【Unity】URP源码分析(Pass篇)
（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
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