gtk/widget_since_3_8.go
func (v *Widget) GetOpacity() float64 {
	c := C.gtk_widget_get_opacity(v.native())
	return float64(c)
}
func (v *Widget) GetOpacity() float64 {
	c := C.gtk_widget_get_opacity(v.native())
	return float64(c)
}
// GetOpacity is a wrapper around gtk_widget_get_opacity()