172 lines
6.6 KiB
Markdown
172 lines
6.6 KiB
Markdown
---
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title: Untitled
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date: 2024-12-28 21:56:29
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excerpt:
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tags:
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rating: ⭐
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---
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# 前言
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相关论文地址：
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- Reflective Shadow Maps: https://users.soe.ucsc.edu/~pang/160/s13/proposal/mijallen/proposal/media/p203-dachsbacher.pdf
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- Light Propagation Volumes: https://ericpolman.com/
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- VXGI:
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- https://on-demand.gputechconf.com/gtc/2014/preseintations/S4552-rt-voxel-based-global-illumination-gpus.pdf
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- https://docs.nvidia.com/gameworks/content/gameworkslibrary/visualfx/vxgi/product.html
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- https://developer.download.nvidia.com/assets/gameworks/downloads/secure/GDC18_Slides/Advances%20in%20Real-Time%20Voxel-Based%20GI%20-%20GDC%202018.pdf?HAwkc19IdhKMFWUs8jSk-If6y4QowlgUUrY8F9SL1-4qnhWWo-u5_gptg4ITWjMJCd1JrFbGmBw4-ztQCJ4M9Bh61am6lFCerKQVApEjN-HQ4chiSb5MLRLY41TyIse6_XW2DpNAe0_4inrYkZqxVb2iGiyZQhxwzfZ40dByP-X8jRYfWhJVsC1aSIqZ8BkooGkjUoUUGw2r7AAxyWVQole9a4je_76g04KtUwlONQ==
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- Lumen:
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- [https://youtu.be/2GYXuM10riw](https://youtu.be/2GYXuM10riw)
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- https://www.advances.realtimerendering.com/s2021/Radiance%20Caching%20for%20real-time%20Global%20Illumination%20(SIGGRAPH%202021).pptx
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- SSGI: https://www.ea.com/frostbite/news/stochastic-screen-space-reflections
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- DDGI:
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- https://zhuanlan.zhihu.com/p/404520592
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- https://developer.download.nvidia.com/video/gputechconf/gtc/2019/presentation/s9900-irradiance-fields-rtx-diffuse-global-illumination-for-local-and-cloud-graphics.pdf
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# HIZ Tracing
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![[HierachicalTracing2.png]]
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![[HierachicalTracing3.png]]
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![[HierachicalTracing1.png]]# Reflective Shadow Maps（RSM，2005）
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论文地址：https://users.soe.ucsc.edu/~pang/160/s13/proposal/mijallen/proposal/media/p203-dachsbacher.pdf
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Let's inject light in. (Photon Mapping?)
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解决如何把“光”注入到场景中。
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**Cool Ideas**
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- Easy to be implemented
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- Photon Injection with RSM
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- Cone sampling in mipmap
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- Low-res Indirect illumination with error check
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**Cons**
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- Single bounce
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- No visibility check for indirect illumination
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# Light Propagation Volumes
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**"Freeze" the Radiance in Voxel**
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Light Injection
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- Pre-subdivide the scene into a 3D grid
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- For each grid cell, find enclosed virtual light sources
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- Sum up their directional radiance distribution
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- Project to first 2 orders of SHs (4 in total)
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# Sparse Voxel Octree for Real-time Global Illumination (SVOGI)
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## Shading with Cone Tracing in Voxel Tree
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Pass 2 from the camera
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- Emit some cones based on diffuse+specular BRDF
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- Query in octree based on the (growing) size of the cone
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# VXGI（Nvidia UE4 Plugins）
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**Problems in VXGI**
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Incorrect Occlusion(opacity)
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- naively combine the opacity with alpha blending.
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Light Leaking
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- when occlusion wall is much smaller than voxel size
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# SSGI
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SIGGRAPH2015：Advances in Real-Time Rendering course
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**Radiance Sampling in Screen Space**
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For each fragment:
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- **Step 1**: compute many reflection
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rays
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- **Step 2**: march along ray direction
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**(in depth gbuffer)**
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- **Step3**: use color of hit point as
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indirect lighting
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![[SSGI1.png]]
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![[SSGI2.png]]
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中间的RayCast使用RayMarching进行。但使用LinearRayMarching相对比较消耗资源，所以采用HierachicalTracing。
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![[SSGI3.png]]
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最低层级
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![[HierachicalTracing1.png]]
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层级+1，相当于RayMarching2个像素。
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![[HierachicalTracing2.png]]
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层级+2，相当于RayMarching4个像素。此时RayHit。
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![[HierachicalTracing3.png]]
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回退当前HiZ像素的上一层级。
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![[HierachicalTracing4.png]]
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回退当前HiZ像素的上上一层级。
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![[HierachicalTracing5.png]]
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找到RayHit位置。
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![[HierachicalTracing6.png]]
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## Ray Reuse among Neighbor Pixels
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- Store **hitpoint data**
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- Assume visibility is the same between neighbors
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- Regard **ray to neighbor's hitpoint** as valid
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![[ConeTracingWithMipmapFiltering1.png]]
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# Lumen
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## Phase1: Fast Ray Track in Any Hardward
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Signed Distance Field(SDF)
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1. 它是均匀的。
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2. 在空间上是连续的。
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### Cone Tracing with SDF(ie. Soft Shadow)
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## Phase2:Radiance Injection and Cacheing
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![[MeshCard1.png]]
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MeshCard的目的是为了将直接光照存储在模型上（Surface Cache）
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![[GenerateSurfaceCache1.png]]
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![[GenerateSurfaceCache2.png]]
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最终目的是通过SurfaceCache这4张图渲染出SurfaceCache FinalLighting
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![[LightingCachePipeline1.png]]
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1. 计算SurfaceCache DirectLighting
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2. 通过1计算体素光照。
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3. 通过体素光照来计算间接照明。
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4. 最终计算Surface Cache FinalLighting。
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以此进行循环。![[DirectLighting1.png]]
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针对多个光源会渲染对应数量的cache，之后累加在一起。
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![[MultiLightSurfaceCache.png]]
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### Voxel Lighting to Sample
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![[VoxelLightingToSample.png]]
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对于近处的物体可以准确拿到Hit到物体的上一点的Radiance；对于远处的物体，会以相机坐标轴生成一个Voxel形式的表达，之后通过Global SDF拿到对应的Radiance。
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***PS. 该Voxel存储的数据为：每个面对应方向上被其他直接照明照亮的亮度。***
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![[VoxelClipmap.png]]![[BuildVoxelFaces.png]]
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其Voxel的计算是基于SDF的。
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![[InjectLightIntoClipmap.png]]
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![[IndirectLighting.png]]
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在SurfaceCache中 8x8的tile中（行与列间隔4个像素，放置2个探针），进行4次空间Voxel采样。
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之后进行球谐插值：
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![[IndirectLighting_SHLerp.png]]![[Per-PixelIndirectLighting.png]]![[CombineLighting.png]]
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## Phase3:Build a lot of probes with Different Kinds
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![[ScreenProbeStructure.png]]
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每隔 16 * 16 个像素采样一个ScreenSpaceProbe。采样的内容是Radiance与HitDistance，以8面体（Octahedron Mapping）的方式进行存储。
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![[ScreenProbePlacement.png]]![[PlaneDistanceWeightingOfProbeInterpolation.png]]![[DetectNon-InterpolatableCases.png]]![[ScreenProbeAtlas.png]]
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将重采样的结果（部分区域的屏幕空间探针因为实际空间距离太远，进行插值没有意义，所以需要额外填充探针进行重采样）存在Atlas下面的空出来的区域。
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![[ScreenProbeJitter.png]]
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### 重要性采样
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![[ApproximateRadianceImportanceFromLastFrameProbes.png]]![[AccumulateNormalDistributionNearby.png]]![[NearbyNormalAccumulation.png]]![[StructuredImportanceSampling.png]]![[FixBudgetImportanceSampling.png]]
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### Denoise
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![[Denoise_SpatialFilteringForProbe.png]]![[Denoise_GatherRadianceFromNeightbors.png]]![[ClampDistanceMismatching.png]]
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### WorldSpace Probes and Ray Connecting
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![[WorldSapceRadianceCache.png]]![[WorldSpaceRadianceCache.png]]![[ConnectingRays.png]]![[ConnectingRays2.png]]![[ConnectingRay3.png]]![[PlacementAndCacheing.png]]
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## Phase4:Shading Full Pixels with Screen Space Probes
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在ScreenSpaceProbes将场景Radiance都收集好。
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![[ConvertProbeRadianceTo3rdOrderSphericalHarmonic.png]]
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![[FinalIntegarationWithSH.png]]
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## 性能问题
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![[LumenTrackMethod.png]] |