Gets a visual to use for creating windows with an alpha channel.
The windowing system on which GTK+ is running
may not support this capability, in which case NULL will
be returned. Even if a non-NULL value is returned, its
possible that the window's alpha channel won't be honored
when displaying the window on the screen: in particular, for
X an appropriate windowing manager and compositing manager
must be running to provide appropriate display.
This functionality is not implemented in the Windows backend.
For setting an overall opacity for a top-level window, see
gdk_window_set_opacity().
Since 2.8
Gets a visual to use for creating windows with an alpha channel. The windowing system on which GTK+ is running may not support this capability, in which case NULL will be returned. Even if a non-NULL value is returned, its possible that the window's alpha channel won't be honored when displaying the window on the screen: in particular, for X an appropriate windowing manager and compositing manager must be running to provide appropriate display. This functionality is not implemented in the Windows backend. For setting an overall opacity for a top-level window, see gdk_window_set_opacity(). Since 2.8