export_fbx_bin.py

                        # 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)


##### Top-level FBX data container. #####

# Helper container gathering some data we need multiple times:
#     * templates.
#     * objects.
#     * connections.
#     * takes.
FBXData = namedtuple("FBXData", (
    "templates", "templates_users", "connections",
    "settings", "scene", "objects", "animations", "frame_start", "frame_end",
    "data_empties", "data_lamps", "data_cameras", "data_meshes", "mesh_mat_indices",
    "bones_to_posebones", "data_bones", "data_deformers",
    "data_world", "data_materials", "data_textures", "data_videos",
))


def fbx_mat_properties_from_texture(tex):
    """
    Returns a set of FBX metarial properties that are affected by the given texture.
    Quite obviously, this is a fuzzy and far-from-perfect mapping! Amounts of influence are completely lost, e.g.
    Note tex is actually expected to be a texture slot.
    """
    # Tex influence does not exists in FBX, so assume influence < 0.5 = no influence... :/
    INFLUENCE_THRESHOLD = 0.5

    # Mapping Blender -> FBX (blend_use_name, blend_fact_name, fbx_name).
    blend_to_fbx = (
        # Lambert & Phong...
        ("diffuse", "diffuse", b"DiffuseFactor"),
        ("color_diffuse", "diffuse_color", b"DiffuseColor"),
        ("alpha", "alpha", b"TransparencyFactor"),
        ("diffuse", "diffuse", b"TransparentColor"),  # Uses diffuse color in Blender!
        ("emit", "emit", b"EmissiveFactor"),
        ("diffuse", "diffuse", b"EmissiveColor"),  # Uses diffuse color in Blender!
        ("ambient", "ambient", b"AmbientFactor"),
        #("", "", b"AmbientColor"),  # World stuff in Blender, for now ignore...
        ("normal", "normal", b"NormalMap"),
        # Note: unsure about those... :/
        #("", "", b"Bump"),
        #("", "", b"BumpFactor"),
        #("", "", b"DisplacementColor"),
        #("", "", b"DisplacementFactor"),
        # Phong only.
        ("specular", "specular", b"SpecularFactor"),
        ("color_spec", "specular_color", b"SpecularColor"),
        # See Material template about those two!
        ("hardness", "hardness", b"Shininess"),
        ("hardness", "hardness", b"ShininessExponent"),
        ("mirror", "mirror", b"ReflectionColor"),
        ("raymir", "raymir", b"ReflectionFactor"),
    )

    tex_fbx_props = set()
    for use_map_name, name_factor, fbx_prop_name in blend_to_fbx:
        if getattr(tex, "use_map_" + use_map_name) and getattr(tex, name_factor + "_factor") >= INFLUENCE_THRESHOLD:
            tex_fbx_props.add(fbx_prop_name)

    return tex_fbx_props


def fbx_skeleton_from_armature(scene, settings, armature, objects, data_meshes, bones_to_posebones,
                               data_bones, data_deformers, arm_parents):
    """
    Create skeleton from armature/bones (NodeAttribute/LimbNode and Model/LimbNode), and for each deformed mesh,
    create Pose/BindPose(with sub PoseNode) and Deformer/Skin(with Deformer/SubDeformer/Cluster).
    Also supports "parent to bone" (simple parent to Model/LimbNode).
    arm_parents is a set of tuples (armature, object) for all successful armature bindings.
    """
    arm = armature.data
    bones = OrderedDict()
    for bo, pbo in zip(arm.bones, armature.pose.bones):
        key, data_key = get_blender_bone_key(armature, bo)
        objects[bo] = key
        bones_to_posebones[bo] = pbo
        data_bones[bo] = (key, data_key, armature)
        bones[bo.name] = bo

    for obj in objects.keys():
        if not isinstance(obj, Object):
            continue
        if obj.type not in {'MESH'}:
            continue
        if obj.parent != armature:
            continue

        # Always handled by an Armature modifier...
        found = False
        for mod in obj.modifiers:
            if mod.type not in {'ARMATURE'}:
                continue
            # We only support vertex groups binding method, not bone envelopes one!
            if mod.object == armature and mod.use_vertex_groups:
                found = True
                break

        if not found:
            continue

        # Now we have a mesh using this armature. First, find out which bones are concerned!
        # XXX Assuming here non-used bones can have no cluster, this has to be checked!
        used_bones = tuple(bones[vg.name] for vg in obj.vertex_groups if vg.name in bones)
        if not used_bones:
            continue

        # Note: bindpose have no relations at all (no connections), so no need for any preprocess for them.

        # Create skin & clusters relations (note skins are connected to geometry, *not* model!).
        _key, me, _free = data_meshes[obj]
        clusters = {bo: get_blender_bone_cluster_key(armature, me, bo) for bo in used_bones}
        data_deformers.setdefault(armature, {})[me] = (get_blender_armature_skin_key(armature, me), obj, clusters)

        # We don't want a regular parent relationship for those in FBX...
        arm_parents.add((armature, obj))


def fbx_animations_simplify(scene_data, animdata):
    """
    Simplifies FCurves!
    """
    fac = scene_data.settings.bake_anim_simplify_factor
    step = scene_data.settings.bake_anim_step
    # So that, with default factor and step values (1), we get:
    max_frame_diff = step * fac * 10  # max step of 10 frames.
    value_diff_fac = fac / 1000  # min value evolution: 0.1% of whole range.

    for obj, keys in animdata.items():
        if not keys:
            continue
        extremums = [(min(values), max(values)) for values in zip(*(k[1] for k in keys))]
        min_diffs = [max((mx - mn) * value_diff_fac, 0.000001) for mx, mn in extremums]
        p_currframe, p_key, p_key_write = keys[0]
        p_keyed = [(p_currframe - max_frame_diff, val) for val in p_key]
        for currframe, key, key_write in keys:
            for idx, (val, p_val) in enumerate(zip(key, p_key)):
                p_keyedframe, p_keyedval = p_keyed[idx]
                if val == p_val:
                    # Never write keyframe when value is exactly the same as prev one!
                    continue
                if abs(val - p_val) >= min_diffs[idx]:
                    # If enough difference from previous sampled value, key this value *and* the previous one!
                    key_write[idx] = True
                    p_key_write[idx] = True
                    p_keyed[idx] = (currframe, val)
                elif (abs(val - p_keyedval) >= min_diffs[idx]) or (currframe - p_keyedframe >= max_frame_diff):
                    # Else, if enough difference from previous keyed value (or max gap between keys is reached),
                    # key this value only!
                    key_write[idx] = True
                    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_do(scene_data, ref_id, f_start, f_end, start_zero):
    """
    Generate animation data (a single AnimStack) from objects, for a given frame range.
    """
    objects = scene_data.objects
    bake_step = scene_data.settings.bake_anim_step
    scene = scene_data.scene
    bone_map = scene_data.bones_to_posebones

    # 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())

    p_rots = {}

    currframe = f_start
    while currframe < f_end:
        real_currframe = currframe - f_start if start_zero else currframe
        scene.frame_set(int(currframe), currframe - int(currframe))
        for obj in objects.keys():
            # Get PoseBone from bone...
            tobj = bone_map[obj] if isinstance(obj, Bone) else obj
            # We compute baked loc/rot/scale for all objects (rot being euler-compat with previous value!).
            p_rot = p_rots.get(tobj, None)
            loc, rot, scale, _m, _mr = fbx_object_tx(scene_data, tobj, p_rot)
            p_rots[tobj] = rot
            tx = tuple(loc) + tuple(units_convert_iter(rot, "radian", "degree")) + tuple(scale)
            animdata[obj].append((real_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:
            for idx, (val, wrt) in enumerate(zip(key, key_write)):
                if wrt:
                    curves[idx].append((currframe, val))

        # Get PoseBone from bone...
        #tobj = bone_map[obj] if isinstance(obj, Bone) else obj
        #loc, rot, scale, _m, _mr = fbx_object_tx(scene_data, tobj)
        #tx = tuple(loc) + tuple(units_convert_iter(rot, "radian", "degree")) + tuple(scale)
        dtx = (0.0, 0.0, 0.0) + (0.0, 0.0, 0.0) + (1.0, 1.0, 1.0)
        # 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, dtx[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(scene, obj), final_keys)

    astack_key = get_blender_anim_stack_key(scene, ref_id)
    alayer_key = get_blender_anim_layer_key(scene, ref_id)
    name = (ref_id.name if ref_id else scene.name).encode()

    if start_zero:
        f_end -= f_start
        f_start = 0.0

    return (astack_key, animations, alayer_key, name, f_start, f_end) if animations else None


def fbx_animations_objects(scene_data):
    """
    Generate global animation data from objects.
    """
    scene = scene_data.scene
    animations = []
    frame_start = 1e100
    frame_end = -1e100

    # Per-NLA strip animstacks.
    if scene_data.settings.bake_anim_use_nla_strips:
        strips = []
        for obj in scene_data.objects:
            # NLA tracks only for objects, not bones!
            if not isinstance(obj, Object) or not obj.animation_data:
                continue
            for track in obj.animation_data.nla_tracks:
                if track.mute:
                    continue
                for strip in track.strips:
                    if strip.mute:
                        continue
                    strips.append(strip)
                    strip.mute = True

        for strip in strips:
            strip.mute = False
            anim = fbx_animations_objects_do(scene_data, strip, strip.frame_start, strip.frame_end, True)
            if anim is not None:
                animations.append(anim)
                f_start, f_end = anim [4:6]
                if f_start < frame_start:
                    frame_start = f_start
                if f_end > frame_end:
                    frame_end = f_end
            strip.mute = True

        for strip in strips:
            strip.mute = False

    # Global (containing everything) animstack.
    if not scene_data.settings.bake_anim_use_nla_strips or not animations:
        anim = fbx_animations_objects_do(scene_data, None, scene.frame_start, scene.frame_end, False)
        if anim is not None:
            animations.append(anim)
            if scene.frame_start < frame_start:
                frame_start = scene.frame_start
            if scene.frame_end > frame_end:
                frame_end = scene.frame_end

    return animations, frame_start, frame_end


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

    ##### 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 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')
    # Yep! Contains nothing, but needed!
    data_empties = OrderedDict((obj, get_blender_empty_key(obj)) for obj in objects if obj.type == 'EMPTY')

    data_meshes = OrderedDict()
    for obj in objects:
        if obj.type not in BLENDER_OBJECT_TYPES_MESHLIKE:
            continue
        if settings.use_mesh_modifiers or obj.type in BLENDER_OTHER_OBJECT_TYPES:
            tmp_mods = []
            if obj.type == 'MESH' and settings.bake_anim:
                # For meshes, when anim export is enabled, disable Armature modifiers here!
                for mod in obj.modifiers:
                    if mod.type == 'ARMATURE':
                        tmp_mods.append((mod, mod.show_render))
                        mod.show_render = False
            tmp_me = obj.to_mesh(scene, apply_modifiers=True, settings='RENDER')
            data_meshes[obj] = (get_blenderID_key(tmp_me), tmp_me, True)
            # Re-enable temporary disabled modifiers.
            for mod, show_render in tmp_mods:
                mod.show_render = show_render
        else:
            data_meshes[obj] = (get_blenderID_key(obj.data), obj.data, False)

    # Armatures!
    data_bones = OrderedDict()
    data_deformers = OrderedDict()
    bones_to_posebones = dict()
    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_meshes, bones_to_posebones,
                                   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 BLENDER_OBJECT_TYPES_MESHLIKE:
            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...
    animations = ()
    if settings.bake_anim:
        # From objects & bones 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, 0.0, 0.0,
            data_empties, data_lamps, data_cameras, data_meshes, None,
            bones_to_posebones, data_bones, data_deformers,
            data_world, data_materials, data_textures, data_videos,
        )
        animations, frame_start, frame_end = fbx_animations_objects(tmp_scdata)

    ##### Creation of templates...

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

    if data_empties:
        templates[b"Null"] = fbx_template_def_null(scene, settings, nbr_users=len(data_empties))

    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:
        nbr_astacks = len(animations)
        nbr_acnodes = 0
        nbr_acurves = 0
        for _astack_key, astack, _al, _n, _fs, _fe in animations:
            for _alayer_key, alayer in astack.values():
                for _acnode_key, acnode, _acnode_name in alayer.values():
                    nbr_acnodes += 1
                    for _acurve_key, _dval, acurve, acurve_valid in acnode.values():
                        if acurve:
                            nbr_acurves += 1

        templates[b"AnimationStack"] = fbx_template_def_animstack(scene, settings, nbr_users=nbr_astacks)
        # Would be nice to have one layer per animated object, but this seems tricky and not that well supported.
        # So for now, only one layer per anim stack.
        templates[b"AnimationLayer"] = fbx_template_def_animlayer(scene, settings, nbr_users=nbr_astacks)
        templates[b"AnimationCurveNode"] = fbx_template_def_animcurvenode(scene, settings, nbr_users=nbr_acnodes)
        templates[b"AnimationCurve"] = fbx_template_def_animcurve(scene, settings, nbr_users=nbr_acurves)

    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))

    # Empties
    for empty_obj, empty_key in data_empties.items():
        empty_obj_key = objects[empty_obj]
        connections.append((b"OO", get_fbxuid_from_key(empty_key), get_fbxuid_from_key(empty_obj_key), 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 in BLENDER_OBJECT_TYPES_MESHLIKE:
            mesh_key, _me, _free = data_meshes[obj]
            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, _me, _free = data_meshes[obj]
            assert(me == _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
    for astack_key, astack, alayer_key, _name, _fstart, _fend in animations:
        # Animstack itself is linked nowhere!
        astack_id = get_fbxuid_from_key(astack_key)
        # For now, only one layer!
        alayer_id = get_fbxuid_from_key(alayer_key)
        connections.append((b"OO", alayer_id, astack_id, None))
        for obj, (alayer_key, acurvenodes) in astack.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, frame_start, frame_end,
        data_empties, data_lamps, data_cameras, data_meshes, mesh_mat_indices,
        bones_to_posebones, data_bones, data_deformers,
        data_world, data_materials, data_textures, data_videos,
    )


def fbx_scene_data_cleanup(scene_data):
    """
    Some final cleanup...
    """
    # Delete temp meshes.
    for _key, me, free in scene_data.data_meshes.values():
        if free:
            bpy.data.meshes.remove(me)


##### 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
    fbx_fps, fbx_fps_mode = FBX_FRAMERATES[0]  # Custom framerate.
    for ref_fps, fps_mode in FBX_FRAMERATES:
        if similar_values(fps, ref_fps):
            fbx_fps = ref_fps
            fbx_fps_mode = fps_mode
    elem_props_set(props, "p_enum", b"TimeMode", fbx_fps_mode)
    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", fbx_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 empty in scene_data.data_empties.keys():
        fbx_data_empty_elements(objects, empty, scene_data)

    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 me_obj in scene_data.data_meshes.keys():
        fbx_data_mesh_elements(objects, me_obj, 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.
    """
    # 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 not animations:
        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_data.frame_start / fps, "second", "ktime"))
    scene_end_ktime = int(units_convert(scene_data.frame_end + 1 / fps, "second", "ktime"))  # +1 is unity hack...

    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_use_nla_strips", "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_use_nla_strips=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', 'OTHER'}

    if 'OTHER' in object_types:
        object_types |= BLENDER_OTHER_OBJECT_TYPES

    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_use_nla_strips, 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)

    # Cleanup!
    fbx_scene_data_cleanup(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,