case GRAD_MIDHOR:
                $steps = ceil(abs($yb - $yt) / 2);
                $delta = $yb >= $yt ? 1 : -1;
                $this->GetColArray($from_color, $to_color, $steps, $colors, $this->numcolors);
                for ($y = $yt, $i = 0; $i < $steps; ++$i) {