The code I used below is a little bit different to the testcairo
examples. In testcairo, cairo context is created within the callback
of expose-event, while in my code, I want to initialize the context
and set it to a global variable, so that I don't need to pass it
But running the program, there were errors told me that The slot
GTK:WINDOW is unbound in the drawing-area object.
After an hour of debugging, I finally found that if I place
gdk:cairo-create after gtk:widget-show-all, then it works.
So I'm wondering if it's caused by the initialization sequences in clg.
And do you have any suggestions for using cairo efficiently in clg
(like being a graphics editor within a scrolled-window)