Painting refers to how widgets present themselves graphically (using: colors, transparencies, and so on), as well as cropping.
Graphics are always translated so that the origin 0,0 is positioned at the top, left corner of the widget. The graphics crop
(visible area) is set to the widget's size. Alpha and transparent pixels blend with the pixels already drawn.
The system draws widgets in property order with the first widget at the bottom, and the last widget on the top. Effective
z-order is reverse of property order.