export_fbx_bin.py

        bo = obj
        matrix = (bo.matrix if is_posebone else bo.matrix_local) * MAT_CONVERT_BONE

        # Bones are in armature (object) space currently, either bring them to global space or real
        # local space (relative to parent bone).
        if is_global:
            matrix = armature.matrix_world * matrix
        else:  # Handle parent bone is needed.
            par_matrix = None
            if is_posebone and bo.bone.parent:
                par_matrix = scene_data.bones_to_posebones[bo.bone.parent].matrix
            elif bo.parent:
                par_matrix = bo.parent.matrix_local
            if par_matrix:
                par_matrix = par_matrix * MAT_CONVERT_BONE
                matrix = par_matrix.inverted() * matrix
    else:
        matrix = obj.matrix_local

        # Lamps, and cameras need to be rotated (in local space!).
        if obj.type == 'LAMP':
            matrix = matrix * MAT_CONVERT_LAMP
        elif obj.type == 'CAMERA':
            matrix = matrix * MAT_CONVERT_CAMERA

        if obj.parent:
            if is_global:
                # Move matrix to global Blender space.
                matrix = obj.parent.matrix_world * matrix
            elif use_bake_space_transform(scene_data, obj.parent):
                # Blender's and FBX's local space of parent may differ if we use bake_space_transform...
                # Apply parent's *Blender* local space...
                matrix = obj.parent.matrix_local * matrix
                # ...and move it back into parent's *FBX* local space.
                par_mat = fbx_object_matrix(scene_data, obj.parent, local_space=True)
                matrix = par_mat.inverted() * matrix

    if use_bake_space_transform(scene_data, obj):
        # If we bake the transforms we need to post-multiply inverse global transform.
        # This means that the global transform will not apply to children of this transform.
        matrix = matrix * scene_data.settings.global_matrix_inv
    if is_global:
        # In any case, pre-multiply the global matrix to get it in FBX global space!
        matrix = scene_data.settings.global_matrix * matrix

    return matrix


def fbx_object_tx(scene_data, obj, rot_euler_compat=None):
    """
    Generate object transform data (always in local space when possible).
    """
    matrix = fbx_object_matrix(scene_data, obj)
    loc, rot, scale = matrix.decompose()
    matrix_rot = rot.to_matrix()
    # quat -> euler, we always use 'XYZ' order, use ref rotation if given.
    if rot_euler_compat is not None:
        rot = rot.to_euler('XYZ', rot_euler_compat)
    else:
        rot = rot.to_euler('XYZ')

    return loc, rot, scale, matrix, matrix_rot


def fbx_name_class(name, cls):
    return FBX_NAME_CLASS_SEP.join((name, cls))


def fbx_data_element_custom_properties(props, bid):
    """
    Store custom properties of blender ID bid (any mapping-like object, in fact) into FBX properties props.
    """
    for k, v in bid.items():
        if isinstance(v, str):
            elem_props_set(props, "p_string", k.encode(), v, custom=True)
        elif isinstance(v, int):
            elem_props_set(props, "p_integer", k.encode(), v, custom=True)
        if isinstance(v, float):
            elem_props_set(props, "p_double", k.encode(), v, custom=True)


def fbx_data_empty_elements(root, empty, scene_data):
    """
    Write the Empty data block.
    """
    empty_key = scene_data.data_empties[empty]

    null = elem_data_single_int64(root, b"NodeAttribute", get_fbxuid_from_key(empty_key))
    null.add_string(fbx_name_class(empty.name.encode(), b"NodeAttribute"))
    null.add_string(b"Null")

    elem_data_single_string(null, b"TypeFlags", b"Null")

    tmpl = elem_props_template_init(scene_data.templates, b"Null")
    props = elem_properties(null)
    elem_props_template_finalize(tmpl, props)

    # No custom properties, already saved with object (Model).


def fbx_data_lamp_elements(root, lamp, scene_data):
    """
    Write the Lamp data block.
    """
    gscale = scene_data.settings.global_scale

    lamp_key = scene_data.data_lamps[lamp]
    do_light = True
    decay_type = FBX_LIGHT_DECAY_TYPES['CONSTANT']
    do_shadow = False
    shadow_color = Vector((0.0, 0.0, 0.0))
    if lamp.type not in {'HEMI'}:
        if lamp.type not in {'SUN'}:
            decay_type = FBX_LIGHT_DECAY_TYPES[lamp.falloff_type]
        do_light = (not lamp.use_only_shadow) and (lamp.use_specular or lamp.use_diffuse)
        do_shadow = lamp.shadow_method not in {'NOSHADOW'}
        shadow_color = lamp.shadow_color

    light = elem_data_single_int64(root, b"NodeAttribute", get_fbxuid_from_key(lamp_key))
    light.add_string(fbx_name_class(lamp.name.encode(), b"NodeAttribute"))
    light.add_string(b"Light")

    elem_data_single_int32(light, b"GeometryVersion", FBX_GEOMETRY_VERSION)  # Sic...

    tmpl = elem_props_template_init(scene_data.templates, b"Light")
    props = elem_properties(light)
    elem_props_template_set(tmpl, props, "p_enum", b"LightType", FBX_LIGHT_TYPES[lamp.type])
    elem_props_template_set(tmpl, props, "p_bool", b"CastLight", do_light)
    elem_props_template_set(tmpl, props, "p_color", b"Color", lamp.color)
    elem_props_template_set(tmpl, props, "p_number", b"Intensity", lamp.energy * 100.0)
    elem_props_template_set(tmpl, props, "p_enum", b"DecayType", decay_type)
    elem_props_template_set(tmpl, props, "p_double", b"DecayStart", lamp.distance * gscale)
    elem_props_template_set(tmpl, props, "p_bool", b"CastShadows", do_shadow)
    elem_props_template_set(tmpl, props, "p_color", b"ShadowColor", shadow_color)
    if lamp.type in {'SPOT'}:
        elem_props_template_set(tmpl, props, "p_double", b"OuterAngle", math.degrees(lamp.spot_size))
        elem_props_template_set(tmpl, props, "p_double", b"InnerAngle",
                                math.degrees(lamp.spot_size * (1.0 - lamp.spot_blend)))
    elem_props_template_finalize(tmpl, props)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, lamp)


def fbx_data_camera_elements(root, cam_obj, scene_data):
    """
    Write the Camera data blocks.
    """
    gscale = scene_data.settings.global_scale

    cam_data = cam_obj.data
    cam_key = scene_data.data_cameras[cam_obj]

    # Real data now, good old camera!
    # Object transform info.
    loc, rot, scale, matrix, matrix_rot = fbx_object_tx(scene_data, cam_obj)
    up = matrix_rot * Vector((0.0, 1.0, 0.0))
    to = matrix_rot * Vector((0.0, 0.0, -1.0))
    # Render settings.
    # TODO We could export much more...
    render = scene_data.scene.render
    width = render.resolution_x
    height = render.resolution_y
    aspect = width / height
    # Film width & height from mm to inches
    filmwidth = units_convert(cam_data.sensor_width, "millimeter", "inch")
    filmheight = units_convert(cam_data.sensor_height, "millimeter", "inch")
    filmaspect = filmwidth / filmheight
    # Film offset
    offsetx = filmwidth * cam_data.shift_x
    offsety = filmaspect * filmheight * cam_data.shift_y

    cam = elem_data_single_int64(root, b"NodeAttribute", get_fbxuid_from_key(cam_key))
    cam.add_string(fbx_name_class(cam_data.name.encode(), b"NodeAttribute"))
    cam.add_string(b"Camera")

    tmpl = elem_props_template_init(scene_data.templates, b"Camera")
    props = elem_properties(cam)

    elem_props_template_set(tmpl, props, "p_vector", b"Position", loc)
    elem_props_template_set(tmpl, props, "p_vector", b"UpVector", up)
    elem_props_template_set(tmpl, props, "p_vector", b"InterestPosition", loc + to)  # Point, not vector!
    # Should we use world value?
    elem_props_template_set(tmpl, props, "p_color", b"BackgroundColor", (0.0, 0.0, 0.0))
    elem_props_template_set(tmpl, props, "p_bool", b"DisplayTurnTableIcon", True)

    elem_props_template_set(tmpl, props, "p_double", b"FilmWidth", filmwidth)
    elem_props_template_set(tmpl, props, "p_double", b"FilmHeight", filmheight)
    elem_props_template_set(tmpl, props, "p_double", b"FilmAspectRatio", filmaspect)
    elem_props_template_set(tmpl, props, "p_double", b"FilmOffsetX", offsetx)
    elem_props_template_set(tmpl, props, "p_double", b"FilmOffsetY", offsety)

    elem_props_template_set(tmpl, props, "p_enum", b"ApertureMode", 3)  # FocalLength.
    elem_props_template_set(tmpl, props, "p_enum", b"GateFit", 2)  # FitHorizontal.
    elem_props_template_set(tmpl, props, "p_fov", b"FieldOfView", math.degrees(cam_data.angle_x))
    elem_props_template_set(tmpl, props, "p_fov_x", b"FieldOfViewX", math.degrees(cam_data.angle_x))
    elem_props_template_set(tmpl, props, "p_fov_y", b"FieldOfViewY", math.degrees(cam_data.angle_y))
    # No need to convert to inches here...
    elem_props_template_set(tmpl, props, "p_double", b"FocalLength", cam_data.lens)
    elem_props_template_set(tmpl, props, "p_double", b"SafeAreaAspectRatio", aspect)

    elem_props_template_set(tmpl, props, "p_double", b"NearPlane", cam_data.clip_start * gscale)
    elem_props_template_set(tmpl, props, "p_double", b"FarPlane", cam_data.clip_end * gscale)
    elem_props_template_set(tmpl, props, "p_enum", b"BackPlaneDistanceMode", 1)  # RelativeToCamera.
    elem_props_template_set(tmpl, props, "p_double", b"BackPlaneDistance", cam_data.clip_end * gscale)

    elem_props_template_finalize(tmpl, props)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, cam_data)

    elem_data_single_string(cam, b"TypeFlags", b"Camera")
    elem_data_single_int32(cam, b"GeometryVersion", 124)  # Sic...
    elem_data_vec_float64(cam, b"Position", loc)
    elem_data_vec_float64(cam, b"Up", up)
    elem_data_vec_float64(cam, b"LookAt", to)
    elem_data_single_int32(cam, b"ShowInfoOnMoving", 1)
    elem_data_single_int32(cam, b"ShowAudio", 0)
    elem_data_vec_float64(cam, b"AudioColor", (0.0, 1.0, 0.0))
    elem_data_single_float64(cam, b"CameraOrthoZoom", 1.0)


def fbx_data_mesh_elements(root, me_obj, scene_data):
    """
    Write the Mesh (Geometry) data block.
    """
    # Ugly helper... :/
    def _infinite_gen(val):
        while 1:
            yield val

    me_key, me, _free = scene_data.data_meshes[me_obj]

    # No gscale/gmat here, all data are supposed to be in object space.
    smooth_type = scene_data.settings.mesh_smooth_type

    do_bake_space_transform = use_bake_space_transform(scene_data, me_obj)

    # Vertices are in object space, but we are post-multiplying all transforms with the inverse of the
    # global matrix, so we need to apply the global matrix to the vertices to get the correct result.
    geom_mat_co = scene_data.settings.global_matrix if do_bake_space_transform else None
    # We need to apply the inverse transpose of the global matrix when transforming normals.
    geom_mat_no = Matrix(scene_data.settings.global_matrix_inv_transposed) if do_bake_space_transform else None
    if geom_mat_no is not None:
        # Remove translation & scaling!
        geom_mat_no.translation = Vector()
        geom_mat_no.normalize()

    geom = elem_data_single_int64(root, b"Geometry", get_fbxuid_from_key(me_key))
    geom.add_string(fbx_name_class(me.name.encode(), b"Geometry"))
    geom.add_string(b"Mesh")

    tmpl = elem_props_template_init(scene_data.templates, b"Geometry")
    props = elem_properties(geom)

    elem_props_template_finalize(tmpl, props)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, me)

    elem_data_single_int32(geom, b"GeometryVersion", FBX_GEOMETRY_VERSION)

    # Vertex cos.
    t_co = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.vertices) * 3
    me.vertices.foreach_get("co", t_co)
    if geom_mat_co is not None:
        def _vcos_transformed_gen(raw_cos, m=None):
            # Note: we could most likely get much better performances with numpy, but will leave this as TODO for now.
            return chain(*(m * Vector(v) for v in zip(*(iter(raw_cos),) * 3)))
        t_co = _vcos_transformed_gen(t_co, geom_mat_co)
    elem_data_single_float64_array(geom, b"Vertices", t_co)
    del t_co

    # Polygon indices.
    #
    # We do loose edges as two-vertices faces, if enabled...
    #
    # Note we have to process Edges in the same time, as they are based on poly's loops...
    loop_nbr = len(me.loops)
    t_pvi = array.array(data_types.ARRAY_INT32, (0,)) * loop_nbr
    t_ls = [None] * len(me.polygons)

    me.loops.foreach_get("vertex_index", t_pvi)
    me.polygons.foreach_get("loop_start", t_ls)

    # Add "fake" faces for loose edges.
    if scene_data.settings.use_mesh_edges:
        t_le = tuple(e.vertices for e in me.edges if e.is_loose)
        t_pvi.extend(chain(*t_le))
        t_ls.extend(range(loop_nbr, loop_nbr + len(t_le), 2))
        del t_le

    # Edges...
    # Note: Edges are represented as a loop here: each edge uses a single index, which refers to the polygon array.
    #       The edge is made by the vertex indexed py this polygon's point and the next one on the same polygon.
    #       Advantage: Only one index per edge.
    #       Drawback: Only polygon's edges can be represented (that's why we have to add fake two-verts polygons
    #                 for loose edges).
    #       We also have to store a mapping from real edges to their indices in this array, for edge-mapped data
    #       (like e.g. crease).
    t_eli = array.array(data_types.ARRAY_INT32)
    edges_map = {}
    edges_nbr = 0
    if t_ls and t_pvi:
        t_ls = set(t_ls)
        todo_edges = [None] * len(me.edges) * 2
        me.edges.foreach_get("vertices", todo_edges)
        todo_edges = set((v1, v2) if v1 < v2 else (v2, v1) for v1, v2 in zip(*(iter(todo_edges),) * 2))

        li = 0
        vi = vi_start = t_pvi[0]
        for li_next, vi_next in enumerate(t_pvi[1:] + t_pvi[:1], start=1):
            if li_next in t_ls:  # End of a poly's loop.
                vi2 = vi_start
                vi_start = vi_next
            else:
                vi2 = vi_next

            e_key = (vi, vi2) if vi < vi2 else (vi2, vi)
            if e_key in todo_edges:
                t_eli.append(li)
                todo_edges.remove(e_key)
                edges_map[e_key] = edges_nbr
                edges_nbr += 1

            vi = vi_next
            li = li_next
    # End of edges!

    # We have to ^-1 last index of each loop.
    for ls in t_ls:
        t_pvi[ls - 1] ^= -1

    # And finally we can write data!
    elem_data_single_int32_array(geom, b"PolygonVertexIndex", t_pvi)
    elem_data_single_int32_array(geom, b"Edges", t_eli)
    del t_pvi
    del t_ls
    del t_eli

    # And now, layers!

    # Smoothing.
    if smooth_type in {'FACE', 'EDGE'}:
        t_ps = None
        _map = b""
        if smooth_type == 'FACE':
            t_ps = array.array(data_types.ARRAY_INT32, (0,)) * len(me.polygons)
            me.polygons.foreach_get("use_smooth", t_ps)
            _map = b"ByPolygon"
        else:  # EDGE
            # Write Edge Smoothing.
            t_ps = array.array(data_types.ARRAY_INT32, (0,)) * edges_nbr
            for e in me.edges:
                if e.key not in edges_map:
                    continue  # Only loose edges, in theory!
                t_ps[edges_map[e.key]] = not e.use_edge_sharp
            _map = b"ByEdge"
        lay_smooth = elem_data_single_int32(geom, b"LayerElementSmoothing", 0)
        elem_data_single_int32(lay_smooth, b"Version", FBX_GEOMETRY_SMOOTHING_VERSION)
        elem_data_single_string(lay_smooth, b"Name", b"")
        elem_data_single_string(lay_smooth, b"MappingInformationType", _map)
        elem_data_single_string(lay_smooth, b"ReferenceInformationType", b"Direct")
        elem_data_single_int32_array(lay_smooth, b"Smoothing", t_ps)  # Sight, int32 for bool...
        del t_ps

    # TODO: Edge crease (LayerElementCrease).

    # And we are done with edges!
    del edges_map

    # Loop normals.
    # NOTE: this is not supported by importer currently.
    # XXX Official docs says normals should use IndexToDirect,
    #     but this does not seem well supported by apps currently...
    me.calc_normals_split()

    def _nortuples_gen(raw_nors, m):
        # Great, now normals are also expected 4D!
        # XXX Back to 3D normals for now!
        #gen = zip(*(iter(raw_nors),) * 3 + (_infinite_gen(1.0),))
        gen = zip(*(iter(raw_nors),) * 3)
        return gen if m is None else (m * Vector(v) for v in gen)

    t_ln = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops) * 3
    me.loops.foreach_get("normal", t_ln)
    t_ln = _nortuples_gen(t_ln, geom_mat_no)
    if 0:
        t_ln = tuple(t_ln)  # No choice... :/

        lay_nor = elem_data_single_int32(geom, b"LayerElementNormal", 0)
        elem_data_single_int32(lay_nor, b"Version", FBX_GEOMETRY_NORMAL_VERSION)
        elem_data_single_string(lay_nor, b"Name", b"")
        elem_data_single_string(lay_nor, b"MappingInformationType", b"ByPolygonVertex")
        elem_data_single_string(lay_nor, b"ReferenceInformationType", b"IndexToDirect")

        ln2idx = tuple(set(t_ln))
        elem_data_single_float64_array(lay_nor, b"Normals", chain(*ln2idx))
        # Normal weights, no idea what it is.
        #t_lnw = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(ln2idx)
        #elem_data_single_float64_array(lay_nor, b"NormalsW", t_lnw)

        ln2idx = {nor: idx for idx, nor in enumerate(ln2idx)}
        elem_data_single_int32_array(lay_nor, b"NormalsIndex", (ln2idx[n] for n in t_ln))

        del ln2idx
        #del t_lnw
    else:
        lay_nor = elem_data_single_int32(geom, b"LayerElementNormal", 0)
        elem_data_single_int32(lay_nor, b"Version", FBX_GEOMETRY_NORMAL_VERSION)
        elem_data_single_string(lay_nor, b"Name", b"")
        elem_data_single_string(lay_nor, b"MappingInformationType", b"ByPolygonVertex")
        elem_data_single_string(lay_nor, b"ReferenceInformationType", b"Direct")
        elem_data_single_float64_array(lay_nor, b"Normals", chain(*t_ln))
        # Normal weights, no idea what it is.
        #t_ln = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops)
        #elem_data_single_float64_array(lay_nor, b"NormalsW", t_ln)
    del t_ln

    # tspace
    tspacenumber = 0
    if scene_data.settings.use_tspace:
        tspacenumber = len(me.uv_layers)
        if tspacenumber:
            t_ln = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops) * 3
            #t_lnw = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops)
            for idx, uvlayer in enumerate(me.uv_layers):
                name = uvlayer.name
                me.calc_tangents(name)
                # Loop bitangents (aka binormals).
                # NOTE: this is not supported by importer currently.
                me.loops.foreach_get("bitangent", t_ln)
                lay_nor = elem_data_single_int32(geom, b"LayerElementBinormal", idx)
                elem_data_single_int32(lay_nor, b"Version", FBX_GEOMETRY_BINORMAL_VERSION)
                elem_data_single_string_unicode(lay_nor, b"Name", name)
                elem_data_single_string(lay_nor, b"MappingInformationType", b"ByPolygonVertex")
                elem_data_single_string(lay_nor, b"ReferenceInformationType", b"Direct")
                elem_data_single_float64_array(lay_nor, b"Binormals", chain(*_nortuples_gen(t_ln, geom_mat_no)))
                # Binormal weights, no idea what it is.
                #elem_data_single_float64_array(lay_nor, b"BinormalsW", t_lnw)

                # Loop tangents.
                # NOTE: this is not supported by importer currently.
                me.loops.foreach_get("tangent", t_ln)
                lay_nor = elem_data_single_int32(geom, b"LayerElementTangent", idx)
                elem_data_single_int32(lay_nor, b"Version", FBX_GEOMETRY_TANGENT_VERSION)
                elem_data_single_string_unicode(lay_nor, b"Name", name)
                elem_data_single_string(lay_nor, b"MappingInformationType", b"ByPolygonVertex")
                elem_data_single_string(lay_nor, b"ReferenceInformationType", b"Direct")
                elem_data_single_float64_array(lay_nor, b"Binormals", chain(*_nortuples_gen(t_ln, geom_mat_no)))
                # Tangent weights, no idea what it is.
                #elem_data_single_float64_array(lay_nor, b"TangentsW", t_lnw)

            del t_ln
            #del t_lnw
            me.free_tangents()

    me.free_normals_split()
    del _nortuples_gen

    # Write VertexColor Layers
    # note, no programs seem to use this info :/
    vcolnumber = len(me.vertex_colors)
    if vcolnumber:
        def _coltuples_gen(raw_cols):
            return zip(*(iter(raw_cols),) * 3 + (_infinite_gen(1.0),))  # We need a fake alpha...

        t_lc = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops) * 3
        for colindex, collayer in enumerate(me.vertex_colors):
            collayer.data.foreach_get("color", t_lc)
            lay_vcol = elem_data_single_int32(geom, b"LayerElementColor", colindex)
            elem_data_single_int32(lay_vcol, b"Version", FBX_GEOMETRY_VCOLOR_VERSION)
            elem_data_single_string_unicode(lay_vcol, b"Name", collayer.name)
            elem_data_single_string(lay_vcol, b"MappingInformationType", b"ByPolygonVertex")
            elem_data_single_string(lay_vcol, b"ReferenceInformationType", b"IndexToDirect")

            col2idx = tuple(set(_coltuples_gen(t_lc)))
            elem_data_single_float64_array(lay_vcol, b"Colors", chain(*col2idx))  # Flatten again...

            col2idx = {col: idx for idx, col in enumerate(col2idx)}
            elem_data_single_int32_array(lay_vcol, b"ColorIndex", (col2idx[c] for c in _coltuples_gen(t_lc)))
            del col2idx
        del t_lc
        del _coltuples_gen

    # Write UV layers.
    # Note: LayerElementTexture is deprecated since FBX 2011 - luckily!
    #       Textures are now only related to materials, in FBX!
    uvnumber = len(me.uv_layers)
    if uvnumber:
        def _uvtuples_gen(raw_uvs):
            return zip(*(iter(raw_uvs),) * 2)

        t_luv = array.array(data_types.ARRAY_FLOAT64, (0.0,)) * len(me.loops) * 2
        for uvindex, uvlayer in enumerate(me.uv_layers):
            uvlayer.data.foreach_get("uv", t_luv)
            lay_uv = elem_data_single_int32(geom, b"LayerElementUV", uvindex)
            elem_data_single_int32(lay_uv, b"Version", FBX_GEOMETRY_UV_VERSION)
            elem_data_single_string_unicode(lay_uv, b"Name", uvlayer.name)
            elem_data_single_string(lay_uv, b"MappingInformationType", b"ByPolygonVertex")
            elem_data_single_string(lay_uv, b"ReferenceInformationType", b"IndexToDirect")

            uv2idx = tuple(set(_uvtuples_gen(t_luv)))
            elem_data_single_float64_array(lay_uv, b"UV", chain(*uv2idx))  # Flatten again...

            uv2idx = {uv: idx for idx, uv in enumerate(uv2idx)}
            elem_data_single_int32_array(lay_uv, b"UVIndex", (uv2idx[uv] for uv in _uvtuples_gen(t_luv)))
            del uv2idx
        del t_luv
        del _uvtuples_gen

    # Face's materials.
    me_fbxmats_idx = None
    if me in scene_data.mesh_mat_indices:
        me_fbxmats_idx = scene_data.mesh_mat_indices[me]
        me_blmats = me.materials
        if me_fbxmats_idx and me_blmats:
            lay_mat = elem_data_single_int32(geom, b"LayerElementMaterial", 0)
            elem_data_single_int32(lay_mat, b"Version", FBX_GEOMETRY_MATERIAL_VERSION)
            elem_data_single_string(lay_mat, b"Name", b"")
            nbr_mats = len(me_fbxmats_idx)
            if nbr_mats > 1:
                t_pm = array.array(data_types.ARRAY_INT32, (0,)) * len(me.polygons)
                me.polygons.foreach_get("material_index", t_pm)

                # We have to validate mat indices, and map them to FBX indices.
                blmats_to_fbxmats_idxs = [me_fbxmats_idx[m] for m in me_blmats]
                mat_idx_limit = len(blmats_to_fbxmats_idxs)
                def_mat = blmats_to_fbxmats_idxs[0]
                _gen = (blmats_to_fbxmats_idxs[m] if m < mat_idx_limit else def_mat for m in t_pm)
                t_pm = array.array(data_types.ARRAY_INT32, _gen)

                elem_data_single_string(lay_mat, b"MappingInformationType", b"ByPolygon")
                # XXX Logically, should be "Direct" reference type, since we do not have any index array, and have one
                #     value per polygon...
                #     But looks like FBX expects it to be IndexToDirect here (maybe because materials are already
                #     indices??? *sigh*).
                elem_data_single_string(lay_mat, b"ReferenceInformationType", b"IndexToDirect")
                elem_data_single_int32_array(lay_mat, b"Materials", t_pm)
                del t_pm
            else:
                elem_data_single_string(lay_mat, b"MappingInformationType", b"AllSame")
                elem_data_single_string(lay_mat, b"ReferenceInformationType", b"IndexToDirect")
                elem_data_single_int32_array(lay_mat, b"Materials", [0])

    # And the "layer TOC"...

    layer = elem_data_single_int32(geom, b"Layer", 0)
    elem_data_single_int32(layer, b"Version", FBX_GEOMETRY_LAYER_VERSION)
    lay_nor = elem_empty(layer, b"LayerElement")
    elem_data_single_string(lay_nor, b"Type", b"LayerElementNormal")
    elem_data_single_int32(lay_nor, b"TypedIndex", 0)
    if smooth_type in {'FACE', 'EDGE'}:
        lay_smooth = elem_empty(layer, b"LayerElement")
        elem_data_single_string(lay_smooth, b"Type", b"LayerElementSmoothing")
        elem_data_single_int32(lay_smooth, b"TypedIndex", 0)
    if vcolnumber:
        lay_vcol = elem_empty(layer, b"LayerElement")
        elem_data_single_string(lay_vcol, b"Type", b"LayerElementColor")
        elem_data_single_int32(lay_vcol, b"TypedIndex", 0)
    if uvnumber:
        lay_uv = elem_empty(layer, b"LayerElement")
        elem_data_single_string(lay_uv, b"Type", b"LayerElementUV")
        elem_data_single_int32(lay_uv, b"TypedIndex", 0)
    if me_fbxmats_idx is not None:
        lay_mat = elem_empty(layer, b"LayerElement")
        elem_data_single_string(lay_mat, b"Type", b"LayerElementMaterial")
        elem_data_single_int32(lay_mat, b"TypedIndex", 0)

    # Add other uv and/or vcol layers...
    for vcolidx, uvidx, tspaceidx in zip_longest(range(1, vcolnumber), range(1, uvnumber), range(1, tspacenumber),
                                                 fillvalue=0):
        layer = elem_data_single_int32(geom, b"Layer", max(vcolidx, uvidx))
        elem_data_single_int32(layer, b"Version", FBX_GEOMETRY_LAYER_VERSION)
        if vcolidx:
            lay_vcol = elem_empty(layer, b"LayerElement")
            elem_data_single_string(lay_vcol, b"Type", b"LayerElementColor")
            elem_data_single_int32(lay_vcol, b"TypedIndex", vcolidx)
        if uvidx:
            lay_uv = elem_empty(layer, b"LayerElement")
            elem_data_single_string(lay_uv, b"Type", b"LayerElementUV")
            elem_data_single_int32(lay_uv, b"TypedIndex", uvidx)
        if tspaceidx:
            lay_binor = elem_empty(layer, b"LayerElement")
            elem_data_single_string(lay_binor, b"Type", b"LayerElementBinormal")
            elem_data_single_int32(lay_binor, b"TypedIndex", tspaceidx)
            lay_tan = elem_empty(layer, b"LayerElement")
            elem_data_single_string(lay_tan, b"Type", b"LayerElementTangent")
            elem_data_single_int32(lay_tan, b"TypedIndex", tspaceidx)


def fbx_data_material_elements(root, mat, scene_data):
    """
    Write the Material data block.
    """
    ambient_color = (0.0, 0.0, 0.0)
    if scene_data.data_world:
        ambient_color = next(iter(scene_data.data_world.keys())).ambient_color

    mat_key, _objs = scene_data.data_materials[mat]
    # Approximation...
    mat_type = b"Phong" if mat.specular_shader in {'COOKTORR', 'PHONG', 'BLINN'} else b"Lambert"

    fbx_mat = elem_data_single_int64(root, b"Material", get_fbxuid_from_key(mat_key))
    fbx_mat.add_string(fbx_name_class(mat.name.encode(), b"Material"))
    fbx_mat.add_string(b"")

    elem_data_single_int32(fbx_mat, b"Version", FBX_MATERIAL_VERSION)
    # those are not yet properties, it seems...
    elem_data_single_string(fbx_mat, b"ShadingModel", mat_type)
    elem_data_single_int32(fbx_mat, b"MultiLayer", 0)  # Should be bool...

    tmpl = elem_props_template_init(scene_data.templates, b"Material")
    props = elem_properties(fbx_mat)

    elem_props_template_set(tmpl, props, "p_string", b"ShadingModel", mat_type.decode())
    elem_props_template_set(tmpl, props, "p_color", b"EmissiveColor", mat.diffuse_color)
    elem_props_template_set(tmpl, props, "p_number", b"EmissiveFactor", mat.emit)
    elem_props_template_set(tmpl, props, "p_color", b"AmbientColor", ambient_color)
    elem_props_template_set(tmpl, props, "p_number", b"AmbientFactor", mat.ambient)
    elem_props_template_set(tmpl, props, "p_color", b"DiffuseColor", mat.diffuse_color)
    elem_props_template_set(tmpl, props, "p_number", b"DiffuseFactor", mat.diffuse_intensity)
    elem_props_template_set(tmpl, props, "p_color", b"TransparentColor",
                            mat.diffuse_color if mat.use_transparency else (1.0, 1.0, 1.0))
    elem_props_template_set(tmpl, props, "p_number", b"TransparencyFactor",
                            1.0 - mat.alpha if mat.use_transparency else 0.0)
    elem_props_template_set(tmpl, props, "p_number", b"Opacity", mat.alpha if mat.use_transparency else 1.0)
    elem_props_template_set(tmpl, props, "p_vector_3d", b"NormalMap", (0.0, 0.0, 0.0))
    # Not sure about those...
    """
    b"Bump": ((0.0, 0.0, 0.0), "p_vector_3d"),
    b"BumpFactor": (1.0, "p_double"),
    b"DisplacementColor": ((0.0, 0.0, 0.0), "p_color_rgb"),
    b"DisplacementFactor": (0.0, "p_double"),
    """
    if mat_type == b"Phong":
        elem_props_template_set(tmpl, props, "p_color", b"SpecularColor", mat.specular_color)
        elem_props_template_set(tmpl, props, "p_number", b"SpecularFactor", mat.specular_intensity / 2.0)
        # See Material template about those two!
        elem_props_template_set(tmpl, props, "p_number", b"Shininess", (mat.specular_hardness - 1.0) / 5.10)
        elem_props_template_set(tmpl, props, "p_number", b"ShininessExponent", (mat.specular_hardness - 1.0) / 5.10)
        elem_props_template_set(tmpl, props, "p_color", b"ReflectionColor", mat.mirror_color)
        elem_props_template_set(tmpl, props, "p_number", b"ReflectionFactor",
                                mat.raytrace_mirror.reflect_factor if mat.raytrace_mirror.use else 0.0)

    elem_props_template_finalize(tmpl, props)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, mat)


def _gen_vid_path(img, scene_data):
    msetts = scene_data.settings.media_settings
    fname_rel = bpy_extras.io_utils.path_reference(img.filepath, msetts.base_src, msetts.base_dst, msetts.path_mode,
                                                   msetts.subdir, msetts.copy_set, img.library)
    fname_abs = os.path.normpath(os.path.abspath(os.path.join(msetts.base_dst, fname_rel)))
    return fname_abs, fname_rel


def fbx_data_texture_file_elements(root, tex, scene_data):
    """
    Write the (file) Texture data block.
    """
    # XXX All this is very fuzzy to me currently...
    #     Textures do not seem to use properties as much as they could.
    #     For now assuming most logical and simple stuff.

    tex_key, _mats = scene_data.data_textures[tex]
    img = tex.texture.image
    fname_abs, fname_rel = _gen_vid_path(img, scene_data)

    fbx_tex = elem_data_single_int64(root, b"Texture", get_fbxuid_from_key(tex_key))
    fbx_tex.add_string(fbx_name_class(tex.name.encode(), b"Texture"))
    fbx_tex.add_string(b"")

    elem_data_single_string(fbx_tex, b"Type", b"TextureVideoClip")
    elem_data_single_int32(fbx_tex, b"Version", FBX_TEXTURE_VERSION)
    elem_data_single_string(fbx_tex, b"TextureName", fbx_name_class(tex.name.encode(), b"Texture"))
    elem_data_single_string(fbx_tex, b"Media", fbx_name_class(img.name.encode(), b"Video"))
    elem_data_single_string_unicode(fbx_tex, b"FileName", fname_abs)
    elem_data_single_string_unicode(fbx_tex, b"RelativeFilename", fname_rel)

    alpha_source = 0  # None
    if img.use_alpha:
        if tex.texture.use_calculate_alpha:
            alpha_source = 1  # RGBIntensity as alpha.
        else:
            alpha_source = 2  # Black, i.e. alpha channel.
    # BlendMode not useful for now, only affects layered textures afaics.
    mapping = 0  # None.
    if tex.texture_coords in {'ORCO'}:  # XXX Others?
        if tex.mapping in {'FLAT'}:
            mapping = 1  # Planar
        elif tex.mapping in {'CUBE'}:
            mapping = 4  # Box
        elif tex.mapping in {'TUBE'}:
            mapping = 3  # Cylindrical
        elif tex.mapping in {'SPHERE'}:
            mapping = 2  # Spherical
    elif tex.texture_coords in {'UV'}:
        # XXX *HOW* do we link to correct UVLayer???
        mapping = 6  # UV
    wrap_mode = 1  # Clamp
    if tex.texture.extension in {'REPEAT'}:
        wrap_mode = 0  # Repeat

    tmpl = elem_props_template_init(scene_data.templates, b"TextureFile")
    props = elem_properties(fbx_tex)
    elem_props_template_set(tmpl, props, "p_enum", b"AlphaSource", alpha_source)
    elem_props_template_set(tmpl, props, "p_bool", b"PremultiplyAlpha",
                            img.alpha_mode in {'STRAIGHT'})  # Or is it PREMUL?
    elem_props_template_set(tmpl, props, "p_enum", b"CurrentMappingType", mapping)
    elem_props_template_set(tmpl, props, "p_enum", b"WrapModeU", wrap_mode)
    elem_props_template_set(tmpl, props, "p_enum", b"WrapModeV", wrap_mode)
    elem_props_template_set(tmpl, props, "p_vector_3d", b"Translation", tex.offset)
    elem_props_template_set(tmpl, props, "p_vector_3d", b"Scaling", tex.scale)
    elem_props_template_set(tmpl, props, "p_bool", b"UseMipMap", tex.texture.use_mipmap)
    elem_props_template_finalize(tmpl, props)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, tex.texture)


def fbx_data_video_elements(root, vid, scene_data):
    """
    Write the actual image data block.
    """
    vid_key, _texs = scene_data.data_videos[vid]
    fname_abs, fname_rel = _gen_vid_path(vid, scene_data)

    fbx_vid = elem_data_single_int64(root, b"Video", get_fbxuid_from_key(vid_key))
    fbx_vid.add_string(fbx_name_class(vid.name.encode(), b"Video"))
    fbx_vid.add_string(b"Clip")

    elem_data_single_string(fbx_vid, b"Type", b"Clip")
    # XXX No Version???
    elem_data_single_string_unicode(fbx_vid, b"FileName", fname_abs)
    elem_data_single_string_unicode(fbx_vid, b"RelativeFilename", fname_rel)

    if scene_data.settings.media_settings.embed_textures:
        try:
            with open(vid.filepath, 'br') as f:
                elem_data_single_byte_array(fbx_vid, b"Content", f.read())
        except Exception as e:
            print("WARNING: embeding file {} failed ({})".format(vid.filepath, e))
            elem_data_single_byte_array(fbx_vid, b"Content", b"")
    else:
        elem_data_single_byte_array(fbx_vid, b"Content", b"")


def fbx_data_armature_elements(root, armature, scene_data):
    """
    Write:
        * Bones "data" (NodeAttribute::LimbNode, contains pretty much nothing!).
        * Deformers (i.e. Skin), bind between an armature and a mesh.
        ** SubDeformers (i.e. Cluster), one per bone/vgroup pair.
        * BindPose.
    Note armature itself has no data, it is a mere "Null" Model...
    """

    # Bones "data".
    for bo in armature.data.bones:
        _bo_key, bo_data_key, _arm = scene_data.data_bones[bo]
        fbx_bo = elem_data_single_int64(root, b"NodeAttribute", get_fbxuid_from_key(bo_data_key))
        fbx_bo.add_string(fbx_name_class(bo.name.encode(), b"NodeAttribute"))
        fbx_bo.add_string(b"LimbNode")
        elem_data_single_string(fbx_bo, b"TypeFlags", b"Skeleton")

        tmpl = elem_props_template_init(scene_data.templates, b"Bone")
        props = elem_properties(fbx_bo)
        elem_props_template_set(tmpl, props, "p_double", b"Size", (bo.tail_local - bo.head_local).length)
        elem_props_template_finalize(tmpl, props)

        # Custom properties.
        if scene_data.settings.use_custom_properties:
            fbx_data_element_custom_properties(props, bo)

    # Deformers and BindPoses.
    # Note: we might also use Deformers for our "parent to vertex" stuff???
    deformer = scene_data.data_deformers.get(armature, None)
    if deformer is not None:
        for me, (skin_key, obj, clusters) in deformer.items():
            # BindPose.
            # We assume bind pose for our bones are their "Editmode" pose...
            # All matrices are expected in global (world) space.
            bindpose_key = get_blender_armature_bindpose_key(armature, me)
            fbx_pose = elem_data_single_int64(root, b"Pose", get_fbxuid_from_key(bindpose_key))
            fbx_pose.add_string(fbx_name_class(me.name.encode(), b"Pose"))
            fbx_pose.add_string(b"BindPose")

            elem_data_single_string(fbx_pose, b"Type", b"BindPose")
            elem_data_single_int32(fbx_pose, b"Version", FBX_POSE_BIND_VERSION)
            elem_data_single_int32(fbx_pose, b"NbPoseNodes", 1 + len(armature.data.bones))

            # First node is mesh/object.
            mat_world_obj = fbx_object_matrix(scene_data, obj, global_space=True)
            fbx_posenode = elem_empty(fbx_pose, b"PoseNode")
            elem_data_single_int64(fbx_posenode, b"Node", get_fbxuid_from_key(scene_data.objects[obj]))
            elem_data_single_float64_array(fbx_posenode, b"Matrix", matrix_to_array(mat_world_obj))
            # And all bones of armature!
            mat_world_bones = {}
            for bo in armature.data.bones:
                bomat = fbx_object_matrix(scene_data, bo, armature, global_space=True)
                mat_world_bones[bo] = bomat
                fbx_posenode = elem_empty(fbx_pose, b"PoseNode")
                elem_data_single_int64(fbx_posenode, b"Node", get_fbxuid_from_key(scene_data.objects[bo]))
                elem_data_single_float64_array(fbx_posenode, b"Matrix", matrix_to_array(bomat))

            # Deformer.
            fbx_skin = elem_data_single_int64(root, b"Deformer", get_fbxuid_from_key(skin_key))
            fbx_skin.add_string(fbx_name_class(armature.name.encode(), b"Deformer"))
            fbx_skin.add_string(b"Skin")

            elem_data_single_int32(fbx_skin, b"Version", FBX_DEFORMER_SKIN_VERSION)
            elem_data_single_float64(fbx_skin, b"Link_DeformAcuracy", 50.0)  # Only vague idea what it is...

            for bo, clstr_key in clusters.items():
                # Find which vertices are affected by this bone/vgroup pair, and matching weights.
                indices = []
                weights = []
                vg_idx = obj.vertex_groups[bo.name].index
                for idx, v in enumerate(me.vertices):
                    vert_vg = [vg for vg in v.groups if vg.group == vg_idx]
                    if not vert_vg:
                        continue
                    indices.append(idx)
                    weights.append(vert_vg[0].weight)

                # Create the cluster.
                fbx_clstr = elem_data_single_int64(root, b"Deformer", get_fbxuid_from_key(clstr_key))
                fbx_clstr.add_string(fbx_name_class(bo.name.encode(), b"SubDeformer"))
                fbx_clstr.add_string(b"Cluster")

                elem_data_single_int32(fbx_clstr, b"Version", FBX_DEFORMER_CLUSTER_VERSION)
                # No idea what that user data might be...
                fbx_userdata = elem_data_single_string(fbx_clstr, b"UserData", b"")
                fbx_userdata.add_string(b"")
                if indices:
                    elem_data_single_int32_array(fbx_clstr, b"Indexes", indices)
                    elem_data_single_float64_array(fbx_clstr, b"Weights", weights)
                # Transform and TransformLink matrices...
                # They seem to be mostly the same as BindPose ones???
                # WARNING! Even though official FBX API presents Transform in global space,
                #          **it is stored in bone space in FBX data!** See:
                #          http://area.autodesk.com/forum/autodesk-fbx/fbx-sdk/why-the-values-return-
                #                 by-fbxcluster-gettransformmatrix-x-not-same-with-the-value-in-ascii-fbx-file/
                elem_data_single_float64_array(fbx_clstr, b"Transform",
                                               matrix_to_array(mat_world_bones[bo].inverted() * mat_world_obj))
                elem_data_single_float64_array(fbx_clstr, b"TransformLink", matrix_to_array(mat_world_bones[bo]))


def fbx_data_object_elements(root, obj, scene_data):
    """
    Write the Object (Model) data blocks.
    Note we handle "Model" part of bones as well here!
    """
    obj_type = b"Null"  # default, sort of empty...
    if isinstance(obj, Bone):
        obj_type = b"LimbNode"
    elif (obj.type in BLENDER_OBJECT_TYPES_MESHLIKE):
        obj_type = b"Mesh"
    elif (obj.type == 'LAMP'):
        obj_type = b"Light"
    elif (obj.type == 'CAMERA'):
        obj_type = b"Camera"
    obj_key = scene_data.objects[obj]
    model = elem_data_single_int64(root, b"Model", get_fbxuid_from_key(obj_key))
    model.add_string(fbx_name_class(obj.name.encode(), b"Model"))
    model.add_string(obj_type)

    elem_data_single_int32(model, b"Version", FBX_MODELS_VERSION)

    # Object transform info.
    loc, rot, scale, matrix, matrix_rot = fbx_object_tx(scene_data, obj)
    rot = tuple(units_convert_iter(rot, "radian", "degree"))

    tmpl = elem_props_template_init(scene_data.templates, b"Model")
    # For now add only loc/rot/scale...
    props = elem_properties(model)
    elem_props_template_set(tmpl, props, "p_lcl_translation", b"Lcl Translation", loc)
    elem_props_template_set(tmpl, props, "p_lcl_rotation", b"Lcl Rotation", rot)
    elem_props_template_set(tmpl, props, "p_lcl_scaling", b"Lcl Scaling", scale)

    # Custom properties.
    if scene_data.settings.use_custom_properties:
        fbx_data_element_custom_properties(props, obj)

    # Those settings would obviously need to be edited in a complete version of the exporter, may depends on
    # object type, etc.
    elem_data_single_int32(model, b"MultiLayer", 0)
    elem_data_single_int32(model, b"MultiTake", 0)
    elem_data_single_bool(model, b"Shading", True)
    elem_data_single_string(model, b"Culling", b"CullingOff")

    if isinstance(obj, Object) and obj.type == 'CAMERA':
        # Why, oh why are FBX cameras such a mess???
        # And WHY add camera data HERE??? Not even sure this is needed...
        render = scene_data.scene.render
        width = render.resolution_x * 1.0
        height = render.resolution_y * 1.0
        elem_props_template_set(tmpl, props, "p_enum", b"ResolutionMode", 0)  # Don't know what it means
        elem_props_template_set(tmpl, props, "p_double", b"AspectW", width)
        elem_props_template_set(tmpl, props, "p_double", b"AspectH", height)
        elem_props_template_set(tmpl, props, "p_bool", b"ViewFrustum", True)
        elem_props_template_set(tmpl, props, "p_enum", b"BackgroundMode", 0)  # Don't know what it means
        elem_props_template_set(tmpl, props, "p_bool", b"ForegroundTransparent", True)

    elem_props_template_finalize(tmpl, props)


def fbx_data_animation_elements(root, scene_data):
    """
    Write animation data.
    """
    animations = scene_data.animations
    if not animations:
        return
    scene = scene_data.scene

    fps = scene.render.fps / scene.render.fps_base

    def keys_to_ktimes(keys):
        return (int(v) for v in units_convert_iter((f / fps for f, _v in keys), "second", "ktime"))

    # Animation stacks.
    for astack_key, alayers, alayer_key, name, f_start, f_end in animations:
        astack = elem_data_single_int64(root, b"AnimationStack", get_fbxuid_from_key(astack_key))
        astack.add_string(fbx_name_class(name, b"AnimStack"))
        astack.add_string(b"")

        astack_tmpl = elem_props_template_init(scene_data.templates, b"AnimationStack")
        astack_props = elem_properties(astack)
        r = scene_data.scene.render
        fps = r.fps / r.fps_base
        start = int(units_convert(f_start / fps, "second", "ktime"))
        end = int(units_convert(f_end / fps, "second", "ktime"))
        elem_props_template_set(astack_tmpl, astack_props, "p_timestamp", b"LocalStart", start)
        elem_props_template_set(astack_tmpl, astack_props, "p_timestamp", b"LocalStop", end)
        elem_props_template_set(astack_tmpl, astack_props, "p_timestamp", b"ReferenceStart", start)
        elem_props_template_set(astack_tmpl, astack_props, "p_timestamp", b"ReferenceStop", end)
        elem_props_template_finalize(astack_tmpl, astack_props)

        # For now, only one layer for all animations.
        alayer = elem_data_single_int64(root, b"AnimationLayer", get_fbxuid_from_key(alayer_key))
        alayer.add_string(fbx_name_class(name, b"AnimLayer"))
        alayer.add_string(b"")

        for obj, (alayer_key, acurvenodes) in alayers.items():
            # Animation layer.
            # alayer = elem_data_single_int64(root, b"AnimationLayer", get_fbxuid_from_key(alayer_key))
            # alayer.add_string(fbx_name_class(obj.name.encode(), b"AnimLayer"))
            # alayer.add_string(b"")

            for fbx_prop, (acurvenode_key, acurves, acurvenode_name) in acurvenodes.items():
                # Animation curve node.
                acurvenode = elem_data_single_int64(root, b"AnimationCurveNode", get_fbxuid_from_key(acurvenode_key))
                acurvenode.add_string(fbx_name_class(acurvenode_name.encode(), b"AnimCurveNode"))
                acurvenode.add_string(b"")

                acn_tmpl = elem_props_template_init(scene_data.templates, b"AnimationCurveNode")
                acn_props = elem_properties(acurvenode)

                for fbx_item, (acurve_key, def_value, keys, _acurve_valid) in acurves.items():
                    elem_props_template_set(acn_tmpl, acn_props, "p_number", fbx_item.encode(), def_value, animatable=True)

                    # Only create Animation curve if needed!
                    if keys:
                        acurve = elem_data_single_int64(root, b"AnimationCurve", get_fbxuid_from_key(acurve_key))
                        acurve.add_string(fbx_name_class(b"", b"AnimCurve"))
                        acurve.add_string(b"")

                        # key attributes...
                        nbr_keys = len(keys)
                        # flags...
                        keyattr_flags = (
                            1 << 3 |   # interpolation mode, 1 = constant, 2 = linear, 3 = cubic.
                            1 << 8 |   # tangent mode, 8 = auto, 9 = TCB, 10 = user, 11 = generic break,
                            1 << 13 |  # tangent mode, 12 = generic clamp, 13 = generic time independent,
                            1 << 14 |  # tangent mode, 13 + 14 = generic clamp progressive.
                            0,
                        )
                        # Maybe values controlling TCB & co???
                        keyattr_datafloat = (0.0, 0.0, 9.419963346924634e-30, 0.0)

                        # And now, the *real* data!
                        elem_data_single_float64(acurve, b"Default", def_value)
                        elem_data_single_int32(acurve, b"KeyVer", FBX_ANIM_KEY_VERSION)
                        elem_data_single_int64_array(acurve, b"KeyTime", keys_to_ktimes(keys))
                        elem_data_single_float32_array(acurve, b"KeyValueFloat", (v for _f, v in keys))
                        elem_data_single_int32_array(acurve, b"KeyAttrFlags", keyattr_flags)
                        elem_data_single_float32_array(acurve, b"KeyAttrDataFloat", keyattr_datafloat)
                        elem_data_single_int32_array(acurve, b"KeyAttrRefCount", (nbr_keys,))

                elem_props_template_finalize(acn_tmpl, acn_props)