Window.setOpacity

Set window to render as partially transparent, with opacity 0 being fully transparent and 1 fully opaque. (Values of the opacity parameter are clamped to the 0,1 range.)

For toplevel windows this depends on support from the windowing system that may not always be there. For instance, On X11, this works only on X screens with a compositing manager running. On Wayland, there is no per-window opacity value that the compositor would apply. Instead, use gdk_window_set_opaque_region (window, NULL) to tell the compositor that the entire window is (potentially) non-opaque, and draw your content with alpha, or use gtk.widget.Widget.setOpacity to set an overall opacity for your widgets.

For child windows this function only works for non-native windows.

For setting up per-pixel alpha topelevels, see gdk.screen.Screen.getRgbaVisual, and for non-toplevels, see gdk.window.Window.setComposited.

Support for non-toplevel windows was added in 3.8.