$size = 25;
        $x = (xvals zeroes $size+1,$size+1) / $size;
        $y = (yvals zeroes $size+1,$size+1) / $size;
        $z = 0.5 + 0.5 * (sin($x*6.3) * sin($y*6.3)) ** 3;   # Bumps

        $r = $x; $g = $y; $b = $z;
        line3d [$x,$y,$z], [$r,$g,$b];  # Draw several colored lines