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。 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。 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。 ### 780~889：计算变量并且填充FMaterialPixelParameters MaterialParameters。BaseColor、Metallic、Specular就位于867~877。 ### 915~1072：计算GBuffer或者DBuffer - 915~942:计算贴花相关的DBuffer - 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） - 1041：GBuffer.DiffuseColor = BaseColor - BaseColor * Metallic; - 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） ### 1081~1146： #### 1086~1116：计算DiffuseColorForIndirect DiffuseColorForIndirect（DiffuseDir只在Hair中计算） - 次表面与皮肤：DiffuseColorForIndirect += SubsurfaceColor; - 布料：DiffuseColorForIndirect += SubsurfaceColor * saturate(GetMaterialCustomData0(MaterialParameters)); - 头发：DiffuseColorForIndirect = 2*PI * HairShading( GBuffer, L, V, N, 1, TransmittanceData, 0, 0.2, uint2(0,0); #### 1118~1120：计算预间接光照结果 GetPrecomputedIndirectLightingAndSkyLight： 采样对应的预结算缓存： 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。 2. CACHED_VOLUME_INDIRECT_LIGHTING：采样IndirectLightingCache，最后累加到最后累加到OutDiffuseLighting上。 3. 采样HQ_TEXTURE_LIGHTMAP或者LQ_TEXTURE_LIGHTMAP，最后累加到OutDiffuseLighting上。 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。 #### 1138：计算DiffuseColor DiffuseColor=Diffuse间接照明 * Diffse颜色 + 次表面间接光照 * 次表面颜色+AO ```c# DiffuseColor += (DiffuseIndirectLighting * DiffuseColorForIndirect + SubsurfaceIndirectLighting * SubsurfaceColor) * AOMultiBounce( GBuffer.BaseColor, DiffOcclusion ); ``` #### 1140~1146：SingleLayerWater 覆盖颜色操作 ```c# GBuffer.DiffuseColor *= BaseMaterialCoverageOverWater; DiffuseColor *= BaseMaterialCoverageOverWater; ``` ### 1148~1211 1. 使用ForwardDirectLighting的DiffuseLighting与SpecularLighting累加，Color，THIN_TRANSLUCENT Model则为 DiffuseColor与ColorSeparateSpecular。 2. SIMPLE_FORWARD_DIRECTIONAL_LIGHT：调用GetSimpleForwardLightingDirectionalLight()计算方向光结果。 根据光照模式累加，最后累加到Color上： ```c# #if STATICLIGHTING_SIGNEDDISTANCEFIELD DirectionalLighting *= GBuffer.PrecomputedShadowFactors.x; #elif PRECOMPUTED_IRRADIANCE_VOLUME_LIGHTING DirectionalLighting *= GetVolumetricLightmapDirectionalLightShadowing(VolumetricLightmapBrickTextureUVs); #elif CACHED_POINT_INDIRECT_LIGHTING DirectionalLighting *= IndirectLightingCache.DirectionalLightShadowing; #endif Color += DirectionalLighting; ``` ```c# float3 GetSimpleForwardLightingDirectionalLight(FGBufferData GBuffer, float3 DiffuseColor, float3 SpecularColor, float Roughness, float3 WorldNormal, float3 CameraVector) { float3 V = -CameraVector; float3 N = WorldNormal; float3 L = ResolvedView.DirectionalLightDirection; float NoL = saturate( dot( N, L ) ); float3 LightColor = ResolvedView.DirectionalLightColor.rgb * PI; FShadowTerms Shadow = { 1, 1, 1, InitHairTransmittanceData() }; FDirectLighting Lighting = EvaluateBxDF( GBuffer, N, V, L, NoL, Shadow ); // Not computing specular, material was forced fully rough return LightColor * (Lighting.Diffuse + Lighting.Transmission); } ``` ### 1213~1273：渲染雾效果 包括VertexFog、PixelFog、体积雾，以及体积光效果（lit translucency) 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);。 ### 1283~1310：取得材质中自发光值得计算结果并且累加到Color上 ```c# half3 Emissive = GetMaterialEmissive(PixelMaterialInputs); #if !POST_PROCESS_SUBSURFACE && !MATERIAL_SHADINGMODEL_THIN_TRANSLUCENT // For skin we need to keep them separate. We also keep them separate for thin translucent. // Otherwise just add them together. Color += DiffuseColor; #endif #if !MATERIAL_SHADINGMODEL_THIN_TRANSLUCENT Color += Emissive; ``` ### 1312~1349：SingleLayerWater光照计算 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) ```c# const float3 SunIlluminance = ResolvedView.DirectionalLightColor.rgb * PI; // times PI because it is divided by PI on CPU (=luminance) and we want illuminance here. const float3 WaterDiffuseIndirectIlluminance = DiffuseIndirectLighting * PI;// DiffuseIndirectLighting is luminance. So we need to multiply by PI to get illuminance. ``` ### 1352~1372：超薄透明物体光照计算 ### 1375~1529：GBuffer相关 1. BlendMode处理 2. GBuffer.IndirectIrradiance = IndirectIrradiance; 3. 调用LightAccumulator_Add()累加关照对BaseColor的影响。Out.MRT[0]=FLightAccumulator.TotalLight 4. 调用EncodeGBuffer(),填充GBuffer12345数据。 5. Out.MRT[4] = OutVelocity; 6. Out.MRT[GBUFFER_HAS_VELOCITY ? 5 : 4] = OutGBufferD; 7. Out.MRT[GBUFFER_HAS_VELOCITY ? 6 : 5] = OutGBufferE; 8. Out.MRT[0].rgb *= ViewPreExposure; ### 1553：FinalizeVirtualTextureFeedback # UE5 ## Lumen相关 - GetSkyLighting() - Lumen - GetTranslucencyGIVolumeLighting() - SkyLighting - GetEffectiveSkySHDiffuse() - GetVolumetricLightmapSkyBentNormal() - GetSkyBentNormalAndOcclusion() **GetSkyLighting()** 演示了采样SkyLight与Lumen的方法。 ### SkyLighting GetEffectiveSkySHDiffuse()是一个宏，会根据平台指向下面2个函数： ```c++ /** * Computes sky diffuse lighting from the SH irradiance map. * This has the SH basis evaluation and diffuse convolution weights combined for minimal ALU's - see "Stupid Spherical Harmonics (SH) Tricks" */ float3 GetSkySHDiffuse(float3 Normal) { float4 NormalVector = float4(Normal, 1.0f); float3 Intermediate0, Intermediate1, Intermediate2; Intermediate0.x = dot(SkyIrradianceEnvironmentMap[0], NormalVector); Intermediate0.y = dot(SkyIrradianceEnvironmentMap[1], NormalVector); Intermediate0.z = dot(SkyIrradianceEnvironmentMap[2], NormalVector); float4 vB = NormalVector.xyzz * NormalVector.yzzx; Intermediate1.x = dot(SkyIrradianceEnvironmentMap[3], vB); Intermediate1.y = dot(SkyIrradianceEnvironmentMap[4], vB); Intermediate1.z = dot(SkyIrradianceEnvironmentMap[5], vB); float vC = NormalVector.x * NormalVector.x - NormalVector.y * NormalVector.y; Intermediate2 = SkyIrradianceEnvironmentMap[6].xyz * vC; // max to not get negative colors return max(0, Intermediate0 + Intermediate1 + Intermediate2); } /** * Computes sky diffuse lighting from the SH irradiance map. * This has the SH basis evaluation and diffuse convolution weights combined for minimal ALU's - see "Stupid Spherical Harmonics (SH) Tricks" * Only does the first 3 components for speed. */ float3 GetSkySHDiffuseSimple(float3 Normal) { float4 NormalVector = float4(Normal, 1); float3 Intermediate0; Intermediate0.x = dot(SkyIrradianceEnvironmentMap[0], NormalVector); Intermediate0.y = dot(SkyIrradianceEnvironmentMap[1], NormalVector); Intermediate0.z = dot(SkyIrradianceEnvironmentMap[2], NormalVector); // max to not get negative colors return max(0, Intermediate0); } ```