export_fbx_bin.py

    fbx_objects_elements(root, scene_data)

    # How data are inter-connected.
    fbx_connections_elements(root, scene_data)

    # Animation.
    fbx_takes_elements(root, scene_data)

    # Cleanup!
    fbx_scene_data_cleanup(scene_data)

    # And we are down, we can write the whole thing!
    encode_bin.write(filepath, root, FBX_VERSION)

    # Clear cached ObjectWrappers!
    ObjectWrapper.cache_clear()

    # copy all collected files, if we did not embed them.
    if not media_settings.embed_textures:
        bpy_extras.io_utils.path_reference_copy(media_settings.copy_set)

    print('export finished in %.4f sec.' % (time.process_time() - start_time))
    return {'FINISHED'}


# defaults for applications, currently only unity but could add others.
def defaults_unity3d():
    return {
        # These options seem to produce the same result as the old Ascii exporter in Unity3D:
        "axis_up": 'Y',
        "axis_forward": '-Z',
        "global_matrix": Matrix.Rotation(-math.pi / 2.0, 4, 'X'),
        # Should really be True, but it can cause problems if a model is already in a scene or prefab
        # with the old transforms.
        "bake_space_transform": False,

        "use_selection": False,

        "object_types": {'ARMATURE', 'EMPTY', 'MESH', 'OTHER'},
        "use_mesh_modifiers": True,
        "use_mesh_modifiers_render": True,
        "use_mesh_edges": False,
        "mesh_smooth_type": 'FACE',
        "use_tspace": False,  # XXX Why? Unity is expected to support tspace import...

        "use_armature_deform_only": True,

        "use_custom_props": True,

        "bake_anim": True,
        "bake_anim_simplify_factor": 1.0,
        "bake_anim_step": 1.0,
        "bake_anim_use_nla_strips": True,
        "bake_anim_use_all_actions": True,
        "add_leaf_bones": False,  # Avoid memory/performance cost for something only useful for modelling
        "primary_bone_axis": 'Y',  # Doesn't really matter for Unity, so leave unchanged
        "secondary_bone_axis": 'X',

        "path_mode": 'AUTO',
        "embed_textures": False,
        "batch_mode": 'OFF',
    }


def save(operator, context,
         filepath="",
         use_selection=False,
         use_active_collection=False,
         batch_mode='OFF',
         use_batch_own_dir=False,
         **kwargs
         ):
    """
    This is a wrapper around save_single, which handles multi-scenes (or collections) cases, when batch-exporting
    a whole .blend file.
    """

    ret = {'FINISHED'}

    active_object = context.view_layer.objects.active

    org_mode = None
    if active_object and active_object.mode != 'OBJECT' and bpy.ops.object.mode_set.poll():
        org_mode = active_object.mode
        bpy.ops.object.mode_set(mode='OBJECT')

    if batch_mode == 'OFF':
        kwargs_mod = kwargs.copy()
        if use_active_collection:
            if use_selection:
                ctx_objects = tuple(obj
                                    for obj in context.view_layer.active_layer_collection.collection.all_objects
                                    if obj.select_get())
            else:
                ctx_objects = context.view_layer.active_layer_collection.collection.all_objects
        else:
            if use_selection:
                ctx_objects = context.selected_objects
            else:
                ctx_objects = context.view_layer.objects
        kwargs_mod["context_objects"] = ctx_objects

        ret = save_single(operator, context.scene, context.depsgraph, filepath, **kwargs_mod)
    else:
        # XXX We need a way to generate a depsgraph for inactive view_layers first...
        # XXX Also, what to do in case of batch-exporting scenes, when there is more than one view layer?
        #     Scenes have no concept of 'active' view layer, that's on window level...
        fbxpath = filepath

        prefix = os.path.basename(fbxpath)
        if prefix:
            fbxpath = os.path.dirname(fbxpath)

        if batch_mode == 'COLLECTION':
            data_seq = tuple((coll, coll.name, 'objects') for coll in bpy.data.collections if coll.objects)
        elif batch_mode in {'SCENE_COLLECTION', 'ACTIVE_SCENE_COLLECTION'}:
            scenes = [context.scene] if batch_mode == 'ACTIVE_SCENE_COLLECTION' else bpy.data.scenes
            data_seq = []
            for scene in scenes:
                if not scene.objects:
                    continue
                #                                      Needed to avoid having tens of 'Master Collection' entries.
                todo_collections = [(scene.collection, "_".join((scene.name, scene.collection.name)))]
                while todo_collections:
                    coll, coll_name = todo_collections.pop()
                    todo_collections.extend(((c, c.name) for c in coll.children if c.all_objects))
                    data_seq.append((coll, coll_name, 'all_objects'))
        else:
            data_seq = tuple((scene, scene.name, 'objects') for scene in bpy.data.scenes if scene.objects)

        # call this function within a loop with BATCH_ENABLE == False

        new_fbxpath = fbxpath  # own dir option modifies, we need to keep an original
        for data, data_name, data_obj_propname in data_seq:  # scene or collection
            newname = "_".join((prefix, bpy.path.clean_name(data_name))) if prefix else bpy.path.clean_name(data_name)

            if use_batch_own_dir:
                new_fbxpath = os.path.join(fbxpath, newname)
                # path may already exist... and be a file.
                while os.path.isfile(new_fbxpath):
                    new_fbxpath = "_".join((new_fbxpath, "dir"))
                if not os.path.exists(new_fbxpath):
                    os.makedirs(new_fbxpath)

            filepath = os.path.join(new_fbxpath, newname + '.fbx')

            print('\nBatch exporting %s as...\n\t%r' % (data, filepath))

            if batch_mode in {'COLLECTION', 'SCENE_COLLECTION', 'ACTIVE_SCENE_COLLECTION'}:
                # Collection, so that objects update properly, add a dummy scene.
                scene = bpy.data.scenes.new(name="FBX_Temp")
                src_scenes = {}  # Count how much each 'source' scenes are used.
                for obj in getattr(data, data_obj_propname):
                    for src_sce in obj.users_scene:
                        src_scenes[src_sce] = src_scenes.setdefault(src_sce, 0) + 1
                    scene.collection.objects.link(obj)

                # Find the 'most used' source scene, and use its unit settings. This is somewhat weak, but should work
                # fine in most cases, and avoids stupid issues like T41931.
                best_src_scene = None
                best_src_scene_users = -1
                for sce, nbr_users in src_scenes.items():
                    if (nbr_users) > best_src_scene_users:
                        best_src_scene_users = nbr_users
                        best_src_scene = sce
                scene.unit_settings.system = best_src_scene.unit_settings.system
                scene.unit_settings.system_rotation = best_src_scene.unit_settings.system_rotation
                scene.unit_settings.scale_length = best_src_scene.unit_settings.scale_length

                scene.update()
                # TODO - BUMMER! Armatures not in the group wont animate the mesh
            else:
                scene = data

            kwargs_batch = kwargs.copy()
            kwargs_batch["context_objects"] = getattr(data, data_obj_propname)

            save_single(operator, scene, scene.view_layers[0].depsgraph, filepath, **kwargs_batch)

            if batch_mode in {'COLLECTION', 'SCENE_COLLECTION', 'ACTIVE_SCENE_COLLECTION'}:
                # Remove temp collection scene.
                bpy.data.scenes.remove(scene)

    if active_object and org_mode:
        context.view_layer.objects.active = active_object
        if bpy.ops.object.mode_set.poll():
            bpy.ops.object.mode_set(mode=org_mode)

    return ret