Keep global rest of unmapped bones if no mapped bone descendants

editor/import/3d/post_import_plugin_skeleton_rest_fixer.cpp

@@ -42,6 +42,7 @@ void PostImportPluginSkeletonRestFixer::get_internal_import_options(InternalImpo
 		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/apply_node_transforms"), true));
 		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/normalize_position_tracks"), true));
 		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/overwrite_axis"), true));
+		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/keep_unmapped_axis"), false));
 		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/reset_all_bone_poses_after_import"), true));
 		r_options->push_back(ResourceImporter::ImportOption(PropertyInfo(Variant::BOOL, "retarget/rest_fixer/fix_silhouette/enable"), false));
 		// TODO: PostImportPlugin need to be implemented such as validate_option(PropertyInfo &property, const Dictionary &p_options).
@@ -447,6 +448,54 @@ void PostImportPluginSkeletonRestFixer::internal_process(InternalImportCategory
 				old_skeleton_global_rest.push_back(src_skeleton->get_bone_global_rest(i));
 			}
 
+			bool keep_unmapped_axis = bool(p_options["retarget/rest_fixer/keep_unmapped_axis"]);
+
+			// Scan hierarchy and populate a whitelist of unmapped bones without mapped descendants.
+			Vector<int> keep_bone_rest;
+			if (keep_unmapped_axis) {
+				// Scan descendants for mapped bones.
+				std::function<bool(int)> has_mapped_desc = [&](int parent_bone) {
+					Vector<int> bones_to_process = src_skeleton->get_bone_children(parent_bone);
+					while (bones_to_process.size() > 0) {
+						int src_idx = bones_to_process[0];
+						bones_to_process.erase(src_idx);
+						Vector<int> src_children = src_skeleton->get_bone_children(src_idx);
+						for (int i = 0; i < src_children.size(); i++) {
+							bones_to_process.push_back(src_children[i]);
+						}
+
+						StringName src_bone_name = is_renamed ? StringName(src_skeleton->get_bone_name(src_idx)) : bone_map->find_profile_bone_name(src_skeleton->get_bone_name(src_idx));
+						if (src_bone_name != StringName()) {
+							if (profile->has_bone(src_bone_name)) {
+								return true;
+							}
+						}
+					}
+
+					return false;
+				};
+
+				// Populate list
+				Vector<int> bones_to_process = src_skeleton->get_parentless_bones();
+				while (bones_to_process.size() > 0) {
+					int src_idx = bones_to_process[0];
+					bones_to_process.erase(src_idx);
+					Vector<int> src_children = src_skeleton->get_bone_children(src_idx);
+					for (int i = 0; i < src_children.size(); i++) {
+						bones_to_process.push_back(src_children[i]);
+					}
+
+					StringName src_bone_name = is_renamed ? StringName(src_skeleton->get_bone_name(src_idx)) : bone_map->find_profile_bone_name(src_skeleton->get_bone_name(src_idx));
+					if (src_bone_name != StringName()) {
+						if (!profile->has_bone(src_bone_name)) {
+							if (!has_mapped_desc(src_idx)) {
+								keep_bone_rest.push_back(src_idx); // No mapped descendants. Add to whitelist.
+							}
+						}
+					}
+				}
+			}
+
 			Vector<Basis> diffs;
 			diffs.resize(src_skeleton->get_bone_count());
 			Basis *diffs_w = diffs.ptrw();
@@ -472,13 +521,11 @@ void PostImportPluginSkeletonRestFixer::internal_process(InternalImportCategory
 					int prof_idx = profile->find_bone(src_bone_name);
 					if (prof_idx >= 0) {
 						tgt_rot = src_pg.inverse() * prof_skeleton->get_bone_global_rest(prof_idx).basis; // Mapped bone uses reference pose.
-					}
-					/*
-					// If there is rest-relative animation, this logic may be work fine, but currently not so...
 					} else {
-						// tgt_rot = src_pg.inverse() * old_skeleton_global_rest[src_idx].basis; // Non-Mapped bone keeps global rest.
+						if (keep_unmapped_axis && keep_bone_rest.has(src_idx)) {
+							tgt_rot = src_pg.inverse() * old_skeleton_global_rest[src_idx].basis; // Non-Mapped bone without mapped children keeps global rest.
+						}
 					}
-					*/
 				}
 
 				if (src_skeleton->get_bone_parent(src_idx) >= 0) {