我是一名资深游戏开发，小时候喜欢看十万个为什么

介绍

• 本文旨在搞清楚延迟渲染在unity下如何实现的，为自己写延迟渲染打一个基础，打开从知到行的大门
• 延迟渲染 = 输出物体表面信息(rt1, rt2, rt3, …) + 着色(rt1, rt2, rt3, …)
• 研究完感觉核心特征像后处理，像屏幕空间效果

要研究的问题

怎么生成G-Buffer，生成了哪些数据

生成G-Buffer

DeferredLights类里创建G-Buffer纹理资源句柄，管线setup时创建实际的RT资源

GBufferPass类里填充G-Buffer

• Config方法里ConfigureTarget
  • 调用CoreUtils绑定RenderTarget，最终调用CommandBuffer的SetRenderTarget把GBuffer对应纹理绑定输出
• ExecutePass方法中绘制物体
  • context.DrawRenderers(renderingData.cullResults, ref data.drawingSettings, ref data.filteringSettings, s_ShaderTagUniversalMaterialType, false, tagValues, stateBlocks);
• shader中填充数据，见 UnityGBuffer.hlsl 中 SurfaceDataToGbuffer、 BRDFDataToGbuffer 方法

输出了下面的数据

见文件：UnityGBuffer.hlsl

half4 GBuffer0 : SV_Target0; //diffuse，表面颜色
half4 GBuffer1 : SV_Target1; //metallic/specular，高光
half4 GBuffer2 : SV_Target2; //encode normal，法线
half4 GBuffer3 : SV_Target3; // Camera color attachment，GI，全局光#ifdef GBUFFER_OPTIONAL_SLOT_1
GBUFFER_OPTIONAL_SLOT_1_TYPE GBuffer4 : SV_Target4; //clip z，剪裁空间z值，即深度
#endif

怎么传入多个光源计算光照

逐类型光源

DeferredLights里RenderStencilLights，逐个调用直射光、点光源、射灯进行渲染

using (new ProfilingScope(cmd, m_ProfilingSamplerDeferredStencilPass))
{NativeArray<VisibleLight> visibleLights = renderingData.lightData.visibleLights;if (HasStencilLightsOfType(LightType.Directional))RenderStencilDirectionalLights(cmd, ref renderingData, visibleLights, renderingData.lightData.mainLightIndex);if (HasStencilLightsOfType(LightType.Point))RenderStencilPointLights(cmd, ref renderingData, visibleLights);if (HasStencilLightsOfType(LightType.Spot))RenderStencilSpotLights(cmd, ref renderingData, visibleLights);
}

绘制命令

• 直射光，遍历光源，逐光源DrawCall

for (int soffset = m_stencilVisLightOffsets[(int)LightType.Directional]; soffset < m_stencilVisLights.Length; ++soffset)省略cmd.SetGlobalVector(ShaderConstants._LightColor, lightColor); // VisibleLight.finalColor already returns color in active color spacecmd.SetGlobalVector(ShaderConstants._LightDirection, lightDir);cmd.SetGlobalInt(ShaderConstants._LightFlags, lightFlags);cmd.SetGlobalInt(ShaderConstants._LightLayerMask, (int)lightLayerMask);// 因为GBufferPass已经把光照数据都输出到纹理，这里只需要绘制全屏的mesh，在shader中采样之前输出的GBuffer计算光照// Lighting pass.cmd.DrawMesh(m_FullscreenMesh, Matrix4x4.identity, m_StencilDeferredMaterial, 0, m_StencilDeferredPasses[(int)StencilDeferredPasses.DirectionalLit]);cmd.DrawMesh(m_FullscreenMesh, Matrix4x4.identity, m_StencilDeferredMaterial, 0, m_StencilDeferredPasses[(int)StencilDeferredPasses.DirectionalSimpleLit]);省略

• 点光源、射灯也是遍历光源，逐光源DrawCall，但是mesh不是全屏mesh，是代表光源形状的memsh，代码不赘述，今天不水文

渲染

入口StencilDeferred.shader

half4 DeferredShading(Varyings input) : SV_Target//省略部分代码，这些代码是：取GBuffer的值，拼出计算光照需要的数据//计算光照InputData inputData = InputDataFromGbufferAndWorldPosition(gbuffer2, posWS.xyz);#if defined(_LIT)#if SHADER_API_MOBILE || SHADER_API_SWITCH// Specular highlights are still silenced by setting specular to 0.0 during gbuffer pass and GPU timing is still reduced.bool materialSpecularHighlightsOff = false;#elsebool materialSpecularHighlightsOff = (materialFlags & kMaterialFlagSpecularHighlightsOff);#endifBRDFData brdfData = BRDFDataFromGbuffer(gbuffer0, gbuffer1, gbuffer2);color = LightingPhysicallyBased(brdfData, unityLight, inputData.normalWS, inputData.viewDirectionWS, materialSpecularHighlightsOff);#elif defined(_SIMPLELIT)SurfaceData surfaceData = SurfaceDataFromGbuffer(gbuffer0, gbuffer1, gbuffer2, kLightingSimpleLit);half3 attenuatedLightColor = unityLight.color * (unityLight.distanceAttenuation * unityLight.shadowAttenuation);half3 diffuseColor = LightingLambert(attenuatedLightColor, unityLight.direction, inputData.normalWS);half smoothness = exp2(10 * surfaceData.smoothness + 1);half3 specularColor = LightingSpecular(attenuatedLightColor, unityLight.direction, inputData.normalWS, inputData.viewDirectionWS, half4(surfaceData.specular, 1), smoothness);// TODO: if !defined(_SPECGLOSSMAP) && !defined(_SPECULAR_COLOR), force specularColor to 0 in gbuffer codecolor = diffuseColor * surfaceData.albedo + specularColor;#endifreturn half4(color, alpha);

渲染物体

不透明物体

输出G-Buffer，渲染着色

半透物体

延迟渲染不支持半透，所以走Forward渲染，用额外一个 ScriptableRenderPass 渲染半透，见UniversalRenderer 的 m_RenderTransparentForwardPass

贴花

使用方法

• URP管线资源里创建Renderer，设置使用Deferred
• 相机里Renderer选上面创建的Renderer

延伸知识

SSAO

• Screen Space Ambient Occlusion -> 屏幕空间环境光遮蔽
• SSAO 通过使用深度缓冲、法线缓冲和随机采样核生成遮蔽效果，模拟场景中物体周围环境光被遮挡的情况，从而增强画面的真实感和层次感，让场景看起来更有深度

源码分析

结论

管线流程

• 生成GBuffer
  • shader中通过SV_TargetXXX指定输出到某个绑定的缓冲区
  • 要求图形接口支持一次输出到多个目标
• 通过GBuffer渲染

管线

GBufferPass

输出GBuffer

DeferredPass

用GBuffer着色

DrawObjectsPass

绘制物体，不透、半透

RenderGraph

渲染节点图，可以通过编辑器定制渲染管线

DeferredLights

延迟渲染具体的逻辑

shader源码分析

Lit.shader

GBuffer Pass，输出GBuffer数据的Pass

LitGBufferPass.hlsl

输出GBuffer的Pass源码

UnityGBuffer.hlsl

真干活的着色代码

像素着色器输出
struct FragmentOutput
{half4 GBuffer0 : SV_Target0; //diffuse，表面颜色half4 GBuffer1 : SV_Target1; //metallic/specular，高光half4 GBuffer2 : SV_Target2; //encode normal，法线half4 GBuffer3 : SV_Target3; // Camera color attachment，GI，全局光#ifdef GBUFFER_OPTIONAL_SLOT_1GBUFFER_OPTIONAL_SLOT_1_TYPE GBuffer4 : SV_Target4; //clip z，剪裁空间z值，即深度#endif#ifdef GBUFFER_OPTIONAL_SLOT_2half4 GBuffer5 : SV_Target5;#endif#ifdef GBUFFER_OPTIONAL_SLOT_3half4 GBuffer6 : SV_Target6;#endif
};输出GBuffer
FragmentOutput SurfaceDataToGbuffer(SurfaceData surfaceData, InputData inputData, half3 globalIllumination, int lightingMode)
{half3 packedNormalWS = PackNormal(inputData.normalWS);uint materialFlags = 0;// SimpleLit does not use _SPECULARHIGHLIGHTS_OFF to disable specular highlights.#ifdef _RECEIVE_SHADOWS_OFFmaterialFlags |= kMaterialFlagReceiveShadowsOff;#endif#if defined(LIGHTMAP_ON) && defined(_MIXED_LIGHTING_SUBTRACTIVE)materialFlags |= kMaterialFlagSubtractiveMixedLighting;#endifFragmentOutput output;output.GBuffer0 = half4(surfaceData.albedo.rgb, PackMaterialFlags(materialFlags));   // albedo          albedo          albedo          materialFlags   (sRGB rendertarget)output.GBuffer1 = half4(surfaceData.specular.rgb, surfaceData.occlusion);            // specular        specular        specular        occlusionoutput.GBuffer2 = half4(packedNormalWS, surfaceData.smoothness);                     // encoded-normal  encoded-normal  encoded-normal  smoothnessoutput.GBuffer3 = half4(globalIllumination, 1);                                      // GI              GI              GI              unused          (lighting buffer)#if _RENDER_PASS_ENABLEDoutput.GBuffer4 = inputData.positionCS.z;#endif#if OUTPUT_SHADOWMASKoutput.GBUFFER_SHADOWMASK = inputData.shadowMask; // will have unity_ProbesOcclusion value if subtractive lighting is used (baked)#endif#ifdef _WRITE_RENDERING_LAYERSuint renderingLayers = GetMeshRenderingLayer();output.GBUFFER_LIGHT_LAYERS = float4(EncodeMeshRenderingLayer(renderingLayers), 0.0, 0.0, 0.0);#endifreturn output;
}

StencilDeferred.shader

使用GBuffer进行着色

StencilDeferred.hlsl

顶点、像素方法

着色

half4 DeferredShading(Varyings input) : SV_Target...省略代码，不水字数，感兴趣的朋友看URP源码即可