Accord.Imaging.Filters.QuadTransformationCalcs.MapSquareToQuad C# (CSharp) Method

        private static double[,] MapSquareToQuad( List<IntPoint> quad )
        {
            double[,] sq = new double[3, 3];
            double px, py;

            px = quad[0].X - quad[1].X + quad[2].X - quad[3].X;
            py = quad[0].Y - quad[1].Y + quad[2].Y - quad[3].Y;

            if ( ( px < TOLERANCE ) && ( px > -TOLERANCE ) &&
                 ( py < TOLERANCE ) && ( py > -TOLERANCE ) )
            {
                sq[0, 0] = quad[1].X - quad[0].X;
                sq[0, 1] = quad[2].X - quad[1].X;
                sq[0, 2] = quad[0].X;

                sq[1, 0] = quad[1].Y - quad[0].Y;
                sq[1, 1] = quad[2].Y - quad[1].Y;
                sq[1, 2] = quad[0].Y;

                sq[2, 0] = 0.0;
                sq[2, 1] = 0.0;
                sq[2, 2] = 1.0;
            }
            else
            {
                double dx1, dx2, dy1, dy2, del;

                dx1 = quad[1].X - quad[2].X;
                dx2 = quad[3].X - quad[2].X;
                dy1 = quad[1].Y - quad[2].Y;
                dy2 = quad[3].Y - quad[2].Y;

                del = Det2( dx1, dx2, dy1, dy2 );

                if ( del == 0.0 )
                    return null;

                sq[2, 0] = Det2( px, dx2, py, dy2 ) / del;
                sq[2, 1] = Det2( dx1, px, dy1, py ) / del;
                sq[2, 2] = 1.0;

                sq[0, 0] = quad[1].X - quad[0].X + sq[2, 0] * quad[1].X;
                sq[0, 1] = quad[3].X - quad[0].X + sq[2, 1] * quad[3].X;
                sq[0, 2] = quad[0].X;

                sq[1, 0] = quad[1].Y - quad[0].Y + sq[2, 0] * quad[1].Y;
                sq[1, 1] = quad[3].Y - quad[0].Y + sq[2, 1] * quad[3].Y;
                sq[1, 2] = quad[0].Y;
            }
            return sq;
        }