Add option to import skeleton rest as RESET animation

Also creates an AnimationPlayer if one does not exist.
Designed to be used in conjunction with loading rest pose in another importer.

doc/classes/ResourceImporterScene.xml

@@ -21,6 +21,9 @@
 		<member name="animation/import" type="bool" setter="" getter="" default="true">
 			If [code]true[/code], import animations from the 3D scene.
 		</member>
+		<member name="animation/import_rest_as_RESET" type="bool" setter="" getter="" default="false">
+			If [code]true[/code], adds an [Animation] named [code]RESET[/code], containing the [method Skeleton3D.get_bone_rest] from [Skeleton3D] nodes. This can be useful to extract an animation in the reference pose.
+		</member>
 		<member name="animation/remove_immutable_tracks" type="bool" setter="" getter="" default="true">
 			If [code]true[/code], remove animation tracks that only contain default values. This can reduce output file size and memory usage with certain 3D scenes, depending on the contents of their animation tracks.
 		</member>

editor/import/3d/resource_importer_scene.cpp

@@ -312,6 +312,71 @@ String ResourceImporterScene::get_preset_name(int p_idx) const {
 	return String();
 }
 
+void ResourceImporterScene::_pre_fix_global(Node *p_scene, const HashMap<StringName, Variant> &p_options) const {
+	if (p_options.has("animation/import_rest_as_RESET") && (bool)p_options["animation/import_rest_as_RESET"]) {
+		TypedArray<Node> anim_players = p_scene->find_children("*", "AnimationPlayer");
+		if (anim_players.is_empty()) {
+			AnimationPlayer *anim_player = memnew(AnimationPlayer);
+			anim_player->set_name("AnimationPlayer");
+			p_scene->add_child(anim_player);
+			anim_player->set_owner(p_scene);
+			anim_players.append(anim_player);
+		}
+		Ref<Animation> reset_anim;
+		for (int i = 0; i < anim_players.size(); i++) {
+			AnimationPlayer *player = cast_to<AnimationPlayer>(anim_players[i]);
+			if (player->has_animation(SNAME("RESET"))) {
+				reset_anim = player->get_animation(SNAME("RESET"));
+				break;
+			}
+		}
+		if (reset_anim.is_null()) {
+			AnimationPlayer *anim_player = cast_to<AnimationPlayer>(anim_players[0]);
+			reset_anim.instantiate();
+			Ref<AnimationLibrary> anim_library;
+			if (anim_player->has_animation_library(StringName())) {
+				anim_library = anim_player->get_animation_library(StringName());
+			} else {
+				anim_library.instantiate();
+				anim_player->add_animation_library(StringName(), anim_library);
+			}
+			anim_library->add_animation(SNAME("RESET"), reset_anim);
+		}
+		TypedArray<Node> skeletons = p_scene->find_children("*", "Skeleton3D");
+		for (int i = 0; i < skeletons.size(); i++) {
+			Skeleton3D *skeleton = cast_to<Skeleton3D>(skeletons[i]);
+			NodePath skeleton_path = p_scene->get_path_to(skeleton);
+
+			HashSet<NodePath> existing_pos_tracks;
+			HashSet<NodePath> existing_rot_tracks;
+			for (int trk_i = 0; trk_i < reset_anim->get_track_count(); trk_i++) {
+				NodePath np = reset_anim->track_get_path(trk_i);
+				if (reset_anim->track_get_type(trk_i) == Animation::TYPE_POSITION_3D) {
+					existing_pos_tracks.insert(np);
+				}
+				if (reset_anim->track_get_type(trk_i) == Animation::TYPE_ROTATION_3D) {
+					existing_rot_tracks.insert(np);
+				}
+			}
+			for (int bone_i = 0; bone_i < skeleton->get_bone_count(); bone_i++) {
+				NodePath bone_path(skeleton_path.get_names(), Vector<StringName>{ skeleton->get_bone_name(bone_i) }, false);
+				if (!existing_pos_tracks.has(bone_path)) {
+					int pos_t = reset_anim->add_track(Animation::TYPE_POSITION_3D);
+					reset_anim->track_set_path(pos_t, bone_path);
+					reset_anim->position_track_insert_key(pos_t, 0.0, skeleton->get_bone_rest(bone_i).origin);
+					reset_anim->track_set_imported(pos_t, true);
+				}
+				if (!existing_rot_tracks.has(bone_path)) {
+					int rot_t = reset_anim->add_track(Animation::TYPE_ROTATION_3D);
+					reset_anim->track_set_path(rot_t, bone_path);
+					reset_anim->rotation_track_insert_key(rot_t, 0.0, skeleton->get_bone_rest(bone_i).basis.get_rotation_quaternion());
+					reset_anim->track_set_imported(rot_t, true);
+				}
+			}
+		}
+	}
+}
+
 static bool _teststr(const String &p_what, const String &p_str) {
 	String what = p_what;
 
@@ -1945,6 +2010,7 @@ void ResourceImporterScene::get_import_options(const String &p_path, List<Import
 	r_options->push_back(ImportOption(PropertyInfo(Variant::FLOAT, "animation/fps", PROPERTY_HINT_RANGE, "1,120,1"), 30));
 	r_options->push_back(ImportOption(PropertyInfo(Variant::BOOL, "animation/trimming"), false));
 	r_options->push_back(ImportOption(PropertyInfo(Variant::BOOL, "animation/remove_immutable_tracks"), true));
+	r_options->push_back(ImportOption(PropertyInfo(Variant::BOOL, "animation/import_rest_as_RESET"), false));
 	r_options->push_back(ImportOption(PropertyInfo(Variant::STRING, "import_script/path", PROPERTY_HINT_FILE, script_ext_hint), ""));
 
 	r_options->push_back(ImportOption(PropertyInfo(Variant::DICTIONARY, "_subresources", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR), Dictionary()));
@@ -2387,6 +2453,8 @@ Node *ResourceImporterScene::pre_import(const String &p_source_file, const HashM
 		return nullptr;
 	}
 
+	_pre_fix_global(scene, p_options);
+
 	HashMap<Ref<ImporterMesh>, Vector<Ref<Shape3D>>> collision_map;
 	List<Pair<NodePath, Node *>> node_renames;
 	_pre_fix_node(scene, scene, collision_map, nullptr, node_renames);
@@ -2521,6 +2589,8 @@ Error ResourceImporterScene::import(const String &p_source_file, const String &p
 		}
 	}
 
+	_pre_fix_global(scene, p_options);
+
 	HashSet<Ref<ImporterMesh>> scanned_meshes;
 	HashMap<Ref<ImporterMesh>, Vector<Ref<Shape3D>>> collision_map;
 	Pair<PackedVector3Array, PackedInt32Array> occluder_arrays;

editor/import/3d/resource_importer_scene.h

@@ -282,6 +282,7 @@ class ResourceImporterScene : public ResourceImporter {
 	// Import scenes *after* everything else (such as textures).
 	virtual int get_import_order() const override { return ResourceImporter::IMPORT_ORDER_SCENE; }
 
+	void _pre_fix_global(Node *p_scene, const HashMap<StringName, Variant> &p_options) const;
 	Node *_pre_fix_node(Node *p_node, Node *p_root, HashMap<Ref<ImporterMesh>, Vector<Ref<Shape3D>>> &r_collision_map, Pair<PackedVector3Array, PackedInt32Array> *r_occluder_arrays, List<Pair<NodePath, Node *>> &r_node_renames);
 	Node *_pre_fix_animations(Node *p_node, Node *p_root, const Dictionary &p_node_data, const Dictionary &p_animation_data, float p_animation_fps);
 	Node *_post_fix_node(Node *p_node, Node *p_root, HashMap<Ref<ImporterMesh>, Vector<Ref<Shape3D>>> &collision_map, Pair<PackedVector3Array, PackedInt32Array> &r_occluder_arrays, HashSet<Ref<ImporterMesh>> &r_scanned_meshes, const Dictionary &p_node_data, const Dictionary &p_material_data, const Dictionary &p_animation_data, float p_animation_fps, float p_applied_root_scale);

editor/import/3d/scene_import_settings.cpp

@@ -433,13 +433,20 @@ void SceneImportSettingsDialog::_update_view_gizmos() {
 		return;
 	}
 	const HashMap<StringName, Variant> &main_settings = scene_import_settings_data->current;
+	bool reshow_settings = false;
 	if (main_settings.has("nodes/import_as_skeleton_bones")) {
 		bool new_import_as_skeleton = main_settings["nodes/import_as_skeleton_bones"];
-		if (new_import_as_skeleton != previous_import_as_skeleton) {
-			previous_import_as_skeleton = new_import_as_skeleton;
-			_re_import();
-			open_settings(base_path);
-		}
+		reshow_settings = reshow_settings || (new_import_as_skeleton != previous_import_as_skeleton);
+		previous_import_as_skeleton = new_import_as_skeleton;
+	}
+	if (main_settings.has("animation/import_rest_as_RESET")) {
+		bool new_rest_as_reset = main_settings["animation/import_rest_as_RESET"];
+		reshow_settings = reshow_settings || (new_rest_as_reset != previous_rest_as_reset);
+		previous_rest_as_reset = new_rest_as_reset;
+	}
+	if (reshow_settings) {
+		_re_import();
+		open_settings(base_path);
 		return;
 	}
 	for (const KeyValue<String, NodeData> &e : node_map) {
@@ -688,6 +695,9 @@ void SceneImportSettingsDialog::open_settings(const String &p_path, bool p_for_a
 	if (main_settings.has("nodes/import_as_skeleton_bones")) {
 		previous_import_as_skeleton = main_settings["nodes/import_as_skeleton_bones"];
 	}
+	if (main_settings.has("animation/import_rest_as_RESET")) {
+		previous_rest_as_reset = main_settings["animation/import_rest_as_RESET"];
+	}
 	popup_centered_ratio();
 	_update_view_gizmos();
 	_update_camera();

editor/import/3d/scene_import_settings.h

@@ -97,6 +97,7 @@ class SceneImportSettingsDialog : public ConfirmationDialog {
 	Animation::LoopMode animation_loop_mode = Animation::LOOP_NONE;
 	bool animation_pingpong = false;
 	bool previous_import_as_skeleton = false;
+	bool previous_rest_as_reset = false;
 
 	Ref<StandardMaterial3D> collider_mat;