Enable Drag and Drop for SubViewports and Windows

Make Drag and Drop an application-wide operation.
This allows do drop on Controls in other Viewports/Windows.

In order to achieve this, `Viewport::_update_mouse_over` is adjusted to
remember the Control, that the mouse is over (possibly within nested
viewports). This Control is used as a basis for the Drop-operation, which
replaces the previous algorithm, which was only aware of the topmost
Viewport.

Also now all nodes in the SceneTree are notified about the Drag and Drop
operation, with the exception of SubViewports that are not children of
SubViewportContainers.

Author: Sauermann

doc/classes/Viewport.xml

@@ -144,7 +144,7 @@
 		<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

@@ -1718,12 +1718,6 @@ 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);
 	}
@@ -1767,6 +1761,12 @@ 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

@@ -1224,14 +1224,16 @@ 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);
 	}
 }
 
@@ -1334,7 +1336,7 @@ 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;
@@ -1689,14 +1691,15 @@ 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;
@@ -1794,13 +1797,13 @@ 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.
@@ -1837,7 +1840,8 @@ 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) {
@@ -1846,12 +1850,13 @@ 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.forced_mouse_focus = false;
 								gui.mouse_focus_mask.clear();
+								gui.dragging = true;
 								break;
 							} else {
 								Control *drag_preview = _gui_get_drag_preview();
@@ -1860,7 +1865,7 @@ 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) {
@@ -1878,7 +1883,7 @@ 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);
 				}
 			}
 		}
@@ -1971,105 +1976,29 @@ 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);
 		}
 	}
@@ -2269,10 +2198,10 @@ 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;
 	}
@@ -2283,10 +2212,12 @@ 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();
 }
@@ -2316,14 +2247,16 @@ 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) {
@@ -3005,6 +2938,7 @@ 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--) {
@@ -3056,6 +2990,7 @@ 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`.
@@ -3178,6 +3113,10 @@ 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.
@@ -3386,7 +3325,7 @@ 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 {
@@ -3580,7 +3519,7 @@ 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 {
@@ -5110,9 +5049,12 @@ 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 {