Dynamic shadows artifacts

[Kalle_H]

I replaced Sobol with simple spiral sampling. With per pixel rotation matrix premultiplied to PCFUVMATRIX. It's not as good looking yet but it's saves 300 assembly lines. This makes me wonder is sobol random worth it. With unrolled loop it's easy to precalculate sampling points. Same optimization can be done to blocker search too. Need more testing.

    PCFUVMatrix = mul(float2x2(FilterRadius, 0, 0, FilterRadius), PCFUVMatrix);
    float RandAngle = 2.0f * PI * frac(7.1721f * Settings.SvPosition.x + 11.131f * Settings.SvPosition.y + View.StateFrameIndexMod8 * 0.125f);
    PCFUVMatrix = mul(float2x2(cos(RandAngle), -sin(RandAngle), sin(RandAngle), cos(RandAngle)), PCFUVMatrix);
    UNROLL
    for (int j = 0; j < PCSS_SAMPLES; j++)
    {
        float angle = j * PI * 4.71f;
        float2 PCFSample = float2(sin(angle), cos(angle)) * sqrt(float(j+1) * (1.0f / float(PCSS_SAMPLES)));
        //float2 PCFSample = RandToCircle(SobolIndex(SobolRandom, j << 3, PCSS_SAMPLE_BITS + 3));
        float2 SampleUVOffset = mul(PCFUVMatrix, PCFSample);
        float2 SampleUV = ShadowPosition + SampleUVOffset * Settings.ShadowTileOffsetAndSize.zw;

        float SampleDepthBias = max(dot(DepthBiasDotFactors, SampleUVOffset), 0);        

        #if FEATURE_GATHER4
            float4 SampleDepth = Settings.ShadowDepthTexture.Gather(Settings.ShadowDepthTextureSampler, SampleUV);
            VisibleLightAccumulation += dot(0.25, saturate(SampleDepth * Settings.TransitionScale + (Settings.TransitionScale * SampleDepthBias + ScaledAndBiasedDepth)));
        #else
            float SampleDepth = Texture2DSampleLevel(Settings.ShadowDepthTexture, Settings.ShadowDepthTextureSampler, SampleUV, 0).r;
            VisibleLightAccumulation += saturate(SampleDepth * Settings.TransitionScale + (Settings.TransitionScale * SampleDepthBias + ScaledAndBiasedDepth));
        #endif
    }

[Kalle_H]

Ditching Sobol reduced ShadowProjection time from 4.04ms to 2.60ms.

[Raildex_]

when will this be in an official build?

[DamirH]

Ditching Sobol reduced ShadowProjection time from 4.04ms to 2.60ms.

Are the visual improvements of Sobol worh the ~1.44ms?

[Kalle_H]

Are the visual improvements of Sobol worh the ~1.44ms?

Very unlikely. Spiral in some cases gives bit nicer self shadow. Both are quite good methods to do sampling. Sobol just isn't free.

[Kalle_H]

    // PCF loop.
    float VisibleLightAccumulation = 0;
    float ScaledAndBiasedDepth = -Settings.SceneDepth * Settings.TransitionScale + 1.f;

    float RandAngle = 2.0f * PI * frac(0.625 * Settings.SvPosition.x + 0.625 * Settings.SvPosition.y + View.StateFrameIndexMod8 * 0.625f);
    float radius = View.StateFrameIndexMod8 % 2 == 0 ? FilterRadius : -FilterRadius;
    PCFUVMatrix = mul(mul(float2x2(radius, 0, 0, radius), float2x2(cos(RandAngle), -sin(RandAngle), sin(RandAngle), cos(RandAngle))), PCFUVMatrix);
    UNROLL
    for (int j = 0; j < PCSS_SAMPLES; j++)
    {
        float angle = j * PI * 2.0f * 0.4171;
        float2 PCFSample = float2(sin(angle), cos(angle)) * sqrt(float(j) * (1.0f / float(PCSS_SAMPLES)));
        //float2 PCFSample = RandToCircle(SobolIndex(SobolRandom, j << 3, PCSS_SAMPLE_BITS + 3));
        float2 SampleUVOffset = mul(PCFUVMatrix, PCFSample);
        float2 SampleUV = ShadowPosition + SampleUVOffset * Settings.ShadowTileOffsetAndSize.zw;

        float SampleDepthBias = max(dot(DepthBiasDotFactors, SampleUVOffset), 0);        

        #if FEATURE_GATHER4
            float4 SampleDepth = Settings.ShadowDepthTexture.Gather(Settings.ShadowDepthTextureSampler, SampleUV);
            VisibleLightAccumulation += dot(0.25, saturate(SampleDepth * Settings.TransitionScale + (Settings.TransitionScale * SampleDepthBias + ScaledAndBiasedDepth)));
        #else
            float SampleDepth = Texture2DSampleLevel(Settings.ShadowDepthTexture, Settings.ShadowDepthTextureSampler, SampleUV, 0).r;
            VisibleLightAccumulation += saturate(SampleDepth * Settings.TransitionScale + (Settings.TransitionScale * SampleDepthBias + ScaledAndBiasedDepth));
        #endif
    }

    float Visibility = VisibleLightAccumulation * (1.0f / float(PCSS_SAMPLES));

This is the final form on spiral tapping. Every pixel is rotated peusdo randomly and samples are mirrored every other frame. Spiral offsets are precalculated and then rotated, scaled and mirrored with 2x2 matrix. So this method has no per sample overhead at all.

[ZacD]

Would love to see some comparisons.

[Kalle_H]

Would love to see some comparisons.

Here you go.

Sobol:

Spiral:

[Zeblote]

Looks nearly identical! No player will know how it was before...

[DamirH]

Indeed, if you didn't have the images side by side you wouldn't be able to tell the difference. Is the difference more obvious in other scenarios maybe?

[Kalle-H]

Finally back at office. Profiled scene before and after softshadow optimizations with GTX 1080Ti. Single directional light with two cascades ShadowProjection time went from 1.51ms to 0.47ms. Non soft shadows cost would be 0.18ms.

[BrUnO XaVIeR]

I just hope they implement when you PR...
Some times it's annoying the long wait when someone PR changes to renderer just to be said "no".

[NilsonLima]

I just hope they implement when you PR...
Some times it's annoying the long wait when someone PR changes to renderer just to be said "no".

Yes, this one as an example: https://forums.unrealengine.com/deve...-aa-sharpening

[DamirH]

Well I think this is a bigger and more advantageous change than TAA sharpening.

[ZacD]

The PR for TAA sharpening kinda conflicts with Epic's perspective and intentions with TAA, Plus Epic was working on Temporal AA upsampling and dynamic resolution.