a bunch of stuff to make tab/window switching work better, and provide Alt-m to toggle between editor+mixer in a sane way

libs/gtkmm2ext/gtkmm2ext/window_proxy.h

@@ -52,8 +52,8 @@ class LIBGTKMM2EXT_API WindowProxy : public PBD::StatefulDestructible, public vi
 	void present ();
 	void maybe_show ();
 
-	bool visible() const { return _visible; }
-	bool not_visible() const { return !_visible; }
+	bool visible() const;
+	bool fully_visible() const;
 	const std::string& name() const { return _name; }
 	const std::string& menu_name() const { return _menu_name; }
 

libs/gtkmm2ext/tabbable.cc

@@ -188,11 +188,8 @@ Tabbable::change_visibility ()
 	}
 
 	if (_window && (current_toplevel() == _window)) {
-		if (_window->is_visible ()) {
-			_window->hide ();
-		} else {
-			_window->present ();
-		}
+		/* Use WindowProxy method which will rotate then hide */
+		toggle();
 	}
 }
 

libs/gtkmm2ext/window_proxy.cc

@@ -233,6 +233,26 @@ WindowProxy::setup ()
 	set_pos_and_size ();
 }
 
+bool
+WindowProxy::visible() const
+{
+	if (vistracker) {
+		/* update with current state */
+		_visible = vistracker->partially_visible();
+	}
+	return _visible;
+}
+
+bool
+WindowProxy::fully_visible () const
+{
+	if (!vistracker) {
+		/* no vistracker .. no window .. cannot be fully visible */
+		return false;
+	}
+	return vistracker->fully_visible();
+}
+
 void
 WindowProxy::show ()
 {