TwistyPuzzleLib

///////////////////////////////////////////////////////////////////////////////////////////////////

  private void computeNormalVector(float[] v0, float[] v1, float[] v2, float[] output)

    {

    float x1 = v0[0];

    float y1 = v0[1];

    float z1 = v0[2];

    float x2 = v1[0];

    float y2 = v1[1];

    float z2 = v1[2];

    float x3 = v2[0];

    float y3 = v2[1];

    float z3 = v2[2];

    float v1x = x2-x1;

    float v1y = y2-y1;

    float v1z = z2-z1;

    float v2x = x3-x1;

    float v2y = y3-y1;

    float v2z = z3-z1;

    output[0] = v1y*v2z - v2y*v1z;

    output[1] = v1z*v2x - v2z*v1x;

    output[2] = v1x*v2y - v2x*v1y;

    double len = output[0]*output[0] + output[1]*output[1] + output[2]*output[2];

    len = Math.sqrt(len);

    output[0] /= len;

    output[1] /= len;

    output[2] /= len;

    }

///////////////////////////////////////////////////////////////////////////////////////////////////

// return surface defined by the face, i.e. a 4-tuple [ (nx,ny,nz), d ]

  public void getFaceSurface(int face, float[] output)

    {

    int[] loopI = mFacesMultigon ? getMultigonIndices()[face][0] : getVertIndices()[face];

    float[] v0 = mVertices[loopI[0]];

    float[] v1 = mVertices[loopI[1]];

    float[] v2 = mVertices[loopI[2]];

    computeNormalVector(v0,v1,v2,output);

    output[3] = output[0]*v0[0] + output[1]*v0[1] + output[2]*v0[2];

    }