UE4 随笔记录1

1、蓝图材质转换HLSL代码

• 在蓝图中创建Post Process Material，然后创建SceneTexture，ID选择CustomStencil，如下图：
  • 
• 在材质编辑器下，点击Window->Shader Code->HLSL Code,copy对应代码，保存生成custom.hsls文件（名称随便命名，目的方便描述该文件）。
  • HLSL code 是基于MaterialTemplate.ush(Engine/Shader/Private)进行生成。
  • 如何生成？目前没有深入研究，待后续更新（如果用到）。
• 对比MaterialTemplate.ush和custom.hsls文件。在VSCode中，左侧目录同时选中两个文件，右键，有compare功能，进行对比哪些是custom.hsls新增的。
  • 实际对比，发现有大量的不同出现，然而我们在材质蓝图中，仅仅增加了一个SceneTexture函数，不应该有很多变化。没有深入分析原因，后面用到再研究。
  • 本次研究的重点是如何获得SceneTexture，测试的ID是CustomStencil。而不是Post Process Material如何被使用，因此下面内容会围绕本次重点展开。
  • 在custom.hsls中找出Emissive Color赋值出现的位置：
    • void CalcPixelMaterialInputs(in out FMaterialPixelParameters Parameters, in out FPixelMaterialInputs PixelMaterialInputs)
      • 不研究CalcPixelMaterialInputs如何被使用，只研究里面的内容。
    • EmissiveColor是有两个数值差值的出来。
      • Local0是和SceneTexture相关，深入研究
      • Material.VectorExpression[1].rgb，不是重点，没有深入研究。
    • 关键部分代码

    • MaterialFloat4 Local0 = SceneTextureLookup(GetDefaultSceneTextureUV(Parameters, 25), 25, false);
      MaterialFloat3 Local1 = erp(Local0.rgba.rgb,Material.VectorExpressions[1].rgb,MaterialFloat(Material.ScalarExpressions[0].x));
      PixelMaterialInputs.EmissiveColor = Local1;

       

• SceneTextureLookup函数介绍

• /** Applies an offset to the scene texture lookup and decodes the HDR linear space color. */
  float4 SceneTextureLookup(float2 UV, int SceneTextureIndex, bool bFiltered)
  {
  #if SCENE_TEXTURES_DISABLED
      return float4(0.0f, 0.0f, 0.0f, 0.0f);
  #endif
  
      FScreenSpaceData ScreenSpaceData = GetScreenSpaceData(UV, false);
      switch(SceneTextureIndex)
      {
          // order needs to match to ESceneTextureId
  
          case PPI_SceneColor:
              return float4(CalcSceneColor(UV), 0);
          case PPI_SceneDepth:
              return ScreenSpaceData.GBuffer.Depth;
          case PPI_DiffuseColor:
              return float4(ScreenSpaceData.GBuffer.DiffuseColor, 0);
          case PPI_SpecularColor:
              return float4(ScreenSpaceData.GBuffer.SpecularColor, 0);
          case PPI_SubsurfaceColor:
              return IsSubsurfaceModel(ScreenSpaceData.GBuffer.ShadingModelID) ? float4( ExtractSubsurfaceColor(ScreenSpaceData.GBuffer), ScreenSpaceData.GBuffer.CustomData.a ) : ScreenSpaceData.GBuffer.CustomData;
          case PPI_BaseColor:
              return float4(ScreenSpaceData.GBuffer.BaseColor, 0);
          case PPI_Specular:
              return ScreenSpaceData.GBuffer.Specular;
          case PPI_Metallic:
              return ScreenSpaceData.GBuffer.Metallic;
          case PPI_WorldNormal:
              return float4(ScreenSpaceData.GBuffer.WorldNormal, 0);
          case PPI_SeparateTranslucency:
              return float4(1, 1, 1, 1);    // todo
          case PPI_Opacity:
              return ScreenSpaceData.GBuffer.CustomData.a;
          case PPI_Roughness:
              return ScreenSpaceData.GBuffer.Roughness;
          case PPI_MaterialAO:
              return ScreenSpaceData.GBuffer.GBufferAO;
          case PPI_CustomDepth:
              return ScreenSpaceData.GBuffer.CustomDepth;
  #if POST_PROCESS_MATERIAL
          case PPI_PostProcessInput0:
              return Texture2DSample(PostProcessInput_0_Texture, bFiltered ? PostProcessInput_BilinearSampler : PostProcessInput_0_SharedSampler, UV);
          case PPI_PostProcessInput1:
              return Texture2DSample(PostProcessInput_1_Texture, bFiltered ? PostProcessInput_BilinearSampler : PostProcessInput_1_SharedSampler, UV);
          case PPI_PostProcessInput2:
              return Texture2DSample(PostProcessInput_2_Texture, bFiltered ? PostProcessInput_BilinearSampler : PostProcessInput_2_SharedSampler, UV);
          case PPI_PostProcessInput3:
              return Texture2DSample(PostProcessInput_3_Texture, bFiltered ? PostProcessInput_BilinearSampler : PostProcessInput_3_SharedSampler, UV);
          case PPI_PostProcessInput4:
              return Texture2DSample(PostProcessInput_4_Texture, bFiltered ? PostProcessInput_BilinearSampler : PostProcessInput_4_SharedSampler, UV);
  #endif // __POST_PROCESS_COMMON__
          case PPI_DecalMask:
              return 0;  // material compiler will return an error
          case PPI_ShadingModelColor:
              return float4(GetShadingModelColor(ScreenSpaceData.GBuffer.ShadingModelID), 1);
          case PPI_ShadingModelID:
              return float4(ScreenSpaceData.GBuffer.ShadingModelID, 0, 0, 0);
          case PPI_AmbientOcclusion:
              return ScreenSpaceData.AmbientOcclusion;
          case PPI_CustomStencil:
              return ScreenSpaceData.GBuffer.CustomStencil;
          case PPI_StoredBaseColor:
              return float4(ScreenSpaceData.GBuffer.StoredBaseColor, 0);
          case PPI_StoredSpecular:
              return float4(ScreenSpaceData.GBuffer.StoredSpecular.rrr, 0);
  #if POST_PROCESS_MATERIAL
          case PPI_Velocity:
              return float4(PostProcessVelocityLookup(ConvertToDeviceZ(ScreenSpaceData.GBuffer.Depth), UV), 0, 0);
  #endif
          case PPI_WorldTangent:
              return float4(ScreenSpaceData.GBuffer.WorldTangent, 0);
          case PPI_Anisotropy:
              return ScreenSpaceData.GBuffer.Anisotropy;
          default:
              return float4(0, 0, 0, 0);
      }
  }

  GetScreenSpaceData 在DeferredShadingCommon.ush文件中。

// @param UV - UV space in the GBuffer textures (BufferSize resolution)
FScreenSpaceData GetScreenSpaceData(float2 UV, bool bGetNormalizedNormal = true)
{
	FScreenSpaceData Out;

	Out.GBuffer = GetGBufferData(UV, bGetNormalizedNormal);
	float4 ScreenSpaceAO = Texture2DSampleLevel(SceneTexturesStruct.ScreenSpaceAOTexture, SceneTexturesStruct.ScreenSpaceAOTextureSampler, UV, 0);

	Out.AmbientOcclusion = ScreenSpaceAO.r;

	return Out;
}

在相同文件内：

// @param UV - UV space in the GBuffer textures (BufferSize resolution)
FGBufferData GetGBufferData(float2 UV, bool bGetNormalizedNormal = true)
{
#if 0 //METAL_MRT_PROFILE
	// @todo metal mrt: The deferred renderer isn't keeping these in tiled memory all the time - we don't know when this makes sense
	// versus just sampling a bound resolved texture
	float4 GBufferA = FramebufferFetchMRT(1);
	float4 GBufferB = FramebufferFetchMRT(2);
	float4 GBufferC = FramebufferFetchMRT(3);
	float4 GBufferD = FramebufferFetchMRT(4);
	// @todo metal mrt: We can't framebuffer fetch the depth, can we jam it in somewhere?
	float CustomNativeDepth = 0.5;
	#if ALLOW_STATIC_LIGHTING
		float4 GBufferE = FramebufferFetchMRT(5);
	#else
		float4 GBufferE = 1;
	#endif
#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;

#if FEATURE_LEVEL >= FEATURE_LEVEL_SM4
	int2 IntUV = (int2)trunc(UV * View.BufferSizeAndInvSize.xy);
	uint CustomStencil = SceneTexturesStruct.CustomStencilTexture.Load(int3(IntUV, 0)) STENCIL_COMPONENT_SWIZZLE;
#else
	uint CustomStencil = 0;
#endif

	#if ALLOW_STATIC_LIGHTING
		float4 GBufferE = Texture2DSampleLevel(SceneTexturesStruct.GBufferETexture, SceneTexturesStruct.GBufferETextureSampler, UV, 0);
	#else
		float4 GBufferE = 1;
	#endif

	#if WRITES_VELOCITY_TO_GBUFFER
		float4 GBufferVelocity = Texture2DSampleLevel(SceneTexturesStruct.GBufferVelocityTexture, SceneTexturesStruct.GBufferVelocityTextureSampler, UV, 0);
	#else
		float4 GBufferVelocity = 0;
	#endif
#endif

	float SceneDepth = CalcSceneDepth(UV);
	
	return DecodeGBufferData(GBufferA, GBufferB, GBufferC, GBufferD, GBufferE, GBufferVelocity, CustomNativeDepth, CustomStencil, SceneDepth, bGetNormalizedNormal, CheckerFromSceneColorUV(UV));
}

在相同文件里：

/** Populates FGBufferData */
// @param bChecker High frequency Checkerboard pattern computed with one of the CheckerFrom.. functions, todo: profile if float 0/1 would be better (need to make sure it's 100% the same)
FGBufferData DecodeGBufferData(
	float4 InGBufferA,
	float4 InGBufferB,
	float4 InGBufferC,
	float4 InGBufferD,
	float4 InGBufferE,
	float4 InGBufferVelocity,
	float CustomNativeDepth,
	uint CustomStencil,
	float SceneDepth,
	bool bGetNormalizedNormal,
	bool bChecker)
{
	FGBufferData GBuffer;

	GBuffer.WorldNormal = DecodeNormal( InGBufferA.xyz );
	if(bGetNormalizedNormal)
	{
		GBuffer.WorldNormal = normalize(GBuffer.WorldNormal);
	}

	GBuffer.PerObjectGBufferData = InGBufferA.a;  
	GBuffer.Metallic	= InGBufferB.r;
	GBuffer.Specular	= InGBufferB.g;
	GBuffer.Roughness	= InGBufferB.b;
	// Note: must match GetShadingModelId standalone function logic
	// Also Note: SimpleElementPixelShader directly sets SV_Target2 ( GBufferB ) to indicate unlit.
	// An update there will be required if this layout changes.
	GBuffer.ShadingModelID = DecodeShadingModelId(InGBufferB.a);
	GBuffer.SelectiveOutputMask = DecodeSelectiveOutputMask(InGBufferB.a);

	GBuffer.BaseColor = DecodeBaseColor(InGBufferC.rgb);

#if ALLOW_STATIC_LIGHTING
	GBuffer.GBufferAO = 1;
	GBuffer.IndirectIrradiance = DecodeIndirectIrradiance(InGBufferC.a);
#else
	GBuffer.GBufferAO = InGBufferC.a;
	GBuffer.IndirectIrradiance = 1;
#endif

	GBuffer.CustomData = !(GBuffer.SelectiveOutputMask & SKIP_CUSTOMDATA_MASK) ? InGBufferD : 0;

	GBuffer.PrecomputedShadowFactors = !(GBuffer.SelectiveOutputMask & SKIP_PRECSHADOW_MASK) ? InGBufferE :  ((GBuffer.SelectiveOutputMask & ZERO_PRECSHADOW_MASK) ? 0 :  1);
	GBuffer.CustomDepth = ConvertFromDeviceZ(CustomNativeDepth);
	GBuffer.CustomStencil = CustomStencil;
	GBuffer.Depth = SceneDepth;

	GBuffer.StoredBaseColor = GBuffer.BaseColor;
	GBuffer.StoredMetallic = GBuffer.Metallic;
	GBuffer.StoredSpecular = GBuffer.Specular;

	FLATTEN
	if( GBuffer.ShadingModelID == SHADINGMODELID_EYE )
	{
		GBuffer.Metallic = 0.0;
#if IRIS_NORMAL
		GBuffer.Specular = 0.25;
#endif
	}

	// derived from BaseColor, Metalness, Specular
	{
		GBuffer.SpecularColor = ComputeF0(GBuffer.Specular, GBuffer.BaseColor, GBuffer.Metallic);

		if (UseSubsurfaceProfile(GBuffer.ShadingModelID))
		{
			AdjustBaseColorAndSpecularColorForSubsurfaceProfileLighting(GBuffer.BaseColor, GBuffer.SpecularColor, GBuffer.Specular, bChecker);
		}

		GBuffer.DiffuseColor = GBuffer.BaseColor - GBuffer.BaseColor * GBuffer.Metallic;

		#if USE_DEVELOPMENT_SHADERS
		{
			// this feature is only needed for development/editor - we can compile it out for a shipping build (see r.CompileShadersForDevelopment cvar help)
			GBuffer.DiffuseColor = GBuffer.DiffuseColor * View.DiffuseOverrideParameter.www + View.DiffuseOverrideParameter.xyz;
			GBuffer.SpecularColor = GBuffer.SpecularColor * View.SpecularOverrideParameter.w + View.SpecularOverrideParameter.xyz;
		}
		#endif //USE_DEVELOPMENT_SHADERS
	}

	GBuffer.Velocity = !(GBuffer.SelectiveOutputMask & SKIP_VELOCITY_MASK) ? InGBufferVelocity : 0;

	return GBuffer;
}

回归到CustomStencil：

#if FEATURE_LEVEL >= FEATURE_LEVEL_SM4
	int2 IntUV = (int2)trunc(UV * View.BufferSizeAndInvSize.xy);
	uint CustomStencil = SceneTexturesStruct.CustomStencilTexture.Load(int3(IntUV, 0)) STENCIL_COMPONENT_SWIZZLE;
#else
	uint CustomStencil = 0;
#endif