queue_draw_area
Description:
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.
width or height may be 0, in this case this function does nothing. Negative values for width and 
        height are not allowed.
Parameters:
| this | a Widget | 
| x | x coordinate of upper-left corner of rectangle to redraw | 
| y | y coordinate of upper-left corner of rectangle to redraw | 
| width | width of region to draw | 
| height | height of region to draw |