra-Fast (> 120 FPS) |
Production WebGPU Shader Optimization Rules
Engine invariants for real-time volumetric pipelines in modern web graphics:
- Temporal Super-Sampling & Blue Noise: Offset ray start positions with blue noise per pixel and accumulate radiance across consecutive frames with Temporal Anti-Aliasing (TAA) to eliminate banding with only 16–32 step counts.
- Hierarchical 3D Texture Pyramids: Store volumetric density fields in mipmapped 3D texture buffers, skipping empty voxel regions during ray traversal.
- Workgroup Shared Memory (WGSL): Cache local light shadow transmittance values in
workgroupSharedarrays to prevent redundant texture lookups across adjacent screen tiles.
Explore Advanced Web Graphics Engineering
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