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

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ToonPostProcess 2024-05-15 16:50:13 ⭐

FFT

Bloom

Bloom主要分

  • Bloom
  • FFTBloom
  • LensFlares

BloomThreshold，ClampMin = "-1.0", UIMax = "8.0"。 相关逻辑位于：

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。

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：

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： 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：

// @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

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。

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

ToneMapping种类

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
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

实现方法

//BlueRose Modify  
FGBufferData SamplerBuffer = GetGBufferData(UV * View.ResolutionFractionAndInv.x, false);  
if (SamplerBuffer.CustomStencil > 1.0f && abs(SamplerBuffer.CustomDepth - SamplerBuffer.Depth) < 1)  
{  
    // OutColor = SampleSceneColor(UV);  
    OutColor = TonemapCommonPS(UV, InVignette, GrainUV, ScreenPos, FullViewUV, SvPosition, Luminance);  
}else  
{  
    OutColor = TonemapCommonPS(UV, InVignette, GrainUV, ScreenPos, FullViewUV, SvPosition, Luminance);  
}  
//BlueRose Modify End