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CPU：
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TextureHandle RenderPostProcess(） {
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    var source = inputColor;
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    ....
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    source = DynamicExposurePass(renderGraph, hdCamera, source);
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    TextureHandle bloomTexture = BloomPass(renderGraph, hdCamera, source, m_LensFlareScreenSpace.bloomMip.value, out screenSpaceLensFlareBloomMipTexture);
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    TextureHandle logLutOutput = ColorGradingPass(renderGraph, hdCamera);
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    ....
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}

1
float SampleLuminance(float2 uv)
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{
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    // 这里获取了上一帧的平均亮度信息，单位是cd/m^2
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    // prevExposure 为亮度值的倒数
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    float prevExposure = ConvertEV100ToExposure(GetPreviousExposureEV100(), LensImperfectionExposureScale);
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    float3 color = SAMPLE_TEXTURE2D_X_LOD(_SourceTexture, s_linear_clamp_sampler, uv, 0.0).xyz;
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    // 根据上一帧的曝光还原原始辐射值，再转换为亮度输出
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    return Luminance(color / prevExposure);
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}
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float WeightSample(uint2 pixel, float2 sourceSize, float luminance) {
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    // 经典的Center-weighted，中心画面权重高
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    float screenDiagonal = 0.5f * (sourceSize.x + sourceSize.y);
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    const float2 kCenter = sourceSize * 0.5f;
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    return 1.0 - saturate(pow(length(kCenter - pixel) / screenDiagonal, 1.0));
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}
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// CPU端传入 这里unity是直接将中度灰定义为12.5
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float MeterCalibrationConstant = 12.5f;
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// 根据EV = log2 (LS / K) 这里 L 是亮度， S是100 ISO 以及中间灰作为矫正常数
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// 计算出矫正后的EV100值。
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float ComputeEV100FromAvgLuminance(float avgLuminance, float calibrationConstant)
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{
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    const float K = calibrationConstant;
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    return log2(avgLuminance * 100.0 / K);
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}
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[numthreads(8,8,1)]
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    void KPrePass(uint2 dispatchThreadId : SV_DispatchThreadID)
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{
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    。。。
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    float2 uv = GetScreenUV();
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    float luma = SampleLuminance(uv);
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    float weight = WeightSample(dispatchThreadId, PREPASS_TEX_SIZE.xx, luma);
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39

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    float logLuma = ComputeEV100FromAvgLuminance(max(luma, 1e-4), MeterCalibrationConstant);
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    //最终输出两数值，一个是像素的亮度转换而成的EV100值，一个是权重
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    _OutputTexture[posInputs.positionSS] = float2(logLuma, weight);
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}

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[numthreads(REDUCTION_GROUP_SIZE,REDUCTION_GROUP_SIZE,1)]
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void KReduction(uint2 groupId : SV_GroupID, uint2 groupThreadId : SV_GroupThreadID) {
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    // 每个线程处理2x2像素块
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    uint2 sampleIdx = (groupId.xy * REDUCTION_GROUP_SIZE + groupThreadId.xy) * 2u;
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    float2 p1 = _InputTexture[sampleIdx + uint2(0u, 0u)].xy;
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    float2 p2 = _InputTexture[sampleIdx + uint2(1u, 0u)].xy;
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    float2 p3 = _InputTexture[sampleIdx + uint2(0u, 1u)].xy;
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    float2 p4 = _InputTexture[sampleIdx + uint2(1u, 1u)].xy;
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    // 分解亮度和权重
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    float4 smp = float4(p1.x, p2.x, p3.x, p4.x);
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    float4 weights = float4(p1.y, p2.y, p3.y, p4.y);
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    // 乘积并存入groupSharedMemory
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    gs_luminances[threadIdx] = smp * weights;
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    gs_weights[threadIdx] = dot(weights, 1.0);
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    // 组内完成同步，确保同group内的线程都计算完成
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    GroupMemoryBarrierWithGroupSync();
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    //并行归约 （4像素->2像素->像素）
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    //合并组内全部像素的亮度和权重
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    for(uint s = REDUCTION_TOTAL_THREADS / 2u; s > 0u; s >>= 1u)
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    {
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        if(threadIdx < s)
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        {
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            gs_luminances[threadIdx] += gs_luminances[threadIdx + s];
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            gs_weights[threadIdx] += gs_weights[threadIdx + s];
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        }
30

31
        GroupMemoryBarrierWithGroupSync();
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    }
33

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    //组内第一个线程去操作，将所有结果输出
35
    if(threadIdx == 0u)
36
    {
37
        _OutputTexture[groupId.xy] = float2(avgLuminance, gs_weights[0]);
38
    }
39
}

1
{
2
    。。。
3

4
    if(threadIdx == 0u) {
5
        float avgLuminance = dot(gs_luminances[0], 0.25);
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7
        if (IsNaN(avgLuminance) || IsInf(avgLuminance))
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            avgLuminance = 1.0;
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        if (gs_weights[0] > 0.0)
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            avgLuminance /= (gs_weights[0] * 0.25);
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        //取上一帧的rt进行lerp，防止曝光突变。
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        float exposure = AdaptExposure(avgLuminance - ParamExposureCompensation);
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        exposure = clamp(exposure, ParamExposureLimitMin, ParamExposureLimitMax);
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        _OutputTexture[groupId.xy] = float2(ConvertEV100ToExposure(exposure, LensImperfectionExposureScale), exposure);
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    }
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}

1
//在下一帧中
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diffuseLighting *= GetCurrentExposureMultiplier();
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specularLighting *= GetCurrentExposureMultiplier();