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English Version

URP Dynamic Diffuse Global Illumination (DDGI)

基于 Unity URP 14.0 + DXR 的动态漫反射全局光照系统，参考 NVIDIA RTXGI SDK 实现。在三维均匀网格上布置光照探针，每帧通过硬件光线追踪更新 irradiance / distance atlas，为场景提供实时间接光照。

效果展示

overview

渲染管线

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

关键技术实现

各阶段可视化

Direct Irradiance Indirect Irradiance Outgoing Radiance Irradiance
direct indirect radiance irradiance
Probe Relocation
relocation

实现细节

  • 直接光照、间接光采样与 radiance 合成压缩至单个 compute pass（LightingCombined），消除中间缓冲区
  • Atlas 采用 ping-pong 双缓冲，写入 Current、读取 Prev，零拷贝交换
  • 光线方向基于 Fibonacci 球面均匀分布 + Halton 序列逐帧随机旋转
  • Monte Carlo 积分使用指数滑动平均（hysteresis），irradiance 采用 gamma 编码（γ=5.0）提升暗部精度
  • Probe Relocation 自动移动陷入几何体的探针，Classification 基于背面命中比例标记无效探针
  • Variability Reduction 通过多级归约 + AsyncGPUReadback 驱动自适应更新频率
  • 漏光抑制：surface bias、Chebyshev visibility test、weight crushing
  • GI 应用阶段三线性插值 + 切比雪夫可见性加权采样周围 8 个探针

目录结构

Assets/DDGILightProbe/
├── Runtime/
│   ├── Core/              DDGIVolume, DDGIRaytracingManager, DDGIProbeUpdater,
│   │                      DDGIAtlasManager, DDGIApplyGIRendererFeature,
│   │                      DDGIProbeVisualizer, DDGISkyOnlyValidator ...
│   └── Shaders/
│       ├── DDGILightingCombined.compute      合并光照 Pass
│       ├── DDGIMonteCarloIntegration.compute  蒙特卡洛积分 + Border Update
│       ├── DDGIProbeRelocation.compute        探针重定位
│       ├── DDGIProbeClassification.compute    探针分类
│       ├── DDGIVariabilityReduction.compute   变异度归约
│       ├── DDGISampling.hlsl                  Atlas 采样公共库
│       ├── DDGIApplyGI.shader                 全屏 GI 叠加
│       └── DDGIRaytracing/                    RayGen, ClosestHit, Miss, GBuffer
└── Editor/                Volume / Updater / Visualizer / Validator Inspector

环境要求

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

配置步骤

  1. URP Renderer 添加 DDGIApplyGIRendererFeature
  2. 场景中创建 GameObject → Light → DDGI Volume
  3. DDGIProbeUpdater 设为 Raytracing 模式，点击「自动查找 Shaders」
  4. 调整 Volume 参数，Play Mode 即可看到实时 GI

参考

  • 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

许可与致谢

本项目包含的 Sponza 场景资源受以下许可约束：

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

详细版权信息见 Assets/com.unity.sponza-urp@5665fb87d0/copyright.txt。