gnome-shell/js/ui/workspacesView.js

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

const Clutter = imports.gi.Clutter;
const Lang = imports.lang;
const Mainloop = imports.mainloop;
const Meta = imports.gi.Meta;
const Shell = imports.gi.Shell;
const St = imports.gi.St;
const Signals = imports.signals;
const Gettext = imports.gettext.domain('gnome-shell');
const _ = Gettext.gettext;

const DND = imports.ui.dnd;
const Main = imports.ui.main;
const Overview = imports.ui.overview;
const Tweener = imports.ui.tweener;
const Workspace = imports.ui.workspace;
const WorkspaceThumbnail = imports.ui.workspaceThumbnail;

const WORKSPACE_SWITCH_TIME = 0.25;
// Note that mutter has a compile-time limit of 36
const MAX_WORKSPACES = 16;


const CONTROLS_POP_IN_TIME = 0.1;


function WorkspacesView(workspaces) {
    this._init(workspaces);
}

WorkspacesView.prototype = {
    _init: function(workspaces) {
        this.actor = new St.Group({ style_class: 'workspaces-view' });

        // The actor itself isn't a drop target, so we don't want to pick on its area
        this.actor.set_size(0, 0);

        this.actor.connect('destroy', Lang.bind(this, this._onDestroy));

        this.actor.connect('style-changed', Lang.bind(this,
            function() {
                let node = this.actor.get_theme_node();
                this._spacing = node.get_length('spacing');
                this._updateWorkspaceActors(false);
            }));
        this.actor.connect('notify::mapped',
                           Lang.bind(this, this._onMappedChanged));

        this._width = 0;
        this._height = 0;
        this._x = 0;
        this._y = 0;
        this._spacing = 0;
        this._lostWorkspaces = [];
        this._animating = false; // tweening
        this._scrolling = false; // swipe-scrolling
        this._animatingScroll = false; // programatically updating the adjustment
        this._zoomOut = false; // zoom to a larger area
        this._inDrag = false; // dragging a window

        let activeWorkspaceIndex = global.screen.get_active_workspace_index();
        this._workspaces = workspaces;

        // Add workspace actors
        for (let w = 0; w < global.screen.n_workspaces; w++)
            this._workspaces[w].actor.reparent(this.actor);
        this._workspaces[activeWorkspaceIndex].actor.raise_top();

        // Position/scale the desktop windows and their children after the
        // workspaces have been created. This cannot be done first because
        // window movement depends on the Workspaces object being accessible
        // as an Overview member.
        this._overviewShowingId =
            Main.overview.connect('showing',
                                 Lang.bind(this, function() {
                for (let w = 0; w < this._workspaces.length; w++)
                    this._workspaces[w].zoomToOverview();
        }));
        this._overviewShownId =
            Main.overview.connect('shown',
                                 Lang.bind(this, function() {
                this.actor.set_clip(this._x, this._y, this._width, this._height);
        }));

        this._scrollAdjustment = new St.Adjustment({ value: activeWorkspaceIndex,
                                                     lower: 0,
                                                     page_increment: 1,
                                                     page_size: 1,
                                                     step_increment: 0,
                                                     upper: this._workspaces.length });
        this._scrollAdjustment.connect('notify::value',
                                       Lang.bind(this, this._onScroll));

        this._timeoutId = 0;

        this._switchWorkspaceNotifyId =
            global.window_manager.connect('switch-workspace',
                                          Lang.bind(this, this._activeWorkspaceChanged));

        this._itemDragBeginId = Main.overview.connect('item-drag-begin',
                                                      Lang.bind(this, this._dragBegin));
        this._itemDragEndId = Main.overview.connect('item-drag-end',
                                                     Lang.bind(this, this._dragEnd));
        this._windowDragBeginId = Main.overview.connect('window-drag-begin',
                                                        Lang.bind(this, this._dragBegin));
        this._windowDragEndId = Main.overview.connect('window-drag-end',
                                                      Lang.bind(this, this._dragEnd));
        this._swipeScrollBeginId = 0;
        this._swipeScrollEndId = 0;
    },

    setGeometry: function(x, y, width, height) {
      if (this._x == x && this._y == y &&
          this._width == width && this._height == height)
          return;
        this._width = width;
        this._height = height;
        this._x = x;
        this._y = y;

        for (let i = 0; i < this._workspaces.length; i++)
            this._workspaces[i].setGeometry(x, y, width, height);
    },

    _lookupWorkspaceForMetaWindow: function (metaWindow) {
        for (let i = 0; i < this._workspaces.length; i++) {
            if (this._workspaces[i].containsMetaWindow(metaWindow))
                return this._workspaces[i];
        }
        return null;
    },

    getActiveWorkspace: function() {
        let active = global.screen.get_active_workspace_index();
        return this._workspaces[active];
    },

    hide: function() {
        let activeWorkspaceIndex = global.screen.get_active_workspace_index();
        let activeWorkspace = this._workspaces[activeWorkspaceIndex];

        activeWorkspace.actor.raise_top();

       this.actor.remove_clip(this._x, this._y, this._width, this._height);

        for (let w = 0; w < this._workspaces.length; w++)
            this._workspaces[w].zoomFromOverview();
    },

    destroy: function() {
        this.actor.destroy();
    },

    syncStacking: function(stackIndices) {
        for (let i = 0; i < this._workspaces.length; i++)
            this._workspaces[i].syncStacking(stackIndices);
    },

    updateWindowPositions: function() {
        for (let w = 0; w < this._workspaces.length; w++)
            this._workspaces[w].positionWindows(Workspace.WindowPositionFlags.ANIMATE);
    },

    _scrollToActive: function(showAnimation) {
        let active = global.screen.get_active_workspace_index();

        this._updateWorkspaceActors(showAnimation);
        this._updateScrollAdjustment(active, showAnimation);
    },

    // Update workspace actors parameters
    // @showAnimation: iff %true, transition between states
    _updateWorkspaceActors: function(showAnimation) {
        let active = global.screen.get_active_workspace_index();

        this._animating = showAnimation;

        for (let w = 0; w < this._workspaces.length; w++) {
            let workspace = this._workspaces[w];

            Tweener.removeTweens(workspace.actor);

            let opacity = (this._inDrag && w != active) ? 200 : 255;
            let y = (w - active) * (this._height + this._spacing);

            if (showAnimation) {
                let params = { y: y,
                               opacity: opacity,
                               time: WORKSPACE_SWITCH_TIME,
                               transition: 'easeOutQuad'
                             };
                // we have to call _updateVisibility() once before the
                // animation and once afterwards - it does not really
                // matter which tween we use, so we pick the first one ...
                if (w == 0) {
                    this._updateVisibility();
                    params.onComplete = Lang.bind(this,
                        function() {
                            this._animating = false;
                            this._updateVisibility();
                        });
                }
                Tweener.addTween(workspace.actor, params);
            } else {
                workspace.actor.set_position(0, y);
                workspace.actor.opacity = opacity;
                if (w == 0)
                    this._updateVisibility();
            }
        }

        for (let l = 0; l < this._lostWorkspaces.length; l++) {
            let workspace = this._lostWorkspaces[l];

            Tweener.removeTweens(workspace.actor);

            workspace.actor.show();
            workspace.hideWindowsOverlays();

            if (showAnimation) {
                Tweener.addTween(workspace.actor,
                                 { y: workspace.x,
                                   time: WORKSPACE_SWITCH_TIME,
                                   transition: 'easeOutQuad',
                                   onComplete: Lang.bind(this,
                                                         this._cleanWorkspaces)
                                 });
            } else {
                this._cleanWorkspaces();
            }
        }
    },

    _updateVisibility: function() {
        let active = global.screen.get_active_workspace_index();

        for (let w = 0; w < this._workspaces.length; w++) {
            let workspace = this._workspaces[w];
            if (this._animating || this._scrolling) {
                workspace.hideWindowsOverlays();
                workspace.actor.show();
            } else {
                workspace.showWindowsOverlays();
                if (this._inDrag)
                    workspace.actor.visible = (Math.abs(w - active) <= 1);
                else
                    workspace.actor.visible = (w == active);
            }
        }
    },

    _cleanWorkspaces: function() {
        if (this._lostWorkspaces.length == 0)
            return;

        for (let l = 0; l < this._lostWorkspaces.length; l++)
            this._lostWorkspaces[l].destroy();
        this._lostWorkspaces = [];

        this._updateWorkspaceActors(false);
    },

    _updateScrollAdjustment: function(index, showAnimation) {
        if (this._scrolling)
            return;

        this._animatingScroll = true;

        if (showAnimation) {
            Tweener.addTween(this._scrollAdjustment, {
               value: index,
               time: WORKSPACE_SWITCH_TIME,
               transition: 'easeOutQuad',
               onComplete: Lang.bind(this,
                   function() {
                       this._animatingScroll = false;
                   })
            });
        } else {
            this._scrollAdjustment.value = index;
            this._animatingScroll = false;
        }
    },

    updateWorkspaces: function(oldNumWorkspaces, newNumWorkspaces, lostWorkspaces) {
        let active = global.screen.get_active_workspace_index();

        for (let l = 0; l < lostWorkspaces.length; l++)
            lostWorkspaces[l].disconnectAll();

        Tweener.addTween(this._scrollAdjustment,
                         { upper: newNumWorkspaces,
                           time: WORKSPACE_SWITCH_TIME,
                           transition: 'easeOutQuad'
                         });

        if (newNumWorkspaces > oldNumWorkspaces) {
            for (let w = oldNumWorkspaces; w < newNumWorkspaces; w++)
                this.actor.add_actor(this._workspaces[w].actor);

            this._updateWorkspaceActors(false);
        } else {
            this._lostWorkspaces = lostWorkspaces;
        }

        this._scrollToActive(true);
    },

    _activeWorkspaceChanged: function(wm, from, to, direction) {
        if (this._scrolling)
            return;

        this._scrollToActive(true);
    },

    _onDestroy: function() {
        this._scrollAdjustment.run_dispose();
        Main.overview.disconnect(this._overviewShowingId);
        Main.overview.disconnect(this._overviewShownId);
        global.window_manager.disconnect(this._switchWorkspaceNotifyId);

        if (this._inDrag)
            this._dragEnd();

        if (this._timeoutId) {
            Mainloop.source_remove(this._timeoutId);
            this._timeoutId = 0;
        }
        if (this._itemDragBeginId > 0) {
            Main.overview.disconnect(this._itemDragBeginId);
            this._itemDragBeginId = 0;
        }
        if (this._itemDragEndId > 0) {
            Main.overview.disconnect(this._itemDragEndId);
            this._itemDragEndId = 0;
        }
        if (this._windowDragBeginId > 0) {
            Main.overview.disconnect(this._windowDragBeginId);
            this._windowDragBeginId = 0;
        }
        if (this._windowDragEndId > 0) {
            Main.overview.disconnect(this._windowDragEndId);
            this._windowDragEndId = 0;
        }
    },

    _onMappedChanged: function() {
        if (this.actor.mapped) {
            let direction = Overview.SwipeScrollDirection.VERTICAL;
            Main.overview.setScrollAdjustment(this._scrollAdjustment,
                                              direction);
            this._swipeScrollBeginId = Main.overview.connect('swipe-scroll-begin',
                                                             Lang.bind(this, this._swipeScrollBegin));
            this._swipeScrollEndId = Main.overview.connect('swipe-scroll-end',
                                                           Lang.bind(this, this._swipeScrollEnd));
        } else {
            Main.overview.disconnect(this._swipeScrollBeginId);
            Main.overview.disconnect(this._swipeScrollEndId);
        }
    },

    _dragBegin: function() {
        if (this._scrolling)
            return;

        this._inDrag = true;

        this._dragMonitor = {
            dragMotion: Lang.bind(this, this._onDragMotion)
        };
        DND.addDragMonitor(this._dragMonitor);
    },

    _onDragMotion: function(dragEvent) {
        if (Main.overview.animationInProgress)
             return DND.DragMotionResult.CONTINUE;

        let primary = global.get_primary_monitor();

        let activeWorkspaceIndex = global.screen.get_active_workspace_index();
        let topWorkspace, bottomWorkspace;
        topWorkspace  = this._workspaces[activeWorkspaceIndex - 1];
        bottomWorkspace = this._workspaces[activeWorkspaceIndex + 1];
        let hoverWorkspace = null;

        // reactive monitor edges
        let topEdge = primary.y;
        let switchTop = (dragEvent.y <= topEdge && topWorkspace);
        if (switchTop && this._dragOverLastY != topEdge) {
            topWorkspace.metaWorkspace.activate(global.get_current_time());
            topWorkspace.setReservedSlot(dragEvent.dragActor._delegate);
            this._dragOverLastY = topEdge;

            return DND.DragMotionResult.CONTINUE;
        }
        let bottomEdge = primary.y + primary.height - 1;
        let switchBottom = (dragEvent.y >= bottomEdge && bottomWorkspace);
        if (switchBottom && this._dragOverLastY != bottomEdge) {
            bottomWorkspace.metaWorkspace.activate(global.get_current_time());
            bottomWorkspace.setReservedSlot(dragEvent.dragActor._delegate);
            this._dragOverLastY = bottomEdge;

            return DND.DragMotionResult.CONTINUE;
        }
        this._dragOverLastY = dragEvent.y;
        let result = DND.DragMotionResult.CONTINUE;

        // check hover state of new workspace area / inactive workspaces
        if (topWorkspace) {
            if (topWorkspace.actor.contains(dragEvent.targetActor)) {
                hoverWorkspace = topWorkspace;
                topWorkspace.opacity = topWorkspace.actor.opacity = 255;
                result = topWorkspace.handleDragOver(dragEvent.source, dragEvent.dragActor);
            } else {
                topWorkspace.opacity = topWorkspace.actor.opacity = 200;
            }
        }

        if (bottomWorkspace) {
            if (bottomWorkspace.actor.contains(dragEvent.targetActor)) {
                hoverWorkspace = bottomWorkspace;
                bottomWorkspace.opacity = bottomWorkspace.actor.opacity = 255;
                result = bottomWorkspace.handleDragOver(dragEvent.source, dragEvent.dragActor);
            } else {
                bottomWorkspace.opacity = bottomWorkspace.actor.opacity = 200;
            }
        }

        // handle delayed workspace switches
        if (hoverWorkspace) {
            if (!this._timeoutId)
                this._timeoutId = Mainloop.timeout_add_seconds(1,
                    Lang.bind(this, function() {
                       hoverWorkspace.metaWorkspace.activate(global.get_current_time());
                       hoverWorkspace.setReservedSlot(dragEvent.dragActor._delegate);
                       return false;
                    }));
        } else {
            if (this._timeoutId) {
                Mainloop.source_remove(this._timeoutId);
                this._timeoutId = 0;
            }
        }

        return result;
    },

    _dragEnd: function() {
        if (this._timeoutId) {
            Mainloop.source_remove(this._timeoutId);
            this._timeoutId = 0;
        }
        DND.removeMonitor(this._dragMonitor);
        this._inDrag = false;

        for (let i = 0; i < this._workspaces.length; i++)
            this._workspaces[i].setReservedSlot(null);
    },

    _swipeScrollBegin: function() {
        this._scrolling = true;
    },

    _swipeScrollEnd: function(overview, result) {
        this._scrolling = false;

        if (result == Overview.SwipeScrollResult.CLICK) {
            let [x, y, mod] = global.get_pointer();
            let actor = global.stage.get_actor_at_pos(Clutter.PickMode.ALL,
                                                      x, y);

            // Only switch to the workspace when there's no application
            // windows open. The problem is that it's too easy to miss
            // an app window and get the wrong one focused.
            let active = global.screen.get_active_workspace_index();
            if (this._workspaces[active].isEmpty() &&
                this.actor.contains(actor))
                Main.overview.hide();
        }

        // Make sure title captions etc are shown as necessary
        this._updateVisibility();
    },

    // sync the workspaces' positions to the value of the scroll adjustment
    // and change the active workspace if appropriate
    _onScroll: function(adj) {
        if (this._animatingScroll)
            return;

        let active = global.screen.get_active_workspace_index();
        let current = Math.round(adj.value);

        if (active != current) {
            let metaWorkspace = this._workspaces[current].metaWorkspace;
            metaWorkspace.activate(global.get_current_time());
        }

        let last = this._workspaces.length - 1;
        let firstWorkspaceY = this._workspaces[0].actor.y;
        let lastWorkspaceY = this._workspaces[last].actor.y;
        let workspacesHeight = lastWorkspaceY - firstWorkspaceY;

        if (adj.upper == 1)
            return;

        let currentY = firstWorkspaceY;
        let newY =  - adj.value / (adj.upper - 1) * workspacesHeight;

        let dy = newY - currentY;

        for (let i = 0; i < this._workspaces.length; i++) {
            this._workspaces[i].hideWindowsOverlays();
            this._workspaces[i].actor.visible = Math.abs(i - adj.value) <= 1;
            this._workspaces[i].actor.y += dy;
        }
    },

    _getWorkspaceIndexToRemove: function() {
        return global.screen.get_active_workspace_index();
    }
};
Signals.addSignalMethods(WorkspacesView.prototype);


function WorkspacesDisplay() {
    this._init();
}

WorkspacesDisplay.prototype = {
    _init: function() {
        this.actor = new Shell.GenericContainer();
        this.actor.connect('get-preferred-width', Lang.bind(this, this._getPreferredWidth));
        this.actor.connect('get-preferred-height', Lang.bind(this, this._getPreferredHeight));
        this.actor.connect('allocate', Lang.bind(this, this._allocate));

        let controls = new St.Bin({ style_class: 'workspace-controls',
                                    request_mode: Clutter.RequestMode.WIDTH_FOR_HEIGHT,
                                    y_align: St.Align.START,
                                    y_fill: true });
        this._controls = controls;
        this.actor.add_actor(controls);

        controls.reactive = true;
        controls.track_hover = true;
        controls.connect('notify::hover',
                         Lang.bind(this, this._onControlsHoverChanged));
        controls.connect('scroll-event',
                         Lang.bind(this, this._onScrollEvent));


        this._thumbnailsBox = new WorkspaceThumbnail.ThumbnailsBox();
        controls.add_actor(this._thumbnailsBox.actor);

        this.workspacesView = null;

        this._inDrag = false;
        this._cancelledDrag = false;
        this._zoomOut = false;
        this._zoomFraction = 0;

        this._nWorkspacesNotifyId = 0;
        this._switchWorkspaceNotifyId = 0;

        this._itemDragBeginId = 0;
        this._itemDragEndId = 0;
        this._windowDragBeginId = 0;
        this._windowDragCancelledId = 0;
        this._windowDragEndId = 0;
    },

   show: function() {
        this._controls.show();
        this._thumbnailsBox.show();

        this._workspaces = [];
        for (let i = 0; i < global.screen.n_workspaces; i++) {
            let metaWorkspace = global.screen.get_workspace_by_index(i);
            this._workspaces[i] = new Workspace.Workspace(metaWorkspace);
        }

        if (this.workspacesView)
            this.workspacesView.destroy();
        this.workspacesView = new WorkspacesView(this._workspaces);
        this._updateWorkspacesGeometry();

        this._nWorkspacesNotifyId =
            global.screen.connect('notify::n-workspaces',
                                  Lang.bind(this, this._workspacesChanged));

        this._restackedNotifyId =
            global.screen.connect('restacked',
                                  Lang.bind(this, this._onRestacked));

        if (this._itemDragBeginId == 0)
            this._itemDragBeginId = Main.overview.connect('item-drag-begin',
                                                          Lang.bind(this, this._dragBegin));
        if (this._itemDragEndId == 0)
            this._itemDragEndId = Main.overview.connect('item-drag-end',
                                                        Lang.bind(this, this._dragEnd));
        if (this._windowDragBeginId == 0)
            this._windowDragBeginId = Main.overview.connect('window-drag-begin',
                                                            Lang.bind(this, this._dragBegin));
        if (this._windowDragCancelledId == 0)
            this._windowDragCancelledId = Main.overview.connect('window-drag-cancelled',
                                                            Lang.bind(this, this._dragCancelled));
        if (this._windowDragEndId == 0)
            this._windowDragEndId = Main.overview.connect('window-drag-end',
                                                          Lang.bind(this, this._dragEnd));

        this._onRestacked();
        this._zoomOut = false;
        this._zoomFraction = 0;
        this._updateZoom();
    },

    hide: function() {
        this._controls.hide();
        this._thumbnailsBox.hide();

        if (this._nWorkspacesNotifyId > 0) {
            global.screen.disconnect(this._nWorkspacesNotifyId);
            this._nWorkspacesNotifyId = 0;
        }
        if (this._restackedNotifyId > 0){
            global.screen.disconnect(this._restackedNotifyId);
            this._restackedNotifyId = 0;
        }
        if (this._itemDragBeginId > 0) {
            Main.overview.disconnect(this._itemDragBeginId);
            this._itemDragBeginId = 0;
        }
        if (this._itemEndBeginId > 0) {
            Main.overview.disconnect(this._itemDragEndId);
            this._itemDragEndId = 0;
        }
        if (this._windowDragBeginId > 0) {
            Main.overview.disconnect(this._windowDragBeginId);
            this._windowDragBeginId = 0;
        }
        if (this._windowDragCancelledId > 0) {
            Main.overview.disconnect(this._windowDragCancelledId);
            this._windowDragCancelledId = 0;
        }
        if (this._windowDragEndId > 0) {
            Main.overview.disconnect(this._windowDragEndId);
            this._windowDragEndId = 0;
        }

        this.workspacesView.destroy();
        this.workspacesView = null;
        for (let w = 0; w < this._workspaces.length; w++) {
            this._workspaces[w].disconnectAll();
            this._workspaces[w].destroy();
        }
    },

    // zoomFraction property allows us to tween the controls sliding in and out
    set zoomFraction(fraction) {
        this._zoomFraction = fraction;
        this.actor.queue_relayout();
    },

    get zoomFraction() {
        return this._zoomFraction;
    },

    _getPreferredWidth: function (actor, forHeight, alloc) {
        // pass through the call in case the child needs it, but report 0x0
        this._controls.get_preferred_width(forHeight);
    },

    _getPreferredHeight: function (actor, forWidth, alloc) {
        // pass through the call in case the child needs it, but report 0x0
        this._controls.get_preferred_height(forWidth);
    },

    _allocate: function (actor, box, flags) {
        let childBox = new Clutter.ActorBox();

        let totalWidth = box.x2 - box.x1;

        // width of the controls
        let [controlsMin, controlsNatural] = this._controls.get_preferred_width(box.y2 - box.y1);

        // Amount of space on the screen we reserve for the visible control
        let controlsVisible = this._controls.get_theme_node().get_length('visible-width');
        let controlsReserved = controlsVisible * (1 - this._zoomFraction) + controlsNatural * this._zoomFraction;

        let rtl = (St.Widget.get_default_direction () == St.TextDirection.RTL);
        if (rtl) {
            childBox.x2 = controlsReserved;
            childBox.x1 = childBox.x2 - controlsNatural;
        } else {
            childBox.x1 = totalWidth - controlsReserved;
            childBox.x2 = childBox.x1 + controlsNatural;
        }

        childBox.y1 = 0;
        childBox.y2 = box.y2- box.y1;
        this._controls.allocate(childBox, flags);

        this._updateWorkspacesGeometry();
    },

    _updateWorkspacesGeometry: function() {
        if (!this.workspacesView)
            return;

        let width = this.actor.allocation.x2 - this.actor.allocation.x1;
        let height = this.actor.allocation.y2 - this.actor.allocation.y1;

        let [controlsMin, controlsNatural] = this._controls.get_preferred_width(height);
        let controlsVisible = this._controls.get_theme_node().get_length('visible-width');

        let [x, y] = this.actor.get_transformed_position();

        let rtl = (St.Widget.get_default_direction () == St.TextDirection.RTL);

        if (this._zoomOut) {
            width -= controlsNatural;
            if (rtl)
                x += controlsNatural;
        } else {
            width -= controlsVisible;
            if (rtl)
                x += controlsVisible;
        }

        this.workspacesView.setGeometry(x, y, width, height);
    },

    _onRestacked: function() {
        let stack = global.get_window_actors();
        let stackIndices = {};

        for (let i = 0; i < stack.length; i++) {
            // Use the stable sequence for an integer to use as a hash key
            stackIndices[stack[i].get_meta_window().get_stable_sequence()] = i;
        }

        this.workspacesView.syncStacking(stackIndices);
        this._thumbnailsBox.syncStacking(stackIndices);
    },

    _workspacesChanged: function() {
        let oldNumWorkspaces = this._workspaces.length;
        let newNumWorkspaces = global.screen.n_workspaces;
        let active = global.screen.get_active_workspace_index();

        if (oldNumWorkspaces == newNumWorkspaces)
            return;

        let lostWorkspaces = [];
        if (newNumWorkspaces > oldNumWorkspaces) {
            // Assume workspaces are only added at the end
            for (let w = oldNumWorkspaces; w < newNumWorkspaces; w++) {
                let metaWorkspace = global.screen.get_workspace_by_index(w);
                this._workspaces[w] = new Workspace.Workspace(metaWorkspace);
            }

            this._thumbnailsBox.addThumbnails(oldNumWorkspaces, newNumWorkspaces - oldNumWorkspaces);
        } 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 metaWorkspace = global.screen.get_workspace_by_index(w);
                if (this._workspaces[w].metaWorkspace != metaWorkspace) {
                    removedIndex = w;
                    break;
                }
            }

            lostWorkspaces = this._workspaces.splice(removedIndex,
                                                     removedNum);

            // Don't let the user try to select this workspace as it's
            // making its exit.
            for (let l = 0; l < lostWorkspaces.length; l++)
                lostWorkspaces[l].setReactive(false);

            this._thumbnailsBox.removeThumbmails(removedIndex, removedNum);
        }

        this.workspacesView.updateWorkspaces(oldNumWorkspaces,
                                             newNumWorkspaces,
                                             lostWorkspaces);
    },

    _updateZoom : function() {
        if (Main.overview.animationInProgress)
            return;

        let shouldZoom = this._controls.hover || (this._inDrag && !this._cancelledDrag);
        if (shouldZoom != this._zoomOut) {
            this._zoomOut = shouldZoom;
            this._updateWorkspacesGeometry();

            if (!this.workspacesView)
                return;

            Tweener.addTween(this,
                             { zoomFraction: this._zoomOut ? 1 : 0,
                               time: WORKSPACE_SWITCH_TIME,
                               transition: 'easeOutQuad' });

            this.workspacesView.updateWindowPositions();
        }
    },

    _onControlsHoverChanged: function() {
        this._updateZoom();
    },

    _dragBegin: function() {
        this._inDrag = true;
        this._cancelledDrag = false;
        this._updateZoom();
    },

    _dragCancelled: function() {
        this._cancelledDrag = true;
        this._updateZoom();
    },

    _dragEnd: function() {
        this._inDrag = false;

        // We do this deferred because drag-end is emitted before dnd.js emits
        // event/leave events that were suppressed during the drag. If we didn't
        // defer this, we'd zoom out then immediately zoom in because of the
        // enter event we received. That would normally be invisible but we
        // might as well avoid it.
        Meta.later_add(Meta.LaterType.BEFORE_REDRAW,
                       Lang.bind(this, this._updateZoom));
    },

    _onScrollEvent: function (actor, event) {
        switch ( event.get_scroll_direction() ) {
        case Clutter.ScrollDirection.UP:
            Main.wm.actionMoveWorkspaceUp();
            break;
        case Clutter.ScrollDirection.DOWN:
            Main.wm.actionMoveWorkspaceDown();
            break;
        }
    }
};
Signals.addSignalMethods(WorkspacesDisplay.prototype);