Add an OSD monitor labeler exposed on DBus

This DBus API is intended to be used by gnome-control-center's
displays panel to show monitor labels.

Each output (i.e. hardware monitor) identified by its
org.gnome.Mutter.DisplayConfig API ID has at most one label. On
mirrored setups, all the labels for outputs corresponding to the same
logical monitor (i.e. showing the same contents in the same mode) are
shown together.

At most, only one DBus client at a time is allowed to show labels.

https://bugzilla.gnome.org/show_bug.cgi?id=743744

js/ui/osdMonitorLabeler.js

@@ -0,0 +1,141 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+const Clutter = imports.gi.Clutter;
+const Gio = imports.gi.Gio;
+const St = imports.gi.St;
+
+const Lang = imports.lang;
+const Main = imports.ui.main;
+const Tweener = imports.ui.tweener;
+const Meta = imports.gi.Meta;
+
+const FADE_TIME = 0.1;
+
+const OsdMonitorLabel = new Lang.Class({
+    Name: 'OsdMonitorLabel',
+
+    _init: function(monitor, label) {
+        this._actor = new St.Widget({ opacity: 0,
+                                      x_expand: true,
+                                      y_expand: true });
+
+        this._monitor = monitor;
+
+        this._box = new St.BoxLayout({ style_class: 'osd-window',
+                                       vertical: true });
+        this._actor.add_actor(this._box);
+
+        this._label = new St.Label({ style_class: 'osd-monitor-label',
+                                     text: label });
+        this._box.add(this._label);
+
+        Main.uiGroup.add_child(this._actor);
+        Main.uiGroup.set_child_above_sibling(this._actor, null);
+        this._position();
+
+        Meta.disable_unredirect_for_screen(global.screen);
+        Tweener.addTween(this._actor,
+                         { opacity: 255,
+                           time: FADE_TIME,
+                           transition: 'easeOutQuad' });
+    },
+
+    _position: function() {
+        let workArea = Main.layoutManager.getWorkAreaForMonitor(this._monitor);
+
+        if (Clutter.get_default_text_direction() == Clutter.TextDirection.RTL)
+            this._box.x = workArea.x + (workArea.width - this._box.width);
+        else
+            this._box.x = workArea.x;
+
+        this._box.y = workArea.y;
+    },
+
+    destroy: function() {
+        Tweener.addTween(this._actor,
+                         { opacity: 0,
+                           time: FADE_TIME,
+                           transition: 'easeOutQuad',
+                           onComplete: Lang.bind(this, function() {
+                               this._actor.destroy();
+                               Meta.enable_unredirect_for_screen(global.screen);
+                           })
+                         });
+    }
+});
+
+const OsdMonitorLabeler = new Lang.Class({
+    Name: 'OsdMonitorLabeler',
+
+    _init: function() {
+        this._monitorManager = Meta.MonitorManager.get();
+        this._client = null;
+        this._clientWatchId = 0;
+        this._osdLabels = [];
+        this._monitorLabels = null;
+        Main.layoutManager.connect('monitors-changed',
+                                    Lang.bind(this, this._reset));
+        this._reset();
+    },
+
+    _reset: function() {
+        for (let i in this._osdLabels)
+            this._osdLabels[i].destroy();
+        this._osdLabels = [];
+        this._monitorLabels = new Map();
+        let monitors = Main.layoutManager.monitors;
+        for (let i in monitors)
+            this._monitorLabels.set(monitors[i].index, []);
+    },
+
+    _trackClient: function(client) {
+        if (this._client)
+            return (this._client == client);
+
+        this._client = client;
+        this._clientWatchId = Gio.bus_watch_name(Gio.BusType.SESSION, client, 0, null,
+                                                 Lang.bind(this, function(c, name) {
+                                                     this.hide(name);
+                                                 }));
+        return true;
+    },
+
+    _untrackClient: function(client) {
+        if (!this._client || this._client != client)
+            return false;
+
+        Gio.bus_unwatch_name(this._clientWatchId);
+        this._clientWatchId = 0;
+        this._client = null;
+        return true;
+    },
+
+    show: function(client, params) {
+        if (!this._trackClient(client))
+            return;
+
+        this._reset();
+
+        for (let id in params) {
+            let monitor = this._monitorManager.get_monitor_for_output(id);
+            if (monitor == -1)
+                continue;
+            this._monitorLabels.get(monitor).push(params[id].deep_unpack());
+        }
+
+        // In mirrored display setups, more than one physical outputs
+        // might be showing the same logical monitor. In that case, we
+        // join each output's labels on the same OSD widget.
+        for (let [monitor, labels] of this._monitorLabels.entries()) {
+            labels.sort();
+            this._osdLabels.push(new OsdMonitorLabel(monitor, labels.join(' ')));
+        }
+    },
+
+    hide: function(client) {
+        if (!this._untrackClient(client))
+            return;
+
+        this._reset();
+    }
+});