我是一名資深游戲開發，小時候喜歡看十萬個為什么

介紹

• 本文旨在搞清楚延遲渲染在unity下如何實現的，為自己寫延遲渲染打一個基礎，打開從知到行的大門
• 延遲渲染 = 輸出物體表面信息(rt1, rt2, rt3, …) + 著色(rt1, rt2, rt3, …)
• 研究完感覺核心特征像后處理，像屏幕空間效果

要研究的問題

怎么生成G-Buffer，生成了哪些數據

生成G-Buffer

DeferredLights類里創建G-Buffer紋理資源句柄，管線setup時創建實際的RT資源

GBufferPass類里填充G-Buffer

• Config方法里ConfigureTarget
  • 調用CoreUtils綁定RenderTarget，最終調用CommandBuffer的SetRenderTarget把GBuffer對應紋理綁定輸出
• ExecutePass方法中繪制物體
  • context.DrawRenderers(renderingData.cullResults, ref data.drawingSettings, ref data.filteringSettings, s_ShaderTagUniversalMaterialType, false, tagValues, stateBlocks);
• shader中填充數據，見 UnityGBuffer.hlsl 中 SurfaceDataToGbuffer、 BRDFDataToGbuffer 方法

輸出了下面的數據

見文件：UnityGBuffer.hlsl

half4 GBuffer0 : SV_Target0; //diffuse，表面顏色
half4 GBuffer1 : SV_Target1; //metallic/specular，高光
half4 GBuffer2 : SV_Target2; //encode normal，法線
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，剪裁空間z值，即深度
#endif

怎么傳入多個光源計算光照

逐類型光源

DeferredLights里RenderStencilLights，逐個調用直射光、點光源、射燈進行渲染

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);
}

繪制命令

• 直射光，遍歷光源，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);// 因為GBufferPass已經把光照數據都輸出到紋理，這里只需要繪制全屏的mesh，在shader中采樣之前輸出的GBuffer計算光照// 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

• 點光源、射燈也是遍歷光源，逐光源DrawCall，但是mesh不是全屏mesh，是代表光源形狀的memsh，代碼不贅述，今天不水文

渲染

入口StencilDeferred.shader

half4 DeferredShading(Varyings input) : SV_Target//省略部分代碼，這些代碼是：取GBuffer的值，拼出計算光照需要的數據//計算光照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);

渲染物體

不透明物體

輸出G-Buffer，渲染著色

半透物體

延遲渲染不支持半透，所以走Forward渲染，用額外一個 ScriptableRenderPass 渲染半透，見UniversalRenderer 的 m_RenderTransparentForwardPass

貼花

使用方法

• URP管線資源里創建Renderer，設置使用Deferred
• 相機里Renderer選上面創建的Renderer

延伸知識

SSAO

• Screen Space Ambient Occlusion -> 屏幕空間環境光遮蔽
• SSAO 通過使用深度緩沖、法線緩沖和隨機采樣核生成遮蔽效果，模擬場景中物體周圍環境光被遮擋的情況，從而增強畫面的真實感和層次感，讓場景看起來更有深度

源碼分析

結論

管線流程

• 生成GBuffer
  • shader中通過SV_TargetXXX指定輸出到某個綁定的緩沖區
  • 要求圖形接口支持一次輸出到多個目標
• 通過GBuffer渲染

管線

GBufferPass

輸出GBuffer

DeferredPass

用GBuffer著色

DrawObjectsPass

繪制物體，不透、半透

RenderGraph

渲染節點圖，可以通過編輯器定制渲染管線

DeferredLights

延遲渲染具體的邏輯

shader源碼分析

Lit.shader

GBuffer Pass，輸出GBuffer數據的Pass

LitGBufferPass.hlsl

輸出GBuffer的Pass源碼

UnityGBuffer.hlsl

真干活的著色代碼

像素著色器輸出
struct FragmentOutput
{half4 GBuffer0 : SV_Target0; //diffuse，表面顏色half4 GBuffer1 : SV_Target1; //metallic/specular，高光half4 GBuffer2 : SV_Target2; //encode normal，法線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，剪裁空間z值，即深度#endif#ifdef GBUFFER_OPTIONAL_SLOT_2half4 GBuffer5 : SV_Target5;#endif#ifdef GBUFFER_OPTIONAL_SLOT_3half4 GBuffer6 : SV_Target6;#endif
};輸出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進行著色

StencilDeferred.hlsl

頂點、像素方法

著色

half4 DeferredShading(Varyings input) : SV_Target...省略代碼，不水字數，感興趣的朋友看URP源碼即可