UPR Forward渲染路径下的Screen Space Reflection实践¶

public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
{
    ref var cameraData = ref renderingData.cameraData;
    if (cameraData.renderer.cameraColorTargetHandle == null)
        return;
    var cmd = CommandBufferPool.Get();
    using (new ProfilingScope(cmd, profilingSampler))
    {
        context.ExecuteCommandBuffer(cmd);
        cmd.Clear();
        cmd.SetRenderTarget(_forwardGBufferTarget, cameraData.renderer.cameraDepthTargetHandle);
        context.ExecuteCommandBuffer(cmd);
        var drawSettings = CreateDrawingSettings(_shaderTagIdList,
            ref renderingData, renderingData.cameraData.defaultOpaqueSortFlags);
        drawSettings.overrideShader = _gBufferShader;
        context.DrawRenderers(renderingData.cullResults, ref drawSettings,
            ref _filteringSettings);
    }
    context.ExecuteCommandBuffer(cmd);
    CommandBufferPool.Release(cmd);
}

Pass
{
    Name "ForwardGBuffer"
    Tags
    {
        "LightMode" = "ForwardGBuffer"
    }

    ZWrite Off
    Cull Off
    ZTest Equal

    // To be able to tag stencil with disableSSR information for forward
    Stencil
    {
        WriteMask [_StencilWriteMaskGBuffer]
        Ref [_StencilRefGBuffer]
        Comp Always
        Pass Replace
    }

    HLSLPROGRAM
    #pragma target 4.5
    #pragma shader_feature_local_fragment _SPECULAR_SETUP

    //--------------------------------------
    // GPU Instancing
    #pragma multi_compile_instancing
    #pragma instancing_options renderinglayer
    #include_with_pragmas "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DOTS.hlsl"

    #include "LitForwardGBufferPass.hlsl"

    #pragma vertex LitPassVertex
    #pragma fragment LitForwardGBufferPassFragment

    half4 LitForwardGBufferPassFragment(Varyings input) : SV_Target
    {
        UNITY_SETUP_INSTANCE_ID(input);
        UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);

        SurfaceData surfaceData = (SurfaceData)0;
        InitializeStandardLitSurfaceData(input.uv, surfaceData);
        BRDFData brdfData = (BRDFData)0;

        // NOTE: can modify "surfaceData"...
        InitializeBRDFData(surfaceData, brdfData);
        return surfaceData.smoothness;
    }
    ENDHLSL
}

bool doesntReceiveSSR = false;
uint stencilValue = GetStencilValue(LOAD_TEXTURE2D_X(_StencilTexture, positionSS.xy));
doesntReceiveSSR = (stencilValue & STENCIL_USAGE_IS_SSR) == 0;
if (doesntReceiveSSR)
{
    return half4(0, 0, 0, 0);
}

var depthTexture = GetCameraDepthTexture(); // _CameraDepthAttachment 或 _CameraDepthTexture 根据你的Stencil写入在哪
cmd.SetGlobalTexture("_StencilTexture", depthTexture, RenderTextureSubElement.Stencil);

StructuredBuffer<int2>  _DepthPyramidMipLevelOffsets;
TEXTURE2D_X(_DepthPyramid);

float SampleDepthPyramid(float2 uv, int mipLevel)
{
    int2 mipCoord  = (int2)uv.xy >> mipLevel;
    int2 mipOffset = _DepthPyramidMipLevelOffsets[mipLevel];
    return  LOAD_TEXTURE2D_X(_DepthPyramid, mipOffset + mipCoord).r;
}

// 采样SSR（屏幕空间反射）或Planar Reflection（平面反射）贴图
float4 SSR = Texture2DSample(ScreenSpaceReflectionsTexture, ScreenSpaceReflectionsSampler, BufferUV);

// 直接把SSR的RGB写入Color，表示当前像素的反射初值来自SSR
Color.rgb = SSR.rgb;

// SSR.a 通常是“屏幕空间反射的遮罩”或“可见性”，1表示完全有SSR，0表示没有SSR。
// 这里用 1-SSR.a 作为后续IBL混合的权重（即SSR越强，IBL越弱）
Color.a = 1 - SSR.a;

// 计算Specular Occlusion
float AO = GBuffer.GBufferAO * AmbientOcclusion;
float RoughnessSq = GBuffer.Roughness * GBuffer.Roughness;
float SpecularOcclusion = GetSpecularOcclusion(NoV, RoughnessSq, AO);

// SSR的权重再乘以Specular Occlusion，进一步抑制被遮蔽区域的反射
Color.a *= SpecularOcclusion;

// 用SSR的剩余权重（Color.a）去采样IBL（反射球/天光），并加到Color.rgb上
Color.rgb += PreExposure * GatherRadiance(
    Color.a, WorldPosition, R, GBuffer.Roughness, BentNormal, IndirectIrradiance,
    GBuffer.ShadingModelID, NumCulledReflectionCaptures, DataStartIndex
);

// 最后乘上环境BRDF预积分项，URP自带的是曲线拟合的EnvBRDFApproximate版本，HDRP的是采样PreIntegratedFGD。
Color.rgb *= EnvBRDF(GBuffer.SpecularColor, GBuffer.Roughness, NoV);

half3 indirectDiffuse = bakedGI;
half3 indirectSpecular = GlossyEnvironmentReflection(reflectVector, positionWS, brdfData.perceptualRoughness,
        1.0h, normalizedScreenSpaceUV);

#if _SCREEN_SPACE_REFLECTION // multi_compile_fragment
    half4 reflection = SampleScreenSpaceReflection(normalizedScreenSpaceUV);
    indirectSpecular += reflection.rgb; // accumulate since color is already premultiplied by opacity for SSR
#endif

/* Then calculate env brdf */

public static Matrix4x4 CalculateNonJitterViewProjMatrix(ref CameraData cameraData)
{
    float4x4 viewMat = cameraData.GetViewMatrix();
    float4x4 projMat = cameraData.GetGPUProjectionMatrixNoJitter();
    return math.mul(projMat, viewMat);
}