A GtkWindow's allocation includes the titlebar, borders, and shadows; we only want to draw our custom alpha content over the child allocation of the GtkWindow. https://bugzilla.gnome.org/show_bug.cgi?id=756886
A GtkWindow's allocation includes the titlebar, borders, and shadows; we only want to draw our custom alpha content over the child allocation of the GtkWindow. https://bugzilla.gnome.org/show_bug.cgi?id=756886