For optimisation purposes, compositing window managers may
like to not draw obscured regions of surfaces, or turn off blending
during for these regions. With RGB windows with no transparency,
this is just the shape of the window, but with ARGB32 windows, the
compositor does not know what regions of the window are transparent
or not.
This function only works for toplevel surfaces.
GTK will update this property automatically if the @surface background
is opaque, as we know where the opaque regions are. If your surface
background is not opaque, please update this property in your
#GtkWidgetClass.css_changed() handler.
Marks a region of the GdkSurface as opaque.
For optimisation purposes, compositing window managers may like to not draw obscured regions of surfaces, or turn off blending during for these regions. With RGB windows with no transparency, this is just the shape of the window, but with ARGB32 windows, the compositor does not know what regions of the window are transparent or not.
This function only works for toplevel surfaces.
GTK will update this property automatically if the @surface background is opaque, as we know where the opaque regions are. If your surface background is not opaque, please update this property in your #GtkWidgetClass.css_changed() handler.