Merge pull request #67531 from Sauermann/fix-drag-n-drop

Enable Drag and Drop between SubViewports and Windows

doc/classes/Viewport.xml

@@ -151,7 +151,7 @@
 		<method name="gui_is_dragging" qualifiers="const">
 			<return type="bool" />
 			<description>
-				Returns [code]true[/code] if the viewport is currently performing a drag operation.
+				Returns [code]true[/code] if a drag operation is currently ongoing and where the drop action could happen in this viewport.
 				Alternative to [constant Node.NOTIFICATION_DRAG_BEGIN] and [constant Node.NOTIFICATION_DRAG_END] when you prefer polling the value.
 			</description>
 		</method>

platform/linuxbsd/x11/display_server_x11.cpp

@@ -1787,12 +1787,6 @@ void DisplayServerX11::delete_sub_window(WindowID p_id) {
 		_send_window_event(windows[p_id], WINDOW_EVENT_MOUSE_EXIT);
 	}
 
-	window_set_rect_changed_callback(Callable(), p_id);
-	window_set_window_event_callback(Callable(), p_id);
-	window_set_input_event_callback(Callable(), p_id);
-	window_set_input_text_callback(Callable(), p_id);
-	window_set_drop_files_callback(Callable(), p_id);
-
 	while (wd.transient_children.size()) {
 		window_set_transient(*wd.transient_children.begin(), INVALID_WINDOW_ID);
 	}
@@ -1836,6 +1830,12 @@ void DisplayServerX11::delete_sub_window(WindowID p_id) {
 	XUnmapWindow(x11_display, wd.x11_window);
 	XDestroyWindow(x11_display, wd.x11_window);
 
+	window_set_rect_changed_callback(Callable(), p_id);
+	window_set_window_event_callback(Callable(), p_id);
+	window_set_input_event_callback(Callable(), p_id);
+	window_set_input_text_callback(Callable(), p_id);
+	window_set_drop_files_callback(Callable(), p_id);
+
 	windows.erase(p_id);
 }
 

scene/main/viewport.cpp

@@ -1235,14 +1235,16 @@ Ref<World2D> Viewport::find_world_2d() const {
 	}
 }
 
-void Viewport::_propagate_viewport_notification(Node *p_node, int p_what) {
+void Viewport::_propagate_drag_notification(Node *p_node, int p_what) {
+	// Send notification to p_node and all children and descendant nodes of p_node, except to SubViewports which are not children of a SubViewportContainer.
 	p_node->notification(p_what);
+	bool is_svc = Object::cast_to<SubViewportContainer>(p_node);
 	for (int i = 0; i < p_node->get_child_count(); i++) {
 		Node *c = p_node->get_child(i);
-		if (Object::cast_to<Viewport>(c)) {
+		if (!is_svc && Object::cast_to<SubViewport>(c)) {
 			continue;
 		}
-		_propagate_viewport_notification(c, p_what);
+		Viewport::_propagate_drag_notification(c, p_what);
 	}
 }
 
@@ -1345,7 +1347,7 @@ Ref<InputEvent> Viewport::_make_input_local(const Ref<InputEvent> &ev) {
 
 Vector2 Viewport::get_mouse_position() const {
 	ERR_READ_THREAD_GUARD_V(Vector2());
-	if (!is_directly_attached_to_screen()) {
+	if (get_section_root_viewport() != SceneTree::get_singleton()->get_root()) {
 		// Rely on the most recent mouse coordinate from an InputEventMouse in push_input.
 		// In this case get_screen_transform is not applicable, because it is ambiguous.
 		return gui.last_mouse_pos;
@@ -1701,14 +1703,15 @@ Control *Viewport::_gui_find_control_at_pos(CanvasItem *p_node, const Point2 &p_
 }
 
 bool Viewport::_gui_drop(Control *p_at_control, Point2 p_at_pos, bool p_just_check) {
-	// Attempt grab, try parent controls too.
+	// Attempt drop, try parent controls too.
 	CanvasItem *ci = p_at_control;
+	Viewport *section_root = get_section_root_viewport();
 	while (ci) {
 		Control *control = Object::cast_to<Control>(ci);
 		if (control) {
-			if (control->can_drop_data(p_at_pos, gui.drag_data)) {
+			if (control->can_drop_data(p_at_pos, section_root->gui.drag_data)) {
 				if (!p_just_check) {
-					control->drop_data(p_at_pos, gui.drag_data);
+					control->drop_data(p_at_pos, section_root->gui.drag_data);
 				}
 
 				return true;
@@ -1806,13 +1809,13 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 
 			if (gui.dragging && mb->get_button_index() == MouseButton::LEFT) {
 				// Alternate drop use (when using force_drag(), as proposed by #5342).
-				_perform_drop(gui.mouse_focus, pos);
+				_perform_drop(gui.mouse_focus);
 			}
 
 			_gui_cancel_tooltip();
 		} else {
 			if (gui.dragging && mb->get_button_index() == MouseButton::LEFT) {
-				_perform_drop(gui.drag_mouse_over, gui.drag_mouse_over_pos);
+				_perform_drop(gui.drag_mouse_over);
 			}
 
 			gui.mouse_focus_mask.clear_flag(mouse_button_to_mask(mb->get_button_index())); // Remove from mask.
@@ -1848,7 +1851,8 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 		Point2 mpos = mm->get_position();
 
 		// Drag & drop.
-		if (!gui.drag_attempted && gui.mouse_focus && (mm->get_button_mask().has_flag(MouseButtonMask::LEFT))) {
+		Viewport *section_root = get_section_root_viewport();
+		if (!gui.drag_attempted && gui.mouse_focus && section_root && !section_root->gui.global_dragging && (mm->get_button_mask().has_flag(MouseButtonMask::LEFT))) {
 			gui.drag_accum += mm->get_relative();
 			float len = gui.drag_accum.length();
 			if (len > 10) {
@@ -1857,11 +1861,12 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 					while (ci) {
 						Control *control = Object::cast_to<Control>(ci);
 						if (control) {
-							gui.dragging = true;
-							gui.drag_data = control->get_drag_data(control->get_global_transform_with_canvas().affine_inverse().xform(mpos - gui.drag_accum));
-							if (gui.drag_data.get_type() != Variant::NIL) {
+							section_root->gui.global_dragging = true;
+							section_root->gui.drag_data = control->get_drag_data(control->get_global_transform_with_canvas().affine_inverse().xform(mpos - gui.drag_accum));
+							if (section_root->gui.drag_data.get_type() != Variant::NIL) {
 								gui.mouse_focus = nullptr;
 								gui.mouse_focus_mask.clear();
+								gui.dragging = true;
 								break;
 							} else {
 								Control *drag_preview = _gui_get_drag_preview();
@@ -1870,7 +1875,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 									memdelete(drag_preview);
 									gui.drag_preview_id = ObjectID();
 								}
-								gui.dragging = false;
+								section_root->gui.global_dragging = false;
 							}
 
 							if (control->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
@@ -1888,7 +1893,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 
 				gui.drag_attempted = true;
 				if (gui.dragging) {
-					_propagate_viewport_notification(this, NOTIFICATION_DRAG_BEGIN);
+					Viewport::_propagate_drag_notification(section_root, NOTIFICATION_DRAG_BEGIN);
 				}
 			}
 		}
@@ -1986,105 +1991,29 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 		}
 
 		if (gui.dragging) {
-			// Handle drag & drop.
+			// Handle drag & drop. This happens in the viewport where dragging started.
 
 			Control *drag_preview = _gui_get_drag_preview();
 			if (drag_preview) {
 				drag_preview->set_position(mpos);
 			}
 
-			gui.drag_mouse_over = over;
-			gui.drag_mouse_over_pos = Vector2();
-
-			// Find the window this is above of.
-			// See if there is an embedder.
-			Viewport *embedder = nullptr;
-			Vector2 viewport_pos;
-
-			if (is_embedding_subwindows()) {
-				embedder = this;
-				viewport_pos = mpos;
-			} else {
-				// Not an embedder, but may be a subwindow of an embedder.
-				Window *w = Object::cast_to<Window>(this);
-				if (w) {
-					if (w->is_embedded()) {
-						embedder = w->get_embedder();
-
-						viewport_pos = get_final_transform().xform(mpos) + w->get_position(); // To parent coords.
-					}
-				}
-			}
-
-			Viewport *viewport_under = nullptr;
-
-			if (embedder) {
-				// Use embedder logic.
-
-				for (int i = embedder->gui.sub_windows.size() - 1; i >= 0; i--) {
-					Window *sw = embedder->gui.sub_windows[i].window;
-					Rect2 swrect = Rect2i(sw->get_position(), sw->get_size());
-					if (!sw->get_flag(Window::FLAG_BORDERLESS)) {
-						int title_height = sw->theme_cache.title_height;
-						swrect.position.y -= title_height;
-						swrect.size.y += title_height;
-					}
-
-					if (swrect.has_point(viewport_pos)) {
-						viewport_under = sw;
-						viewport_pos -= sw->get_position();
-					}
-				}
-
-				if (!viewport_under) {
-					// Not in a subwindow, likely in embedder.
-					viewport_under = embedder;
-				}
-			} else {
-				// Use DisplayServer logic.
-				Vector2i screen_mouse_pos = DisplayServer::get_singleton()->mouse_get_position();
-
-				DisplayServer::WindowID window_id = DisplayServer::get_singleton()->get_window_at_screen_position(screen_mouse_pos);
-
-				if (window_id != DisplayServer::INVALID_WINDOW_ID) {
-					ObjectID object_under = DisplayServer::get_singleton()->window_get_attached_instance_id(window_id);
-
-					if (object_under != ObjectID()) { // Fetch window.
-						Window *w = Object::cast_to<Window>(ObjectDB::get_instance(object_under));
-						if (w) {
-							viewport_under = w;
-							viewport_pos = w->get_final_transform().affine_inverse().xform(screen_mouse_pos - w->get_position());
-						}
-					}
+			gui.drag_mouse_over = section_root->gui.target_control;
+			if (gui.drag_mouse_over) {
+				if (!_gui_drop(gui.drag_mouse_over, gui.drag_mouse_over->get_local_mouse_position(), true)) {
+					gui.drag_mouse_over = nullptr;
 				}
-			}
-
-			if (viewport_under) {
-				if (viewport_under != this) {
-					Transform2D ai = viewport_under->get_final_transform().affine_inverse();
-					viewport_pos = ai.xform(viewport_pos);
-				}
-				// Find control under at position.
-				gui.drag_mouse_over = viewport_under->gui_find_control(viewport_pos);
 				if (gui.drag_mouse_over) {
-					Transform2D localizer = gui.drag_mouse_over->get_global_transform_with_canvas().affine_inverse();
-					gui.drag_mouse_over_pos = localizer.xform(viewport_pos);
-
-					bool can_drop = _gui_drop(gui.drag_mouse_over, gui.drag_mouse_over_pos, true);
-
-					if (!can_drop) {
-						ds_cursor_shape = DisplayServer::CURSOR_FORBIDDEN;
-					} else {
-						ds_cursor_shape = DisplayServer::CURSOR_CAN_DROP;
-					}
+					ds_cursor_shape = DisplayServer::CURSOR_CAN_DROP;
+				} else {
+					ds_cursor_shape = DisplayServer::CURSOR_FORBIDDEN;
 				}
-
-			} else {
-				gui.drag_mouse_over = nullptr;
 			}
 		}
 
-		if (DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_CURSOR_SHAPE) && !Object::cast_to<SubViewportContainer>(over)) {
+		if (DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_CURSOR_SHAPE) && (gui.dragging || (!section_root->gui.global_dragging && !Object::cast_to<SubViewportContainer>(over)))) {
+			// If dragging is active, then set the cursor shape only from the Viewport where dragging started.
+			// If dragging is inactive, then set the cursor shape only when not over a SubViewportContainer.
 			DisplayServer::get_singleton()->cursor_set_shape(ds_cursor_shape);
 		}
 	}
@@ -2284,10 +2213,10 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 	}
 }
 
-void Viewport::_perform_drop(Control *p_control, Point2 p_pos) {
+void Viewport::_perform_drop(Control *p_control) {
 	// Without any arguments, simply cancel Drag and Drop.
 	if (p_control) {
-		gui.drag_successful = _gui_drop(p_control, p_pos, false);
+		gui.drag_successful = _gui_drop(p_control, p_control->get_local_mouse_position(), false);
 	} else {
 		gui.drag_successful = false;
 	}
@@ -2298,10 +2227,12 @@ void Viewport::_perform_drop(Control *p_control, Point2 p_pos) {
 		gui.drag_preview_id = ObjectID();
 	}
 
-	gui.drag_data = Variant();
+	Viewport *section_root = get_section_root_viewport();
+	section_root->gui.drag_data = Variant();
 	gui.dragging = false;
+	section_root->gui.global_dragging = false;
 	gui.drag_mouse_over = nullptr;
-	_propagate_viewport_notification(this, NOTIFICATION_DRAG_END);
+	Viewport::_propagate_drag_notification(section_root, NOTIFICATION_DRAG_END);
 	// Display the new cursor shape instantly.
 	update_mouse_cursor_state();
 }
@@ -2331,14 +2262,16 @@ void Viewport::_gui_force_drag(Control *p_base, const Variant &p_data, Control *
 	ERR_FAIL_COND_MSG(p_data.get_type() == Variant::NIL, "Drag data must be a value.");
 
 	gui.dragging = true;
-	gui.drag_data = p_data;
+	Viewport *section_root = get_section_root_viewport();
+	section_root->gui.global_dragging = true;
+	section_root->gui.drag_data = p_data;
 	gui.mouse_focus = nullptr;
 	gui.mouse_focus_mask.clear();
 
 	if (p_control) {
 		_gui_set_drag_preview(p_base, p_control);
 	}
-	_propagate_viewport_notification(this, NOTIFICATION_DRAG_BEGIN);
+	Viewport::_propagate_drag_notification(section_root, NOTIFICATION_DRAG_BEGIN);
 }
 
 void Viewport::_gui_set_drag_preview(Control *p_base, Control *p_control) {
@@ -3022,6 +2955,7 @@ void Viewport::_update_mouse_over() {
 }
 
 void Viewport::_update_mouse_over(Vector2 p_pos) {
+	gui.last_mouse_pos = p_pos; // Necessary, because mouse cursor can be over Viewports that are not reached by the InputEvent.
 	// Look for embedded windows at mouse position.
 	if (is_embedding_subwindows()) {
 		for (int i = gui.sub_windows.size() - 1; i >= 0; i--) {
@@ -3073,6 +3007,7 @@ void Viewport::_update_mouse_over(Vector2 p_pos) {
 
 	// Look for Controls at mouse position.
 	Control *over = gui_find_control(p_pos);
+	get_section_root_viewport()->gui.target_control = over;
 	bool notify_embedded_viewports = false;
 	if (over != gui.mouse_over || (!over && !gui.mouse_over_hierarchy.is_empty())) {
 		// Find the common ancestor of `gui.mouse_over` and `over`.
@@ -3195,6 +3130,10 @@ void Viewport::_drop_mouse_over(Control *p_until_control) {
 	if (gui.mouse_over && gui.mouse_over->is_inside_tree()) {
 		gui.mouse_over->notification(Control::NOTIFICATION_MOUSE_EXIT_SELF);
 	}
+	Viewport *section_root = get_section_root_viewport();
+	if (section_root && section_root->gui.target_control == gui.mouse_over) {
+		section_root->gui.target_control = nullptr;
+	}
 	gui.mouse_over = nullptr;
 
 	// Send Mouse Exit notifications to children first. Don't send to p_until_control or above.
@@ -3403,7 +3342,7 @@ bool Viewport::is_input_disabled() const {
 
 Variant Viewport::gui_get_drag_data() const {
 	ERR_READ_THREAD_GUARD_V(Variant());
-	return gui.drag_data;
+	return get_section_root_viewport()->gui.drag_data;
 }
 
 PackedStringArray Viewport::get_configuration_warnings() const {
@@ -3597,7 +3536,7 @@ bool Viewport::is_snap_2d_vertices_to_pixel_enabled() const {
 
 bool Viewport::gui_is_dragging() const {
 	ERR_READ_THREAD_GUARD_V(false);
-	return gui.dragging;
+	return get_section_root_viewport()->gui.global_dragging;
 }
 
 bool Viewport::gui_is_drag_successful() const {
@@ -5156,9 +5095,12 @@ Transform2D SubViewport::get_popup_base_transform() const {
 	return c->get_screen_transform() * container_transform * get_final_transform();
 }
 
-bool SubViewport::is_directly_attached_to_screen() const {
-	// SubViewports, that are used as Textures are not considered to be directly attached to screen.
-	return Object::cast_to<SubViewportContainer>(get_parent()) && get_parent()->get_viewport() && get_parent()->get_viewport()->is_directly_attached_to_screen();
+Viewport *SubViewport::get_section_root_viewport() const {
+	if (Object::cast_to<SubViewportContainer>(get_parent()) && get_parent()->get_viewport()) {
+		return get_parent()->get_viewport()->get_section_root_viewport();
+	}
+	SubViewport *vp = const_cast<SubViewport *>(this);
+	return vp;
 }
 
 bool SubViewport::is_attached_in_viewport() const {

scene/main/viewport.h

@@ -281,7 +281,7 @@ private:
 
 	bool disable_3d = false;
 
-	void _propagate_viewport_notification(Node *p_node, int p_what);
+	static void _propagate_drag_notification(Node *p_node, int p_what);
 
 	void _update_global_transform();
 
@@ -362,7 +362,6 @@ private:
 		Window *subwindow_over = nullptr; // mouse_over and subwindow_over are mutually exclusive. At all times at least one of them is nullptr.
 		Window *windowmanager_window_over = nullptr; // Only used in root Viewport.
 		Control *drag_mouse_over = nullptr;
-		Vector2 drag_mouse_over_pos;
 		Control *tooltip_control = nullptr;
 		Window *tooltip_popup = nullptr;
 		Label *tooltip_label = nullptr;
@@ -371,7 +370,7 @@ private:
 		Point2 last_mouse_pos;
 		Point2 drag_accum;
 		bool drag_attempted = false;
-		Variant drag_data;
+		Variant drag_data; // Only used in root-Viewport and SubViewports, that are not children of a SubViewportContainer.
 		ObjectID drag_preview_id;
 		Ref<SceneTreeTimer> tooltip_timer;
 		double tooltip_delay = 0.0;
@@ -379,8 +378,10 @@ private:
 		List<Control *> roots;
 		HashSet<ObjectID> canvas_parents_with_dirty_order;
 		int canvas_sort_index = 0; //for sorting items with canvas as root
-		bool dragging = false;
+		bool dragging = false; // Is true in the viewport in which dragging started while dragging is active.
+		bool global_dragging = false; // Is true while dragging is active. Only used in root-Viewport and SubViewports that are not children of a SubViewportContainer.
 		bool drag_successful = false;
+		Control *target_control = nullptr; // Control that the mouse is over in the innermost nested Viewport. Only used in root-Viewport and SubViewports, that are not children of a SubViewportContainer.
 		bool embed_subwindows_hint = false;
 
 		Window *subwindow_focused = nullptr;
@@ -408,7 +409,7 @@ private:
 	Control *_gui_find_control_at_pos(CanvasItem *p_node, const Point2 &p_global, const Transform2D &p_xform);
 
 	void _gui_input_event(Ref<InputEvent> p_event);
-	void _perform_drop(Control *p_control = nullptr, Point2 p_pos = Point2());
+	void _perform_drop(Control *p_control = nullptr);
 	void _gui_cleanup_internal_state(Ref<InputEvent> p_event);
 
 	void _push_unhandled_input_internal(const Ref<InputEvent> &p_event);
@@ -672,9 +673,9 @@ public:
 	Transform2D get_screen_transform() const;
 	virtual Transform2D get_screen_transform_internal(bool p_absolute_position = false) const;
 	virtual Transform2D get_popup_base_transform() const { return Transform2D(); }
-	virtual bool is_directly_attached_to_screen() const { return false; };
-	virtual bool is_attached_in_viewport() const { return false; };
-	virtual bool is_sub_viewport() const { return false; };
+	virtual Viewport *get_section_root_viewport() const { return nullptr; }
+	virtual bool is_attached_in_viewport() const { return false; }
+	virtual bool is_sub_viewport() const { return false; }
 
 private:
 	// 2D audio, camera, and physics. (don't put World2D here because World2D is needed for Control nodes).
@@ -836,9 +837,9 @@ public:
 
 	virtual Transform2D get_screen_transform_internal(bool p_absolute_position = false) const override;
 	virtual Transform2D get_popup_base_transform() const override;
-	virtual bool is_directly_attached_to_screen() const override;
+	virtual Viewport *get_section_root_viewport() const override;
 	virtual bool is_attached_in_viewport() const override;
-	virtual bool is_sub_viewport() const override { return true; };
+	virtual bool is_sub_viewport() const override { return true; }
 
 	void _validate_property(PropertyInfo &p_property) const;
 	SubViewport();

scene/main/window.cpp

@@ -2755,12 +2755,16 @@ Transform2D Window::get_popup_base_transform() const {
 	return popup_base_transform;
 }
 
-bool Window::is_directly_attached_to_screen() const {
+Viewport *Window::get_section_root_viewport() const {
 	if (get_embedder()) {
-		return get_embedder()->is_directly_attached_to_screen();
+		return get_embedder()->get_section_root_viewport();
 	}
-	// Distinguish between the case that this is a native Window and not inside the tree.
-	return is_inside_tree();
+	if (is_inside_tree()) {
+		// Native window.
+		return SceneTree::get_singleton()->get_root();
+	}
+	Window *vp = const_cast<Window *>(this);
+	return vp;
 }
 
 bool Window::is_attached_in_viewport() const {

scene/main/window.h

@@ -469,7 +469,7 @@ public:
 	virtual Transform2D get_final_transform() const override;
 	virtual Transform2D get_screen_transform_internal(bool p_absolute_position = false) const override;
 	virtual Transform2D get_popup_base_transform() const override;
-	virtual bool is_directly_attached_to_screen() const override;
+	virtual Viewport *get_section_root_viewport() const override;
 	virtual bool is_attached_in_viewport() const override;
 
 	Rect2i get_parent_rect() const;

tests/scene/test_viewport.h

@@ -119,8 +119,23 @@ public:
 class DragTarget : public NotificationControlViewport {
 	GDCLASS(DragTarget, NotificationControlViewport);
 
+protected:
+	void _notification(int p_what) {
+		switch (p_what) {
+			case NOTIFICATION_DRAG_BEGIN: {
+				during_drag = true;
+			} break;
+
+			case NOTIFICATION_DRAG_END: {
+				during_drag = false;
+			} break;
+		}
+	}
+
 public:
 	Variant drag_data;
+	bool valid_drop = false;
+	bool during_drag = false;
 	virtual bool can_drop_data(const Point2 &p_point, const Variant &p_data) const override {
 		StringName string_data = p_data;
 		// Verify drag data is compatible.
@@ -136,6 +151,7 @@ public:
 
 	virtual void drop_data(const Point2 &p_point, const Variant &p_data) override {
 		drag_data = p_data;
+		valid_drop = true;
 	}
 };
 
@@ -1107,12 +1123,10 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 	SUBCASE("[Viewport][GuiInputEvent] Drag and Drop") {
 		// FIXME: Drag-Preview will likely change. Tests for this part would have to be rewritten anyway.
 		// See https://github.com/godotengine/godot/pull/67531#issuecomment-1385353430 for details.
-		// FIXME: Testing Drag and Drop with non-embedded windows would require DisplayServerMock additions
-		// FIXME: Drag and Drop currently doesn't work with embedded Windows and SubViewports - not testing.
-		// See https://github.com/godotengine/godot/issues/28522 for example.
+		// Note: Testing Drag and Drop with non-embedded windows would require DisplayServerMock additions.
 		int min_grab_movement = 11;
-		SUBCASE("[Viewport][GuiInputEvent] Drag from one Control to another in the same viewport.") {
-			SUBCASE("[Viewport][GuiInputEvent] Perform successful Drag and Drop on a different Control.") {
+		SUBCASE("[Viewport][GuiInputEvent][DnD] Drag from one Control to another in the same viewport.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Perform successful Drag and Drop on a different Control.") {
 				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 
@@ -1131,7 +1145,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				CHECK((StringName)node_d->drag_data == SNAME("Drag Data"));
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Perform unsuccessful drop on Control.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Perform unsuccessful drop on Control.") {
 				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 
@@ -1157,7 +1171,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				CHECK_FALSE(root->gui_is_drag_successful());
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Perform unsuccessful drop on No-Control.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Perform unsuccessful drop on No-Control.") {
 				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 
@@ -1171,7 +1185,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 
 				// Move away from Controls.
 				SEND_GUI_MOUSE_MOTION_EVENT(on_background, MouseButtonMask::LEFT, Key::NONE);
-				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_ARROW); // This could also be CURSOR_FORBIDDEN.
+				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_ARROW);
 
 				CHECK(root->gui_is_dragging());
 				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_background, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
@@ -1179,7 +1193,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				CHECK_FALSE(root->gui_is_drag_successful());
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Perform unsuccessful drop outside of window.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Perform unsuccessful drop outside of window.") {
 				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 
@@ -1192,7 +1206,6 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 
 				// Move outside of window.
 				SEND_GUI_MOUSE_MOTION_EVENT(on_outside, MouseButtonMask::LEFT, Key::NONE);
-				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_ARROW);
 				CHECK(root->gui_is_dragging());
 
 				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_outside, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
@@ -1200,7 +1213,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				CHECK_FALSE(root->gui_is_drag_successful());
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Drag and Drop doesn't work with other Mouse Buttons than LMB.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag and Drop doesn't work with other Mouse Buttons than LMB.") {
 				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::MIDDLE, MouseButtonMask::MIDDLE, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 
@@ -1209,7 +1222,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_a, MouseButton::MIDDLE, MouseButtonMask::NONE, Key::NONE);
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Drag and Drop parent propagation.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag and Drop parent propagation.") {
 				Node2D *node_aa = memnew(Node2D);
 				Control *node_aaa = memnew(Control);
 				Node2D *node_dd = memnew(Node2D);
@@ -1318,7 +1331,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				memdelete(node_aa);
 			}
 
-			SUBCASE("[Viewport][GuiInputEvent] Force Drag and Drop.") {
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Force Drag and Drop.") {
 				SEND_GUI_MOUSE_MOTION_EVENT(on_background, MouseButtonMask::NONE, Key::NONE);
 				CHECK_FALSE(root->gui_is_dragging());
 				node_a->force_drag(SNAME("Drag Data"), nullptr);
@@ -1339,6 +1352,111 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_d, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
 			}
 		}
+
+		SUBCASE("[Viewport][GuiInputEvent][DnD] Drag to a different Viewport.") {
+			SubViewportContainer *svc = memnew(SubViewportContainer);
+			svc->set_size(Size2(100, 100));
+			svc->set_position(Point2(200, 50));
+			root->add_child(svc);
+
+			SubViewport *sv = memnew(SubViewport);
+			sv->set_embedding_subwindows(true);
+			sv->set_size(Size2i(100, 100));
+			svc->add_child(sv);
+
+			DragStart *sv_a = memnew(DragStart);
+			sv_a->set_position(Point2(10, 10));
+			sv_a->set_size(Size2(10, 10));
+			sv->add_child(sv_a);
+			Point2i on_sva = Point2i(215, 65);
+
+			DragTarget *sv_b = memnew(DragTarget);
+			sv_b->set_position(Point2(30, 30));
+			sv_b->set_size(Size2(20, 20));
+			sv->add_child(sv_b);
+			Point2i on_svb = Point2i(235, 85);
+
+			Window *ew = memnew(Window);
+			ew->set_position(Point2(50, 200));
+			ew->set_size(Size2(100, 100));
+			root->add_child(ew);
+
+			DragStart *ew_a = memnew(DragStart);
+			ew_a->set_position(Point2(10, 10));
+			ew_a->set_size(Size2(10, 10));
+			ew->add_child(ew_a);
+			Point2i on_ewa = Point2i(65, 215);
+
+			DragTarget *ew_b = memnew(DragTarget);
+			ew_b->set_position(Point2(30, 30));
+			ew_b->set_size(Size2(20, 20));
+			ew->add_child(ew_b);
+			Point2i on_ewb = Point2i(85, 235);
+
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag to SubViewport") {
+				sv_b->valid_drop = false;
+				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_a + Point2i(min_grab_movement, 0), MouseButtonMask::LEFT, Key::NONE);
+				CHECK(root->gui_is_dragging());
+				CHECK(sv_b->during_drag);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_svb, MouseButtonMask::LEFT, Key::NONE);
+				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_CAN_DROP);
+
+				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_svb, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
+				CHECK(sv_b->valid_drop);
+				CHECK(!sv_b->during_drag);
+			}
+
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag from SubViewport") {
+				node_d->valid_drop = false;
+				SEND_GUI_MOUSE_BUTTON_EVENT(on_sva, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_sva + Point2i(min_grab_movement, 0), MouseButtonMask::LEFT, Key::NONE);
+				CHECK(sv->gui_is_dragging());
+				CHECK(node_d->during_drag);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_d, MouseButtonMask::LEFT, Key::NONE);
+				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_CAN_DROP);
+
+				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_d, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
+				CHECK(node_d->valid_drop);
+				CHECK(!node_d->during_drag);
+			}
+
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag to embedded Window") {
+				ew_b->valid_drop = false;
+				SEND_GUI_MOUSE_BUTTON_EVENT(on_a, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_a + Point2i(min_grab_movement, 0), MouseButtonMask::LEFT, Key::NONE);
+				CHECK(root->gui_is_dragging());
+				CHECK(ew_b->during_drag);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_ewb, MouseButtonMask::LEFT, Key::NONE);
+				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_CAN_DROP);
+
+				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_ewb, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
+				CHECK(ew_b->valid_drop);
+				CHECK(!ew_b->during_drag);
+			}
+
+			SUBCASE("[Viewport][GuiInputEvent][DnD] Drag from embedded Window") {
+				node_d->valid_drop = false;
+				SEND_GUI_MOUSE_BUTTON_EVENT(on_ewa, MouseButton::LEFT, MouseButtonMask::LEFT, Key::NONE);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_ewa + Point2i(min_grab_movement, 0), MouseButtonMask::LEFT, Key::NONE);
+				CHECK(ew->gui_is_dragging());
+				CHECK(node_d->during_drag);
+				SEND_GUI_MOUSE_MOTION_EVENT(on_d, MouseButtonMask::LEFT, Key::NONE);
+				CHECK(DS->get_cursor_shape() == DisplayServer::CURSOR_CAN_DROP);
+
+				SEND_GUI_MOUSE_BUTTON_RELEASED_EVENT(on_d, MouseButton::LEFT, MouseButtonMask::NONE, Key::NONE);
+				CHECK(node_d->valid_drop);
+				CHECK(!node_d->during_drag);
+			}
+
+			memdelete(ew_a);
+			memdelete(ew_b);
+			memdelete(ew);
+			memdelete(sv_a);
+			memdelete(sv_b);
+			memdelete(sv);
+			memdelete(svc);
+		}
 	}
 
 	memdelete(node_j);