public function set_line_style($style1, $style2 = '', $preserve_defaults = false) {
        //Check if we got 2 or three parameters
        if (is_bool($style2)) {
            $preserve_defaults = $style2;
            $style2 = '';
        }

        //Actually set the new styles
        if (!$preserve_defaults) {
            $this->line_style1 = $style1;
            $this->line_style2 = $style2;
        } else {
            $this->line_style1 .= $style1;
            $this->line_style2 .= $style2;
        }
    }