Allow canceling Drag and Drop with the Escape-Key

This patch implements the functionality to cancel Drag and Drop
by using the escape key or more general, the ui_cancel action.

Since this would be the third location, where the finalization of
Drag and Drop would have to be implemented, that functionality was
put into the private function _perform_drop.

Simplified gui.drag_data.get_type() != Variant::NIL to gui.dragging
because they are equivalent.

2 files changed, 34 insertions, 35 deletions

diff --git a/scene/main/viewport.cpp b/scene/main/viewport.cpp
index f8b0a66a71..7155cb0df9 100644
--- a/scene/main/viewport.cpp
+++ b/scene/main/viewport.cpp
@@ -1561,44 +1561,15 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 				set_input_as_handled();
 			}
 
-			if (gui.drag_data.get_type() != Variant::NIL && mb->get_button_index() == MouseButton::LEFT) {
+			if (gui.dragging && mb->get_button_index() == MouseButton::LEFT) {
 				// Alternate drop use (when using force_drag(), as proposed by #5342).
-				gui.drag_successful = false;
-				if (gui.mouse_focus) {
-					gui.drag_successful = _gui_drop(gui.mouse_focus, pos, false);
-				}
-
-				gui.drag_data = Variant();
-				gui.dragging = false;
-
-				Control *drag_preview = _gui_get_drag_preview();
-				if (drag_preview) {
-					memdelete(drag_preview);
-					gui.drag_preview_id = ObjectID();
-				}
-				_propagate_viewport_notification(this, NOTIFICATION_DRAG_END);
-				get_base_window()->update_mouse_cursor_shape();
+				_perform_drop(gui.mouse_focus, pos);
 			}
 
 			_gui_cancel_tooltip();
 		} else {
-			if (gui.drag_data.get_type() != Variant::NIL && mb->get_button_index() == MouseButton::LEFT) {
-				gui.drag_successful = false;
-				if (gui.drag_mouse_over) {
-					gui.drag_successful = _gui_drop(gui.drag_mouse_over, gui.drag_mouse_over_pos, false);
-				}
-
-				Control *drag_preview = _gui_get_drag_preview();
-				if (drag_preview) {
-					memdelete(drag_preview);
-					gui.drag_preview_id = ObjectID();
-				}
-
-				gui.drag_data = Variant();
-				gui.dragging = false;
-				gui.drag_mouse_over = nullptr;
-				_propagate_viewport_notification(this, NOTIFICATION_DRAG_END);
-				get_base_window()->update_mouse_cursor_shape();
+			if (gui.dragging && mb->get_button_index() == MouseButton::LEFT) {
+				_perform_drop(gui.drag_mouse_over, gui.drag_mouse_over_pos);
 			}
 
 			gui.mouse_focus_mask &= ~mouse_button_to_mask(mb->get_button_index()); // Remove from mask.
@@ -1682,7 +1653,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 				}
 
 				gui.drag_attempted = true;
-				if (gui.drag_data.get_type() != Variant::NIL) {
+				if (gui.dragging) {
 					_propagate_viewport_notification(this, NOTIFICATION_DRAG_BEGIN);
 				}
 			}
@@ -1795,7 +1766,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 			}
 		}
 
-		if (gui.drag_data.get_type() != Variant::NIL) {
+		if (gui.dragging) {
 			// Handle drag & drop.
 
 			Control *drag_preview = _gui_get_drag_preview();
@@ -1997,6 +1968,12 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 	}
 
 	if (mm.is_null() && mb.is_null() && p_event->is_action_type()) {
+		if (gui.dragging && p_event->is_action_pressed("ui_cancel") && Input::get_singleton()->is_action_just_pressed("ui_cancel")) {
+			_perform_drop();
+			set_input_as_handled();
+			return;
+		}
+
 		if (gui.key_focus && !gui.key_focus->is_visible_in_tree()) {
 			gui.key_focus->release_focus();
 		}
@@ -2078,6 +2055,27 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 	}
 }
 
+void Viewport::_perform_drop(Control *p_control, Point2 p_pos) {
+	// Without any arguments, simply cancel Drag and Drop.
+	if (p_control) {
+		gui.drag_successful = _gui_drop(p_control, p_pos, false);
+	} else {
+		gui.drag_successful = false;
+	}
+
+	Control *drag_preview = _gui_get_drag_preview();
+	if (drag_preview) {
+		memdelete(drag_preview);
+		gui.drag_preview_id = ObjectID();
+	}
+
+	gui.drag_data = Variant();
+	gui.dragging = false;
+	gui.drag_mouse_over = nullptr;
+	_propagate_viewport_notification(this, NOTIFICATION_DRAG_END);
+	get_base_window()->update_mouse_cursor_shape();
+}
+
 void Viewport::_gui_cleanup_internal_state(Ref<InputEvent> p_event) {
 	ERR_FAIL_COND(p_event.is_null());
 
diff --git a/scene/main/viewport.h b/scene/main/viewport.h
index 8911aea335..dc69ec24d8 100644
--- a/scene/main/viewport.h
+++ b/scene/main/viewport.h
@@ -405,6 +405,7 @@ private:
 	Control *_gui_find_control_at_pos(CanvasItem *p_node, const Point2 &p_global, const Transform2D &p_xform, Transform2D &r_inv_xform);
 
 	void _gui_input_event(Ref<InputEvent> p_event);
+	void _perform_drop(Control *p_control = nullptr, Point2 p_pos = Point2());
 	void _gui_cleanup_internal_state(Ref<InputEvent> p_event);
 
 	_FORCE_INLINE_ Transform2D _get_input_pre_xform() const;