Ipseity-Demo/Assets/_Content/Shaders/Include/Details.hlsl

#ifndef DETAILS_HLSL
#define DETAILS_HLSL

#include "Assets/_Content/Shaders/Include/Utilities.hlsl"

void GetDetailLOD
(
    float Depth,
    float DetailSizeA,
    float LODJitter,
    out float DetailSizeAA,
    out float DetailSizeAB,
    out float LODBlend
)
{
    const float lodRatio = 4;
    const float lodSize = DetailSizeA / lodRatio * 2;

    float dist = max(Depth, 1e-5);
    float lod = log(dist) / log(lodRatio) + LODJitter; // log2(dist);

    float lodFloor = floor(lod);
    float lodFrac = lod - lodFloor;

    LODBlend = lodFrac * lodFrac * (3 - 2 * lodFrac);

    DetailSizeAA = lodSize * pow(lodRatio, lodFloor);
    DetailSizeAB = lodSize * pow(lodRatio, lodFloor + 1);
}

float4 SampleBombedTexture
(
    UnityTexture2D Tex,
    float2 UV
)
{
    const float cellBlend = 4;
    
    float2 cell = floor(UV);
    float2 local = frac(UV);

    float4 result = 0;
    float weightSum = 0;

    [unroll]
    for (int y = 0; y < 2; y++)
    {
        [unroll]
        for (int x = 0; x < 2; x++)
        {
            float2 currentCell = cell + float2(x, y);

            float2 randomOffset = (Hash2D(currentCell) - .5) * .35;
            float randomAngle = Hash1From2D(currentCell) * TWO_PI;

            float2 center = float2(x, y) + randomOffset;
            float2 delta = local - center;

            float weight =
                pow(saturate(1 - abs(delta.x)), cellBlend) *
                pow(saturate(1 - abs(delta.y)), cellBlend);

            float2 sampleUV = UV + randomOffset;

            sampleUV = RotateUV
            (
                sampleUV,
                currentCell + .5,
                randomAngle
            );

            result += Tex.tex.Sample
            (
                Tex.samplerstate,
                sampleUV
            ) * weight;

            weightSum += weight;
        }
    }

    return result / max(weightSum, 1e-5);
}

struct ProjectionData
{
    float2 uv[7];
    float mask[7];
};

ProjectionData GetProjections
(
    float3 PositionOS,
    float3 NormalOS,
    float ProjectionBlend
)
{
    ProjectionData data;

    float3 normal = normalize(NormalOS);

    float3 projectionNormals[7] =
    {
        normalize(float3(1, 1, 1)),
        normalize(float3(-1, 1, 1)),
        normalize(float3(1, -1, 1)),
        normalize(float3(-1, -1, 1)),
        float3(1, 0, 0),
        float3(0, 1, 0),
        float3(0, 0, 1)
    };

    float sharpness = lerp(2, 32, saturate(ProjectionBlend));

    float maskSum = 0;

    [unroll]
    for (int i = 0; i < 7; i++)
    {
        float3 n = projectionNormals[i];

        float d = abs(dot(normal, n));

        data.mask[i] = pow(saturate(d), sharpness);
        maskSum += data.mask[i];

        float3 up = abs(n.y) < .999
            ? float3(0, 1, 0)
            : float3(1, 0, 0);

        float3 tangent = normalize(cross(up, n));
        float3 bitangent = normalize(cross(n, tangent));

        data.uv[i] = float2
        (
            dot(PositionOS, tangent),
            dot(PositionOS, bitangent)
        );
    }

    maskSum = max(maskSum, 1e-5);

    [unroll]
    for (int i = 0; i < 7; i++)
        data.mask[i] /= maskSum;

    return data;
}


float4 SampleProjectedDetailLOD
(
    UnityTexture2D DetailTex,
    float3 PositionOS,
    float3 NormalOS,
    float ProjectionBlend,
    float DetailSizeA,
    float Depth
)
{
    const float lodJitterStrength = .8;
    const float lodJitterSize = 1.5;

    float4 detail = 0;
    float totalMask = 0;

    ProjectionData projections = GetProjections
    (
        PositionOS,
        NormalOS,
        ProjectionBlend
    );

    [unroll]
    for (int i = 0; i < 7; i++)
    {
        float mask = projections.mask[i];

        float lodJitter = (Hash1From2D(floor(projections.uv[i] * lodJitterSize) + i * 17.13) - .5) * lodJitterStrength;

        float DetailSizeAA;
        float DetailSizeAB;
        float lodBlend;

        GetDetailLOD
        (
            Depth,
            DetailSizeA,
            lodJitter,
            DetailSizeAA,
            DetailSizeAB,
            lodBlend
        );

        float4 detailA = SampleBombedTexture
        (
            DetailTex,
            projections.uv[i] / DetailSizeAA
        );

        float4 detailB = SampleBombedTexture
        (
            DetailTex,
            projections.uv[i] / DetailSizeAB
        );

        detail += lerp(detailA, detailB, lodBlend) * mask;
        totalMask += mask;
    }

    return detail / max(totalMask, 1e-5);
}

#endif