// NiloToon Character Fur - Geometry Shader
// Shell-based fur generation (based on lilToon implementation)

#ifndef NILOTOON_CHARACTER_FUR_GEOMETRY_INCLUDED
#define NILOTOON_CHARACTER_FUR_GEOMETRY_INCLUDED

//------------------------------------------------------------------------------------------------------------------------------
// Barycentric Interpolation Helper
//------------------------------------------------------------------------------------------------------------------------------
float  LerpBary(float  a, float  b, float  c, float3 factor) { return a * factor.x + b * factor.y + c * factor.z; }
float2 LerpBary(float2 a, float2 b, float2 c, float3 factor) { return a * factor.x + b * factor.y + c * factor.z; }
float3 LerpBary(float3 a, float3 b, float3 c, float3 factor) { return a * factor.x + b * factor.y + c * factor.z; }
float4 LerpBary(float4 a, float4 b, float4 c, float3 factor) { return a * factor.x + b * factor.y + c * factor.z; }

//------------------------------------------------------------------------------------------------------------------------------
// Append Single Fur Shell (Base + Tip)
//------------------------------------------------------------------------------------------------------------------------------
void AppendFurShell(
    inout TriangleStream<Varyings> outStream,
    V2G input[3],
    float3 furVectors[3],
    float3 factor,
    float layerProgress  // 0 = base, 1 = outer
)
{
    Varyings output = (Varyings)0;

    UNITY_TRANSFER_INSTANCE_ID(input[0], output);
    UNITY_TRANSFER_VERTEX_OUTPUT_STEREO(input[0], output);

    // Interpolate base attributes
    output.uv = LerpBary(input[0].uv, input[1].uv, input[2].uv, factor);
    output.normalWS = normalize(LerpBary(input[0].normalWS, input[1].normalWS, input[2].normalWS, factor));
    output.tangentWS = LerpBary(input[0].tangentWS, input[1].tangentWS, input[2].tangentWS, factor);
    output.tangentWS.xyz = normalize(output.tangentWS.xyz);
    output.fogFactor = LerpBary(input[0].fogFactor, input[1].fogFactor, input[2].fogFactor, factor);

    // Base position (furLayer = 0)
    float3 basePositionWS = LerpBary(input[0].positionWS, input[1].positionWS, input[2].positionWS, factor);

    output.positionWS = basePositionWS;
    output.positionCS = TransformWorldToHClip(basePositionWS);
    output.furLayer = 0;

    // Clipping canceller for near plane
    #if defined(UNITY_REVERSED_Z)
        if(output.positionCS.w < _ProjectionParams.y * 1.01 && output.positionCS.w > 0)
        {
            output.positionCS.z = output.positionCS.z * 0.0001 + output.positionCS.w * 0.999;
        }
    #else
        if(output.positionCS.w < _ProjectionParams.y * 1.01 && output.positionCS.w > 0)
        {
            output.positionCS.z = output.positionCS.z * 0.0001 - output.positionCS.w * 0.999;
        }
    #endif

    outStream.Append(output);

    // Tip position (furLayer = 1)
    float3 mixedFurVector = LerpBary(furVectors[0], furVectors[1], furVectors[2], factor);
    float3 tipPositionWS = basePositionWS + mixedFurVector;

    output.positionWS = tipPositionWS;
    output.positionCS = TransformWorldToHClip(tipPositionWS);
    output.furLayer = layerProgress;

    // Clipping canceller for near plane
    #if defined(UNITY_REVERSED_Z)
        if(output.positionCS.w < _ProjectionParams.y * 1.01 && output.positionCS.w > 0)
        {
            output.positionCS.z = output.positionCS.z * 0.0001 + output.positionCS.w * 0.999;
        }
    #else
        if(output.positionCS.w < _ProjectionParams.y * 1.01 && output.positionCS.w > 0)
        {
            output.positionCS.z = output.positionCS.z * 0.0001 - output.positionCS.w * 0.999;
        }
    #endif

    outStream.Append(output);
}

//------------------------------------------------------------------------------------------------------------------------------
// Geometry Shader - Shell Generation
// Based on lilToon's fur geometry shader
//------------------------------------------------------------------------------------------------------------------------------
[maxvertexcount(40)]
void geom_fur(triangle V2G input[3], inout TriangleStream<Varyings> outStream)
{
    UNITY_SETUP_INSTANCE_ID(input[0]);
    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input[0]);

    // Get fur vectors for each vertex
    float3 furVectors[3];
    furVectors[0] = input[0].furVector;
    furVectors[1] = input[1].furVector;
    furVectors[2] = input[2].furVector;

    // Apply procedural randomization using vertex IDs (from lilToon)
    uint3 n0 = (input[0].vertexID * 3 + input[1].vertexID * 1 + input[2].vertexID * 1) * uint3(1597334677U, 3812015801U, 2912667907U);
    uint3 n1 = (input[0].vertexID * 1 + input[1].vertexID * 3 + input[2].vertexID * 1) * uint3(1597334677U, 3812015801U, 2912667907U);
    uint3 n2 = (input[0].vertexID * 1 + input[1].vertexID * 1 + input[2].vertexID * 3) * uint3(1597334677U, 3812015801U, 2912667907U);

    float3 noise0 = normalize(float3(n0) * (2.0 / float(0xffffffffU)) - 1.0);
    float3 noise1 = normalize(float3(n1) * (2.0 / float(0xffffffffU)) - 1.0);
    float3 noise2 = normalize(float3(n2) * (2.0 / float(0xffffffffU)) - 1.0);

    furVectors[0] += noise0 * _FurVector.w * _FurRandomize;
    furVectors[1] += noise1 * _FurVector.w * _FurRandomize;
    furVectors[2] += noise2 * _FurVector.w * _FurRandomize;

    // Generate shells based on layer count
    // Layer pattern from lilToon: spreads shells across triangle vertices

    if (_FurLayerNum >= 1)
    {
        // 3 shells at each vertex
        AppendFurShell(outStream, input, furVectors, float3(1.0, 0.0, 0.0), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.0, 1.0, 0.0), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.0, 0.0, 1.0), 1.0);
    }

    if (_FurLayerNum >= 2)
    {
        // 3 more shells at edge midpoints
        AppendFurShell(outStream, input, furVectors, float3(0.0, 0.5, 0.5), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.5, 0.0, 0.5), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.5, 0.5, 0.0), 1.0);
    }

    if (_FurLayerNum >= 3)
    {
        // 6 more shells for dense fur
        AppendFurShell(outStream, input, furVectors, float3(1.0/6.0, 4.0/6.0, 1.0/6.0), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.0, 0.5, 0.5), 0.8);
        AppendFurShell(outStream, input, furVectors, float3(1.0/6.0, 1.0/6.0, 4.0/6.0), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.5, 0.0, 0.5), 0.8);
        AppendFurShell(outStream, input, furVectors, float3(4.0/6.0, 1.0/6.0, 1.0/6.0), 1.0);
        AppendFurShell(outStream, input, furVectors, float3(0.5, 0.5, 0.0), 0.8);
    }

    // Final shell at first vertex to close the strip
    AppendFurShell(outStream, input, furVectors, float3(1.0, 0.0, 0.0), 1.0);

    outStream.RestartStrip();
}

#endif // NILOTOON_CHARACTER_FUR_GEOMETRY_INCLUDED