public void mark_paint_from_clip (Context cr)
If you call this during a paint (e.
g. between begin_paint_region and end_paint then GDK will mark the current clip region of the window as being drawn. This is required when mixing GL rendering via cairo_draw_from_gl and cairo rendering, as otherwise GDK has no way of knowing when something paints over the GL-drawn regions.
This is typically called automatically by GTK+ and you don't need to care about this.