The chief advantage of drawing your own GTK arrow rather than using the GtkArrow widget is that you can shape it, using the width and height parameters. The fill parameter refers to the color of the arrow, with false giving it the same color as the area it is drawn onto. All positions and sizes are absolute in terms of the underlying drawable.

gtk::draw_arrow($style, $gdkwindow, GTK_STATE_NORMAL, GTK_SHADOW_OUT, GTK_ARROW_RIGHT, false, $x, $y, $width, $height);