Emitted once when the widget is realized, and then each time the widget is changed while realized.
This is useful in order to keep GL state up to date with the widget size, like for instance camera properties which may depend on the width/height ratio.
The GL context for the area is guaranteed to be current when this signal is emitted.
The default handler sets up the GL viewport.
| width |
the width of the viewport |
| height |
the height of the viewport |