141 lines
6.9 KiB
Markdown
141 lines
6.9 KiB
Markdown
## Ue4后处理逻辑简析
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### APostProcessVolume
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通常我们在后处理体积，也就是APostProcessVolume设置后处理效果。它存储了struct FPostProcessSettings Settings;
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加入关卡后，会存储在UWorld的PostProcessVolumes中，之后依次调用DoPostProcessVolume=》OverridePostProcessSettings，之后修改FSceneView中的FFinalPostProcessSettings FinalPostProcessSettings。（对所有属性进行插值计算）
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最后就可以通过View.FinalPostProcessSettings来读取后处理参数了。
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### AddPostProcessingPasses
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控制渲染的变量主要用下方式获取
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- 从FViewInfo里直接获取
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- 从FFinalPostProcessSettings获取（View.FinalPostProcessSettings）
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- 从FEngineShowFlags获取（View.Family->EngineShowFlags）
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- 从ConsoleVariable中获取
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获取各种Buffer与变量之后
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```c#
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const FIntRect PrimaryViewRect = View.ViewRect;
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const FSceneTextureParameters SceneTextureParameters = GetSceneTextureParameters(GraphBuilder, Inputs.SceneTextures);
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const FScreenPassRenderTarget ViewFamilyOutput = FScreenPassRenderTarget::CreateViewFamilyOutput(Inputs.ViewFamilyTexture, View);
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const FScreenPassTexture SceneDepth(SceneTextureParameters.SceneDepthTexture, PrimaryViewRect);
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const FScreenPassTexture SeparateTranslucency(Inputs.SeparateTranslucencyTextures->GetColorForRead(GraphBuilder), PrimaryViewRect);
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const FScreenPassTexture CustomDepth((*Inputs.SceneTextures)->CustomDepthTexture, PrimaryViewRect);
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const FScreenPassTexture Velocity(SceneTextureParameters.GBufferVelocityTexture, PrimaryViewRect);
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const FScreenPassTexture BlackDummy(GSystemTextures.GetBlackDummy(GraphBuilder));
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// Scene color is updated incrementally through the post process pipeline.
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FScreenPassTexture SceneColor((*Inputs.SceneTextures)->SceneColorTexture, PrimaryViewRect);
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// Assigned before and after the tonemapper.
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FScreenPassTexture SceneColorBeforeTonemap;
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FScreenPassTexture SceneColorAfterTonemap;
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// Unprocessed scene color stores the original input.
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const FScreenPassTexture OriginalSceneColor = SceneColor;
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// Default the new eye adaptation to the last one in case it's not generated this frame.
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const FEyeAdaptationParameters EyeAdaptationParameters = GetEyeAdaptationParameters(View, ERHIFeatureLevel::SM5);
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FRDGTextureRef LastEyeAdaptationTexture = GetEyeAdaptationTexture(GraphBuilder, View);
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FRDGTextureRef EyeAdaptationTexture = LastEyeAdaptationTexture;
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// Histogram defaults to black because the histogram eye adaptation pass is used for the manual metering mode.
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FRDGTextureRef HistogramTexture = BlackDummy.Texture;
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const FEngineShowFlags& EngineShowFlags = View.Family->EngineShowFlags;
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const bool bVisualizeHDR = EngineShowFlags.VisualizeHDR;
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const bool bViewFamilyOutputInHDR = GRHISupportsHDROutput && IsHDREnabled();
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const bool bVisualizeGBufferOverview = IsVisualizeGBufferOverviewEnabled(View);
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const bool bVisualizeGBufferDumpToFile = IsVisualizeGBufferDumpToFileEnabled(View);
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const bool bVisualizeGBufferDumpToPIpe = IsVisualizeGBufferDumpToPipeEnabled(View);
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const bool bOutputInHDR = IsPostProcessingOutputInHDR();
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```
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读取参数并设置
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```c#
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TOverridePassSequence<EPass> PassSequence(ViewFamilyOutput);
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PassSequence.SetNames(PassNames, UE_ARRAY_COUNT(PassNames));
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PassSequence.SetEnabled(EPass::VisualizeStationaryLightOverlap, EngineShowFlags.StationaryLightOverlap);
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PassSequence.SetEnabled(EPass::VisualizeLightCulling, EngineShowFlags.VisualizeLightCulling);
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#if WITH_EDITOR
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PassSequence.SetEnabled(EPass::SelectionOutline, GIsEditor && EngineShowFlags.Selection && EngineShowFlags.SelectionOutline && !EngineShowFlags.Wireframe && !bVisualizeHDR && !IStereoRendering::IsStereoEyeView(View));
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PassSequence.SetEnabled(EPass::EditorPrimitive, FSceneRenderer::ShouldCompositeEditorPrimitives(View));
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#else
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PassSequence.SetEnabled(EPass::SelectionOutline, false);
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PassSequence.SetEnabled(EPass::EditorPrimitive, false);
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#endif
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PassSequence.SetEnabled(EPass::VisualizeShadingModels, EngineShowFlags.VisualizeShadingModels);
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PassSequence.SetEnabled(EPass::VisualizeGBufferHints, EngineShowFlags.GBufferHints);
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PassSequence.SetEnabled(EPass::VisualizeSubsurface, EngineShowFlags.VisualizeSSS);
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PassSequence.SetEnabled(EPass::VisualizeGBufferOverview, bVisualizeGBufferOverview || bVisualizeGBufferDumpToFile || bVisualizeGBufferDumpToPIpe);
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PassSequence.SetEnabled(EPass::VisualizeHDR, EngineShowFlags.VisualizeHDR);
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#if WITH_EDITOR
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PassSequence.SetEnabled(EPass::PixelInspector, View.bUsePixelInspector);
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#else
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PassSequence.SetEnabled(EPass::PixelInspector, false);
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#endif
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PassSequence.SetEnabled(EPass::HMDDistortion, EngineShowFlags.StereoRendering && EngineShowFlags.HMDDistortion);
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PassSequence.SetEnabled(EPass::HighResolutionScreenshotMask, IsHighResolutionScreenshotMaskEnabled(View));
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PassSequence.SetEnabled(EPass::PrimaryUpscale, PaniniConfig.IsEnabled() || (View.PrimaryScreenPercentageMethod == EPrimaryScreenPercentageMethod::SpatialUpscale && PrimaryViewRect.Size() != View.GetSecondaryViewRectSize()));
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PassSequence.SetEnabled(EPass::SecondaryUpscale, View.RequiresSecondaryUpscale() || View.Family->GetSecondarySpatialUpscalerInterface() != nullptr);
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```
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这些操作一直到`PassSequence.Finalize();`。
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### 后处理Pass处理
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主要的Pass有这么一些：
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```c#
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TEXT("MotionBlur"),
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TEXT("Tonemap"),
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TEXT("FXAA"),
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TEXT("PostProcessMaterial (AfterTonemapping)"),
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TEXT("VisualizeDepthOfField"),
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TEXT("VisualizeStationaryLightOverlap"),
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TEXT("VisualizeLightCulling"),
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TEXT("SelectionOutline"),
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TEXT("EditorPrimitive"),
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TEXT("VisualizeShadingModels"),
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TEXT("VisualizeGBufferHints"),
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TEXT("VisualizeSubsurface"),
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TEXT("VisualizeGBufferOverview"),
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TEXT("VisualizeHDR"),
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TEXT("PixelInspector"),
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TEXT("HMDDistortion"),
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TEXT("HighResolutionScreenshotMask"),
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TEXT("PrimaryUpscale"),
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TEXT("SecondaryUpscale")
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```
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之前读取了参数，对这些Pass是否开启进行了设置。之后以这种格式使用Shader对传入的图形进行后处理。
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```c#
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if (PassSequence.IsEnabled(EPass::MotionBlur))
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{
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FMotionBlurInputs PassInputs;
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PassSequence.AcceptOverrideIfLastPass(EPass::MotionBlur, PassInputs.OverrideOutput);
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PassInputs.SceneColor = SceneColor;
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PassInputs.SceneDepth = SceneDepth;
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PassInputs.SceneVelocity = Velocity;
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PassInputs.Quality = GetMotionBlurQuality();
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PassInputs.Filter = GetMotionBlurFilter();
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// Motion blur visualization replaces motion blur when enabled.
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if (bVisualizeMotionBlur)
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{
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SceneColor = AddVisualizeMotionBlurPass(GraphBuilder, View, PassInputs);
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}
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else
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{
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SceneColor = AddMotionBlurPass(GraphBuilder, View, PassInputs);
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}
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}
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SceneColor = AddAfterPass(EPass::MotionBlur, SceneColor);
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```
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这些效果的代码都在UnrealEngine\Engine\Source\Runtime\Renderer\Private\PostProcess中。
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### 后处理材质调用
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AddPostProcessMaterialChain
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=》
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AddPostProcessMaterialPass()为实际的绘制函数。最后在AddDrawScreenPass()中进行绘制。（DrawScreenPass()=>DrawPostProcessPass=>DrawPostProcessPass()）
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### 推荐参考的后处理代码
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PostProcessBloomSetup.h
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VisualizeShadingModels.cpp |