If you call this during a paint (e.g. between gdk_window_begin_paint_region()
and gdk_window_end_paint() then GDK will mark the current clip region of the
window as being drawn. This is required when mixing GL rendering via
gdk_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.
If you call this during a paint (e.g. between gdk_window_begin_paint_region() and gdk_window_end_paint() then GDK will mark the current clip region of the window as being drawn. This is required when mixing GL rendering via gdk_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.