195 lines
9.4 KiB
Markdown
195 lines
9.4 KiB
Markdown
---
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title: Untitled
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date: 2024-12-08 12:18:54
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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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阴影渲染笔记：[[Shadow]]
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实现功能：
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1. [ ] 控制深度偏移
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2. [ ] CustomDepth制作头发阴影偏移效果哦 https://zhuanlan.zhihu.com/p/689578355
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3. [ ] ContactShadow接触阴影实现衣服细节的DetailShadow
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4. [ ] 半程阴影
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# 半程阴影
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由晨风&Neverwind提出：
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- 【[UFSH2024]用虚幻引擎5为《幻塔》定制高品质动画流程风格化渲染管线 | 晨风 Neverwind 完美世界游戏】 【精准空降到 07:27】 https://www.bilibili.com/video/BV1rW2LYvEox/?share_source=copy_web&vd_source=fe8142e8e12816535feaeabd6f6cdc8e&t=447
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**阴影Setup阶段**:
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```c++
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if 启用半程阴影:
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{
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额外进行一次CreatePerObjectProjectedShadow()
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{
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处理阴影光照Matrix //猜测：
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//在ProjectedShadowInfo->SetupPerObjectProjection()中调整，FProjectedShadowInfo.TranslatedWorldToView。
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//在LightSceneInfo->Proxy->GetPerObjectProjectedShadowInitializer(Bounds, ShadowInitializer)之后，修改WorldTolight。
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向阴影信息写入IsHalfViewShadowFlag//猜测：在FProjectedShadowInfo中添加判断Flag并且写入。
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用新的光源方向画Atlas //猜测：给带有对应Flog的DirectionLigh多创建一个对应的Atlas？
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}
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}
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```
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截图代码(半程阴影修改LightDirection逻辑)：
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```c++
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if(PrimitiveSceneinfo->Proxy->IsToonDisableSelfShadow())
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{
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...
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
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{
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const FViewInfo& View = Views[ViewIndex];
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const FMatrix& ViewMatrix = View.ShadowViewMatrices.GetViewMatrix()
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FVector LightDirection = Lightsceneinfo->Proxy->GetDirection();
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const FVector CameraDirection = ViewMatrix.GetColumn(2).GetSafeNormal()
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float LightViewBlendFactor = PrimitiveSceneinfo->Proxy->GetToonHalfVienShadowFactor();
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Fvector HalfViewLightDir = (LightDirection + ( 1 - LightViewBlendFactor) + CameraDirection * LightViewBlendFactor).GetSafeNormal();
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FMatrix FinalCombineMatrix = FInverseRotationMatrix(HalfViewLightDir.Rotation())
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ShadowInitializer.WorldToLight = FinalCombineMatrix;
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}
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...
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}
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```
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相关代码位于`FDirectionalLightSceneProxy::GetPerObjectProjectedShadowInitializer()`，在在FSceneRenderer::CreatePerObjectProjectedShadow()被调用。
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```c++
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virtual bool GetPerObjectProjectedShadowInitializer(const FBoxSphereBounds& SubjectBounds,FPerObjectProjectedShadowInitializer& OutInitializer) const override
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{
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OutInitializer.PreShadowTranslation = -SubjectBounds.Origin;
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OutInitializer.WorldToLight = FInverseRotationMatrix(FVector(WorldToLight.M[0][0],WorldToLight.M[1][0],WorldToLight.M[2][0]).GetSafeNormal().Rotation());
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OutInitializer.Scales = FVector2D(1.0f / SubjectBounds.SphereRadius,1.0f / SubjectBounds.SphereRadius);
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OutInitializer.SubjectBounds = FBoxSphereBounds(FVector::ZeroVector,SubjectBounds.BoxExtent,SubjectBounds.SphereRadius);
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OutInitializer.WAxis = FVector4(0,0,0,1);
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OutInitializer.MinLightW = -UE_OLD_HALF_WORLD_MAX;
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// Reduce casting distance on a directional light
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// This is necessary to improve floating point precision in several places, especially when deriving frustum verts from InvReceiverMatrix
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// This takes the object size into account to ensure that large objects get an extended distance
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OutInitializer.MaxDistanceToCastInLightW = FMath::Clamp(SubjectBounds.SphereRadius * CVarPerObjectCastDistanceRadiusScale.GetValueOnRenderThread(), CVarPerObjectCastDistanceMin.GetValueOnRenderThread(), (float)WORLD_MAX);
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return true;
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}
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```
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PS.很有可能需要创建2个Atlas。Atlas的创建位于***FSceneRenderer::AllocateCachedShadowDepthTargets()***。数据存储在***SortedShadowsForShadowDepthPass.ShadowMapAtlases***中。大致由FSceneRenderer::FinishInitDynamicShadows()调用。
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**阴影Projection阶段**:
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//此阶段需要屏蔽角色投射到自己的非半程阴影
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//和角色投射到场景中会跟随视角移动的阴影
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```c++
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if(Toon材质,且没有半程阴影Flag的阴影
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&&非Toon材质但有半程阴影Flag的阴影)
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{
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屏蔽此阴影
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}
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```
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PS.很有可能在FProjectedShadowInfo::RenderProjection()阶段进行判断以此保证合成正确的**ScreenShadowMask**。
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# 实现方法
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```c++
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const FMaterialRenderProxy* MaterialRenderProxy = MeshBatch.MaterialRenderProxy;
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bool bEnableToonMeshDrawOutline = MaterialRenderProxy->GetToonOutlineDataAssetRT()->Settings.bEnableToonMeshDrawOutline;
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```
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FProjectedShadowInfo->Scene
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FPrimitiveSceneProxy
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## 深度偏移
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### ~~方法一~~
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1. FProjectedShadowInfo添加变量。
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FSceneRenderer::RenderShadowDepthMaps() => RenderShadowDepthMapAtlases() => ProjectedShadowInfo->RenderDepth()
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已放弃，FProjectedShadowInfo无法判断MeshSection。
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### 方法二（最终实现方法）
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在材质中使用ShadowPassSwitch再对ViewSpace的Z轴方向（使用DirectionalLightVector比较可以只对方向光进行偏移）进行WPO偏移实现。
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其优点就是可以用贴图来控制偏移过渡。
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## DirectionOffsetToViewShadow
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### 最终实现方法
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1. 在**FProjectionShadowInfo**中添加**bDirectionOffsetToViewShadow**标记以及对应的判断函数IsDirectionOffsetToViewShadow()来判断是否是DirectionOffsetToViewShadow。
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1. 在**FSceneRenderer::CreatePerObjectProjectedShadow()** 中再次调用SetupPerObjectProjection()逻辑创建**DirectionOffsetToViewShadow**时将FProjectedShadowInfo的***bDirectionOffsetToViewShadow设置成true***。
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2. 在PrimitiveSceneProxy.h 中添加DirectionOffsetToViewShadowAlpha变量作为偏移Alpha，同事添加函数UseDirectionOffsetToViewShadow()来判断是否开启这个功能。
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1. 在**FSceneRenderer::CreatePerObjectProjectedShadow()** 中取得PrimitiveSceneProxy中的DirectionOffsetToViewShadowAlpha，最后计算向量来设置***ShadowInitializer.WorldToLight***。大致为[[#DirectionOffsetToViewShadow Direction Code]]
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3. 在ToonDataAsset中添加RecivedViewOffsetShadow作为是否接收DirectionOffsetToViewShadow的依据。
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1. 将数据渲染到ToonDataAsset Texture中。
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2. 最终在ShadowProjectionPixelShader.usf获取并且计算。代码如下：
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```c++
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//BlueRose Modify
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#if SHADING_PATH_DEFERRED && !FORWARD_SHADING && !SUBPIXEL_SHADOW && !STRATA_ENABLED /*&& !USE_TRANSMISSION*/
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FGBufferData GBufferData_Toon = GetGBufferData(ScreenUV);
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const uint ToonDataAssetID = GetToonDataAssetIDFromGBuffer(GBufferData_Toon);
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float RecivedViewOffsetShadow = GetRecivedViewOffsetShadow(ToonDataAssetID);
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if (IsDirectionOffsetToViewShadow > 0)//ViewShadow ProjectionShadowInfo
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{
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/*if (RecivedViewOffsetShadow > 0)//ViewOffsetShadow
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{
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PerObjectDistanceFadeFraction *= 1.0;
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}*/
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if (RecivedViewOffsetShadow == 0)
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{
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PerObjectDistanceFadeFraction *= 0.0;
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}
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}else//Normal ProjectionShadowInfo
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{
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if (RecivedViewOffsetShadow > 0)
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{
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PerObjectDistanceFadeFraction *= 0.0;
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}
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}
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#endif
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//BlueRose Modify End
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float FadedShadow = lerp(1.0f, Shadow, ShadowFadeFraction * PerObjectDistanceFadeFraction);
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#if FORWARD_SHADING || SHADING_PATH_MOBILE
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float LightInfluenceMask = GetLightInfluenceMask(TranslateWorldPosition);
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// Constrain shadowing from this light to pixels inside the light's influence, since other non-overlapping lights are packed into the same channel
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FadedShadow = lerp(1, FadedShadow, LightInfluenceMask);
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// Write into all channels, the write mask will constrain to the correct one
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OutColor = EncodeLightAttenuation(FadedShadow);
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#else
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float FadedSSSShadow = lerp(1.0f, SSSTransmission, ShadowFadeFraction * PerObjectDistanceFadeFraction);
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// the channel assignment is documented in ShadowRendering.cpp (look for Light Attenuation channel assignment)
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OutColor = EncodeLightAttenuation(half4(FadedShadow, FadedSSSShadow, FadedShadow, FadedSSSShadow));
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#endif
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```
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#### DirectionOffsetToViewShadow Direction Code
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```c++
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...
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bool bToonDirectionOffsetToViewShadow = ToonDirectionOffsetToViewShadowCVar->GetValueOnRenderThread();
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float LightViewBlendFactor = PrimitiveSceneInfo->Proxy->DirectionOffsetToViewShadowAlpha;
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if (bToonDirectionOffsetToViewShadow && LightSceneInfo->Proxy->GetLightType() == LightType_Directional && LightViewBlendFactor > 0.0f)
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{
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//计算半程向量，针对每个View都会生成一个FProjectedShadowInfo，之后在RenderShadowProjection()中判断？
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for (int32 ViewIndex = 0; ViewIndex < Views.Num(); ViewIndex++)
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{
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const FViewInfo& View = Views[ViewIndex];
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const FMatrix& ViewMatrix = View.ShadowViewMatrices.GetViewMatrix();
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FVector LightDirection = LightSceneInfo->Proxy->GetDirection();
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const FVector CameraDirection = ViewMatrix.GetColumn(2).GetSafeNormal();
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FVector HalfViewLightDir = (LightDirection * ( 1 - LightViewBlendFactor) + CameraDirection * LightViewBlendFactor).GetSafeNormal();
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FMatrix FinalCombineMatrix = FInverseRotationMatrix(HalfViewLightDir.Rotation());
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ShadowInitializer.WorldToLight = FinalCombineMatrix;
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...
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}
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}
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```
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# ~~NoSelfShadow~~此方法是错误的
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https://zhuanlan.zhihu.com/p/10073818586?utm_psn=1877051516055076866
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UPrimitiveComponent::bSelfShadowOnly
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=>
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FPrimitiveSceneProxy::bSelfShadowOnly => **CastsSelfShadowOnly()**
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=>
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FProjectedShadowInfo::bSelfShadowOnly
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- FProjectedShadowInfo::SetupMeshDrawCommandsForProjectionStenciling()：设置Stencil为1。
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- 在`FProjectedShadowInfo::GatherDynamicMeshElements()`被调用，FSceneRenderer::GatherShadowDynamicMeshElements()。
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- FProjectedShadowInfo::SetupProjectionStencilMask：设置Stencil为7（ pre-shadow/per-object static shadow）。
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- 在`FProjectedShadowInfo::RenderProjectionInternal()`被调用。
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FProjectedShadowInfo::RenderProjectionInternal() |