BlueRoseNote/03-UnrealEngine/卡通渲染相关资料/渲染功能/PostProcess/ToonPostProcess.md

---
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<const FViewInfo*>(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