For positive m and n, each quadrangle or triangle is interpolated m-times and n-times in the respective direction. For negative m and n, the interpolation frequency is chosen so that there will be at least 3#3m3#3 and 3#3n3#3 points drawn; you can consider this as a special gridding function.
Note: interpolate 0,0, will automatically choose an optimal number of interpolated surface points.
Note: Currently color interpolation is always linear, even if corners2color
is set to a nonlinear scheme such as the geometric mean.