Unity Raytracing

// com.unity.render-pipelines.high-definition@12.1.6\Runtime\RenderPipeline\HDRenderPipeline.cs
protected override void Render(ScriptableRenderContext renderContext, List<Camera> cameras)
{
    // culling loop
    static bool TryCull(Camera camera, HDCamera hdCamera, ScriptableRenderContext renderContext, SkyManager skyManager, ScriptableCullingParameters cullingParams, HDRenderPipelineAsset hdrp, ref HDCullingResults cullingResults)
    {
        // 开启 ray tracing 后会对Culling参数进行重写
        static void OverrideCullingForRayTracing(HDCamera hdCamera, Camera camera, ref ScriptableCullingParameters cullingParams)
    }

    // add render request
    // add HDProbeRenderRequests

    // execute render request
    ExecuteRenderRequest(renderRequest, renderContext, cmd, AOVRequestData.defaultAOVRequestDataNonAlloc);
    {
        // 为 ray tracing 构建加速结构
        BuildRayTracingAccelerationStructure(hdCamera);
        // 为 ray tracing 执行culling TODO
        CullForRayTracing(cmd, hdCamera);

        //
        PrepareLightsForGPU(cmd, hdCamera, cullingResults, hdProbeCullingResults, localVolumetricFog, m_CurrentDebugDisplaySettings, aovRequest);

        // 更新 constant buffers
        UpdateGlobalConstantBuffers(hdCamera, cmd);

        // 构建 light data
        BuildRayTracingLightData(cmd, hdCamera, m_CurrentDebugDisplaySettings);

        // 配置Keywords
        ConfigureKeywords(enableBakeShadowMask, hdCamera, cmd);

        // 执行 RenderGraph
        ExecuteWithRenderGraph(renderRequest, aovRequest, aovBuffers, aovCustomPassBuffers, renderContext, cmd);
        {
            // com.unity.render-pipelines.high-definition@12.1.6\Runtime\RenderPipeline\HDRenderPipeline.RenderGraph.cs
            RecordRenderGraph()
            {
                // prepass
                RenderPrepass(m_RenderGraph, colorBuffer, lightingBuffers.sssBuffer, vtFeedbackBuffer, cullingResults, customPassCullingResults, hdCamera, aovRequest, aovBuffers);

                // ao
                RenderAmbientOcclusion(m_RenderGraph, hdCamera, prepassOutput.depthPyramidTexture, prepassOutput.resolvedNormalBuffer, prepassOutput.resolvedMotionVectorsBuffer, historyValidationTexture, hdCamera.depthBufferMipChainInfo, m_ShaderVariablesRayTracingCB, rayCountTexture);

                // shadows
                RenderShadows(m_RenderGraph, hdCamera, cullingResults, ref shadowResult);

                // render ssr
                RenderSSR(m_RenderGraph, hdCamera, ref prepassOutput, clearCoatMask, rayCountTexture, m_SkyManager.GetSkyReflection(hdCamera), transparent: false);

                // ssgi
                RenderScreenSpaceIndirectDiffuse(hdCamera, prepassOutput, rayCountTexture, historyValidationTexture, gpuLightListOutput.lightList);

                // screen space shadows
                RenderScreenSpaceShadows(m_RenderGraph, hdCamera, prepassOutput, prepassOutput.depthBuffer, prepassOutput.normalBuffer, prepassOutput.motionVectorsBuffer, historyValidationTexture, rayCountTexture);

                // volumetric lighting
                VolumetricLightingPass(m_RenderGraph, hdCamera, prepassOutput.depthPyramidTexture, volumetricDensityBuffer, maxZMask, gpuLightListOutput.bigTileLightList, shadowResult);

                // deferred lighting
                RenderDeferredLighting(m_RenderGraph, hdCamera, colorBuffer, prepassOutput.depthBuffer, prepassOutput.depthPyramidTexture, lightingBuffers, prepassOutput.gbuffer, shadowResult, gpuLightListOutput);

                // forward opaque
                RenderForwardOpaque(m_RenderGraph, hdCamera, colorBuffer, lightingBuffers, gpuLightListOutput, prepassOutput.depthBuffer, vtFeedbackBuffer, shadowResult, prepassOutput.dbuffer, cullingResults);

                // sss
                RenderSubsurfaceScattering(m_RenderGraph, hdCamera, colorBuffer, historyValidationTexture, ref lightingBuffers, ref prepassOutput);

                // sky
                RenderSky(m_RenderGraph, hdCamera, colorBuffer, volumetricLighting, prepassOutput.depthBuffer, msaa ? prepassOutput.depthAsColor : prepassOutput.depthPyramidTexture);

                // volumetric clouds
                RenderVolumetricClouds(m_RenderGraph, hdCamera, colorBuffer, prepassOutput.depthPyramidTexture, prepassOutput.motionVectorsBuffer, volumetricLighting, maxZMask);

                // transparency
                RenderTransparency(m_RenderGraph, hdCamera, colorBuffer, prepassOutput.resolvedNormalBuffer, vtFeedbackBuffer, currentColorPyramid, volumetricLighting, rayCountTexture, m_SkyManager.GetSkyReflection(hdCamera), gpuLightListOutput, ref prepassOutput, shadowResult, cullingResults, customPassCullingResults, aovRequest, aovCustomPassBuffers);

                // distortion
                RenderDistortion(m_RenderGraph, hdCamera, colorBuffer, prepassOutput.resolvedDepthBuffer, currentColorPyramid, distortionBuffer, distortionRendererList);
            }
        }
    }
}

// com.unity.render-pipelines.high-definition@12.1.6\Runtime\RenderPipeline\Raytracing\HDRaytracingManager.cs
internal void BuildRayTracingAccelerationStructure(HDCamera hdCamera)
{
    // 获取场景中所有的灯光 fetch all the lights in the scene
    // 1. 判断灯光是否开启ray tracing shadow，并且是否开启了屏幕空间阴影
    // m_RayTracedShadowsRequired |= (hdLight.useRayTracedShadows && screenSpaceShadowsSupported);
    // m_RayTracedContactShadowsRequired |= (hdLight.useContactShadow.@override && hdLight.rayTraceContactShadow);
    // 2. 判断灯光是否有位置变化。TODO

    // Tips: ReflectionProbe 也被当作RayTracing 的光源

    // 判断下列各种效果的设置中是否开启了RayTracing
    // AmbientOcclusion       开启了 rayTracing，并且camera开启了ScreenSpaceAO
    // ScreenSpaceReflection  自身开启了或开了半透明物体的反射，并且开启了 rayTracing，并且camera开启了 ssr
    // GlobalIllumination     自身开启了，并且开启了 rayTracing, 并且 camera 开启了SSGI
    // RecursiveRendering     自身开启了
    // SubSurfaceScattering   开启了 rayTracing，并且camera开启了 SubsurfaceScattering
    // PathTracing            自身开启了

    // 以上任何一个效果开启，就表示需要进行 Ray Tracing了

    // 遍历场景中所有区域光源, 为其生成Acceleration Structure
    // 遍历场景中所有LODGroup，根据摄像机距离获得当前使用的Lod，为对应的MeshRenderer 生成Acceleration Structure
    // 遍历场景中所有 Renderer, 若还没有为其生成 Acceleration Structure 则为其生成
    // RayTracingAccelerationStructure m_CurrentRAS; // 该变量用于存储 Acceleration Structure
    // AddInstanceToRAS() 函数用于执行具体生成Acceleration Structure 的逻辑 TODO

    // 构建GPU 端的加速结构数据
    m_CurrentRAS.Build(hdCamera.mainViewConstants.worldSpaceCameraPos);
}