The main eventloop of the GUI library
val run :
Widget.widget -> unit
This function takes a widget, which is the "root" of the GUI interface.
It creates the "top-level" Gctx, and then it goes into an infinite loopx.
The loop simply repeats these steps forever:
- clear the graphics window
- ask the widget to repaint itself
- wait for a user input event
- forward the event to the widget's event handler