#pragma kernel March

#include "MarchingTable.hlsl"

struct Triangle
{
    float3 a;
    float3 b;
    float3 c;
};

int reference;
int sizeX;
int sizeY;
int sizeZ;

StructuredBuffer<float4> vertAndDensity;
AppendStructuredBuffer<Triangle> triangles;

int coordToIndex(int x, int y, int z);
float3 lerpVerts(float4 a, float4 b);

[numthreads(8, 8, 8)]
void March(uint3 id : SV_DispatchThreadID)
{
    if (id.x > sizeX || id.y > sizeY > id.z > sizeZ)
        return;

    float4 vert[8] =
    {
        vertAndDensity[coordToIndex(id.x, id.y, id.z)],
        vertAndDensity[coordToIndex(id.x + 1, id.y, id.z)],
        vertAndDensity[coordToIndex(id.x + 1, id.y, id.z + 1)],
        vertAndDensity[coordToIndex(id.x, id.y, id.z + 1)],
        vertAndDensity[coordToIndex(id.x, id.y + 1, id.z)],
        vertAndDensity[coordToIndex(id.x + 1, id.y + 1, id.z)],
        vertAndDensity[coordToIndex(id.x + 1, id.y + 1, id.z + 1)],
        vertAndDensity[coordToIndex(id.x, id.y + 1, id.z + 1)]
    };

    int edgeState = 0;
    for (int i = 0; i < 8; ++i)
        if (vert[i].w < reference)
            edgeState |= 1 << i;

    Triangle a;
    a.a = vert[0];
    a.b = id;
    a.c = float3(sizeX, sizeY, vert[0].w);
    triangles.Append(a);

    int tri[16] = edgeToTri[edgeState];
    for (int i = 0; tri[i] != -1; i += 3)
    {
        Triangle t;
        // t.a = lerpVerts(vert[edgeToTwoVerts[tri[i]][0]], vert[edgeToTwoVerts[tri[i]][1]]);
        // t.b = lerpVerts(vert[edgeToTwoVerts[tri[i + 1]][0]], vert[edgeToTwoVerts[tri[i + 1]][1]]);
        // t.c = lerpVerts(vert[edgeToTwoVerts[tri[i + 2]][0]], vert[edgeToTwoVerts[tri[i + 2]][1]]);
        t.a = float3(1, 1, 1);
        t.b = float3(1, 1, 1);
        t.c = float3(1, 1, 1);
        triangles.Append(t);
    }
}

int coordToIndex(int x, int y, int z)
{
    return x + y * sizeX + z * sizeX * sizeY;
}

float3 lerpVerts(float4 a, float4 b)
{
    return a.xyz + (b.xyz - a.xyz) * (a.w - b.w);
}