Make drag and drop into viewport add to root node by default

When dragging and dropping a texture, mesh, or scene from the FileSystem into the
2D or 3D viewport, it will be added as a child of the current scene's root node.

editor/plugins/canvas_item_editor_plugin.cpp

@@ -5733,11 +5733,14 @@ void CanvasItemEditorViewport::_create_preview(const Vector<String> &files) cons
 				preview_node->add_child(sprite);
 				label->show();
 				label_desc->show();
+				label_desc->set_text(TTR("Drag and drop to add as child of current scene's root node.\nHold Ctrl when dropping to add as child of selected node.\nHold Shift when dropping to add as sibling of selected node.\nHold Alt when dropping to add as a different node type."));
 			} else {
 				if (scene.is_valid()) {
 					Node *instance = scene->instantiate();
 					if (instance) {
 						preview_node->add_child(instance);
+						label_desc->show();
+						label_desc->set_text(TTR("Drag and drop to add as child of current scene's root node.\nHold Ctrl when dropping to add as child of selected node.\nHold Shift when dropping to add as sibling of selected node."));
 					}
 				}
 			}
@@ -6036,6 +6039,7 @@ bool CanvasItemEditorViewport::_only_packed_scenes_selected() const {
 
 void CanvasItemEditorViewport::drop_data(const Point2 &p_point, const Variant &p_data) {
 	bool is_shift = Input::get_singleton()->is_key_pressed(KEY_SHIFT);
+	bool is_ctrl = Input::get_singleton()->is_key_pressed(KEY_CTRL);
 	bool is_alt = Input::get_singleton()->is_key_pressed(KEY_ALT);
 
 	selected_files.clear();
@@ -6047,24 +6051,25 @@ void CanvasItemEditorViewport::drop_data(const Point2 &p_point, const Variant &p
 		return;
 	}
 
-	List<Node *> list = editor->get_editor_selection()->get_selected_node_list();
-	if (list.size() == 0) {
-		Node *root_node = editor->get_edited_scene();
+	List<Node *> selected_nodes = editor->get_editor_selection()->get_selected_node_list();
+	Node *root_node = editor->get_edited_scene();
+	if (selected_nodes.size() > 0) {
+		Node *selected_node = selected_nodes[0];
+		target_node = root_node;
+		if (is_ctrl) {
+			target_node = selected_node;
+		} else if (is_shift && selected_node != root_node) {
+			target_node = selected_node->get_parent();
+		}
+	} else {
 		if (root_node) {
-			list.push_back(root_node);
+			target_node = root_node;
 		} else {
 			drop_pos = p_point;
 			target_node = nullptr;
 		}
 	}
 
-	if (list.size() > 0) {
-		target_node = list[0];
-		if (is_shift && target_node != editor->get_edited_scene()) {
-			target_node = target_node->get_parent();
-		}
-	}
-
 	drop_pos = p_point;
 
 	if (is_alt && !_only_packed_scenes_selected()) {
@@ -6145,7 +6150,6 @@ CanvasItemEditorViewport::CanvasItemEditorViewport(EditorNode *p_node, CanvasIte
 	canvas_item_editor->get_controls_container()->add_child(label);
 
 	label_desc = memnew(Label);
-	label_desc->set_text(TTR("Drag & drop + Shift : Add node as sibling\nDrag & drop + Alt : Change node type"));
 	label_desc->add_theme_color_override("font_color", Color(0.6f, 0.6f, 0.6f, 1));
 	label_desc->add_theme_color_override("font_shadow_color", Color(0.2f, 0.2f, 0.2f, 1));
 	label_desc->add_theme_constant_override("shadow_as_outline", 1 * EDSCALE);

editor/plugins/node_3d_editor_plugin.cpp

@@ -4066,6 +4066,7 @@ void Node3DEditorViewport::drop_data_fw(const Point2 &p_point, const Variant &p_
 	}
 
 	bool is_shift = Input::get_singleton()->is_key_pressed(KEY_SHIFT);
+	bool is_ctrl = Input::get_singleton()->is_key_pressed(KEY_CTRL);
 
 	selected_files.clear();
 	Dictionary d = p_data;
@@ -4073,29 +4074,32 @@ void Node3DEditorViewport::drop_data_fw(const Point2 &p_point, const Variant &p_
 		selected_files = d["files"];
 	}
 
-	List<Node *> list = editor->get_editor_selection()->get_selected_node_list();
-	if (list.size() == 0) {
-		Node *root_node = editor->get_edited_scene();
+	List<Node *> selected_nodes = editor->get_editor_selection()->get_selected_node_list();
+	Node *root_node = editor->get_edited_scene();
+	if (selected_nodes.size() == 1) {
+		Node *selected_node = selected_nodes[0];
+		target_node = root_node;
+		if (is_ctrl) {
+			target_node = selected_node;
+		} else if (is_shift && selected_node != root_node) {
+			target_node = selected_node->get_parent();
+		}
+	} else if (selected_nodes.size() == 0) {
 		if (root_node) {
-			list.push_back(root_node);
+			target_node = root_node;
 		} else {
-			accept->set_text(TTR("No parent to instance a child at."));
+			accept->set_text(TTR("Cannot drag and drop into scene with no root node."));
 			accept->popup_centered();
 			_remove_preview();
 			return;
 		}
-	}
-	if (list.size() != 1) {
-		accept->set_text(TTR("This operation requires a single selected node."));
+	} else {
+		accept->set_text(TTR("Cannot drag and drop into multiple selected nodes."));
 		accept->popup_centered();
 		_remove_preview();
 		return;
 	}
 
-	target_node = list[0];
-	if (is_shift && target_node != editor->get_edited_scene()) {
-		target_node = target_node->get_parent();
-	}
 	drop_pos = p_point;
 
 	_perform_drop_data();