fix embedded plugin UI keyboard handling

When the GUI is opened the first time all is fine, focus is on the
embedded widget. However once a user presses one of the preset buttons
(Add, Save,...) there is no possibility to return focus to the
embedded widget. Ardour always 'sees' it as focus=GtkButton and passes
the event to the editor.

gtk2_ardour/au_pluginui.h

@@ -76,6 +76,7 @@ class AUPluginUI : public PlugUIBase, public Gtk::VBox
 	void lower_box_realized ();
 	void cocoa_view_resized ();
 	void on_realize ();
+	void grab_focus();
 	void forward_key_event (GdkEventKey*);
 
 	bool on_window_show (const std::string& /*title*/);

gtk2_ardour/au_pluginui.mm

@@ -677,6 +677,13 @@ AUPluginUI::parent_cocoa_window ()
 	return 0;
 }
 
+void
+AUPluginUI::grab_focus()
+{
+	if (au_view) {
+		[au_view becomeFirstResponder];
+	}
+}
 void
 AUPluginUI::forward_key_event (GdkEventKey* ev)
 {

gtk2_ardour/lv2_plugin_ui.cc

@@ -341,6 +341,8 @@ LV2PluginUI::lv2ui_instantiate(const std::string& title)
 				container->add(*Gtk::manage(Glib::wrap(c_widget)));
 			}
 			container->show_all();
+			gtk_widget_set_can_focus(c_widget, true);
+			gtk_widget_grab_focus(c_widget);
 		} else {
 			_external_ui_ptr = (struct lv2_external_ui*)GET_WIDGET(_inst);
 		}
@@ -368,6 +370,15 @@ LV2PluginUI::lv2ui_instantiate(const std::string& title)
 	}
 }
 
+void
+LV2PluginUI::grab_focus()
+{
+	if (_inst && !_lv2->is_external_ui()) {
+		GtkWidget* c_widget = (GtkWidget*)GET_WIDGET(_inst);
+		gtk_widget_grab_focus(c_widget);
+	}
+}
+
 void
 LV2PluginUI::lv2ui_free()
 {

gtk2_ardour/lv2_plugin_ui.h

@@ -60,6 +60,7 @@ class LV2PluginUI : public PlugUIBase, public Gtk::VBox
 	bool stop_updating(GdkEventAny*);
 
 	int package (Gtk::Window&);
+	void grab_focus ();
 
   private:
 

gtk2_ardour/plugin_ui.cc

@@ -353,6 +353,7 @@ PluginUIWindow::on_key_press_event (GdkEventKey* event)
 {
 	if (_keyboard_focused) {
 		if (_pluginui) {
+			_pluginui->grab_focus();
 			if (_pluginui->non_gtk_gui()) {
 				_pluginui->forward_key_event (event);
 			} else {
@@ -366,6 +367,7 @@ PluginUIWindow::on_key_press_event (GdkEventKey* event)
 		*/
 
 		if (_pluginui) {
+			_pluginui->grab_focus();
 			if (_pluginui->non_gtk_gui()) {
 				/* pass editor window as the window for the event
 				   to be handled in, not this one, because there are

gtk2_ardour/plugin_ui.h

@@ -103,7 +103,8 @@ class PlugUIBase : public virtual sigc::trackable, public PBD::ScopedConnectionL
 	virtual void on_window_hide() {}
 
 	virtual void forward_key_event (GdkEventKey*) {}
-        virtual bool non_gtk_gui() const { return false; }
+	virtual void grab_focus () {}
+  virtual bool non_gtk_gui() const { return false; }
 
 	sigc::signal<void,bool> KeyboardFocused;