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03-UnrealEngine/Rendering/RenderingPipeline/Lighting/Lighting阶段的ShadowMap逻辑.md

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+---
+title: Lighting阶段的ShadowMap逻辑
+date: 2023-04-10 14:45:45
+excerpt: 
+tags: 
+rating: ⭐
+---
+
+## PS Parameter
+`FDeferredLightPS::FParameters GetDeferredLightPSParameters()`
+
+- LightAttenuationTexture = ShadowMaskTexture ? ShadowMaskTexture : WhiteDummy;
+- One pass projection
+	- VirtualShadowMap = VirtualShadowMapUniformBuffer;
+	- VirtualShadowMapId = VirtualShadowMapId;
+	- ShadowMaskBits = ShadowMaskBits ? ShadowMaskBits : GSystemTextures.GetZeroUIntDummy(GraphBuilder);
+
+最后输出
+- SceneColorTexture  
+- SceneDepthTexture
+
+## Lighting阶段中VSM 渲染函数
+RenderDeferredShadowProjections()，输出`ScreenShadowMaskTexture`。
+
+## 问题所在
+LightAttenuation
+- x：整个场景的方向光阴影。
+- y：整个场景的方向光SSS阴影。
+- z：Light function + per-object shadows
+- w：per-object SSS shadowing in w
+
+zw用于非方向光或者移动端渲染路径。
+```c++
+if (LightData.bRadialLight || SHADING_PATH_MOBILE)  
+{  
+   // Remapping the light attenuation buffer (see ShadowRendering.cpp)  
+  
+   Shadow.SurfaceShadow = LightAttenuation.z * StaticShadowing;  
+   // SSS uses a separate shadowing term that allows light to penetrate the surface  
+   //@todo - how to do static shadowing of SSS correctly?   Shadow.TransmissionShadow = LightAttenuation.w * StaticShadowing;  
+  
+   Shadow.TransmissionThickness = LightAttenuation.w;  
+}  
+else  
+{  
+   // Remapping the light attenuation buffer (see ShadowRendering.cpp)  
+   // Also fix up the fade between dynamic and static shadows   // to work with plane splits rather than spheres.  
+   float DynamicShadowFraction = DistanceFromCameraFade(SceneDepth, LightData);  
+   // For a directional light, fade between static shadowing and the whole scene dynamic shadowing based on distance + per object shadows  
+   Shadow.SurfaceShadow = lerp(LightAttenuation.x, StaticShadowing, DynamicShadowFraction);  
+   // Fade between SSS dynamic shadowing and static shadowing based on distance  
+   Shadow.TransmissionShadow = min(lerp(LightAttenuation.y, StaticShadowing, DynamicShadowFraction), LightAttenuation.w);  
+  
+   Shadow.SurfaceShadow *= LightAttenuation.z;  
+   Shadow.TransmissionShadow *= LightAttenuation.z;  
+  
+   // Need this min or backscattering will leak when in shadow which cast by non perobject shadow(Only for directional light)  
+   Shadow.TransmissionThickness = min(LightAttenuation.y, LightAttenuation.w);  
+}
+```
+
+
+**DeferredLightingCommon.ush**与**DeferredLightPixelShaders.usf**中的**LightAttenuation**即为ShadowMap数据。具体可以参考**GetLightAttenuationFromShadow()**，可以看得出EPIC之后打算通过抖动来消除VSM的阴影锯齿。
+
+主要的阴影效果由**LightAttenuation**与ShadingModels.ush中的NoL提供。我们只需要调整自阴影也就是z通道，其他的整个场景的阴影。

03-UnrealEngine/Rendering/RenderingPipeline/Lighting/RenderLights.md

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+---
+title: RenderLights
+date: 2023-04-09 10:23:21
+excerpt: 
+tags: 
+rating: ⭐
+---
+# 关键函数
+取得所有ShadowMap的投影信息
+```c++
+const FVisibleLightInfo& VisibleLightInfo = VisibleLightInfos[LightSceneInfo->Id];  
+const TArray<FProjectedShadowInfo*, SceneRenderingAllocator>& ShadowMaps = VisibleLightInfo.ShadowsToProject;  
+for (int32 ShadowIndex = 0; ShadowIndex < ShadowMaps.Num(); ShadowIndex++)  
+{  
+   const FProjectedShadowInfo* ProjectedShadowInfo = ShadowMaps[ShadowIndex];
+}
+```
+
+# 透明体积图元渲染
+## InjectSimpleTranslucencyLightingVolumeArray
+插入简单透明体积物体渲染。应该是根据3D贴图渲染体积效果。默认状态下不运行。
+- InjectSimpleLightsTranslucentLighting
+- InjectSimpleTranslucentLightArray 
+
+## InjectTranslucencyLightingVolume
+在收集用于渲染透明体积的灯光代理信息后进行渲染，主要用于云的渲染。
+- InjectTranslucencyLightingVolume
+
+# 直接光照
+## RenderVirtualShadowMapProjectionMaskBits
+- VirtualShadowMapProjectionMaskBits
+- VirtualShadowMapProjection(RayCount:%u(%s),SamplesPerRay:%u,Input:%s%s)
+
+输出到名为`Shadow.Virtual.MaskBits`与`Shadow.Virtual.MaskBits(HairStrands)`的UAV。
+
+## AddClusteredDeferredShadingPass
+
+## RenderSimpleLightsStandardDeferred
+
+## RenderLight
+针对每个灯在ShadowProjectionOnOpaque渲染ShadowMask
+- VirualShadowMapProjection
+- CompositeVirtualShadowMapMask
+