export_fbx_bin.py

                    p_keyed[idx] = (currframe, val)
            p_currframe, p_key, p_key_write = currframe, key, key_write
        # Always key last sampled values (we ignore curves with a single valid key anyway).
        p_key_write[:] = [True] * len(p_key_write)


def fbx_animations_objects(scene_data):
    """
    Generate animation data from objects.
    """
    objects = scene_data.objects
    bake_step = scene_data.settings.bake_anim_step
    scene = scene_data.scene

    # FBX mapping info: Property affected, and name of the "sub" property (to distinguish e.g. vector's channels).
    fbx_names = (
        ("Lcl Translation", "T", "d|X"), ("Lcl Translation", "T", "d|Y"), ("Lcl Translation", "T", "d|Z"),
        ("Lcl Rotation", "R", "d|X"), ("Lcl Rotation", "R", "d|Y"), ("Lcl Rotation", "R", "d|Z"),
        ("Lcl Scaling", "S", "d|X"), ("Lcl Scaling", "S", "d|Y"), ("Lcl Scaling", "S", "d|Z"),
    )

    back_currframe = scene.frame_current
    animdata = OrderedDict((obj, []) for obj in objects.keys())

    currframe = scene.frame_start
    while currframe < scene.frame_end:
        scene.frame_set(int(currframe), currframe - int(currframe))
        for obj in objects.keys():
            if isinstance(obj, Bone):
                continue  # TODO!
            # We compute baked loc/rot/scale for all objects.
            loc, rot, scale, _m, _mr = fbx_object_tx(scene_data, obj)
            tx = tuple(loc) + tuple(units_convert_iter(rot, "radian", "degree")) + tuple(scale)
            animdata[obj].append((currframe, tx, [False] * len(tx)))
        currframe += bake_step

    scene.frame_set(back_currframe, 0.0)

    fbx_animations_simplify(scene_data, animdata)

    animations = OrderedDict()

    # And now, produce final data (usable by FBX export code)...
    for obj, keys in animdata.items():
        if not keys:
            continue
        curves = [[] for k in keys[0][1]]
        for currframe, key, key_write in keys:
            #if obj.name == "Cube":
                #print(currframe, key, key_write)
            for idx, (val, wrt) in enumerate(zip(key, key_write)):
                if wrt:
                    curves[idx].append((currframe, val))

        loc, rot, scale, _m, _mr = fbx_object_tx(scene_data, obj)
        tx = tuple(loc) + tuple(units_convert_iter(rot, "radian", "degree")) + tuple(scale)
        # If animation for a channel, (True, keyframes), else (False, current value).
        final_keys = OrderedDict()
        for idx, c in enumerate(curves):
            fbx_group, fbx_gname, fbx_item = fbx_names[idx]
            fbx_item_key = get_blender_anim_curve_key(obj, fbx_group, fbx_item)
            if fbx_group not in final_keys:
                final_keys[fbx_group] = (get_blender_anim_curve_node_key(obj, fbx_group), OrderedDict(), fbx_gname)
            final_keys[fbx_group][1][fbx_item] = (fbx_item_key, tx[idx], c, True if len(c) > 1 else False)
        # And now, remove anim groups (i.e. groups of curves affecting a single FBX property) with no curve at all!
        del_groups = []
        for grp, (_k, data, _n) in final_keys.items():
            if True in (d[3] for d in data.values()):
                continue
            del_groups.append(grp)
        for grp in del_groups:
            del final_keys[grp]

        if final_keys:
            animations[obj] = (get_blender_anim_layer_key(obj), final_keys)

    return (get_blender_anim_stack_key(scene), animations) if animations else None


def fbx_data_from_scene(scene, settings):
    """
    Do some pre-processing over scene's data...
    """
    objtypes = settings.object_types

    ##### Gathering data...

    # This is rather simple for now, maybe we could end generating templates with most-used values
    # instead of default ones?
    objects = OrderedDict((obj, get_blenderID_key(obj)) for obj in scene.objects if obj.type in objtypes)
    data_lamps = OrderedDict((obj.data, get_blenderID_key(obj.data)) for obj in objects if obj.type == 'LAMP')
    # Unfortunately, FBX camera data contains object-level data (like position, orientation, etc.)...
    data_cameras = OrderedDict((obj, get_blenderID_key(obj.data)) for obj in objects if obj.type == 'CAMERA')
    data_meshes = OrderedDict((obj.data, (get_blenderID_key(obj.data), obj)) for obj in objects if obj.type == 'MESH')

    # Armatures!
    data_bones = OrderedDict()
    data_deformers = OrderedDict()
    arm_parents = set()
    for obj in tuple(objects.keys()):
        if obj.type not in {'ARMATURE'}:
            continue
        fbx_skeleton_from_armature(scene, settings, obj, objects, data_bones, data_deformers, arm_parents)

    # Some world settings are embedded in FBX materials...
    if scene.world:
        data_world = OrderedDict(((scene.world, get_blenderID_key(scene.world)),))
    else:
        data_world = OrderedDict()

    # TODO: Check all the mat stuff works even when mats are linked to Objects
    #       (we can then have the same mesh used with different materials...).
    #       *Should* work, as FBX always links its materials to Models (i.e. objects).
    #       XXX However, material indices would probably break...
    data_materials = OrderedDict()
    for obj in objects:
        # Only meshes for now!
        if not isinstance(obj, Object) or obj.type not in {'MESH'}:
            continue
        for mat_s in obj.material_slots:
            mat = mat_s.material
            # Note theoretically, FBX supports any kind of materials, even GLSL shaders etc.
            # However, I doubt anything else than Lambert/Phong is really portable!
            # We support any kind of 'surface' shader though, better to have some kind of default Lambert than nothing.
            # TODO: Support nodes (*BIG* todo!).
            if mat.type in {'SURFACE'} and not mat.use_nodes:
                if mat in data_materials:
                    data_materials[mat][1].append(obj)
                else:
                    data_materials[mat] = (get_blenderID_key(mat), [obj])

    # Note FBX textures also hold their mapping info.
    # TODO: Support layers?
    data_textures = OrderedDict()
    # FbxVideo also used to store static images...
    data_videos = OrderedDict()
    # For now, do not use world textures, don't think they can be linked to anything FBX wise...
    for mat in data_materials.keys():
        for tex in mat.texture_slots:
            if tex is None:
                continue
            # For now, only consider image textures.
            # Note FBX does has support for procedural, but this is not portable at all (opaque blob),
            # so not useful for us.
            # TODO I think ENVIRONMENT_MAP should be usable in FBX as well, but for now let it aside.
            #if tex.texture.type not in {'IMAGE', 'ENVIRONMENT_MAP'}:
            if tex.texture.type not in {'IMAGE'}:
                continue
            img = tex.texture.image
            if img is None:
                continue
            # Find out whether we can actually use this texture for this material, in FBX context.
            tex_fbx_props = fbx_mat_properties_from_texture(tex)
            if not tex_fbx_props:
                continue
            if tex in data_textures:
                data_textures[tex][1][mat] = tex_fbx_props
            else:
                data_textures[tex] = (get_blenderID_key(tex), OrderedDict((mat, tex_fbx_props)))
            if img in data_videos:
                data_videos[img][1].append(tex)
            else:
                data_videos[img] = (get_blenderID_key(img), [tex])

    # Animation...
    # From objects only for a start.
    tmp_scdata = FBXData(  # Kind of hack, we need a temp scene_data for object's space handling to bake animations...
        None, None, None,
        settings, scene, objects, None,
        data_lamps, data_cameras, data_meshes, None,
        data_bones, data_deformers,
        data_world, data_materials, data_textures, data_videos,
    )
    animations = fbx_animations_objects(tmp_scdata)

    ##### Creation of templates...

    templates = OrderedDict()
    templates[b"GlobalSettings"] = fbx_template_def_globalsettings(scene, settings, nbr_users=1)

    # XXX Looks like there can only be one NodeAttribute template? At lest, never found a light template... :/
    if data_lamps:
        templates[b"Light"] = fbx_template_def_light(scene, settings, nbr_users=len(data_lamps))

    if data_cameras:
        templates[b"Camera"] = fbx_template_def_camera(scene, settings, nbr_users=len(data_cameras))

    if data_bones:
        templates[b"Bone"] = fbx_template_def_bone(scene, settings, nbr_users=len(data_bones))

    if data_meshes:
        templates[b"Geometry"] = fbx_template_def_geometry(scene, settings, nbr_users=len(data_meshes))

    if objects:
        templates[b"Model"] = fbx_template_def_model(scene, settings, nbr_users=len(objects))

    if arm_parents:
        # Number of Pose|BindPose elements should be the same as number of meshes-parented-to-armatures
        templates[b"BindPose"] = fbx_template_def_pose(scene, settings, nbr_users=len(arm_parents))

    if data_deformers:
        nbr = len(data_deformers)
        nbr += sum(len(clusters) for def_me in data_deformers.values() for a, b, clusters in def_me.values())
        templates[b"Deformers"] = fbx_template_def_deformer(scene, settings, nbr_users=nbr)

    # No world support in FBX...
    """
    if data_world:
        templates[b"World"] = fbx_template_def_world(scene, settings, nbr_users=len(data_world))
    """

    if data_materials:
        templates[b"Material"] = fbx_template_def_material(scene, settings, nbr_users=len(data_materials))

    if data_textures:
        templates[b"TextureFile"] = fbx_template_def_texture_file(scene, settings, nbr_users=len(data_textures))

    if data_videos:
        templates[b"Video"] = fbx_template_def_video(scene, settings, nbr_users=len(data_videos))

    if animations:
        # One stack!
        templates[b"AnimationStack"] = fbx_template_def_animstack(scene, settings, nbr_users=1)
        # One layer per animated object.
        templates[b"AnimationLayer"] = fbx_template_def_animlayer(scene, settings, nbr_users=len(animations[1]))
        # As much curve node as animated properties.
        nbr = sum(len(al) for _kal, al in animations[1].values())
        templates[b"AnimationCurveNode"] = fbx_template_def_animcurvenode(scene, settings, nbr_users=nbr)
        # And the number of curves themselves...
        nbr = sum(1 if ac else 0 for _kal, al in animations[1].values()
                                 for _kacn, acn, _acn_n in al.values()
                                 for _kac, _dv, ac, _acv in acn.values())
        templates[b"AnimationCurve"] = fbx_template_def_animcurve(scene, settings, nbr_users=nbr)

    templates_users = sum(tmpl.nbr_users for tmpl in templates.values())

    ##### Creation of connections...

    connections = []

    # Objects (with classical parenting).
    for obj, obj_key in objects.items():
        # Bones are handled later.
        if isinstance(obj, Object):
            par = obj.parent
            par_key = 0  # Convention, "root" node (never explicitly written).
            if par and par in objects:
                par_type = obj.parent_type
                if par_type in {'OBJECT', 'BONE'}:
                    # Meshes parented to armature also have 'OBJECT' par_type, in FBX this is handled separately,
                    # we do not want an extra object parenting!
                    if (par, obj) not in arm_parents:
                        par_key = objects[par]
                else:
                    print("Sorry, “{}” parenting type is not supported".format(par_type))
            connections.append((b"OO", get_fbxuid_from_key(obj_key), get_fbxuid_from_key(par_key), None))

    # Armature & Bone chains.
    for bo, (bo_key, _bo_data_key, arm) in data_bones.items():
        par = bo.parent
        if not par:  # Root bone.
            par = arm
        if par not in objects:
            continue
        connections.append((b"OO", get_fbxuid_from_key(bo_key), get_fbxuid_from_key(objects[par]), None))

    # Cameras
    for obj_cam, cam_key in data_cameras.items():
        cam_obj_key = objects[obj_cam]
        connections.append((b"OO", get_fbxuid_from_key(cam_key), get_fbxuid_from_key(cam_obj_key), None))

    # Object data.
    for obj, obj_key in objects.items():
        if isinstance(obj, Bone):
            _bo_key, bo_data_key, _arm = data_bones[obj]
            assert(_bo_key == obj_key)
            connections.append((b"OO", get_fbxuid_from_key(bo_data_key), get_fbxuid_from_key(obj_key), None))
        elif obj.type == 'LAMP':
            lamp_key = data_lamps[obj.data]
            connections.append((b"OO", get_fbxuid_from_key(lamp_key), get_fbxuid_from_key(obj_key), None))
        elif obj.type == 'MESH':
            mesh_key, _obj = data_meshes[obj.data]
            connections.append((b"OO", get_fbxuid_from_key(mesh_key), get_fbxuid_from_key(obj_key), None))

    # Deformers (armature-to-geometry, only for meshes currently)...
    for arm, deformed_meshes in data_deformers.items():
        for me, (skin_key, _obj, clusters) in deformed_meshes.items():
            # skin -> geometry
            mesh_key, _obj = data_meshes[me]
            connections.append((b"OO", get_fbxuid_from_key(skin_key), get_fbxuid_from_key(mesh_key), None))
            for bo, clstr_key in clusters.items():
                # cluster -> skin
                connections.append((b"OO", get_fbxuid_from_key(clstr_key), get_fbxuid_from_key(skin_key), None))
                # bone -> cluster
                connections.append((b"OO", get_fbxuid_from_key(objects[bo]), get_fbxuid_from_key(clstr_key), None))

    # Materials
    mesh_mat_indices = OrderedDict()
    _objs_indices = {}
    for mat, (mat_key, objs) in data_materials.items():
        for obj in objs:
            obj_key = objects[obj]
            connections.append((b"OO", get_fbxuid_from_key(mat_key), get_fbxuid_from_key(obj_key), None))
            # Get index of this mat for this object.
            # Mat indices for mesh faces are determined by their order in 'mat to ob' connections.
            # Only mats for meshes currently...
            me = obj.data
            idx = _objs_indices[obj] = _objs_indices.get(obj, -1) + 1
            mesh_mat_indices.setdefault(me, OrderedDict())[mat] = idx
    del _objs_indices

    # Textures
    for tex, (tex_key, mats) in data_textures.items():
        for mat, fbx_mat_props in mats.items():
            mat_key, _objs = data_materials[mat]
            for fbx_prop in fbx_mat_props:
                # texture -> material properties
                connections.append((b"OP", get_fbxuid_from_key(tex_key), get_fbxuid_from_key(mat_key), fbx_prop))

    # Images
    for vid, (vid_key, texs) in data_videos.items():
        for tex in texs:
            tex_key, _texs = data_textures[tex]
            connections.append((b"OO", get_fbxuid_from_key(vid_key), get_fbxuid_from_key(tex_key), None))

    #Animations
    if animations:
        # Animstack itself is linked nowhere!
        astack_id = get_fbxuid_from_key(animations[0])
        for obj, (alayer_key, acurvenodes) in animations[1].items():
            obj_id = get_fbxuid_from_key(objects[obj])
            # Animlayer -> animstack.
            alayer_id = get_fbxuid_from_key(alayer_key)
            connections.append((b"OO", alayer_id, astack_id, None))
            for fbx_prop, (acurvenode_key, acurves, acurvenode_name) in acurvenodes.items():
                # Animcurvenode -> animalayer.
                acurvenode_id = get_fbxuid_from_key(acurvenode_key)
                connections.append((b"OO", acurvenode_id, alayer_id, None))
                # Animcurvenode -> object property.
                connections.append((b"OP", acurvenode_id, obj_id, fbx_prop.encode()))
                for fbx_item, (acurve_key, dafault_value, acurve, acurve_valid) in acurves.items():
                    if acurve:
                        # Animcurve -> Animcurvenode.
                        connections.append((b"OP", get_fbxuid_from_key(acurve_key), acurvenode_id, fbx_item.encode()))

    ##### And pack all this!

    return FBXData(
        templates, templates_users, connections,
        settings, scene, objects, animations,
        data_lamps, data_cameras, data_meshes, mesh_mat_indices,
        data_bones, data_deformers,
        data_world, data_materials, data_textures, data_videos,
    )


##### Top-level FBX elements generators. #####

def fbx_header_elements(root, scene_data, time=None):
    """
    Write boiling code of FBX root.
    time is expected to be a datetime.datetime object, or None (using now() in this case).
    """
    ##### Start of FBXHeaderExtension element.
    header_ext = elem_empty(root, b"FBXHeaderExtension")

    elem_data_single_int32(header_ext, b"FBXHeaderVersion", FBX_HEADER_VERSION)

    elem_data_single_int32(header_ext, b"FBXVersion", FBX_VERSION)

    # No encryption!
    elem_data_single_int32(header_ext, b"EncryptionType", 0)

    if time is None:
        time = datetime.datetime.now()
    elem = elem_empty(header_ext, b"CreationTimeStamp")
    elem_data_single_int32(elem, b"Version", 1000)
    elem_data_single_int32(elem, b"Year", time.year)
    elem_data_single_int32(elem, b"Month", time.month)
    elem_data_single_int32(elem, b"Day", time.day)
    elem_data_single_int32(elem, b"Hour", time.hour)
    elem_data_single_int32(elem, b"Minute", time.minute)
    elem_data_single_int32(elem, b"Second", time.second)
    elem_data_single_int32(elem, b"Millisecond", time.microsecond // 1000)

    elem_data_single_string_unicode(header_ext, b"Creator", "Blender version %s" % bpy.app.version_string)

    # 'SceneInfo' seems mandatory to get a valid FBX file...
    # TODO use real values!
    # XXX Should we use scene.name.encode() here?
    scene_info = elem_data_single_string(header_ext, b"SceneInfo", fbx_name_class(b"GlobalInfo", b"SceneInfo"))
    scene_info.add_string(b"UserData")
    elem_data_single_string(scene_info, b"Type", b"UserData")
    elem_data_single_int32(scene_info, b"Version", FBX_SCENEINFO_VERSION)
    meta_data = elem_empty(scene_info, b"MetaData")
    elem_data_single_int32(meta_data, b"Version", FBX_SCENEINFO_VERSION)
    elem_data_single_string(meta_data, b"Title", b"")
    elem_data_single_string(meta_data, b"Subject", b"")
    elem_data_single_string(meta_data, b"Author", b"")
    elem_data_single_string(meta_data, b"Keywords", b"")
    elem_data_single_string(meta_data, b"Revision", b"")
    elem_data_single_string(meta_data, b"Comment", b"")

    props = elem_properties(scene_info)
    elem_props_set(props, "p_string_url", b"DocumentUrl", "/foobar.fbx")
    elem_props_set(props, "p_string_url", b"SrcDocumentUrl", "/foobar.fbx")
    original = elem_props_compound(props, b"Original")
    original("p_string", b"ApplicationVendor", "Blender Foundation")
    original("p_string", b"ApplicationName", "Blender")
    original("p_string", b"ApplicationVersion", "2.70")
    original("p_datetime", b"DateTime_GMT", "01/01/1970 00:00:00.000")
    original("p_string", b"FileName", "/foobar.fbx")
    lastsaved = elem_props_compound(props, b"LastSaved")
    lastsaved("p_string", b"ApplicationVendor", "Blender Foundation")
    lastsaved("p_string", b"ApplicationName", "Blender")
    lastsaved("p_string", b"ApplicationVersion", "2.70")
    lastsaved("p_datetime", b"DateTime_GMT", "01/01/1970 00:00:00.000")

    ##### End of FBXHeaderExtension element.

    # FileID is replaced by dummy value currently...
    elem_data_single_bytes(root, b"FileId", b"FooBar")

    # CreationTime is replaced by dummy value currently, but anyway...
    elem_data_single_string_unicode(root, b"CreationTime",
                                    "{:04}-{:02}-{:02} {:02}:{:02}:{:02}:{:03}"
                                    "".format(time.year, time.month, time.day, time.hour, time.minute, time.second,
                                              time.microsecond * 1000))

    elem_data_single_string_unicode(root, b"Creator", "Blender version %s" % bpy.app.version_string)

    ##### Start of GlobalSettings element.
    global_settings = elem_empty(root, b"GlobalSettings")

    elem_data_single_int32(global_settings, b"Version", 1000)

    props = elem_properties(global_settings)
    up_axis, front_axis, coord_axis = RIGHT_HAND_AXES[scene_data.settings.to_axes]
    elem_props_set(props, "p_integer", b"UpAxis", up_axis[0])
    elem_props_set(props, "p_integer", b"UpAxisSign", up_axis[1])
    elem_props_set(props, "p_integer", b"FrontAxis", front_axis[0])
    elem_props_set(props, "p_integer", b"FrontAxisSign", front_axis[1])
    elem_props_set(props, "p_integer", b"CoordAxis", coord_axis[0])
    elem_props_set(props, "p_integer", b"CoordAxisSign", coord_axis[1])
    elem_props_set(props, "p_integer", b"OriginalUpAxis", -1)
    elem_props_set(props, "p_integer", b"OriginalUpAxisSign", 1)
    elem_props_set(props, "p_double", b"UnitScaleFactor", 1.0)
    elem_props_set(props, "p_double", b"OriginalUnitScaleFactor", 1.0)
    elem_props_set(props, "p_color_rgb", b"AmbientColor", (0.0, 0.0, 0.0))
    elem_props_set(props, "p_string", b"DefaultCamera", "Producer Perspective")

    # Global timing data.
    r = scene_data.scene.render
    fps = r.fps / r.fps_base
    f_start = scene_data.scene.frame_start
    f_end = scene_data.scene.frame_end
    elem_props_set(props, "p_enum", b"TimeMode", 14)  # FPS, 14 = custom...
    elem_props_set(props, "p_timestamp", b"TimeSpanStart", int(units_convert(f_start / fps, "second", "ktime")))
    elem_props_set(props, "p_timestamp", b"TimeSpanStop", int(units_convert(f_end / fps, "second", "ktime")))
    #elem_props_set(props, "p_timestamp", b"TimeSpanStart", 0)
    #elem_props_set(props, "p_timestamp", b"TimeSpanStop", FBX_KTIME)
    elem_props_set(props, "p_double", b"CustomFrameRate", fps)

    ##### End of GlobalSettings element.


def fbx_documents_elements(root, scene_data):
    """
    Write 'Document' part of FBX root.
    Seems like FBX support multiple documents, but until I find examples of such, we'll stick to single doc!
    time is expected to be a datetime.datetime object, or None (using now() in this case).
    """
    name = scene_data.scene.name

    ##### Start of Documents element.
    docs = elem_empty(root, b"Documents")

    elem_data_single_int32(docs, b"Count", 1)

    doc_uid = get_fbxuid_from_key("__FBX_Document__" + name)
    doc = elem_data_single_int64(docs, b"Document", doc_uid)
    doc.add_string_unicode(name)
    doc.add_string_unicode(name)

    props = elem_properties(doc)
    elem_props_set(props, "p_object", b"SourceObject")
    elem_props_set(props, "p_string", b"ActiveAnimStackName", "")

    # XXX Some kind of ID? Offset?
    #     Anyway, as long as we have only one doc, probably not an issue.
    elem_data_single_int64(doc, b"RootNode", 0)


def fbx_references_elements(root, scene_data):
    """
    Have no idea what references are in FBX currently... Just writing empty element.
    """
    docs = elem_empty(root, b"References")


def fbx_definitions_elements(root, scene_data):
    """
    Templates definitions. Only used by Objects data afaik (apart from dummy GlobalSettings one).
    """
    definitions = elem_empty(root, b"Definitions")

    elem_data_single_int32(definitions, b"Version", FBX_TEMPLATES_VERSION)
    elem_data_single_int32(definitions, b"Count", scene_data.templates_users)

    fbx_templates_generate(definitions, scene_data.templates)


def fbx_objects_elements(root, scene_data):
    """
    Data (objects, geometry, material, textures, armatures, etc.
    """
    objects = elem_empty(root, b"Objects")

    for lamp in scene_data.data_lamps.keys():
        fbx_data_lamp_elements(objects, lamp, scene_data)

    for cam in scene_data.data_cameras.keys():
        fbx_data_camera_elements(objects, cam, scene_data)

    for mesh in scene_data.data_meshes.keys():
        fbx_data_mesh_elements(objects, mesh, scene_data)

    for obj in scene_data.objects.keys():
        fbx_data_object_elements(objects, obj, scene_data)

    for obj in scene_data.objects.keys():
        if not isinstance(obj, Object) or obj.type not in {'ARMATURE'}:
            continue
        fbx_data_armature_elements(objects, obj, scene_data)

    for mat in scene_data.data_materials.keys():
        fbx_data_material_elements(objects, mat, scene_data)

    for tex in scene_data.data_textures.keys():
        fbx_data_texture_file_elements(objects, tex, scene_data)

    for vid in scene_data.data_videos.keys():
        fbx_data_video_elements(objects, vid, scene_data)

    fbx_data_animation_elements(objects, scene_data)


def fbx_connections_elements(root, scene_data):
    """
    Relations between Objects (which material uses which texture, and so on).
    """
    connections = elem_empty(root, b"Connections")

    for c in scene_data.connections:
        elem_connection(connections, *c)


def fbx_takes_elements(root, scene_data):
    """
    Animations. Have yet to check how this work...
    """
    # XXX Are takes needed at all in new anim system?
    takes = elem_empty(root, b"Takes")
    elem_data_single_string(takes, b"Current", b"")

    animations = scene_data.animations
    if animations is None:
        return
    scene = scene_data.scene
    take_name = scene.name.encode()
    fps = scene.render.fps / scene.render.fps_base
    scene_start_ktime = int(units_convert(scene.frame_start / fps, "second", "ktime"))
    scene_end_ktime = int(units_convert(scene.frame_end / fps, "second", "ktime"))

    take = elem_data_single_string(takes, b"Take", take_name)
    elem_data_single_string(take, b"FileName", take_name + b".tak")
    take_loc_time = elem_data_single_int64(take, b"LocalTime", scene_start_ktime)
    take_loc_time.add_int64(scene_end_ktime)
    take_ref_time = elem_data_single_int64(take, b"ReferenceTime", scene_start_ktime)
    take_ref_time.add_int64(scene_end_ktime)


##### "Main" functions. #####
FBXSettingsMedia = namedtuple("FBXSettingsMedia", (
    "path_mode", "base_src", "base_dst", "subdir",
    "embed_textures", "copy_set",
))
FBXSettings = namedtuple("FBXSettings", (
    "to_axes", "global_matrix", "global_scale",
    "bake_space_transform", "global_matrix_inv", "global_matrix_inv_transposed",
    "context_objects", "object_types", "use_mesh_modifiers",
    "mesh_smooth_type", "use_mesh_edges", "use_tspace", "use_armature_deform_only",
    "bake_anim", "bake_anim_step", "bake_anim_simplify_factor",
    "use_metadata", "media_settings", "use_custom_properties",
))


# This func can be called with just the filepath
def save_single(operator, scene, filepath="",
                global_matrix=Matrix(),
                axis_up="Z",
                axis_forward="Y",
                context_objects=None,
                object_types=None,
                use_mesh_modifiers=True,
                mesh_smooth_type='FACE',
                bake_anim=True,
                bake_anim_step=1.0,
                bake_anim_simplify_factor=1.0,
                use_metadata=True,
                path_mode='AUTO',
                use_mesh_edges=True,
                use_tspace=True,
                embed_textures=False,
                use_custom_properties=False,
                bake_space_transform=False,
                **kwargs
                ):

    if object_types is None:
        object_types = {'EMPTY', 'CAMERA', 'LAMP', 'ARMATURE', 'MESH'}

    global_scale = global_matrix.median_scale
    global_matrix_inv = global_matrix.inverted()
    # For transforming mesh normals.
    global_matrix_inv_transposed = global_matrix_inv.transposed()

    # Only embed textures in COPY mode!
    if embed_textures and path_mode != 'COPY':
        embed_textures = False

    media_settings = FBXSettingsMedia(
        path_mode,
        os.path.dirname(bpy.data.filepath),  # base_src
        os.path.dirname(filepath),  # base_dst
        # Local dir where to put images (medias), using FBX conventions.
        os.path.splitext(os.path.basename(filepath))[0] + ".fbm",  # subdir
        embed_textures,
        set(),  # copy_set
    )

    settings = FBXSettings(
        (axis_up, axis_forward), global_matrix, global_scale,
        bake_space_transform, global_matrix_inv, global_matrix_inv_transposed,
        context_objects, object_types, use_mesh_modifiers,
        mesh_smooth_type, use_mesh_edges, use_tspace, False,
        bake_anim, bake_anim_step, bake_anim_simplify_factor,
        False, media_settings, use_custom_properties,
    )

    import bpy_extras.io_utils

    print('\nFBX export starting... %r' % filepath)
    start_time = time.process_time()

    # Generate some data about exported scene...
    scene_data = fbx_data_from_scene(scene, settings)

    root = elem_empty(None, b"")  # Root element has no id, as it is not saved per se!

    # Mostly FBXHeaderExtension and GlobalSettings.
    fbx_header_elements(root, scene_data)

    # Documents and References are pretty much void currently.
    fbx_documents_elements(root, scene_data)
    fbx_references_elements(root, scene_data)

    # Templates definitions.
    fbx_definitions_elements(root, scene_data)

    # Actual data.
    fbx_objects_elements(root, scene_data)

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

    # Animation.
    fbx_takes_elements(root, scene_data)

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

    # 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 {
        "global_matrix": Matrix.Rotation(-math.pi / 2.0, 4, 'X'),
        "use_selection": False,
        "object_types": {'ARMATURE', 'EMPTY', 'MESH'},
        "use_mesh_modifiers": True,
        #"use_armature_deform_only": True,
        "bake_anim": True,
        #"use_anim_optimize": False,
        #"use_anim_action_all": True,
        "batch_mode": 'OFF',
        # 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,
    }


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

    ret = None

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

    if batch_mode == 'OFF':
        kwargs_mod = kwargs.copy()
        if use_selection:
            kwargs_mod["context_objects"] = context.selected_objects
        else:
            kwargs_mod["context_objects"] = context.scene.objects

        ret = save_single(operator, context.scene, filepath, **kwargs_mod)
    else:
        fbxpath = filepath

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

        if batch_mode == 'GROUP':
            data_seq = bpy.data.groups
        else:
            data_seq = bpy.data.scenes

        # call this function within a loop with BATCH_ENABLE == False
        # no scene switching done at the moment.
        # orig_sce = context.scene

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

            if use_batch_own_dir:
                new_fbxpath = os.path.join(fbxpath, newname)
                # path may already exist
                # TODO - might exist but be a file. unlikely but should probably account for it.

                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 == 'GROUP':  # group
                # group, so objects update properly, add a dummy scene.
                scene = bpy.data.scenes.new(name="FBX_Temp")
                scene.layers = [True] * 20
                # bpy.data.scenes.active = scene # XXX, cant switch
                for ob_base in data.objects:
                    scene.objects.link(ob_base)

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

            kwargs_batch = kwargs.copy()
            kwargs_batch["context_objects"] = data.objects

            save_single(operator, scene, filepath, **kwargs_batch)

            if batch_mode == 'GROUP':
                # remove temp group scene
                bpy.data.scenes.remove(scene)

        # no active scene changing!
        # bpy.data.scenes.active = orig_sce

        ret = {'FINISHED'}  # so the script wont run after we have batch exported.

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

    return ret