GTK2 DrawingArea question

[Marcus Comstedt (ACROSS) (Hail Ilpalazzo!) @ Pike (-) developers forum]

You probably need to draw the line _after_ the window is shown.
Windows in X normally don't have backingstore, so you need to redraw
their contents whenever a previously invisible region becomes
visible.  I imagine there is some signal you should connect to your
draw function to have it called whenever needed.