gnome-shell/js/ui/main.js

/* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */

imports.gi.versions.Clutter = '1.0';
imports.gi.versions.Gio = '2.0';
imports.gi.versions.Gdk = '3.0';
imports.gi.versions.GdkPixbuf = '2.0';
imports.gi.versions.Gtk = '3.0';

const Clutter = imports.gi.Clutter;
const DBus = imports.dbus;
const Gdk = imports.gi.Gdk;
const Gio = imports.gi.Gio;
const GLib = imports.gi.GLib;
const GConf = imports.gi.GConf;
const Lang = imports.lang;
const Mainloop = imports.mainloop;
const Meta = imports.gi.Meta;
const Shell = imports.gi.Shell;
const St = imports.gi.St;
const Gettext = imports.gettext.domain('gnome-shell');
const _ = Gettext.gettext;

const Chrome = imports.ui.chrome;
const CtrlAltTab = imports.ui.ctrlAltTab;
const EndSessionDialog = imports.ui.endSessionDialog;
const PolkitAuthenticationAgent = imports.ui.polkitAuthenticationAgent;
const Environment = imports.ui.environment;
const ExtensionSystem = imports.ui.extensionSystem;
const MessageTray = imports.ui.messageTray;
const Overview = imports.ui.overview;
const Panel = imports.ui.panel;
const PlaceDisplay = imports.ui.placeDisplay;
const RunDialog = imports.ui.runDialog;
const LookingGlass = imports.ui.lookingGlass;
const NotificationDaemon = imports.ui.notificationDaemon;
const WindowAttentionHandler = imports.ui.windowAttentionHandler;
const Scripting = imports.ui.scripting;
const ShellDBus = imports.ui.shellDBus;
const TelepathyClient = imports.ui.telepathyClient;
const WindowManager = imports.ui.windowManager;
const Magnifier = imports.ui.magnifier;
const XdndHandler = imports.ui.xdndHandler;
const StatusIconDispatcher = imports.ui.statusIconDispatcher;
const Util = imports.misc.util;

const DEFAULT_BACKGROUND_COLOR = new Clutter.Color();
DEFAULT_BACKGROUND_COLOR.from_pixel(0x2266bbff);

let chrome = null;
let panel = null;
let hotCorners = [];
let placesManager = null;
let overview = null;
let runDialog = null;
let lookingGlass = null;
let wm = null;
let messageTray = null;
let notificationDaemon = null;
let windowAttentionHandler = null;
let telepathyClient = null;
let ctrlAltTabManager = null;
let recorder = null;
let shellDBusService = null;
let modalCount = 0;
let modalActorFocusStack = [];
let uiGroup = null;
let magnifier = null;
let xdndHandler = null;
let statusIconDispatcher = null;
let _errorLogStack = [];
let _startDate;
let _defaultCssStylesheet = null;
let _cssStylesheet = null;

let background = null;

function start() {
    // Add a binding for 'global' in the global JS namespace; (gjs
    // keeps the web browser convention of having that namespace be
    // called 'window'.)
    window.global = Shell.Global.get();

    // Now monkey patch utility functions into the global proxy;
    // This is easier and faster than indirecting down into global
    // if we want to call back up into JS.
    global.logError = _logError;
    global.log = _logDebug;

    Gio.DesktopAppInfo.set_desktop_env('GNOME');

    shellDBusService = new ShellDBus.GnomeShell();
    // Force a connection now; dbus.js will do this internally
    // if we use its name acquisition stuff but we aren't right
    // now; to do so we'd need to convert from its async calls
    // back into sync ones.
    DBus.session.flush();

    // Load the calendar server. Note that we are careful about
    // not loading any events until the user presses the clock
    global.launch_calendar_server();

    Environment.init();

    // Ensure ShellWindowTracker and ShellAppUsage are initialized; this will
    // also initialize ShellAppSystem first.  ShellAppSystem
    // needs to load all the .desktop files, and ShellWindowTracker
    // will use those to associate with windows.  Right now
    // the Monitor doesn't listen for installed app changes
    // and recalculate application associations, so to avoid
    // races for now we initialize it here.  It's better to
    // be predictable anyways.
    Shell.WindowTracker.get_default();
    Shell.AppUsage.get_default();

    // The stage is always covered so Clutter doesn't need to clear it; however
    // the color is used as the default contents for the Mutter root background
    // actor so set it anyways.
    global.stage.color = DEFAULT_BACKGROUND_COLOR;
    global.stage.no_clear_hint = true;

    _defaultCssStylesheet = global.datadir + '/theme/gnome-shell.css';
    loadTheme();

    let shellwm = global.window_manager;
    shellwm.takeover_keybinding('panel_main_menu');
    shellwm.connect('keybinding::panel_main_menu', function () {
        overview.toggle();
    });
    shellwm.takeover_keybinding('panel_run_dialog');
    shellwm.connect('keybinding::panel_run_dialog', function () {
       getRunDialog().open();
    });

    // Set up stage hierarchy to group all UI actors under one container.
    uiGroup = new Clutter.Group();
    global.window_group.reparent(uiGroup);
    global.overlay_group.reparent(uiGroup);
    global.stage.add_actor(uiGroup);

    placesManager = new PlaceDisplay.PlacesManager();
    xdndHandler = new XdndHandler.XdndHandler();
    overview = new Overview.Overview();
    chrome = new Chrome.Chrome();
    magnifier = new Magnifier.Magnifier();
    statusIconDispatcher = new StatusIconDispatcher.StatusIconDispatcher();
    panel = new Panel.Panel();
    wm = new WindowManager.WindowManager();
    messageTray = new MessageTray.MessageTray();
    notificationDaemon = new NotificationDaemon.NotificationDaemon();
    windowAttentionHandler = new WindowAttentionHandler.WindowAttentionHandler();
    telepathyClient = new TelepathyClient.Client();

    overview.init();
    statusIconDispatcher.start(messageTray.actor);

    ctrlAltTabManager = new CtrlAltTab.CtrlAltTabManager();
    ctrlAltTabManager.addGroup(panel.actor, _("Panel"), 'gnome-panel');

    _startDate = new Date();

    let recorderSettings = new Gio.Settings({ schema: 'org.gnome.shell.recorder' });

    global.screen.connect('toggle-recording', function() {
        if (recorder == null) {
            recorder = new Shell.Recorder({ stage: global.stage });
        }

        if (recorder.is_recording()) {
            recorder.pause();
        } else {
            // read the parameters from GSettings always in case they have changed
            recorder.set_framerate(recorderSettings.get_int('framerate'));
            recorder.set_filename('shell-%d%u-%c.' + recorderSettings.get_string('file-extension'));
            let pipeline = recorderSettings.get_string('pipeline');

            if (!pipeline.match(/^\s*$/))
                recorder.set_pipeline(pipeline);
            else
                recorder.set_pipeline(null);

            recorder.record();
        }
    });

    global.screen.override_workspace_layout(Meta.ScreenCorner.TOPLEFT, false, -1, 1);

    // Provide the bus object for gnome-session to
    // initiate logouts.
    EndSessionDialog.init();

    // Attempt to become a PolicyKit authentication agent
    PolkitAuthenticationAgent.init()

    global.gdk_screen.connect('monitors-changed', _relayout);

    ExtensionSystem.init();
    ExtensionSystem.loadExtensions();

    // Perform initial relayout here
    _relayout();

    panel.startStatusArea();
    panel.startupAnimation();

    let display = global.screen.get_display();
    display.connect('overlay-key', Lang.bind(overview, overview.toggle));

    global.stage.connect('captured-event', _globalKeyPressHandler);

    _log('info', 'loaded at ' + _startDate);
    log('GNOME Shell started at ' + _startDate);

    let perfModuleName = GLib.getenv("SHELL_PERF_MODULE");
    if (perfModuleName) {
        let perfOutput = GLib.getenv("SHELL_PERF_OUTPUT");
        let module = eval('imports.perf.' + perfModuleName + ';');
        Scripting.runPerfScript(module, perfOutput);
    }

    global.screen.connect('notify::n-workspaces', _nWorkspacesChanged);
    Mainloop.idle_add(_nWorkspacesChanged);
}

let _workspaces = [];
let _checkWorkspacesId = 0;

/*
 * When the last window closed on a workspace is a dialog or splash
 * screen, we assume that it might be an initial window shown before
 * the main window of an application, and give the app a grace period
 * where it can map another window before we remove the workspace.
 */
const LAST_WINDOW_GRACE_TIME = 1000;

function _checkWorkspaces() {
    let i;
    let emptyWorkspaces = [];

    for (i = 0; i < _workspaces.length; i++) {
        let lastRemoved = _workspaces[i]._lastRemovedWindow;
        if (lastRemoved &&
            (lastRemoved.get_window_type() == Meta.WindowType.SPLASHSCREEN ||
             lastRemoved.get_window_type() == Meta.WindowType.DIALOG ||
             lastRemoved.get_window_type() == Meta.WindowType.MODAL_DIALOG))
                emptyWorkspaces[i] = false;
        else
            emptyWorkspaces[i] = true;
    }

    let windows = global.get_window_actors();
    for (i = 0; i < windows.length; i++) {
        let win = windows[i];

        if (win.get_meta_window().is_on_all_workspaces())
            continue;

        let workspaceIndex = win.get_workspace();
        emptyWorkspaces[workspaceIndex] = false;
    }

    // If we don't have an empty workspace at the end, add one
    if (!emptyWorkspaces[emptyWorkspaces.length -1]) {
        global.screen.append_new_workspace(false, global.get_current_time());
        emptyWorkspaces.push(false);
    }

    // Delete other empty workspaces; do it from the end to avoid index changes
    for (i = emptyWorkspaces.length - 2; i >= 0; i--) {
        if (emptyWorkspaces[i])
            global.screen.remove_workspace(_workspaces[i], global.get_current_time());
    }

    _checkWorkspacesId = 0;
    return false;
}

function _windowRemoved(workspace, window) {
    workspace._lastRemovedWindow = window;
    _queueCheckWorkspaces();
    Mainloop.timeout_add(LAST_WINDOW_GRACE_TIME, function() {
        if (workspace._lastRemovedWindow == window) {
            workspace._lastRemovedWindow = null;
            _queueCheckWorkspaces();
        }
    });
}

function _queueCheckWorkspaces() {
    if (_checkWorkspacesId == 0)
        _checkWorkspacesId = Meta.later_add(Meta.LaterType.BEFORE_REDRAW, _checkWorkspaces);
}

function _nWorkspacesChanged() {
    let oldNumWorkspaces = _workspaces.length;
    let newNumWorkspaces = global.screen.n_workspaces;

    if (oldNumWorkspaces == newNumWorkspaces)
        return false;

    let lostWorkspaces = [];
    if (newNumWorkspaces > oldNumWorkspaces) {
        let w;

        // Assume workspaces are only added at the end
        for (w = oldNumWorkspaces; w < newNumWorkspaces; w++)
            _workspaces[w] = global.screen.get_workspace_by_index(w);

        for (w = oldNumWorkspaces; w < newNumWorkspaces; w++) {
            let workspace = _workspaces[w];
            workspace._windowAddedId = workspace.connect('window-added', _queueCheckWorkspaces);
            workspace._windowRemovedId = workspace.connect('window-removed', _windowRemoved);
        }

    } else {
        // Assume workspaces are only removed sequentially
        // (e.g. 2,3,4 - not 2,4,7)
        let removedIndex;
        let removedNum = oldNumWorkspaces - newNumWorkspaces;
        for (let w = 0; w < oldNumWorkspaces; w++) {
            let workspace = global.screen.get_workspace_by_index(w);
            if (_workspaces[w] != workspace) {
                removedIndex = w;
                break;
            }
        }

        let lostWorkspaces = _workspaces.splice(removedIndex, removedNum);
        lostWorkspaces.forEach(function(workspace) {
                                   workspace.disconnect(workspace._windowAddedId);
                                   workspace.disconnect(workspace._windowRemovedId);
                               });
    }

    _queueCheckWorkspaces();

    return false;
}

/**
 * getThemeStylesheet:
 *
 * Get the theme CSS file that the shell will load
 *
 * Returns: A file path that contains the theme CSS,
 *          null if using the default
 */
function getThemeStylesheet()
{
    return _cssStylesheet;
}

/**
 * setThemeStylesheet:
 * @cssStylesheet: A file path that contains the theme CSS,
 *                  set it to null to use the default
 *
 * Set the theme CSS file that the shell will load
 */
function setThemeStylesheet(cssStylesheet)
{
    _cssStylesheet = cssStylesheet;
}

/**
 * loadTheme:
 *
 * Reloads the theme CSS file
 */
function loadTheme() {
    let themeContext = St.ThemeContext.get_for_stage (global.stage);

    let cssStylesheet = _defaultCssStylesheet;
    if (_cssStylesheet != null)
        cssStylesheet = _cssStylesheet;

    let theme = new St.Theme ({ application_stylesheet: cssStylesheet });
    themeContext.set_theme (theme);
}

/**
 * _log:
 * @category: string message type ('info', 'error')
 * @msg: A message string
 * ...: Any further arguments are converted into JSON notation,
 *      and appended to the log message, separated by spaces.
 *
 * Log a message into the LookingGlass error
 * stream.  This is primarily intended for use by the
 * extension system as well as debugging.
 */
function _log(category, msg) {
    let text = msg;
    if (arguments.length > 2) {
        text += ': ';
        for (let i = 2; i < arguments.length; i++) {
            text += JSON.stringify(arguments[i]);
            if (i < arguments.length - 1)
                text += ' ';
        }
    }
    _errorLogStack.push({timestamp: new Date().getTime(),
                         category: category,
                         message: text });
}

function _logError(msg) {
    return _log('error', msg);
}

function _logDebug(msg) {
    return _log('debug', msg);
}

// Used by the error display in lookingGlass.js
function _getAndClearErrorStack() {
    let errors = _errorLogStack;
    _errorLogStack = [];
    return errors;
}

function _relayout() {
    let monitors = global.get_monitors();
    if (monitors.length != hotCorners.length) {
        // destroy old corners
        for (let i = 0; i < hotCorners.length; i++)
            hotCorners[i].destroy();
        hotCorners = [];
        for (let i = 0; i < monitors.length; i++)
            hotCorners[i] = new Panel.HotCorner();
    }


    let primary = global.get_primary_monitor();
    for (let i = 0; i < monitors.length; i++) {
        let monitor = monitors[i];
        let corner = hotCorners[i];
        let isPrimary = (monitor.x == primary.x &&
                         monitor.y == primary.y &&
                         monitor.width == primary.width &&
                         monitor.height == primary.height);
        if (St.Widget.get_default_direction() == St.TextDirection.RTL)
            corner.actor.set_position(monitor.x + monitor.width, monitor.y);
        else
            corner.actor.set_position(monitor.x, monitor.y);
        if (isPrimary)
            panel.setHotCorner(corner);
    }

    panel.relayout();
    overview.relayout();

    // To avoid updating the position and size of the workspaces
    // in the overview, we just hide the overview. The positions
    // will be updated when it is next shown.
    overview.hide();
}

function isWindowActorDisplayedOnWorkspace(win, workspaceIndex) {
    return win.get_workspace() == workspaceIndex ||
        (win.get_meta_window() && win.get_meta_window().is_on_all_workspaces());
}

function getWindowActorsForWorkspace(workspaceIndex) {
    return global.get_window_actors().filter(function (win) {
        return isWindowActorDisplayedOnWorkspace(win, workspaceIndex);
    });
}

// This function encapsulates hacks to make certain global keybindings
// work even when we are in one of our modes where global keybindings
// are disabled with a global grab. (When there is a global grab, then
// all key events will be delivered to the stage, so ::captured-event
// on the stage can be used for global keybindings.)
function _globalKeyPressHandler(actor, event) {
    if (modalCount == 0)
        return false;
    if (event.type() != Clutter.EventType.KEY_PRESS)
        return false;

    let symbol = event.get_key_symbol();
    let keyCode = event.get_key_code();
    let modifierState = Shell.get_event_state(event);

    let display = global.screen.get_display();
    // This relies on the fact that Clutter.ModifierType is the same as Gdk.ModifierType
    let action = display.get_keybinding_action(keyCode, modifierState);

    // The screenshot action should always be available (even if a
    // modal dialog is present)
    if (action == Meta.KeyBindingAction.COMMAND_SCREENSHOT) {
        let gconf = GConf.Client.get_default();
        let command = gconf.get_string('/apps/metacity/keybinding_commands/command_screenshot');
        if (command != null && command != '')
            Util.spawnCommandLine(command);
        return true;
    }

    // Other bindings are only available when the overview is up and
    // no modal dialog is present.
    if (!overview.visible || modalCount > 1)
        return false;

    // This isn't a Meta.KeyBindingAction yet
    if (symbol == Clutter.Super_L || symbol == Clutter.Super_R) {
        overview.hide();
        return true;
    }

    switch (action) {
        // left/right would effectively act as synonyms for up/down if we enabled them;
        // but that could be considered confusing; we also disable them in the main view.
        //
        // case Meta.KeyBindingAction.WORKSPACE_LEFT:
        //     wm.actionMoveWorkspaceLeft();
        //     return true;
        // case Meta.KeyBindingAction.WORKSPACE_RIGHT:
        //     wm.actionMoveWorkspaceRight();
        //     return true;
        case Meta.KeyBindingAction.WORKSPACE_UP:
            wm.actionMoveWorkspaceUp();
            return true;
        case Meta.KeyBindingAction.WORKSPACE_DOWN:
            wm.actionMoveWorkspaceDown();
            return true;
        case Meta.KeyBindingAction.PANEL_RUN_DIALOG:
        case Meta.KeyBindingAction.COMMAND_2:
            getRunDialog().open();
            return true;
        case Meta.KeyBindingAction.PANEL_MAIN_MENU:
            overview.hide();
            return true;
        case Meta.KeyBindingAction.SWITCH_PANELS:
            ctrlAltTabManager.popup(modifierState & Clutter.ModifierType.SHIFT_MASK);
            return true;
    }

    return false;
}

function _findModal(actor) {
    for (let i = 0; i < modalActorFocusStack.length; i++) {
        if (modalActorFocusStack[i].actor == actor)
            return i;
    }
    return -1;
}

/**
 * pushModal:
 * @actor: #ClutterActor which will be given keyboard focus
 * @timestamp: optional timestamp
 *
 * Ensure we are in a mode where all keyboard and mouse input goes to
 * the stage, and focus @actor. Multiple calls to this function act in
 * a stacking fashion; the effect will be undone when an equal number
 * of popModal() invocations have been made.
 *
 * Next, record the current Clutter keyboard focus on a stack. If the
 * modal stack returns to this actor, reset the focus to the actor
 * which was focused at the time pushModal() was invoked.
 *
 * @timestamp is optionally used to associate the call with a specific user
 * initiated event.  If not provided then the value of
 * global.get_current_time() is assumed.
 *
 * Returns: true iff we successfully acquired a grab or already had one
 */
function pushModal(actor, timestamp) {
    if (timestamp == undefined)
        timestamp = global.get_current_time();

    if (modalCount == 0) {
        if (!global.begin_modal(timestamp)) {
            log('pushModal: invocation of begin_modal failed');
            return false;
        }
    }

    global.set_stage_input_mode(Shell.StageInputMode.FULLSCREEN);

    modalCount += 1;
    let actorDestroyId = actor.connect('destroy', function() {
        let index = _findModal(actor);
        if (index >= 0)
            modalActorFocusStack.splice(index, 1);
    });
    let curFocus = global.stage.get_key_focus();
    let curFocusDestroyId;
    if (curFocus != null) {
        curFocusDestroyId = curFocus.connect('destroy', function() {
            let index = _findModal(actor);
            if (index >= 0)
                modalActorFocusStack[index].actor = null;
        });
    }
    modalActorFocusStack.push({ actor: actor,
                                focus: curFocus,
                                destroyId: actorDestroyId,
                                focusDestroyId: curFocusDestroyId });

    global.stage.set_key_focus(actor);
    return true;
}

/**
 * popModal:
 * @actor: #ClutterActor passed to original invocation of pushModal().
 * @timestamp: optional timestamp
 *
 * Reverse the effect of pushModal().  If this invocation is undoing
 * the topmost invocation, then the focus will be restored to the
 * previous focus at the time when pushModal() was invoked.
 *
 * @timestamp is optionally used to associate the call with a specific user
 * initiated event.  If not provided then the value of
 * global.get_current_time() is assumed.
 */
function popModal(actor, timestamp) {
    if (timestamp == undefined)
        timestamp = global.get_current_time();

    let focusIndex = _findModal(actor);
    if (focusIndex < 0) {
        global.stage.set_key_focus(null);
        global.end_modal(timestamp);
        global.set_stage_input_mode(Shell.StageInputMode.NORMAL);

        throw new Error('incorrect pop');
    }

    modalCount -= 1;

    let record = modalActorFocusStack[focusIndex];
    record.actor.disconnect(record.destroyId);

    if (focusIndex == modalActorFocusStack.length - 1) {
        if (record.focus)
            record.focus.disconnect(record.focusDestroyId);
        global.stage.set_key_focus(record.focus);
    } else {
        let t = modalActorFocusStack[modalActorFocusStack.length - 1];
        if (t.focus)
            t.focus.disconnect(t.focusDestroyId);
        // Remove from the middle, shift the focus chain up
        for (let i = modalActorFocusStack.length - 1; i > focusIndex; i--) {
            modalActorFocusStack[i].focus = modalActorFocusStack[i - 1].focus;
            modalActorFocusStack[i].focusDestroyId = modalActorFocusStack[i - 1].focusDestroyId;
        }
    }
    modalActorFocusStack.splice(focusIndex, 1);

    if (modalCount > 0)
        return;

    global.end_modal(timestamp);
    global.set_stage_input_mode(Shell.StageInputMode.NORMAL);
}

function createLookingGlass() {
    if (lookingGlass == null) {
        lookingGlass = new LookingGlass.LookingGlass();
        lookingGlass.slaveTo(panel.actor);
    }
    return lookingGlass;
}

function getRunDialog() {
    if (runDialog == null) {
        runDialog = new RunDialog.RunDialog();
    }
    return runDialog;
}

/**
 * activateWindow:
 * @window: the Meta.Window to activate
 * @time: (optional) current event time
 * @workspaceNum: (optional) window's workspace number
 *
 * Activates @window, switching to its workspace first if necessary,
 * and switching out of the overview if it's currently active
 */
function activateWindow(window, time, workspaceNum) {
    let activeWorkspaceNum = global.screen.get_active_workspace_index();
    let windowWorkspaceNum = (workspaceNum !== undefined) ? workspaceNum : window.get_workspace().index();

    if (!time)
        time = global.get_current_time();

    if (windowWorkspaceNum != activeWorkspaceNum) {
        let workspace = global.screen.get_workspace_by_index(windowWorkspaceNum);
        workspace.activate_with_focus(window, time);
    } else {
        window.activate(time);
    }

    overview.hide();
}

// TODO - replace this timeout with some system to guess when the user might
// be e.g. just reading the screen and not likely to interact.
const DEFERRED_TIMEOUT_SECONDS = 20;
var _deferredWorkData = {};
// Work scheduled for some point in the future
var _deferredWorkQueue = [];
// Work we need to process before the next redraw
var _beforeRedrawQueue = [];
// Counter to assign work ids
var _deferredWorkSequence = 0;
var _deferredTimeoutId = 0;

function _runDeferredWork(workId) {
    if (!_deferredWorkData[workId])
        return;
    let index = _deferredWorkQueue.indexOf(workId);
    if (index < 0)
        return;

    _deferredWorkQueue.splice(index, 1);
    _deferredWorkData[workId].callback();
    if (_deferredWorkQueue.length == 0 && _deferredTimeoutId > 0) {
        Mainloop.source_remove(_deferredTimeoutId);
        _deferredTimeoutId = 0;
    }
}

function _runAllDeferredWork() {
    while (_deferredWorkQueue.length > 0)
        _runDeferredWork(_deferredWorkQueue[0]);
}

function _runBeforeRedrawQueue() {
    for (let i = 0; i < _beforeRedrawQueue.length; i++) {
        let workId = _beforeRedrawQueue[i];
        _runDeferredWork(workId);
    }
    _beforeRedrawQueue = [];
}

function _queueBeforeRedraw(workId) {
    _beforeRedrawQueue.push(workId);
    if (_beforeRedrawQueue.length == 1) {
        Meta.later_add(Meta.LaterType.BEFORE_REDRAW, function () {
            _runBeforeRedrawQueue();
            return false;
        });
    }
}

/**
 * initializeDeferredWork:
 * @actor: A #ClutterActor
 * @callback: Function to invoke to perform work
 *
 * This function sets up a callback to be invoked when either the
 * given actor is mapped, or after some period of time when the machine
 * is idle.  This is useful if your actor isn't always visible on the
 * screen (for example, all actors in the overview), and you don't want
 * to consume resources updating if the actor isn't actually going to be
 * displaying to the user.
 *
 * Note that queueDeferredWork is called by default immediately on
 * initialization as well, under the assumption that new actors
 * will need it.
 *
 * Returns: A string work identifer
 */
function initializeDeferredWork(actor, callback, props) {
    // Turn into a string so we can use as an object property
    let workId = '' + (++_deferredWorkSequence);
    _deferredWorkData[workId] = { 'actor': actor,
                                  'callback': callback };
    actor.connect('notify::mapped', function () {
        if (!(actor.mapped && _deferredWorkQueue.indexOf(workId) >= 0))
            return;
        _queueBeforeRedraw(workId);
    });
    actor.connect('destroy', function() {
        let index = _deferredWorkQueue.indexOf(workId);
        if (index >= 0)
            _deferredWorkQueue.splice(index, 1);
        delete _deferredWorkData[workId];
    });
    queueDeferredWork(workId);
    return workId;
}

/**
 * queueDeferredWork:
 * @workId: work identifier
 *
 * Ensure that the work identified by @workId will be
 * run on map or timeout.  You should call this function
 * for example when data being displayed by the actor has
 * changed.
 */
function queueDeferredWork(workId) {
    let data = _deferredWorkData[workId];
    if (!data) {
        global.logError('invalid work id ', workId);
        return;
    }
    if (_deferredWorkQueue.indexOf(workId) < 0)
        _deferredWorkQueue.push(workId);
    if (data.actor.mapped) {
        _queueBeforeRedraw(workId);
        return;
    } else if (_deferredTimeoutId == 0) {
        _deferredTimeoutId = Mainloop.timeout_add_seconds(DEFERRED_TIMEOUT_SECONDS, function () {
            _runAllDeferredWork();
            _deferredTimeoutId = 0;
            return false;
        });
    }
}