Improve the UX of ViewportTexture in the editor

The associated `ViewportTexture`s will update the `viewport_path`
in time when the `Viewport`'s nodepath is changed (caused by renaming
the node names or moving in the SceneTree dock).

If the target `Viewport` is changed by resetting the `viewport_path`,
the `ViewportTexture`s will be re-setup and emit `changed` signal in
time.

(cherry picked from commit af58f1e8547c8b6a2e6b83b7de9c3ac9bc05d881)

2 files changed, 45 insertions, 3 deletions

diff --git a/scene/main/viewport.cpp b/scene/main/viewport.cpp
index 8bdcd9302f..4aaa2e8f5b 100644
--- a/scene/main/viewport.cpp
+++ b/scene/main/viewport.cpp
@@ -72,10 +72,9 @@ void ViewportTexture::setup_local_to_scene() {
 
 	if (vp) {
 		vp->viewport_textures.erase(this);
+		vp = nullptr;
 	}
 
-	vp = nullptr;
-
 	if (loc_scene->is_ready()) {
 		_setup_local_to_scene(loc_scene);
 	} else {
@@ -91,8 +90,24 @@ void ViewportTexture::set_viewport_path_in_scene(const NodePath &p_path) {
 
 	path = p_path;
 
-	if (get_local_scene()) {
+	if (vp) {
+		vp->viewport_textures.erase(this);
+		vp = nullptr;
+	}
+
+	if (proxy_ph.is_valid()) {
+		RS::get_singleton()->free(proxy_ph);
+	}
+	if (proxy.is_valid()) {
+		RS::get_singleton()->free(proxy);
+	}
+	proxy_ph = RID();
+	proxy = RID();
+
+	if (get_local_scene() && !path.is_empty()) {
 		setup_local_to_scene();
+	} else {
+		emit_changed();
 	}
 }
 
@@ -171,6 +186,8 @@ void ViewportTexture::_setup_local_to_scene(const Node *p_loc_scene) {
 		proxy = RS::get_singleton()->texture_proxy_create(vp->texture_rid);
 	}
 	vp_pending = false;
+
+	emit_changed();
 }
 
 void ViewportTexture::_bind_methods() {
@@ -408,9 +425,28 @@ int Viewport::_sub_window_find(Window *p_window) {
 	return -1;
 }
 
+void Viewport::_update_viewport_path() {
+	if (viewport_textures.is_empty()) {
+		return;
+	}
+
+	Node *scene_root = get_scene_file_path().is_empty() ? get_owner() : this;
+	if (!scene_root && is_inside_tree()) {
+		scene_root = get_tree()->get_edited_scene_root();
+	}
+	if (scene_root && (scene_root == this || scene_root->is_ancestor_of(this))) {
+		NodePath path_in_scene = scene_root->get_path_to(this);
+		for (ViewportTexture *E : viewport_textures) {
+			E->path = path_in_scene;
+		}
+	}
+}
+
 void Viewport::_notification(int p_what) {
 	switch (p_what) {
 		case NOTIFICATION_ENTER_TREE: {
+			_update_viewport_path();
+
 			if (get_parent()) {
 				parent = get_parent()->get_viewport();
 				RenderingServer::get_singleton()->viewport_set_parent_viewport(viewport, parent->get_viewport_rid());
@@ -503,6 +539,10 @@ void Viewport::_notification(int p_what) {
 			RenderingServer::get_singleton()->viewport_set_parent_viewport(viewport, RID());
 		} break;
 
+		case NOTIFICATION_PATH_RENAMED: {
+			_update_viewport_path();
+		} break;
+
 		case NOTIFICATION_INTERNAL_PHYSICS_PROCESS: {
 			if (!get_tree()) {
 				return;
diff --git a/scene/main/viewport.h b/scene/main/viewport.h
index e88e0628dd..de0abec052 100644
--- a/scene/main/viewport.h
+++ b/scene/main/viewport.h
@@ -317,6 +317,8 @@ private:
 	Ref<ViewportTexture> default_texture;
 	HashSet<ViewportTexture *> viewport_textures;
 
+	void _update_viewport_path();
+
 	SDFOversize sdf_oversize = SDF_OVERSIZE_120_PERCENT;
 	SDFScale sdf_scale = SDF_SCALE_50_PERCENT;