Convenience function that calls queue_draw_region on the region created from the given coordinates.
The region here is specified in widget coordinates. Widget coordinates are a bit odd; for historical reasons, they are defined as this->window coordinates for widgets that return true for get_has_window, and are relative to this ->allocation.x, this->allocation.y otherwise.
height may be 0, in this case this function does nothing. Negative values for
height are not allowed.
x coordinate of upper-left corner of rectangle to redraw
y coordinate of upper-left corner of rectangle to redraw
width of region to draw
height of region to draw