--- title: ToonPostProcess date: 2024-05-15 16:50:13 excerpt: tags: rating: ⭐ --- # FFT # Bloom Bloom主要分 - Bloom - FFTBloom - LensFlares BloomThreshold，ClampMin = "-1.0", UIMax = "8.0"。 相关逻辑位于： ```c++ if (bBloomSetupRequiredEnabled) { const float BloomThreshold = View.FinalPostProcessSettings.BloomThreshold; FBloomSetupInputs SetupPassInputs; SetupPassInputs.SceneColor = DownsampleInput; SetupPassInputs.EyeAdaptationBuffer = EyeAdaptationBuffer; SetupPassInputs.EyeAdaptationParameters = &EyeAdaptationParameters; SetupPassInputs.LocalExposureParameters = &LocalExposureParameters; SetupPassInputs.LocalExposureTexture = CVarBloomApplyLocalExposure.GetValueOnRenderThread() ? LocalExposureTexture : nullptr; SetupPassInputs.BlurredLogLuminanceTexture = LocalExposureBlurredLogLumTexture; SetupPassInputs.Threshold = BloomThreshold; SetupPassInputs.ToonThreshold = View.FinalPostProcessSettings.ToonBloomThreshold; DownsampleInput = AddBloomSetupPass(GraphBuilder, View, SetupPassInputs); } ``` ## FFTBloom ***普通Bloom算法只能做到圆形光斑，对于自定义形状的就需要使用FFTBloom。*** - FFT Bloom:https://zhuanlan.zhihu.com/p/611582936 - Unity FFT Bloom:https://github.com/AKGWSB/FFTConvolutionBloom ### 频域与卷积定理 图像可以视为二维的信号，而一个信号可以通过 **不同频率** 的 Sine & Cosine 函数的线性叠加来近似得到。对于每个频率的函数，我们乘以一个常数振幅并叠加到最终的结果上，这些振幅叫做 **频谱**。值得注意的是所有的 F_k 都是 **复数**： ![](https://pic2.zhimg.com/80/v2-64b4c2d33d90816cc9bfcf875f618d9f_720w.webp) 此时频域上的每个振幅不再代表某个单个的时域样本，而是代表该频段的 Sine & Cosine 函数对时域信号的 **整体** 贡献。频域信号包含了输入图像的全部时域信息，***因此卷积定理告诉我们在时域上对信号做卷积，等同于将源图像与滤波盒图像在频域上的频谱（上图系数 V_k）做简单复数 **乘法***： ![](https://pic1.zhimg.com/80/v2-abc8c8d19dc3ded6c282075cc4d2f022_720w.webp) 一一对位的乘法速度是远远快于需要循环累加的朴素卷积操作。因此接下来我们的目标就是找到一种方法，建立图像信号与其频域之间的联系。在通信领域通常使用傅里叶变换来进行信号的频、时域转换 ### 相关代码 - c++ - AddFFTBloomPass() - FBloomFinalizeApplyConstantsCS （Bloom计算完成） - AddTonemapPass()，PassInputs.Bloom = Bloom与PassInputs.SceneColorApplyParamaters - Shader - **FBloomFindKernelCenterCS**：用于找到Bloom效果的核（Kernel）中心(纹理中找到最亮的像素)。用于在一个，并记录其位置。主要通过计算Luminance来获取到中心区域，而在这里的中心区域可以有多个，这也代表着在最终输出的SceneColor里可以有多个【曝点光晕(Bloom)效果】 # 实用代码 代码位于DeferredShadingCommon.ush： ```c++ // @param UV - UV space in the GBuffer textures (BufferSize resolution) FGBufferData GetGBufferData(float2 UV, bool bGetNormalizedNormal = true) { #if GBUFFER_REFACTOR return DecodeGBufferDataUV(UV,bGetNormalizedNormal); #else float4 GBufferA = Texture2DSampleLevel(SceneTexturesStruct.GBufferATexture, SceneTexturesStruct_GBufferATextureSampler, UV, 0); float4 GBufferB = Texture2DSampleLevel(SceneTexturesStruct.GBufferBTexture, SceneTexturesStruct_GBufferBTextureSampler, UV, 0); float4 GBufferC = Texture2DSampleLevel(SceneTexturesStruct.GBufferCTexture, SceneTexturesStruct_GBufferCTextureSampler, UV, 0); float4 GBufferD = Texture2DSampleLevel(SceneTexturesStruct.GBufferDTexture, SceneTexturesStruct_GBufferDTextureSampler, UV, 0); float CustomNativeDepth = Texture2DSampleLevel(SceneTexturesStruct.CustomDepthTexture, SceneTexturesStruct_CustomDepthTextureSampler, UV, 0).r; // BufferToSceneTextureScale is necessary when translucent materials are rendered in a render target // that has a different resolution than the scene color textures, e.g. r.SeparateTranslucencyScreenPercentage < 100. int2 IntUV = (int2)trunc(UV * View.BufferSizeAndInvSize.xy * View.BufferToSceneTextureScale.xy); uint CustomStencil = SceneTexturesStruct.CustomStencilTexture.Load(int3(IntUV, 0)) STENCIL_COMPONENT_SWIZZLE; #if ALLOW_STATIC_LIGHTING float4 GBufferE = Texture2DSampleLevel(SceneTexturesStruct.GBufferETexture, SceneTexturesStruct_GBufferETextureSampler, UV, 0); #else float4 GBufferE = 1; #endif float4 GBufferF = Texture2DSampleLevel(SceneTexturesStruct.GBufferFTexture, SceneTexturesStruct_GBufferFTextureSampler, UV, 0); #if WRITES_VELOCITY_TO_GBUFFER float4 GBufferVelocity = Texture2DSampleLevel(SceneTexturesStruct.GBufferVelocityTexture, SceneTexturesStruct_GBufferVelocityTextureSampler, UV, 0); #else float4 GBufferVelocity = 0; #endif float SceneDepth = CalcSceneDepth(UV); return DecodeGBufferData(GBufferA, GBufferB, GBufferC, GBufferD, GBufferE, GBufferF, GBufferVelocity, CustomNativeDepth, CustomStencil, SceneDepth, bGetNormalizedNormal, CheckerFromSceneColorUV(UV)); #endif } // Minimal path for just the lighting model, used to branch around unlit pixels (skybox) uint GetShadingModelId(float2 UV) { return DecodeShadingModelId(Texture2DSampleLevel(SceneTexturesStruct.GBufferBTexture, SceneTexturesStruct_GBufferBTextureSampler, UV, 0).a); } ``` ## ShadingModel判断 ```c++ bool IsToonShadingModel(float2 UV) { uint ShadingModel = DecodeShadingModelId(Texture2DSampleLevel(SceneTexturesStruct.GBufferBTexture, SceneTexturesStruct_GBufferBTextureSampler, UV, 0).a); return ShadingModel == SHADINGMODELID_TOONSTANDARD || ShadingModel == SHADINGMODELID_PREINTEGRATED_SKIN; } ``` PS.需要Shader添加FSceneTextureShaderParameters/FSceneTextureUniformParameters。 ```c++ IMPLEMENT_STATIC_UNIFORM_BUFFER_STRUCT(FSceneTextureUniformParameters, "SceneTexturesStruct", SceneTextures); BEGIN_SHADER_PARAMETER_STRUCT(FSceneTextureShaderParameters, ENGINE_API) SHADER_PARAMETER_RDG_UNIFORM_BUFFER(FSceneTextureUniformParameters, SceneTextures) SHADER_PARAMETER_RDG_UNIFORM_BUFFER(FMobileSceneTextureUniformParameters, MobileSceneTextures) END_SHADER_PARAMETER_STRUCT() ``` # ToneMapping - UE4/UE5和ACES工作流程:https://zhuanlan.zhihu.com/p/660965710 ## ToneMapping种类 - ShaderToy效果演示: https://www.shadertoy.com/view/McG3WW - ACES - Narkowicz 2015, "ACES Filmic Tone Mapping Curve" - https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/ - PBR Neutral https://modelviewer.dev/examples/tone-mapping - Uncharted tonemapping - http://filmicworlds.com/blog/filmic-tonemapping-operators/ - https://www.gdcvault.com/play/1012351/Uncharted-2-HDR - AgX - https://github.com/sobotka/AgX - https://www.shadertoy.com/view/cd3XWr ## UE中的相关实现 UE4版本的笔记：[[UE4 ToneMapping]] TonemapCommon.ush中的FilmToneMap()在CombineLUTsCommon()中调用。其顺序为： 1. AddCombineLUTPass() => PostProcessCombineLUTs.usf 2. AddTonemapPass() => PostProcessTonemap.usf ```c++ void AddPostProcessingPasses() { ... { FRDGTextureRef ColorGradingTexture = nullptr; if (bPrimaryView) { ColorGradingTexture = AddCombineLUTPass(GraphBuilder, View); } // We can re-use the color grading texture from the primary view. else if (View.GetTonemappingLUT()) { ColorGradingTexture = TryRegisterExternalTexture(GraphBuilder, View.GetTonemappingLUT()); } else { const FViewInfo* PrimaryView = static_cast(View.Family->Views[0]); ColorGradingTexture = TryRegisterExternalTexture(GraphBuilder, PrimaryView->GetTonemappingLUT()); } FTonemapInputs PassInputs; PassSequence.AcceptOverrideIfLastPass(EPass::Tonemap, PassInputs.OverrideOutput); PassInputs.SceneColor = SceneColorSlice; PassInputs.Bloom = Bloom; PassInputs.SceneColorApplyParamaters = SceneColorApplyParameters; PassInputs.LocalExposureTexture = LocalExposureTexture; PassInputs.BlurredLogLuminanceTexture = LocalExposureBlurredLogLumTexture; PassInputs.LocalExposureParameters = &LocalExposureParameters; PassInputs.EyeAdaptationParameters = &EyeAdaptationParameters; PassInputs.EyeAdaptationBuffer = EyeAdaptationBuffer; PassInputs.ColorGradingTexture = ColorGradingTexture; PassInputs.bWriteAlphaChannel = AntiAliasingMethod == AAM_FXAA || bProcessSceneColorAlpha; PassInputs.bOutputInHDR = bTonemapOutputInHDR; SceneColor = AddTonemapPass(GraphBuilder, View, PassInputs); } ... } ``` ## PostProcessCombineLUTs.usf 相关变量更新函数位于FCachedLUTSettings::GetCombineLUTParameters() ## PostProcessTonemap.usf