【Unity】URP源码分析(Pass篇)

闲鱼技术01

（基于Unity 2021.3.8、URP 12.1.7）


渲染Pass流程 (Render Pass Flow)

Forward Shading

• MainLightShadowCasterPass ->
  
• AdditionalLightsShadowCasterPass ->
  
• DepthNormalPrepass / DepthPrepass ->
  
• ColorGradingLutPass ->
  
• CopyDepthPass (Depth Prepass On) ->
  
• DrawObjectsPass (Opaque) ->
  
• CopyDepthPass (Depth Prepass Off) ->
  
• DrawSkyboxPass ->
  
• MotionVectorPass ->
  
• CopyColorPass ->
  
• DrawObjectsPass (Transparent) ->
  
• PostProcessPass ->
  
• PostProcessPass (FinalPostProcessPass) ->
  
• FinalBlitPass
  

Deferred Shading

• MainLightShadowCasterPass ->
  
• AdditionalLightsShadowCasterPass ->
  
• DepthNormalPrepass ->
  
• ColorGradingLutPass ->
  
• GBufferPass ->
  
• CopyDepthPass ->
  
• TileDepthRangePass ->
  
• TileDepthRangePass (Extra) ->
  
• DeferredPass ->
  
• DrawObjectsPass (Opaque ForwardOnly) ->
  
• DrawSkyboxPass ->
  
• MotionVectorPass ->
  
• CopyColorPass ->
  
• DrawObjectsPass (Transparent) ->
  
• PostProcessPass ->
  
• PostProcessPass (FinalPostProcessPass) ->
  
• FinalBlitPass
  

<hr/>渲染Pass细节 (Render Pass Detail)

ScriptableRenderPass.cs

属性

• colorAttachments、colorAttachment (颜色缓冲区)
  
• depthAttachment (深度缓冲区)
  
• input (Pass所需的Buffer输入)
  
• clearFlag (缓冲区清除标记 (color、depth、stencil))
  
• clearColor (缓冲区清除颜色)
  

方法

• ConfigureInput (配置input)
  
• ConfigureTarget (配置ColorAttachment、DepthAttachment)
  
• ConfigureClear (配置clearFlag、clearColor)
  
• OnCameraSetup (虚函数)
  
• Configure (虚函数)
  
• OnCameraCleanup (虚函数)
  
• OnFinishCameraStackRendering (虚函数)
  
• Execute (抽象函数)
  
• CreateDrawingSettings (创建绘制设置)
  

定义

• ScriptableRenderPassInput (Pass所需的Buffer输入)
  
• RenderPassEvent (渲染Pass的执行时机事件)
  

MainLightShadowCasterPass.cs

• 执行Shader中LightMode为ShadowCaster的Pass, 主光源空间下渲染物体深度, 生成_MainLightShadowmapTexture
  

AdditionalLightsShadowCasterPass.cs

• 执行Shader中LightMode为ShadowCaster的Pass, 额外光源空间下渲染物体深度, 生成_AdditionalLightsShadowmapTexture
  
• 需要在Render Pipeline Asset上勾选Adiitional Lights的Cast Shadows, 并且光源Shadow Type选择Hard Shadows或Soft Shadows
  

DepthNormalOnlyPass.cs

• 执行Shader中LightMode为DepthNormals的Pass, 生成_CameraDepthTexture、_CameraNormalsTexture, 最终传入到Shader中的_CameraDepthNormalsTexture
  
• 需要有后处理用到_CameraNormalsTexture
  

DepthOnlyPass.cs

• 执行Shader中LightMode为DepthOnly的Pass, 生成_CameraDepthTexture
  
• 需要在Renderer Data上Depth Priming Mode中设置为Forced
  

ColorGradingLutPass.cs

• 根据用到的校色后处理 (ChannelMixer、ColorAdjustments、ColorCurves、LiftGammaGain、ShadowsMidtonesHighlights、SplitToning、WhiteBalance) 参数生成Lut校色RT, Shader实现可参考LutBuilderHdr.shader、LutBuilderLdr.shader
  

MotionVectorRenderPass.cs

• 生成运动向量RT
  
• 需要有后处理用到_MotionVectorTexture
  

GBufferPass.cs

• 执行Shader中LightMode为UniversalGBuffer, UniversalMaterialType为Lit、SimpleLit、Unlit的Pass, 生成Gbuffer0 ~ Gbuffer3四张RT
  

DeferredPass.cs

• 根据Stencil Buffer的值和Pass索引光源进行渲染, Shader实现可参考StencilDeferred.shader
  

DrawObjectsPass.cs

• 绘制Opaque、Transparent物体
  

CopyDepthPass.cs

• 拷贝activeCameraDepthAttachment到_CameraDepthTexture (当DepthOnlyPass或DepthNormalOnlyPass存在时不执行)
  

DrawSkyboxPass.cs

• DrawSkybox (绘制天空盒)
  

CopyColorPass.cs

• 拷贝activeCameraColorAttachment到_CameraOpaqueTexture
  

PostProcessPass.cs

• depthOfField、motionBlur、paniniProjection、bloom、lensDistortion、chromaticAberration、vignette、colorLookup、colorAdjustments、tonemapping、filmGrain等后处理的集合, Shader实现可参考UberPost.shader
  

PostProcessPass.cs (FinalPostProcessPass)

• RenderFinalPass, 主要处理FXAA和Render Scale不为1.0时的Up/Down Scaling Blit, Shader实现可参考FinalPost.shader
  

FinalBlitPass.cs

• 将activeCameraColorAttachment Blit到cameraData.targetTexture / BuiltinRenderTextureType.CameraTarget