ffx_fsr2_accumulate.h

// This file is part of the FidelityFX SDK.
//
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#ifndef FFX_FSR2_ACCUMULATE_H
#define FFX_FSR2_ACCUMULATE_H

FfxFloat32 GetPxHrVelocity(FfxFloat32x2 fMotionVector)
{
    return length(fMotionVector * DisplaySize());
}
#if FFX_HALF
FFX_MIN16_F GetPxHrVelocity(FFX_MIN16_F2 fMotionVector)
{
    return length(fMotionVector * FFX_MIN16_F2(DisplaySize()));
}
#endif

void Accumulate(const AccumulationPassCommonParams params, FFX_PARAMETER_INOUT FfxFloat32x3 fHistoryColor, FfxFloat32x3 fAccumulation, FFX_PARAMETER_IN FfxFloat32x4 fUpsampledColorAndWeight)
{
    // Aviod invalid values when accumulation and upsampled weight is 0
    fAccumulation = ffxMax(FSR2_EPSILON.xxx, fAccumulation + fUpsampledColorAndWeight.www);

#if FFX_FSR2_OPTION_HDR_COLOR_INPUT
    //YCoCg -> RGB -> Tonemap -> YCoCg (Use RGB tonemapper to avoid color desaturation)
    fUpsampledColorAndWeight.xyz = RGBToYCoCg(Tonemap(YCoCgToRGB(fUpsampledColorAndWeight.xyz)));
    fHistoryColor = RGBToYCoCg(Tonemap(YCoCgToRGB(fHistoryColor)));
#endif

    const FfxFloat32x3 fAlpha = fUpsampledColorAndWeight.www / fAccumulation;
    fHistoryColor = ffxLerp(fHistoryColor, fUpsampledColorAndWeight.xyz, fAlpha);

    fHistoryColor = YCoCgToRGB(fHistoryColor);

#if FFX_FSR2_OPTION_HDR_COLOR_INPUT
    fHistoryColor = InverseTonemap(fHistoryColor);
#endif
}

void RectifyHistory(
    const AccumulationPassCommonParams params,
    RectificationBox clippingBox,
    FFX_PARAMETER_INOUT FfxFloat32x3 fHistoryColor,
    FFX_PARAMETER_INOUT FfxFloat32x3 fAccumulation,
    FfxFloat32 fLockContributionThisFrame,
    FfxFloat32 fTemporalReactiveFactor,
    FfxFloat32 fLumaInstabilityFactor)
{
    FfxFloat32 fScaleFactorInfluence = ffxMin(20.0f, ffxPow(FfxFloat32(1.0f / length(DownscaleFactor().x * DownscaleFactor().y)), 3.0f));

    const FfxFloat32 fVecolityFactor = ffxSaturate(params.fHrVelocity / 20.0f);
    const FfxFloat32 fBoxScaleT = ffxMax(params.fDepthClipFactor, ffxMax(params.fAccumulationMask, fVecolityFactor));
    FfxFloat32 fBoxScale = ffxLerp(fScaleFactorInfluence, 1.0f, fBoxScaleT);

    FfxFloat32x3 fScaledBoxVec = clippingBox.boxVec * fBoxScale;
    FfxFloat32x3 boxMin = clippingBox.boxCenter - fScaledBoxVec;
    FfxFloat32x3 boxMax = clippingBox.boxCenter + fScaledBoxVec;
    FfxFloat32x3 boxCenter = clippingBox.boxCenter;
    FfxFloat32 boxVecSize = length(clippingBox.boxVec);

    boxMin = ffxMax(clippingBox.aabbMin, boxMin);
    boxMax = ffxMin(clippingBox.aabbMax, boxMax);

    if (any(FFX_GREATER_THAN(boxMin, fHistoryColor)) || any(FFX_GREATER_THAN(fHistoryColor, boxMax))) {

        const FfxFloat32x3 fClampedHistoryColor = clamp(fHistoryColor, boxMin, boxMax);

        FfxFloat32x3 fHistoryContribution = ffxMax(fLumaInstabilityFactor, fLockContributionThisFrame).xxx;
        
        const FfxFloat32 fReactiveFactor = params.fDilatedReactiveFactor;
        const FfxFloat32 fReactiveContribution = 1.0f - ffxPow(fReactiveFactor, 1.0f / 2.0f);
        fHistoryContribution *= fReactiveContribution;

        // Scale history color using rectification info, also using accumulation mask to avoid potential invalid color protection
        fHistoryColor = ffxLerp(fClampedHistoryColor, fHistoryColor, ffxSaturate(fHistoryContribution));

        // Scale accumulation using rectification info
        const FfxFloat32x3 fAccumulationMin = ffxMin(fAccumulation, FFX_BROADCAST_FLOAT32X3(0.1f));
        fAccumulation = ffxLerp(fAccumulationMin, fAccumulation, ffxSaturate(fHistoryContribution));
    }
}

void WriteUpscaledOutput(FfxInt32x2 iPxHrPos, FfxFloat32x3 fUpscaledColor)
{
    StoreUpscaledOutput(iPxHrPos, fUpscaledColor);
}

void FinalizeLockStatus(const AccumulationPassCommonParams params, FfxFloat32x2 fLockStatus, FfxFloat32 fUpsampledWeight)
{
    // we expect similar motion for next frame
    // kill lock if that location is outside screen, avoid locks to be clamped to screen borders
    FfxFloat32x2 fEstimatedUvNextFrame = params.fHrUv - params.fMotionVector;
    if (IsUvInside(fEstimatedUvNextFrame) == false) {
        KillLock(fLockStatus);
    }
    else {
        // Decrease lock lifetime
        const FfxFloat32 fLifetimeDecreaseLanczosMax = FfxFloat32(JitterSequenceLength()) * FfxFloat32(fAverageLanczosWeightPerFrame);
        const FfxFloat32 fLifetimeDecrease = FfxFloat32(fUpsampledWeight / fLifetimeDecreaseLanczosMax);
        fLockStatus[LOCK_LIFETIME_REMAINING] = ffxMax(FfxFloat32(0), fLockStatus[LOCK_LIFETIME_REMAINING] - fLifetimeDecrease);
    }

    StoreLockStatus(params.iPxHrPos, fLockStatus);
}


FfxFloat32x3 ComputeBaseAccumulationWeight(const AccumulationPassCommonParams params, FfxFloat32 fThisFrameReactiveFactor, FfxBoolean bInMotionLastFrame, FfxFloat32 fUpsampledWeight, LockState lockState)
{
    // Always assume max accumulation was reached
    FfxFloat32 fBaseAccumulation = fMaxAccumulationLanczosWeight * FfxFloat32(params.bIsExistingSample) * (1.0f - fThisFrameReactiveFactor) * (1.0f - params.fDepthClipFactor);

    fBaseAccumulation = ffxMin(fBaseAccumulation, ffxLerp(fBaseAccumulation, fUpsampledWeight * 10.0f, ffxMax(FfxFloat32(bInMotionLastFrame), ffxSaturate(params.fHrVelocity * FfxFloat32(10)))));

    fBaseAccumulation = ffxMin(fBaseAccumulation, ffxLerp(fBaseAccumulation, fUpsampledWeight, ffxSaturate(params.fHrVelocity / FfxFloat32(20))));

    return fBaseAccumulation.xxx;
}

FfxFloat32 ComputeLumaInstabilityFactor(const AccumulationPassCommonParams params, RectificationBox clippingBox, FfxFloat32 fThisFrameReactiveFactor, FfxFloat32 fLuminanceDiff)
{
    const FfxFloat32 fUnormThreshold = 1.0f / 255.0f;
    const FfxInt32 N_MINUS_1 = 0;
    const FfxInt32 N_MINUS_2 = 1;
    const FfxInt32 N_MINUS_3 = 2;
    const FfxInt32 N_MINUS_4 = 3;

    FfxFloat32 fCurrentFrameLuma = clippingBox.boxCenter.x;

#if FFX_FSR2_OPTION_HDR_COLOR_INPUT
    fCurrentFrameLuma = fCurrentFrameLuma / (1.0f + ffxMax(0.0f, fCurrentFrameLuma));
#endif

    fCurrentFrameLuma = round(fCurrentFrameLuma * 255.0f) / 255.0f;

    const FfxBoolean bSampleLumaHistory = (ffxMax(ffxMax(params.fDepthClipFactor, params.fAccumulationMask), fLuminanceDiff) < 0.1f) && (params.bIsNewSample == false);
    FfxFloat32x4 fCurrentFrameLumaHistory = bSampleLumaHistory ? SampleLumaHistory(params.fReprojectedHrUv) : FFX_BROADCAST_FLOAT32X4(0.0f);

    FfxFloat32 fLumaInstability = 0.0f;
    FfxFloat32 fDiffs0 = (fCurrentFrameLuma - fCurrentFrameLumaHistory[N_MINUS_1]);

    FfxFloat32 fMin = abs(fDiffs0);

    if (fMin >= fUnormThreshold)
    {
        for (int i = N_MINUS_2; i <= N_MINUS_4; i++) {
            FfxFloat32 fDiffs1 = (fCurrentFrameLuma - fCurrentFrameLumaHistory[i]);

            if (sign(fDiffs0) == sign(fDiffs1)) {
                
                // Scale difference to protect historically similar values
                const FfxFloat32 fMinBias = 1.0f;
                fMin = ffxMin(fMin, abs(fDiffs1) * fMinBias);
            }
        }

        const FfxFloat32 fBoxSize = clippingBox.boxVec.x;
        const FfxFloat32 fBoxSizeFactor = ffxPow(ffxSaturate(fBoxSize / 0.1f), 6.0f);

        fLumaInstability = FfxFloat32(fMin != abs(fDiffs0)) * fBoxSizeFactor;
        fLumaInstability = FfxFloat32(fLumaInstability > fUnormThreshold);

        fLumaInstability *= 1.0f - ffxMax(params.fAccumulationMask, ffxPow(fThisFrameReactiveFactor, 1.0f / 6.0f));
    }

    //shift history
    fCurrentFrameLumaHistory[N_MINUS_4] = fCurrentFrameLumaHistory[N_MINUS_3];
    fCurrentFrameLumaHistory[N_MINUS_3] = fCurrentFrameLumaHistory[N_MINUS_2];
    fCurrentFrameLumaHistory[N_MINUS_2] = fCurrentFrameLumaHistory[N_MINUS_1];
    fCurrentFrameLumaHistory[N_MINUS_1] = fCurrentFrameLuma;

    StoreLumaHistory(params.iPxHrPos, fCurrentFrameLumaHistory);

    return fLumaInstability * FfxFloat32(fCurrentFrameLumaHistory[N_MINUS_4] != 0);
}

FfxFloat32 ComputeTemporalReactiveFactor(const AccumulationPassCommonParams params, FfxFloat32 fTemporalReactiveFactor)
{
    FfxFloat32 fNewFactor = ffxMin(0.99f, fTemporalReactiveFactor);

    fNewFactor = ffxMax(fNewFactor, ffxLerp(fNewFactor, 0.4f, ffxSaturate(params.fHrVelocity)));

    fNewFactor = ffxMax(fNewFactor * fNewFactor, ffxMax(params.fDepthClipFactor * 0.1f, params.fDilatedReactiveFactor));

    // Force reactive factor for new samples
    fNewFactor = params.bIsNewSample ? 1.0f : fNewFactor;

    if (ffxSaturate(params.fHrVelocity * 10.0f) >= 1.0f) {
        fNewFactor = ffxMax(FSR2_EPSILON, fNewFactor) * -1.0f;
    }
    
    return fNewFactor;
}

AccumulationPassCommonParams InitParams(FfxInt32x2 iPxHrPos)
{
    AccumulationPassCommonParams params;

    params.iPxHrPos = iPxHrPos;
    const FfxFloat32x2 fHrUv = (iPxHrPos + 0.5f) / DisplaySize();
    params.fHrUv = fHrUv;
    
    const FfxFloat32x2 fLrUvJittered = fHrUv + Jitter() / RenderSize();
    params.fLrUv_HwSampler = ClampUv(fLrUvJittered, RenderSize(), MaxRenderSize());

    params.fMotionVector = GetMotionVector(iPxHrPos, fHrUv);
    params.fHrVelocity = GetPxHrVelocity(params.fMotionVector);

    ComputeReprojectedUVs(params, params.fReprojectedHrUv, params.bIsExistingSample);

    params.fDepthClipFactor = ffxSaturate(SampleDepthClip(params.fLrUv_HwSampler));
    
    const FfxFloat32x2 fDilatedReactiveMasks = SampleDilatedReactiveMasks(params.fLrUv_HwSampler);
    params.fDilatedReactiveFactor = fDilatedReactiveMasks.x;
    params.fAccumulationMask = fDilatedReactiveMasks.y;
    params.bIsResetFrame = (0 == FrameIndex());

    params.bIsNewSample = (params.bIsExistingSample == false || params.bIsResetFrame);

    return params;
}

void Accumulate(FfxInt32x2 iPxHrPos)
{
    const AccumulationPassCommonParams params = InitParams(iPxHrPos);

    FfxFloat32x3 fHistoryColor = FfxFloat32x3(0, 0, 0);
    FfxFloat32x2 fLockStatus;
    InitializeNewLockSample(fLockStatus);

    FfxFloat32 fTemporalReactiveFactor = 0.0f;
    FfxBoolean bInMotionLastFrame = FFX_FALSE;
    LockState lockState = { FFX_FALSE , FFX_FALSE };
    if (params.bIsExistingSample && !params.bIsResetFrame) {
        ReprojectHistoryColor(params, fHistoryColor, fTemporalReactiveFactor, bInMotionLastFrame);
        lockState = ReprojectHistoryLockStatus(params, fLockStatus);
    }

    FfxFloat32 fThisFrameReactiveFactor = ffxMax(params.fDilatedReactiveFactor, fTemporalReactiveFactor);

    FfxFloat32 fLuminanceDiff = 0.0f;
    FfxFloat32 fLockContributionThisFrame = 0.0f;
    UpdateLockStatus(params, fThisFrameReactiveFactor, lockState, fLockStatus, fLockContributionThisFrame, fLuminanceDiff);

    // Load upsampled input color
    RectificationBox clippingBox;
    FfxFloat32x4 fUpsampledColorAndWeight = ComputeUpsampledColorAndWeight(params, clippingBox, fThisFrameReactiveFactor);
    
    const FfxFloat32 fLumaInstabilityFactor = ComputeLumaInstabilityFactor(params, clippingBox, fThisFrameReactiveFactor, fLuminanceDiff);


    FfxFloat32x3 fAccumulation = ComputeBaseAccumulationWeight(params, fThisFrameReactiveFactor, bInMotionLastFrame, fUpsampledColorAndWeight.w, lockState);

    if (params.bIsNewSample) {
        fHistoryColor = YCoCgToRGB(fUpsampledColorAndWeight.xyz);
    }
    else {
        RectifyHistory(params, clippingBox, fHistoryColor, fAccumulation, fLockContributionThisFrame, fThisFrameReactiveFactor, fLumaInstabilityFactor);

        Accumulate(params, fHistoryColor, fAccumulation, fUpsampledColorAndWeight);
    }

    fHistoryColor = UnprepareRgb(fHistoryColor, Exposure());

    FinalizeLockStatus(params, fLockStatus, fUpsampledColorAndWeight.w);

    // Get new temporal reactive factor
    fTemporalReactiveFactor = ComputeTemporalReactiveFactor(params, fThisFrameReactiveFactor);

    StoreInternalColorAndWeight(iPxHrPos, FfxFloat32x4(fHistoryColor, fTemporalReactiveFactor));

    // Output final color when RCAS is disabled
#if FFX_FSR2_OPTION_APPLY_SHARPENING == 0
    WriteUpscaledOutput(iPxHrPos, fHistoryColor);
#endif
    StoreNewLocks(iPxHrPos, 0);
}

#endif // FFX_FSR2_ACCUMULATE_H