WebGPU Compute Shaders: Parallel SDF Ambient Occlusion & Soft Shadow Cone Tracing
Traditional screen-space ambient occlusion (SSAO) and shadow mapping suffer from edge bleeding, depth discontinuities, and high memory footprints. Signed Distance Fields (SDF) enable analytical cone-traced soft shadows and contact ambient occlusion directly within WebGPU compute shader workgroups.
SDF Cone Tracing & Occlusion Theory
How evaluating distance field gradients along the surface normal creates smooth contact shadowing:
For a surface point $p$ with normal $n$, ambient occlusion is evaluated at $N$ step distances $d_i$ along $n$: $AO = 1.0 - \sum_{i=1}^N w_i \cdot (d_i - \text{map}(p + d_i n))$. Soft shadows are computed by marching towards light position $l$, accumulating shadow factor $k \cdot \min(1.0, \text{map}(p + t d) / t)$ across ray length $t$, yielding physically accurate penumbras at $120\text{ FPS}$.
Shadow & Occlusion Techniques Compared
| Lighting Technique | Sampling Complexity | Shadow Penumbra Quality | VRAM Memory Footprint |
|---|---|---|---|
| Cascaded Shadow Maps (CSM) | $O(4 \times \text{PCF samples})$ | Uniform blur (No contact hardening) | 64 MB – 128 MB 4K Maps |
| Screen-Space Ambient Occlusion | $O(16\text{–}32\text{ depth taps})$ | Approximated (Loses off-screen data) | 16 MB G-Buffer Buffers |
| WebGPU SDF Cone Tracing | $O(8\text{–}12\text{ sphere queries})$ | Analytical contact hardening | < 4 MB Structured Buffer |
WGSL Compute Pipeline Implementation
How the compute shader dispatches parallel tiles across GPU SIMD execution units:
- Workgroup Tiling: Configure `@workgroup_size(16, 16, 1)` compute shaders to process 256 pixel tiles in local shared memory.
- Analytical Step Evaluation: March shadow rays with dynamic step sizes determined by distance field values without ray-triangle intersections.
- Subgroup Wave Intrinsics: Use `subgroupBroadcast` to distribute uniform distance evaluations across 32-thread hardware warps.
Explore Real-Time Graphics & Creative Engineering
Push the boundaries of WebGPU, generative shaders, and digital aesthetics. Read our guide on WebGPU Compute Shaders: Parallel SDF Raymarching & CSG Booleans, explore Linux kernel io_uring network buffer pools on WinWinHost Cloud, inspect V8 Maglev JIT optimization on WebDesigner.la, or collaborate with our GPU engineering team.