问题
When using GTK+2, we can use gtk_widget_shape_combine_mask and gtk_widget_input_shape_combine_mask to make a custom nonrectangular gtklayout.
For example, in the case of a GTKLayout with a circle hole, we can see the widget bottom of the custom gtklayout through the circle hole.
With GTK+3, the gtk_widget_shape_combine_mask is replaced with gtk_widget_shape_combine_region. When using gtk_widget_shape_combine_region and gtk_widget_input_shape_combine_region, we can't see the widget bottom of the custom gtklayout through the circle hole.
Why? How can we implement the nonrectangular GTKLayout in GTK+3?
来源：https://stackoverflow.com/questions/40178161/how-to-make-a-custom-nonrectangular-gtklayout-in-gtk3