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

#ifndef DETAILS_HLSL
#define DETAILS_HLSL

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

/*
    DETAILS - MEDIUM LOD VERSION

    Goal:
    Keep the large performance gain from the optimized triplanar version,
    while restoring the old distance-based "detail upscale" behavior with smoother transitions.

    Main changes compared to the original version:
    - Replaced the 7-direction projection system with standard 3-axis triplanar mapping.
    - Removed the expensive 2x2 texture bombing by default.
    - Restored manual distance-based detail scaling.
    - Reduced the LOD ratio from 4.0 to 2.0 to make transitions less visible.
    - Added stable spatial jitter to avoid the whole screen switching LOD at the same distance.
    - Kept the public function signature SampleProjectedDetailLOD(...)
      so existing Shader Graph nodes do not break.

    Original cost per detail layer:
        7 projections * 2 LOD levels * 4 bombing samples = 56 texture samples.

    This version:
        3 projections * 2 LOD levels = 6 texture samples.

    If EnkiBillal samples both DetailTexA and DetailTexB:
        6 * 2 = 12 texture samples.
    Still much cheaper than the original 112 samples.
*/

#define DETAILS_USE_LIGHT_BOMBING 0

/*
    Distance-based detail LOD.

    This restores the old idea:
    - close camera  -> smaller, sharper details;
    - far camera    -> larger, more readable details.

    Difference from the original:
    lodRatio is reduced from 4.0 to 2.0.
    This makes each transition less visible.
*/
void GetDetailLOD
(
    float Depth,
    float DetailSizeA,
    float LODJitter,
    out float DetailSizeAA,
    out float DetailSizeAB,
    out float LODBlend
)
{
    const float lodRatio = 2.0;
    const float baseScale = 1.0;

    float dist = max(Depth, 1e-5);

    float lod = log(dist) / log(lodRatio) + LODJitter;

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

    /*
        Quintic smootherstep.
        This is smoother than classic smoothstep and helps hide the LOD blend.
    */
    float t = saturate(lodFrac);
    LODBlend = t * t * t * (t * (t * 6.0 - 15.0) + 10.0);

    DetailSizeAA = DetailSizeA * baseScale * pow(lodRatio, lodFloor);
    DetailSizeAB = DetailSizeA * baseScale * pow(lodRatio, lodFloor + 1.0);
}

/*
    Default fast texture sample.
    Uses normal GPU mipmapping.
*/
float4 SampleDetailTextureFast
(
    UnityTexture2D Tex,
    float2 UV
)
{
    return Tex.tex.Sample(Tex.samplerstate, UV);
}

/*
    Optional lightweight texture bombing.

    Disabled by default.

    Compared to the original SampleBombedTexture:
    - original: 4 texture samples + 4 rotations + 4 weights;
    - this version: 1 texture sample with stable per-cell offset and rotation.

    Warning:
    This can create visible cell transitions because neighboring cells are not blended.
*/
float4 SampleDetailTextureLightBombed
(
    UnityTexture2D Tex,
    float2 UV
)
{
    float2 cell = floor(UV);

    float2 randomOffset = (Hash2D(cell) - 0.5) * 0.35;
    float randomAngle = Hash1From2D(cell) * TWO_PI;

    float2 sampleUV = UV + randomOffset;

    sampleUV = RotateUV
    (
        sampleUV,
        cell + 0.5,
        randomAngle
    );

    return Tex.tex.Sample(Tex.samplerstate, sampleUV);
}

/*
    Compatibility function.

    Existing code can still call SampleBombedTexture.
    In Medium mode, it routes to:
    - direct sampling by default;
    - optional one-sample light bombing if enabled.
*/
float4 SampleBombedTexture
(
    UnityTexture2D Tex,
    float2 UV
)
{
#if DETAILS_USE_LIGHT_BOMBING
    return SampleDetailTextureLightBombed(Tex, UV);
#else
    return SampleDetailTextureFast(Tex, UV);
#endif
}

/*
    Triplanar weights.

    ProjectionBlend keeps the same artistic role:
    - low value  -> softer blend between axes;
    - high value -> sharper projection selection.

    The original shader used up to 32.
    This version uses 16 by default to reduce overly sharp transitions.
*/
float3 GetTriplanarWeights
(
    float3 NormalOS,
    float ProjectionBlend
)
{
    float3 n = abs(normalize(NormalOS));

    float sharpness = lerp(2.0, 16.0, saturate(ProjectionBlend));

    float3 w = pow(saturate(n), sharpness);
    float sumW = max(w.x + w.y + w.z, 1e-5);

    return w / sumW;
}

/*
    Compatibility structure.

    Kept because old code or Shader Graph nodes may still expect this type.
    The optimized SampleProjectedDetailLOD below does not use the old 7-projection path.
*/
struct ProjectionData
{
    float2 uv[7];
    float mask[7];
};

/*
    Compatibility fallback.

    Fills only the first three entries using standard triplanar projections.
    Entries 3..6 are disabled.
*/
ProjectionData GetProjections
(
    float3 PositionOS,
    float3 NormalOS,
    float ProjectionBlend
)
{
    ProjectionData data;

    float3 w = GetTriplanarWeights(NormalOS, ProjectionBlend);

    /*
        Standard triplanar UVs:
        - X projection samples the YZ plane.
        - Y projection samples the XZ plane.
        - Z projection samples the XY plane.
    */
    data.uv[0] = PositionOS.zy;
    data.uv[1] = PositionOS.xz;
    data.uv[2] = PositionOS.xy;

    data.mask[0] = w.x;
    data.mask[1] = w.y;
    data.mask[2] = w.z;

    [unroll]
    for (int i = 3; i < 7; i++)
    {
        data.uv[i] = 0.0;
        data.mask[i] = 0.0;
    }

    return data;
}

/*
    Samples one triplanar axis with two distance-based detail sizes.

    This restores the "detail upscale with distance" effect without returning
    to the original 7-projection and 2x2 bombing cost.
*/
float4 SampleDetailAxisLOD
(
    UnityTexture2D DetailTex,
    float2 BaseUV,
    float DetailSizeAA,
    float DetailSizeAB,
    float LODBlend
)
{
    float4 detailA = SampleBombedTexture
    (
        DetailTex,
        BaseUV / max(DetailSizeAA, 1e-5)
    );

    float4 detailB = SampleBombedTexture
    (
        DetailTex,
        BaseUV / max(DetailSizeAB, 1e-5)
    );

    return lerp(detailA, detailB, LODBlend);
}

/*
    Optimized projected detail sampling with smoother distance LOD.

    Cost:
        3 triplanar axes * 2 LOD samples = 6 texture samples.

    The old version also added per-projection jitter.
    This version uses one stable object-space jitter for the whole sample.
    That keeps the transition less synchronized without reintroducing too much cost.
*/
float4 SampleProjectedDetailLOD
(
    UnityTexture2D DetailTex,
    float3 PositionOS,
    float3 NormalOS,
    float ProjectionBlend,
    float DetailSizeA,
    float Depth
)
{
    float detailSize = max(DetailSizeA, 1e-5);

    float3 weights = GetTriplanarWeights(NormalOS, ProjectionBlend);

    /*
        Stable spatial jitter.

        This prevents the whole screen from switching detail scale at exactly
        the same camera distance.

        Keep this value low.
        Too much jitter makes the transition patchy.
    */
    float lodJitter = (Hash1From2D(floor(PositionOS.xz * 0.75)) - 0.5) * 0.35;

    float DetailSizeAA;
    float DetailSizeAB;
    float lodBlend;

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

    /*
        Triplanar base UVs in object space.
    */
    float2 uvX = PositionOS.zy;
    float2 uvY = PositionOS.xz;
    float2 uvZ = PositionOS.xy;

    float4 sampleX = SampleDetailAxisLOD
    (
        DetailTex,
        uvX,
        DetailSizeAA,
        DetailSizeAB,
        lodBlend
    );

    float4 sampleY = SampleDetailAxisLOD
    (
        DetailTex,
        uvY,
        DetailSizeAA,
        DetailSizeAB,
        lodBlend
    );

    float4 sampleZ = SampleDetailAxisLOD
    (
        DetailTex,
        uvZ,
        DetailSizeAA,
        DetailSizeAB,
        lodBlend
    );

    return sampleX * weights.x
         + sampleY * weights.y
         + sampleZ * weights.z;
}

#endif