171 lines
8.2 KiB
Markdown
171 lines
8.2 KiB
Markdown
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BasePassPixelShader.usf中的FPixelShaderInOut_MainPS()，为BasePass阶段Shader的主要逻辑。会被PixelShaderOutputCommon.usf的MainPS(),即PixelShader入口函数中被调用。
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该阶段会取得材质编辑器各个引脚的计算结果，在一些计算下最终输出GBuffer，以备后续光照计算。可以认为是“紧接”材质编辑器的下一步工作。相关的c++逻辑位于FDeferredShadingSceneRenderer::Render()的RenderBasePass()中。
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但因为个人能力与时间所限，只能写一篇杂乱笔记作为记录，以供后续使用。
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<!--more-->
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### 780~889：计算变量并且填充FMaterialPixelParameters MaterialParameters。BaseColor、Metallic、Specular就位于867~877。
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### 915~1072：计算GBuffer或者DBuffer
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- 915~942:计算贴花相关的DBuffer
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- 954~1028：按照ShaderModel来填充GBuffer。（983~1008 Velocity、1013~1022 使用法线来调整粗糙度，在皮肤以及车漆ShaderModel中有用到）
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- 1041：GBuffer.DiffuseColor = BaseColor - BaseColor * Metallic;
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- 1059~1072：使用法线（清漆ShaderModel还会计算的底层法线）计算BentNormal以及GBufferAO。（使用SphericalGaussian）
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### 1081~1146：
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#### 1086~1116：计算DiffuseColorForIndirect
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DiffuseColorForIndirect（DiffuseDir只在Hair中计算）
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- 次表面与皮肤：DiffuseColorForIndirect += SubsurfaceColor;
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- 布料：DiffuseColorForIndirect += SubsurfaceColor * saturate(GetMaterialCustomData0(MaterialParameters));
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- 头发：DiffuseColorForIndirect = 2*PI * HairShading( GBuffer, L, V, N, 1, TransmittanceData, 0, 0.2, uint2(0,0);
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#### 1118~1120：计算预间接光照结果
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GetPrecomputedIndirectLightingAndSkyLight：
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采样对应的预结算缓存：
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1. PRECOMPUTED_IRRADIANCE_VOLUME_LIGHTING：根据TRANSLUCENCY_LIGHTING_VOLUMETRIC_PERVERTEX_NONDIRECTIONAL来判断是进行读取顶点AO值还是采样体积关照贴图来作为IrradianceSH的值。最后累加到OutDiffuseLighting上。
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2. CACHED_VOLUME_INDIRECT_LIGHTING：采样IndirectLightingCache，最后累加到最后累加到OutDiffuseLighting上。
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3. 采样HQ_TEXTURE_LIGHTMAP或者LQ_TEXTURE_LIGHTMAP，最后累加到OutDiffuseLighting上。
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调用GetSkyLighting()取得天光值并累加到OutDiffuseLighting上。最后计算OutDiffuseLighting的亮度值最后作为OutIndirectIrradiance输出。
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#### 1138：计算DiffuseColor
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DiffuseColor=Diffuse间接照明 * Diffse颜色 + 次表面间接光照 * 次表面颜色+AO
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```c#
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DiffuseColor += (DiffuseIndirectLighting * DiffuseColorForIndirect + SubsurfaceIndirectLighting * SubsurfaceColor) * AOMultiBounce( GBuffer.BaseColor, DiffOcclusion );
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```
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#### 1140~1146：SingleLayerWater 覆盖颜色操作
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```c#
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GBuffer.DiffuseColor *= BaseMaterialCoverageOverWater;
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DiffuseColor *= BaseMaterialCoverageOverWater;
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```
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### 1148~1211
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1. 使用ForwardDirectLighting的DiffuseLighting与SpecularLighting累加，Color，THIN_TRANSLUCENT Model则为 DiffuseColor与ColorSeparateSpecular。
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2. SIMPLE_FORWARD_DIRECTIONAL_LIGHT：调用GetSimpleForwardLightingDirectionalLight()计算方向光结果。
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根据光照模式累加，最后累加到Color上：
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```c#
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#if STATICLIGHTING_SIGNEDDISTANCEFIELD
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DirectionalLighting *= GBuffer.PrecomputedShadowFactors.x;
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#elif PRECOMPUTED_IRRADIANCE_VOLUME_LIGHTING
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DirectionalLighting *= GetVolumetricLightmapDirectionalLightShadowing(VolumetricLightmapBrickTextureUVs);
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#elif CACHED_POINT_INDIRECT_LIGHTING
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DirectionalLighting *= IndirectLightingCache.DirectionalLightShadowing;
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#endif
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Color += DirectionalLighting;
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```
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```c#
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float3 GetSimpleForwardLightingDirectionalLight(FGBufferData GBuffer, float3 DiffuseColor, float3 SpecularColor, float Roughness, float3 WorldNormal, float3 CameraVector)
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{
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float3 V = -CameraVector;
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float3 N = WorldNormal;
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float3 L = ResolvedView.DirectionalLightDirection;
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float NoL = saturate( dot( N, L ) );
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float3 LightColor = ResolvedView.DirectionalLightColor.rgb * PI;
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FShadowTerms Shadow = { 1, 1, 1, InitHairTransmittanceData() };
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FDirectLighting Lighting = EvaluateBxDF( GBuffer, N, V, L, NoL, Shadow );
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// Not computing specular, material was forced fully rough
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return LightColor * (Lighting.Diffuse + Lighting.Transmission);
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}
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```
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### 1213~1273：渲染雾效果
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包括VertexFog、PixelFog、体积雾，以及体积光效果（lit translucency)
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体积雾只要使用View.VolumetricFogGridZParams中的值计算UV，调用Texture3DSampleLevel采样FogStruct.IntegratedLightScattering，最后的值为float4(VolumetricFogLookup.rgb + GlobalFog.rgb * VolumetricFogLookup.a, VolumetricFogLookup.a * GlobalFog.a);。
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### 1283~1310：取得材质中自发光值得计算结果并且累加到Color上
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```c#
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half3 Emissive = GetMaterialEmissive(PixelMaterialInputs);
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#if !POST_PROCESS_SUBSURFACE && !MATERIAL_SHADINGMODEL_THIN_TRANSLUCENT
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// For skin we need to keep them separate. We also keep them separate for thin translucent.
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// Otherwise just add them together.
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Color += DiffuseColor;
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#endif
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#if !MATERIAL_SHADINGMODEL_THIN_TRANSLUCENT
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Color += Emissive;
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```
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### 1312~1349：SingleLayerWater光照计算
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计算SunIlluminance、WaterDiffuseIndirectIlluminance、Normal、ViewVector、EnvBrdf（预积分G F * 高光颜色，位于BRDF.ush）后根据设置采用对应的方式(前向渲染与延迟渲染方式)
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```c#
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const float3 SunIlluminance = ResolvedView.DirectionalLightColor.rgb * PI; // times PI because it is divided by PI on CPU (=luminance) and we want illuminance here.
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const float3 WaterDiffuseIndirectIlluminance = DiffuseIndirectLighting * PI;// DiffuseIndirectLighting is luminance. So we need to multiply by PI to get illuminance.
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```
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### 1352~1372：超薄透明物体光照计算
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### 1375~1529：GBuffer相关
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1. BlendMode处理
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2. GBuffer.IndirectIrradiance = IndirectIrradiance;
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3. 调用LightAccumulator_Add()累加关照对BaseColor的影响。Out.MRT[0]=FLightAccumulator.TotalLight
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4. 调用EncodeGBuffer(),填充GBuffer12345数据。
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5. Out.MRT[4] = OutVelocity;
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6. Out.MRT[GBUFFER_HAS_VELOCITY ? 5 : 4] = OutGBufferD;
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7. Out.MRT[GBUFFER_HAS_VELOCITY ? 6 : 5] = OutGBufferE;
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8. Out.MRT[0].rgb *= ViewPreExposure;
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### 1553：FinalizeVirtualTextureFeedback
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# UE5
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## Lumen相关
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- GetSkyLighting()
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- Lumen
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- GetTranslucencyGIVolumeLighting()
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- SkyLighting
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- GetEffectiveSkySHDiffuse()
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- GetVolumetricLightmapSkyBentNormal()
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- GetSkyBentNormalAndOcclusion()
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**GetSkyLighting()** 演示了采样SkyLight与Lumen的方法。
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### SkyLighting
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GetEffectiveSkySHDiffuse()是一个宏，会根据平台指向下面2个函数：
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```c++
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/**
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* Computes sky diffuse lighting from the SH irradiance map.
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* This has the SH basis evaluation and diffuse convolution weights combined for minimal ALU's - see "Stupid Spherical Harmonics (SH) Tricks"
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*/
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float3 GetSkySHDiffuse(float3 Normal)
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{
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float4 NormalVector = float4(Normal, 1.0f);
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float3 Intermediate0, Intermediate1, Intermediate2;
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Intermediate0.x = dot(SkyIrradianceEnvironmentMap[0], NormalVector);
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Intermediate0.y = dot(SkyIrradianceEnvironmentMap[1], NormalVector);
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Intermediate0.z = dot(SkyIrradianceEnvironmentMap[2], NormalVector);
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float4 vB = NormalVector.xyzz * NormalVector.yzzx;
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Intermediate1.x = dot(SkyIrradianceEnvironmentMap[3], vB);
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Intermediate1.y = dot(SkyIrradianceEnvironmentMap[4], vB);
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Intermediate1.z = dot(SkyIrradianceEnvironmentMap[5], vB);
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float vC = NormalVector.x * NormalVector.x - NormalVector.y * NormalVector.y;
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Intermediate2 = SkyIrradianceEnvironmentMap[6].xyz * vC;
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// max to not get negative colors
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return max(0, Intermediate0 + Intermediate1 + Intermediate2);
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}
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/**
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* Computes sky diffuse lighting from the SH irradiance map.
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* This has the SH basis evaluation and diffuse convolution weights combined for minimal ALU's - see "Stupid Spherical Harmonics (SH) Tricks"
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* Only does the first 3 components for speed.
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*/
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float3 GetSkySHDiffuseSimple(float3 Normal)
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{
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float4 NormalVector = float4(Normal, 1);
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float3 Intermediate0;
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Intermediate0.x = dot(SkyIrradianceEnvironmentMap[0], NormalVector);
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Intermediate0.y = dot(SkyIrradianceEnvironmentMap[1], NormalVector);
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Intermediate0.z = dot(SkyIrradianceEnvironmentMap[2], NormalVector);
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// max to not get negative colors
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return max(0, Intermediate0);
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}
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```
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