113 lines
6.8 KiB
Markdown
113 lines
6.8 KiB
Markdown
---
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title: UE GBuffer存储数据
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date: 2022-10-11 13:07:27
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excerpt:
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tags: Rendering
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rating: ⭐
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---
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https://zhuanlan.zhihu.com/p/400677108
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| MRT | R | G | B | A |
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| -------------------------------- | -------------------------- | -------------------------- | -------------------------- | ------------------------------------- |
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| MRT0 | SceneColor.r | SceneColor.g | SceneColor.b | Alpha(Opacity?) |
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| MRT1 GBufferA | WorldNormal.r | WorldNormal.g | WorldNormal.b | PerObjectGBufferData |
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| MRT2 GBUfferB | Metallic | Specular | Roughness | ShadingModelId && SelectiveOutputMask |
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| MRT3 GBUfferC | BaseColor.r | BaseColor.g | BaseColor.b | IndirectIrradiance |
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| MRT4 GBUfferD(根据需求插入) | Velocity.r | Velocity.g | Velocity.b | Velocity.a |
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| MRT5 GBUfferE(Velocity不渲染为D) | CustomData.r | CustomData.g | CustomData.b | CustomData.a |
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| MRT6 GBUfferF(Velocity不渲染为E) | PrecomputedShadowFactors.r | PrecomputedShadowFactors.g | PrecomputedShadowFactors.b | PrecomputedShadowFactors.a |
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| MRT7 | | | | |
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## Depth Stencil
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[0] sandbox bit (bit to be use by any rendering passes, but must be properly reset to 0 after using)
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STENCIL LOD抖动过渡，后处理，贴花，Local光源都有使用，用来绘制临时Mask
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**[001] unallocated**
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**[2] unallocated**
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[3] Temporal AA mask for translucent object.
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标记后TAA将不再读取History数据，用来处理半透物体的TAA问题
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**1-3在移动延迟会被借用储存ShadingMode，但小于ShadingMode总数量，不清楚怎么处理的。但因为毕竟有重复使用，不适合直接占用这两个值。**
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[4] Lighting channels
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[5] Lighting channels
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[6] Lighting channels
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[7] Primitive receive decal bit
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## GBuffer
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**SceneColorDeferred（场景颜色）**
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RGBAHalf（移动默认R11G11B10）
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Emissive直接写入这里，非自发光写入BaseColor。A通道正常储存Alpha值，通常情况没用。
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>**原神将其和BaseColor合并了，由Alpha来标记自发光强度。这使得自发光颜色必须和BaseColor相同，限制了其表达。在需要不同颜色的时候，原神则用叠加半透材质的方法实现。**
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**用这个方法需要给原本在BaseColor.a的IndirectIrradiance * AO 再找个位置。**
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**GBufferA（法线）**
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R10G10B10A2
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移动延迟用八面体Encode法线到RG，B为PrecomputedShadowFactors.x。
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PC直接储存法线到RGB（禁用的分支里可以Encode法线到RG，如果这样做了B可以空出一个10bit，但移动没法使用。不如和移动一样把PrecomputedShadowFactors.x移到这来。不过PrecomputedShadowFactors.x其实也不需要10bit，可以拆2bit做特殊用途）
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A为PerObjectGBufferData（bit1:CastContactShadow，bit2:HasDynamicIndirectShadowCasterRepresentation）
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**GBufferB**
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RGBA8888
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金属，高光，粗糙，ShadingModelID+SelectiveOutputMask（各占4bit，Shading Mode最大值16）
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SelectiveOutputMask记录了绘制时以下宏的开启结果：
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- MATERIAL_USES_ANISOTROPY 禁止计算各向异性
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- !GBUFFER_HAS_PRECSHADOWFACTOR 禁止读取GBufferE数据作为预计算阴影
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- GBUFFER_HAS_PRECSHADOWFACTOR && WRITES_PRECSHADOWFACTOR_ZERO 当不读取GBufferE时，若此值为1时，预计算阴影设为0，否则为1。
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- WRITES_VELOCITY_TO_GBUFFER 禁止从Gbuffer中读取速度值。
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**因为没写速度的时候Buffer里是0，并不是零速度，所以必须靠它来Mask，但如果将速度图Clear为零速度，按说可以不需要这个Mask，就可以用在别处**
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**并不觉得高光值得占用8bit的容量，可以压缩其他数据到高光上。**
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> 常见的做法还有将F0储存至RGB，让SSR无需采样BaseColor，但这样一来粗糙度又需要另找地方储存（可储存在法线B通道上）
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**GBufferC（BaseColor）**
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RGBA8888
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RGB储存Lit物体的BaseColor，A在有静态光照时候储存随机抖动过的IndirectIrradiance * Material AO，否则直接储存Material AO。
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**GBufferD（自定义数据）**
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**GBufferE（静态阴影）**
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**GBufferVelocity（速度）**
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## 实用函数
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LightingPass中的调用：
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```c++
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uint PixelShadingModelID = GetScreenSpaceData(ScreenUV).GBuffer.ShadingModelID;
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```
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最终：
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```c++
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FGBufferData GetGBufferData(float2 UV, bool bGetNormalizedNormal = true)
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{
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float4 GBufferA = Texture2DSampleLevel(SceneTexturesStruct.GBufferATexture, SceneTexturesStruct_GBufferATextureSampler, UV, 0);
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float4 GBufferB = Texture2DSampleLevel(SceneTexturesStruct.GBufferBTexture, SceneTexturesStruct_GBufferBTextureSampler, UV, 0);
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float4 GBufferC = Texture2DSampleLevel(SceneTexturesStruct.GBufferCTexture, SceneTexturesStruct_GBufferCTextureSampler, UV, 0);
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float4 GBufferD = Texture2DSampleLevel(SceneTexturesStruct.GBufferDTexture, SceneTexturesStruct_GBufferDTextureSampler, UV, 0);
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float4 ToonDataA = Texture2DSampleLevel(SceneTexturesStruct.ToonBufferATexture, SceneTexturesStruct_ToonBufferATextureSampler, UV, 0);
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float CustomNativeDepth = Texture2DSampleLevel(SceneTexturesStruct.CustomDepthTexture, SceneTexturesStruct_CustomDepthTextureSampler, UV, 0).r;
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int2 IntUV = (int2)trunc(UV * View.BufferSizeAndInvSize.xy);
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uint CustomStencil = SceneTexturesStruct.CustomStencilTexture.Load(int3(IntUV, 0)) STENCIL_COMPONENT_SWIZZLE;
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#if ALLOW_STATIC_LIGHTING
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float4 GBufferE = Texture2DSampleLevel(SceneTexturesStruct.GBufferETexture, SceneTexturesStruct_GBufferETextureSampler, UV, 0);
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#else
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float4 GBufferE = 1;
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#endif
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float4 GBufferF = Texture2DSampleLevel(SceneTexturesStruct.GBufferFTexture, SceneTexturesStruct_GBufferFTextureSampler, UV, 0);
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#if WRITES_VELOCITY_TO_GBUFFER
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float4 GBufferVelocity = Texture2DSampleLevel(SceneTexturesStruct.GBufferVelocityTexture, SceneTexturesStruct_GBufferVelocityTextureSampler, UV, 0);
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#else
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float4 GBufferVelocity = 0;
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#endif
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float SceneDepth = CalcSceneDepth(UV);
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return DecodeGBufferData(GBufferA, GBufferB, GBufferC, GBufferD, GBufferE, GBufferF, GBufferVelocity, ToonDataA, CustomNativeDepth, CustomStencil, SceneDepth, bGetNormalizedNormal, CheckerFromSceneColorUV(UV));
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}
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```
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>GBuffer.ShadingModelID = DecodeShadingModelId(InGBufferB.a); |