Improve popup menus usability

It seems that popups were intended to "grab" the mouse click that triggered them, but their intent was being lost. This commit does the necessary changes to let it happen and updates items that were trying to get advantage of it, because the semantics of `Control::grab_click_focus()` have changed a bit. Namely, it must be called **before** showing the modal.

This allows to popup a menu and activate an item in it in a single click-point-release cycle, instead of having to click once to open the menu and once more to pick an item.

This ability is extended even to context menus activated with the RMB (or any other mouse button, for that matter). The editor benefits from this in the context menu of the tree dock, which has been patched to opt-in for this feature.

This improves UX a bit by saving unnecessary clicks.

From now on, `PopupMenu` always grabs the click and also invalidates the first button release unless the mouse has moved (that's what `set_invalidate_click_until_motion()` was doing and now it's removed), so there is no longer the need of doing both things at every point a pop-up menu is shown.

3 files changed, 47 insertions, 28 deletions

diff --git a/scene/gui/menu_button.cpp b/scene/gui/menu_button.cpp
index 2e74faa61d..87cf4dc334 100644
--- a/scene/gui/menu_button.cpp
+++ b/scene/gui/menu_button.cpp
@@ -59,7 +59,6 @@ void MenuButton::pressed() {
 	popup->set_size(Size2(size.width, 0));
 	popup->set_parent_rect(Rect2(Point2(gp - popup->get_global_position()), get_size()));
 	popup->popup();
-	popup->set_invalidate_click_until_motion();
 }
 
 void MenuButton::_gui_input(Ref<InputEvent> p_event) {
@@ -109,7 +108,6 @@ MenuButton::MenuButton() {
 	add_child(popup);
 	popup->set_as_toplevel(true);
 	popup->set_pass_on_modal_close_click(false);
-	connect("button_up", popup, "call_deferred", make_binds("grab_click_focus"));
 	set_process_unhandled_key_input(true);
 	set_action_mode(ACTION_MODE_BUTTON_PRESS);
 }
diff --git a/scene/gui/popup_menu.cpp b/scene/gui/popup_menu.cpp
index 747230e69f..27853a8238 100644
--- a/scene/gui/popup_menu.cpp
+++ b/scene/gui/popup_menu.cpp
@@ -284,7 +284,8 @@ void PopupMenu::_gui_input(const Ref<InputEvent> &p_event) {
 		if (b->is_pressed())
 			return;
 
-		switch (b->get_button_index()) {
+		int button_idx = b->get_button_index();
+		switch (button_idx) {
 
 			case BUTTON_WHEEL_DOWN: {
 
@@ -298,30 +299,37 @@ void PopupMenu::_gui_input(const Ref<InputEvent> &p_event) {
 					_scroll(b->get_factor(), b->get_position());
 				}
 			} break;
-			case BUTTON_LEFT: {
-
-				int over = _get_mouse_over(b->get_position());
-
-				if (invalidated_click) {
-					invalidated_click = false;
-					break;
-				}
-				if (over < 0) {
-					hide();
-					break; //non-activable
-				}
-
-				if (items[over].separator || items[over].disabled)
-					break;
-
-				if (items[over].submenu != "") {
-
-					_activate_submenu(over);
-					return;
+			default: {
+				// Allow activating item by releasing the LMB or any that was down when the popup appeared
+				if (button_idx == BUTTON_LEFT || (initial_button_mask & (1 << (button_idx - 1)))) {
+
+					bool was_during_grabbed_click = during_grabbed_click;
+					during_grabbed_click = false;
+
+					int over = _get_mouse_over(b->get_position());
+
+					if (invalidated_click) {
+						invalidated_click = false;
+						break;
+					}
+					if (over < 0) {
+						if (!was_during_grabbed_click) {
+							hide();
+						}
+						break; //non-activable
+					}
+
+					if (items[over].separator || items[over].disabled)
+						break;
+
+					if (items[over].submenu != "") {
+
+						_activate_submenu(over);
+						return;
+					}
+					activate_item(over);
 				}
-				activate_item(over);
-
-			} break;
+			}
 		}
 
 		//update();
@@ -503,6 +511,11 @@ void PopupMenu::_notification(int p_what) {
 				update();
 			}
 		} break;
+		case NOTIFICATION_POST_POPUP: {
+
+			initial_button_mask = Input::get_singleton()->get_mouse_button_mask();
+			during_grabbed_click = (bool)initial_button_mask;
+		} break;
 		case NOTIFICATION_POPUP_HIDE: {
 
 			if (mouse_over >= 0) {
@@ -1216,15 +1229,20 @@ void PopupMenu::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("index_pressed", PropertyInfo(Variant::INT, "index")));
 }
 
-void PopupMenu::set_invalidate_click_until_motion() {
+void PopupMenu::popup(const Rect2 &p_bounds) {
+
+	grab_click_focus();
 	moved = Vector2();
 	invalidated_click = true;
+	Popup::popup(p_bounds);
 }
 
 PopupMenu::PopupMenu() {
 
 	mouse_over = -1;
 	submenu_over = -1;
+	initial_button_mask = 0;
+	during_grabbed_click = false;
 
 	set_focus_mode(FOCUS_ALL);
 	set_as_toplevel(true);
diff --git a/scene/gui/popup_menu.h b/scene/gui/popup_menu.h
index 60f36e95ec..4a62f81a65 100644
--- a/scene/gui/popup_menu.h
+++ b/scene/gui/popup_menu.h
@@ -78,6 +78,8 @@ class PopupMenu : public Popup {
 	Timer *submenu_timer;
 	List<Rect2> autohide_areas;
 	Vector<Item> items;
+	int initial_button_mask;
+	bool during_grabbed_click;
 	int mouse_over;
 	int submenu_over;
 	Rect2 parent_rect;
@@ -178,7 +180,6 @@ public:
 	void add_autohide_area(const Rect2 &p_area);
 	void clear_autohide_areas();
 
-	void set_invalidate_click_until_motion();
 	void set_hide_on_item_selection(bool p_enabled);
 	bool is_hide_on_item_selection() const;
 
@@ -188,6 +189,8 @@ public:
 	void set_hide_on_multistate_item_selection(bool p_enabled);
 	bool is_hide_on_multistate_item_selection() const;
 
+	virtual void popup(const Rect2 &p_bounds = Rect2());
+
 	PopupMenu();
 	~PopupMenu();
 };