Ipseity-Demo/Assets/_Content/Shaders/EnkiBilal/Include/Stripes.hlsl

#ifndef STRIPES_INCLUDED
#define STRIPES_INCLUDED

/*
    STRIPES - MEDIUM VERSION

    Goal:
    Reduce the GPU cost of the procedural stripe pattern.

    Changes from the original version:
    - Removed the dynamic loop over the full stripe count.
      Original behavior: evaluate every stripe from 0 to Count.
      New behavior: evaluate only 6 nearby stripe candidates.
    - Clamped Count to 32 to prevent expensive high-count cases.
    - Kept Van der Corput distribution to preserve stable pseudo-random variation.
    - Kept the two distortion paths to preserve part of the organic look.
    - Visual result is an approximation of the original, but much cheaper.
*/

float VanDerCorput(uint index)
{
    return (float)reversebits(index) * 2.3283064365386963e-10;
}

int WrapIndex(int x, int count)
{
    int r = x % count;
    return r < 0 ? r + count : r;
}

float EvalStripeCandidate(
    uint index,
    uint stripeCount,
    float wrappedXA,
    float wrappedXB,
    float stripDistanceY,
    float density,
    float thicknessInput
)
{
    float vdc = VanDerCorput(index);

    /*
        Same progressive reveal logic as the original shader.

        Original:
        saturate(density * stripeCount - vdc * stripeCount)

        Equivalent simplified form:
        saturate((density - vdc) * stripeCount)
    */
    float localProgress = saturate((density - vdc) * stripeCount);

    if (localProgress <= 0.0001)
        return 0.0;

    /*
        Keep the original two distortion paths.
        Each stripe chooses one path based on its pseudo-random value.
    */
    float wrappedX = vdc >= 0.5 ? wrappedXB : wrappedXA;

    /*
        Keep the original thickness variation.
        This prevents the stripes from looking too uniform.
    */
    float thickness = vdc < 0.3 ? 1.0 : (vdc < 0.6 ? 1.8 : 2.6);
    thickness *= saturate(thicknessInput);

    float stripeCenterX = ((float)index + 0.5) / (float)stripeCount;

    float stripDistanceX = abs(wrappedX - stripeCenterX);
    stripDistanceX = min(stripDistanceX, 1.0 - stripDistanceX);

    float stepX = (1.0 / (float)stripeCount) * localProgress * thickness * 0.5;
    float stepY = localProgress * 0.5 - 0.01;

    /*
        Soft edges are kept from the original shader.
        If more performance is needed, these smoothstep calls can be replaced
        with step calls, but the result will look harsher.
    */
    float widthMask = 1.0 - smoothstep(stepX - 0.01, stepX, stripDistanceX);
    float heightMask = 1.0 - smoothstep(stepY - 0.05, stepY, stripDistanceY);

    return widthMask * heightMask;
}

void Stripes_float(
    float2 UV,
    float Density,
    float Count,
    float Thickness,
    float Offset,
    float DistortionAmplitude,
    float DistortionFrequency,
    out float Stripes
)
{
    float density = saturate(Density);
    float offset = frac(Offset);

    /*
        Intentional clamp.
        Above 32 stripes, the cost increases while the visual gain is usually limited,
        especially on distant objects or in a strongly stylized render.
    */
    uint stripeCount = max((uint)round(Count), 1u);
    stripeCount = min(stripeCount, 32u);

    float distortionAmplitude = DistortionAmplitude * 0.1;

    float2 uv = UV;
    uv.x = frac(uv.x + offset);

    /*
        The two distortion paths are computed once and reused for all nearby candidates.
    */
    float wrappedXA = frac(
        uv.x + cos((uv.y + offset) * sin(uv.x) * DistortionFrequency + offset * 7.8)
        * distortionAmplitude
    );

    float wrappedXB = frac(
        uv.x + sin((uv.y + offset) * cos(uv.x) * DistortionFrequency + offset * 5.3)
        * distortionAmplitude
    );

    float stripDistanceY = abs(saturate(uv.y) - 0.5);

    int sc = (int)stripeCount;

    /*
        Find the nearest stripe indices for both distortion paths.
        Original shader tested every stripe.
        Medium version tests only base - 1, base, base + 1 for A and B.
    */
    int baseA = (int)floor(wrappedXA * sc);
    int baseB = (int)floor(wrappedXB * sc);

    float stripeMax = 0.0;

    [unroll]
    for (int k = -1; k <= 1; k++)
    {
        uint idxA = (uint)WrapIndex(baseA + k, sc);
        uint idxB = (uint)WrapIndex(baseB + k, sc);

        stripeMax = max(
            stripeMax,
            EvalStripeCandidate(
                idxA,
                stripeCount,
                wrappedXA,
                wrappedXB,
                stripDistanceY,
                density,
                Thickness
            )
        );

        stripeMax = max(
            stripeMax,
            EvalStripeCandidate(
                idxB,
                stripeCount,
                wrappedXA,
                wrappedXB,
                stripDistanceY,
                density,
                Thickness
            )
        );
    }

    Stripes = stripeMax;
}

#endif