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URP Dynamic Diffuse Global Illumination (DDGI)

A dynamic diffuse global illumination system built on Unity URP 14.0 + DXR, based on the NVIDIA RTXGI SDK. Light probes are placed on a uniform 3D grid, with hardware ray tracing updating irradiance / distance atlases each frame to provide real-time indirect lighting.

Showcase

Rendering Pipeline

Per Frame:
  Build RTAS → Dispatch Rays → G-Buffer
  → [Probe Relocation] → [Probe Classification]
  → LightingCombined (Direct + Indirect + Radiance, single pass)
  → Monte Carlo Integration (Irradiance + Distance Atlas)
  → [Variability Reduction] → Border Update → Ping-Pong Swap

Apply GI (URP RendererFeature):
  Depth → World Pos → Sample DDGI Atlas (trilinear + Chebyshev) → Additive Composite

Key Technical Details

Per-Stage Visualization

Direct Irradiance	Indirect Irradiance	Outgoing Radiance	Irradiance

Probe Relocation

Implementation Details

• Direct lighting, indirect light sampling, and radiance compositing compressed into a single compute pass (LightingCombined), eliminating intermediate buffers
• Atlas uses ping-pong double buffering — writes to Current, reads from Prev — zero-copy swap
• Ray directions based on Fibonacci sphere uniform distribution + Halton sequence per-frame random rotation
• Monte Carlo integration uses exponential moving average (hysteresis); irradiance uses gamma encoding (γ=5.0) for improved dark region precision
• Probe Relocation automatically moves probes embedded in geometry; Classification marks invalid probes based on backface hit ratio
• Variability Reduction via multi-level reduction + AsyncGPUReadback drives adaptive update frequency
• Light leak suppression: surface bias, Chebyshev visibility test, weight crushing
• GI application stage: trilinear interpolation + Chebyshev visibility-weighted sampling of surrounding 8 probes

Directory Structure

Assets/DDGILightProbe/
├── Runtime/
│   ├── Core/              DDGIVolume, DDGIRaytracingManager, DDGIProbeUpdater,
│   │                      DDGIAtlasManager, DDGIApplyGIRendererFeature,
│   │                      DDGIProbeVisualizer, DDGISkyOnlyValidator ...
│   └── Shaders/
│       ├── DDGILightingCombined.compute      Combined lighting pass
│       ├── DDGIMonteCarloIntegration.compute  Monte Carlo integration + Border Update
│       ├── DDGIProbeRelocation.compute        Probe relocation
│       ├── DDGIProbeClassification.compute    Probe classification
│       ├── DDGIVariabilityReduction.compute   Variability reduction
│       ├── DDGISampling.hlsl                  Atlas sampling utilities
│       ├── DDGIApplyGI.shader                 Full-screen GI composite
│       └── DDGIRaytracing/                    RayGen, ClosestHit, Miss, GBuffer
└── Editor/                Volume / Updater / Visualizer / Validator Inspector

Requirements

• Unity 2022.3+, Windows, DirectX 12
• GPU with DXR 1.0 support (NVIDIA RTX / AMD RX 6000+)
• URP 14.0+, Deferred Rendering Path

Setup

1. Add DDGIApplyGIRendererFeature to the URP Renderer
2. Create a GameObject → Light → DDGI Volume in the scene
3. Set DDGIProbeUpdater to Raytracing mode, click "Auto Find Shaders"
4. Adjust Volume parameters; enter Play Mode to see real-time GI

References

• NVIDIA RTXGI SDK
• Majercik et al., Dynamic Diffuse Global Illumination with Ray-Traced Irradiance Fields, JCGT 2019
• Majercik et al., Scaling Probe-Based Real-Time Dynamic Global Illumination for Production, JCGT 2021

License & Acknowledgments

This project contains Sponza scene assets under the following licenses:

• Sponza model: CC BY 3.0 — © 2010 Frank Meinl, Crytek
• NoEmotion HDRs textures: CC BY-ND 4.0 — © 2022 Peter Sanitra

See Assets/com.unity.sponza-urp@5665fb87d0/copyright.txt for full copyright information.