Unity3d Compute Shader Simplex3d

//DNNKEEPER (17.09.2013)
//Special thanks to Johannes Gotlén for shader example.

// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel Simplex3d

#define F3 1.0/3.0
#define G3 1.0/6.0

//Start position of this chunk
float4 _StartPos;

//Noise parameters
float _Str;
float _NoiseA;
float _NoiseB;
float _NoiseC;

// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture
RWTexture3D<float> Result;

float simplex3d(float3 ws) {
//thanks to Stefan Gustavson, Linköping University, Sweden
    float xin = ws.x;
    float yin = ws.y;
    float zin = ws.z;
    const float3 grad3[12] = {
        float3(1,1,0),float3(-1,1,0),float3(1,-1,0),float3(-1,-1,0),
        float3(1,0,1),float3(-1,0,1),float3(1,0,-1),float3(-1,0,-1),
        float3(0,1,1),float3(0,-1,1),float3(0,1,-1),float3(0,-1,-1)
    };
    const int perm[512] = {151,160,137,91,90,15,
      131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
      190,6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
      88,237,149,56,87,174,20,125,136,171,168,68,175,74,165,71,134,139,48,27,166,
      77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
      102,143,54,65,25,63,161,1,216,80,73,209,76,132,187,208,89,18,169,200,196,
      135,130,116,188,159,86,164,100,109,198,173,186,3,64,52,217,226,250,124,123,
      5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
      223,183,170,213,119,248,152,2,44,154,163,70,221,153,101,155,167,43,172,9,
      129,22,39,253,19,98,108,110,79,113,224,232,178,185,112,104,218,246,97,228,
      251,34,242,193,238,210,144,12,191,179,162,241,81,51,145,235,249,14,239,107,
      49,192,214,31,181,199,106,157,184,84,204,176,115,121,50,45,127,4,150,254,
      138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180,151,160,137,91,90,15,
      131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
      190,6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
      88,237,149,56,87,174,20,125,136,171,168,68,175,74,165,71,134,139,48,27,166,
      77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
      102,143,54,65,25,63,161,1,216,80,73,209,76,132,187,208,89,18,169,200,196,
      135,130,116,188,159,86,164,100,109,198,173,186,3,64,52,217,226,250,124,123,
      5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
      223,183,170,213,119,248,152,2,44,154,163,70,221,153,101,155,167,43,172,9,
      129,22,39,253,19,98,108,110,79,113,224,232,178,185,112,104,218,246,97,228,
      251,34,242,193,238,210,144,12,191,179,162,241,81,51,145,235,249,14,239,107,
      49,192,214,31,181,199,106,157,184,84,204,176,115,121,50,45,127,4,150,254,
      138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
    };

    const int permMod12[512] = {
        7,4,5,7,6,3,11,1,9,11,0,5,2,5,7,9,8,0,7,6,9,10,8,3,1,0,9,10,11,10,6,4,7,0,6,3,
        0,2,5,2,10,0,3,11,9,11,11,8,9,9,9,4,9,5,8,3,6,8,5,4,3,0,8,7,2,9,11,2,7,0,3,10,5
        ,2,2,3,11,3,1,2,0,7,1,2,4,9,8,5,7,10,5,4,4,6,11,6,5,1,3,5,1,0,8,1,5,4,0,7,4,5,
        6,1,8,4,3,10,8,8,3,2,8,4,1,6,5,6,3,4,4,1,10,10,4,3,5,10,2,3,10,6,3,10,1,8,3,2,
        11,11,11,4,10,5,2,9,4,6,7,3,2,9,11,8,8,2,8,10,7,10,5,9,5,11,11,7,4,9,9,10,3,1,7,
        2,0,2,7,5,8,4,10,5,4,8,2,6,1,0,11,10,2,1,10,6,0,0,11,11,6,1,9,3,1,7,9,2,11,11,1,
        0,10,7,1,7,10,1,4,0,0,8,7,1,2,9,7,4,6,2,6,8,1,9,6,6,7,5,0,0,3,9,8,3,6,6,11,1,
        0,0,7,4,5,7,6,3,11,1,9,11,0,5,2,5,7,9,8,0,7,6,9,10,8,3,1,0,9,10,11,10,6,4,7,0,6,3,
        0,2,5,2,10,0,3,11,9,11,11,8,9,9,9,4,9,5,8,3,6,8,5,4,3,0,8,7,2,9,11,2,7,0,3,10,5,
        2,2,3,11,3,1,2,0,7,1,2,4,9,8,5,7,10,5,4,4,6,11,6,5,1,3,5,1,0,8,1,5,4,0,7,4,5,
        6,1,8,4,3,10,8,8,3,2,8,4,1,6,5,6,3,4,4,1,10,10,4,3,5,10,2,3,10,6,3,10,1,8,3,2,
        11,11,11,4,10,5,2,9,4,6,7,3,2,9,11,8,8,2,8,10,7,10,5,9,5,11,11,7,4,9,9,10,3,1,7,
        2,0,2,7,5,8,4,10,5,4,8,2,6,1,0,11,10,2,1,10,6,0,0,11,11,6,1,9,3,1,7,9,2,11,11,1,
        0,10,7,1,7,10,1,4,0,0,8,7,1,2,9,7,4,6,2,6,8,1,9,6,6,7,5,0,0,3,9,8,3,6,6,11,1,0,0
    };
                        float n0,n1,n2,n3; // Noise contributions from the four corners
    // Skew the input space to determine which simplex cell we're in
    float s = (xin+yin+zin)*F3; // Very nice and simple skew factor for 3D
    int i = floor(xin+s);
    int j = floor(yin+s);
    int k = floor(zin+s);
    float t = (i+j+k)*G3;
    float X0 = i-t; // Unskew the cell origin back to (x,y,z) space
    float Y0 = j-t;
    float Z0 = k-t;
    float x0 = xin-X0; // The x,y,z distances from the cell origin
    float y0 = yin-Y0;
    float z0 = zin-Z0;
    // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
    // Determine which simplex we are in.
    int i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
    int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords
    if(x0>=y0) {
      if(y0>=z0)
        { i1=1; j1=0; k1=0; i2=1; j2=1; k2=0; } // X Y Z order
        else if(x0>=z0) { i1=1; j1=0; k1=0; i2=1; j2=0; k2=1; } // X Z Y order
        else { i1=0; j1=0; k1=1; i2=1; j2=0; k2=1; } // Z X Y order
      }
    else { // x0<y0
      if(y0<z0) { i1=0; j1=0; k1=1; i2=0; j2=1; k2=1; } // Z Y X order
      else if(x0<z0) { i1=0; j1=1; k1=0; i2=0; j2=1; k2=1; } // Y Z X order
      else { i1=0; j1=1; k1=0; i2=1; j2=1; k2=0; } // Y X Z order
    }
    // A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z),
    // a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z), and
    // a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z), where
    // c = 1/6.
    float x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
    float y1 = y0 - j1 + G3;
    float z1 = z0 - k1 + G3;
    float x2 = x0 - i2 + 2.0*G3; // Offsets for third corner in (x,y,z) coords
    float y2 = y0 - j2 + 2.0*G3;
    float z2 = z0 - k2 + 2.0*G3;
    float x3 = x0 - 1.0 + 3.0*G3; // Offsets for last corner in (x,y,z) coords
    float y3 = y0 - 1.0 + 3.0*G3;
    float z3 = z0 - 1.0 + 3.0*G3;
    // Work out the hashed gradient indices of the four simplex corners
    int ii = i & 255;
    int jj = j & 255;
    int kk = k & 255;
    int gi0 = permMod12[ii+perm[jj+perm[kk]]];
    int gi1 = permMod12[ii+i1+perm[jj+j1+perm[kk+k1]]];
    int gi2 = permMod12[ii+i2+perm[jj+j2+perm[kk+k2]]];
    int gi3 = permMod12[ii+1+perm[jj+1+perm[kk+1]]];
    // Calculate the contribution from the four corners
    float t0 = 0.6 - x0*x0 - y0*y0 - z0*z0;
    if(t0<0){
        n0 = 0.0;
    }
    else {
      t0 *= t0;
      n0 = t0 * t0 * dot(grad3[gi0], float3(x0, y0, z0));
    }
    float t1 = 0.6 - x1*x1 - y1*y1 - z1*z1;
    if(t1<0){
     n1 = 0.0;
    } else {
      t1 *= t1;
      n1 = t1 * t1 * dot(grad3[gi1],float3(x1, y1, z1));
    }
    float t2 = 0.6 - x2*x2 - y2*y2 - z2*z2;
    if(t2<0){
        n2 = 0.0;
    } else {
      t2 *= t2;
      n2 = t2 * t2 * dot(grad3[gi2],float3(x2,y2,z2));
    }
    float t3 = 0.6 - x3*x3 - y3*y3 - z3*z3;
    if(t3<0){
     n3 = 0.0;
    } else {
      t3 *= t3;
      n3 = t3 * t3 * dot(grad3[gi3],float3( x3,y3,z3));
    }


    // Add contributions from each corner to get the final noise value.
    // The result is scaled to stay just inside [-1,1]
    return 32.0*(n0 + n1 + n2 + n3);
    //return 0;
}

//Calculate some noise in 32x32x32 volume (I found it works only 1x32x32 per one call for my GPU. Just call it 32 times from the script)
[numthreads(1,32,32)]
void Simplex3d (uint3 id : SV_DispatchThreadID)
{
        //Get real position in worldspace for this thread
            int x,y,z;
            x=id.x; y=id.y; z=id.z;

        //Apply offset for this chunk in worldspace
            x += _StartPos.x; y += _StartPos.y; z+=_StartPos.z;

        //Scale coordinates 20-times just to get proper noise
        x *=20; y *=20; z *=20;

            float3 ws = float3(x,y,z);

        //Get some noise here
            float noiseA =  simplex3d(float3(x, y, z)* _NoiseA*_Str)*2 - 0.5;
            float noiseB =  simplex3d(float3(x, y, z)* _NoiseB*_Str);
            float noiseC =  simplex3d(float3(x, y, z)* _NoiseC*_Str);

        //Output it to resulting volume
        Result[float3(id.x,id.y,id.z)] = clamp(saturate(density+noiseA+ noiseB + noiseC / 5),-1.0,1.0);

}