#pragma kernel CSMain

StructuredBuffer<float3> verts;
StructuredBuffer<uint3> indices;
StructuredBuffer<float2> uvs;
AppendStructuredBuffer<uint3> newIndices;
Texture2D alphaTex;
float cubeSize;
uint triCount;
//float3 localCamPos;

float3 trinormal(float3 v0, float3 v1, float3 v2)
{
    float3 p = v0-v1;
    float3 q = v1-v2;
    float3 norm = cross(p,q);
    return normalize(norm);
}

[numthreads(256,1,1)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    if (id.x >= triCount) return;

    uint3 ind = indices[id.x];
    float3 a = verts[ind.x];
    float3 b = verts[ind.y];
    float3 c = verts[ind.z];

    float ab = distance(a,b);
    float bc = distance(b,c);
    float ca = distance(c,a);

    //if (max(max(ab, bc), ca) > 0.9) return;

    float3 n = trinormal(a,b,c);

    float3 dir = normalize(a);// - localCamPos);
    //if (dot(-dir, n) > 0.2f)
    float elimit = 10;
    float dlimit = 900;
    //if (distance(localCamPos, a) < dlimit && distance(localCamPos, b) < dlimit && distance(localCamPos, c) < dlimit)
    if (length(a) < dlimit && length(b) < dlimit && length(c) < dlimit)
    {
        if (dot(-dir, n) > 0.0f)
        {

            float degenerateThreshold = 0.1f;
            bool deg = false;
            if (((bc  + ca) - ab) / ab < degenerateThreshold)
            {
                deg = true;
            }
            else if (((ab  + ca) - bc) / bc < degenerateThreshold)
            {
                deg = true;
            }
            else if (((ab  + bc) - ca) / ca < degenerateThreshold)
            {
                deg = true;
            }
            if (!deg)
            {
                float2 uv0 = uvs[ind.x] * cubeSize;
                float2 uv1 = uvs[ind.y] * cubeSize;
                float2 uv2 = uvs[ind.z] * cubeSize;
                float a0 = alphaTex.Load(int3(uv0.x, uv0.y, 0)).a;
                float a1 = alphaTex.Load(int3(uv1.x, uv1.y, 0)).a;
                float a2 = alphaTex.Load(int3(uv2.x, uv2.y, 0)).a;
                //float a = a0 + a1 + a2;
                float a = a0 * a1 * a2;
                if (a > 1.0f / 255)
                {
                    newIndices.Append(ind);
                }
            }
        }
    }
}