[gnome-shell-extensions/wip/rstrode/heads-up-display: 15/15] heads-up-display: Add extension for showing persistent heads up display message

[Ray Strode <halfline src gnome org>]

commit 9d20099a2016c086f43b8b1a451a6fd616bd0a56
Author: Ray Strode <rstrode redhat com>
Date:   Tue Aug 24 15:03:57 2021 -0400

    heads-up-display: Add extension for showing persistent heads up display message

 extensions/heads-up-display/extension.js           | 436 +++++++++++++++++++++
 extensions/heads-up-display/headsUpMessage.js      | 170 ++++++++
 extensions/heads-up-display/meson.build            |   8 +
 extensions/heads-up-display/metadata.json.in       |  11 +
 ...e.shell.extensions.heads-up-display.gschema.xml |  54 +++
 extensions/heads-up-display/prefs.js               | 194 +++++++++
 extensions/heads-up-display/stylesheet.css         |  32 ++
 meson.build                                        |   1 +
 8 files changed, 906 insertions(+)
---
diff --git a/extensions/heads-up-display/extension.js b/extensions/heads-up-display/extension.js
new file mode 100644
index 0000000..7cebfa9
--- /dev/null
+++ b/extensions/heads-up-display/extension.js
@@ -0,0 +1,436 @@
+/* exported init enable disable */
+
+const Signals = imports.signals;
+
+const {
+    Atk, Clutter, Gio, GLib, GObject, Gtk, Meta, Shell, St,
+} = imports.gi;
+
+const ExtensionUtils = imports.misc.extensionUtils;
+const Me = ExtensionUtils.getCurrentExtension();
+
+const Main = imports.ui.main;
+const Layout = imports.ui.layout;
+const HeadsUpMessage = Me.imports.headsUpMessage;
+
+const _ = ExtensionUtils.gettext;
+
+var HeadsUpConstraint = GObject.registerClass({
+    Properties: {
+        'offset': GObject.ParamSpec.int('offset',
+                                        'Offset', 'offset',
+                                        GObject.ParamFlags.READABLE | GObject.ParamFlags.WRITABLE,
+                                        -1, 0, -1),
+        'active': GObject.ParamSpec.boolean('active',
+                                            'Active', 'active',
+                                            GObject.ParamFlags.READABLE | GObject.ParamFlags.WRITABLE,
+                                            true),
+    },
+}, class HeadsUpConstraint extends Layout.MonitorConstraint {
+    _init(props) {
+        super._init(props);
+        this._offset = 0;
+        this._active = true;
+    }
+
+    get offset() {
+        return this._offset;
+    }
+
+    set offset(o) {
+        this._offset = o
+    }
+
+    get active() {
+        return this._active;
+    }
+
+    set active(a) {
+        this._active = a;
+    }
+
+    vfunc_update_allocation(actor, actorBox) {
+        if (!Main.layoutManager.primaryMonitor)
+            return;
+
+        if (!this.active)
+            return;
+
+        if (actor.has_allocation())
+            return;
+
+        const workArea = Main.layoutManager.getWorkAreaForMonitor(Main.layoutManager.primaryIndex);
+        actorBox.init_rect(workArea.x, workArea.y + this.offset, workArea.width, workArea.height - 
this.offset);
+    }
+});
+
+class Extension {
+    constructor() {
+        ExtensionUtils.initTranslations();
+    }
+
+    enable() {
+        this._settings = ExtensionUtils.getSettings('org.gnome.shell.extensions.heads-up-display');
+        this._settingsChangedId = this._settings.connect('changed', this._updateMessage.bind(this));
+
+        this._idleMonitor = Meta.IdleMonitor.get_core();
+        this._messageInhibitedUntilIdle = false;
+        this._oldMapWindow = Main.wm._mapWindow;
+        Main.wm._mapWindow = this._mapWindow;
+        this._windowManagerMapId = global.window_manager.connect('map', this._onWindowMap.bind(this));
+
+        if (Main.layoutManager._startingUp)
+            this._startupCompleteId = Main.layoutManager.connect('startup-complete', 
this._onStartupComplete.bind(this));
+        else
+            this._onStartupComplete(this);
+    }
+
+    disable() {
+        this._dismissMessage();
+
+        this._stopWatchingForIdle();
+
+        if (this._sessionModeUpdatedId) {
+            Main.sessionMode.disconnect(this._sessionModeUpdatedId);
+            this._sessionModeUpdatedId = 0;
+        }
+
+        if (this._overviewShowingId) {
+            Main.overview.disconnect(this._overviewShowingId);
+            this._overviewShowingId = 0;
+        }
+
+        if (this._overviewHiddenId) {
+            Main.overview.disconnect(this._overviewHiddenId);
+            this._overviewHiddenId = 0;
+        }
+
+        if (this._screenShieldVisibleId) {
+            Main.screenShield._dialog._clock.disconnect(this._screenShieldVisibleId);
+            this._screenShieldVisibleId = 0;
+        }
+
+        if (this._panelConnectionId) {
+            Main.layoutManager.panelBox.disconnect(this._panelConnectionId);
+            this._panelConnectionId = 0;
+        }
+
+        if (this._oldMapWindow) {
+            Main.wm._mapWindow = this._oldMapWindow;
+            this._oldMapWindow = null;
+        }
+
+        if (this._windowManagerMapId) {
+            global.window_manager.disconnect(this._windowManagerMapId);
+            this._windowManagerMapId = 0;
+        }
+
+        if (this._startupCompleteId) {
+            Main.layoutManager.disconnect(this._startupCompleteId);
+            this._startupCompleteId = 0;
+        }
+
+        if (this._settingsChangedId) {
+            this._settings.disconnect(this._settingsChangedId);
+            this._settingsChangedId = 0;
+        }
+    }
+
+    _onWindowMap(shellwm, actor) {
+        const windowObject = actor.meta_window;
+        const windowType = windowObject.get_window_type();
+
+        if (windowType != Meta.WindowType.NORMAL)
+            return;
+
+        if (!this._message || !this._message.visible)
+            return;
+
+        const messageRect = new Meta.Rectangle({ x: this._message.x, y: this._message.y, width: 
this._message.width, height: this._message.height });
+        const windowRect = windowObject.get_frame_rect();
+
+        if (windowRect.intersect(messageRect)) {
+            windowObject.move_frame(false, windowRect.x, this._message.y + this._message.height);
+        }
+    }
+
+    _onStartupComplete() {
+        this._overviewShowingId = Main.overview.connect('showing', this._updateMessage.bind(this));
+        this._overviewHiddenId = Main.overview.connect('hidden', this._updateMessage.bind(this));
+        this._panelConnectionId = Main.layoutManager.panelBox.connect('notify::visible', 
this._updateMessage.bind(this));
+        this._sessionModeUpdatedId = Main.sessionMode.connect('updated', 
this._onSessionModeUpdated.bind(this));
+
+        this._updateMessage();
+    }
+
+    _onSessionModeUpdated() {
+         if (!Main.sessionMode.hasWindows)
+             this._messageInhibitedUntilIdle = false;
+
+        const dialog = Main.screenShield._dialog;
+        if (!Main.sessionMode.isGreeter && dialog && !this._screenShieldVisibleId) {
+            this._screenShieldVisibleId = dialog._clock.connect('notify::visible',
+                                                                this._updateMessage.bind(this));
+            this._screenShieldDestroyId = dialog._clock.connect('destroy', () => {
+                this._screenShieldVisibleId = 0;
+                this._screenShieldDestroyId = 0;
+            });
+        }
+         this._updateMessage();
+    }
+
+    _stopWatchingForIdle() {
+        if (this._idleWatchId) {
+            this._idleMonitor.remove_watch(this._idleWatchId);
+            this._idleWatchId = 0;
+        }
+
+        if (this._idleTimeoutChangedId) {
+            this._settings.disconnect(this._idleTimeoutChangedId);
+            this._idleTimeoutChangedId = 0;
+        }
+    }
+
+    _onIdleTimeoutChanged() {
+        this._stopWatchingForIdle();
+        this._messageInhibitedUntilIdle = false;
+    }
+
+    _onUserIdle() {
+        this._messageInhibitedUntilIdle = false;
+        this._updateMessage();
+    }
+
+    _watchForIdle() {
+        this._stopWatchingForIdle();
+
+        const idleTimeout = this._settings.get_uint('idle-timeout');
+
+        this._idleTimeoutChangedId = this._settings.connect('changed::idle-timeout', 
this._onIdleTimeoutChanged.bind(this));
+        this._idleWatchId = this._idleMonitor.add_idle_watch(idleTimeout * 1000, 
this._onUserIdle.bind(this));
+    }
+
+    _updateMessage() {
+        if (this._messageInhibitedUntilIdle) {
+            if (this._message)
+                this._dismissMessage();
+            return;
+        }
+
+        this._stopWatchingForIdle();
+
+        if (Main.sessionMode.hasOverview && Main.overview.visible) {
+            this._dismissMessage();
+            return;
+        }
+
+        if (!Main.layoutManager.panelBox.visible) {
+            this._dismissMessage();
+            return;
+        }
+
+        let supportedModes = [];
+
+        if (this._settings.get_boolean('show-when-unlocked'))
+            supportedModes.push('user');
+
+        if (this._settings.get_boolean('show-when-unlocking') ||
+            this._settings.get_boolean('show-when-locked'))
+            supportedModes.push('unlock-dialog');
+
+        if (this._settings.get_boolean('show-on-login-screen'))
+            supportedModes.push('gdm');
+
+        if (!supportedModes.includes(Main.sessionMode.currentMode) &&
+            !supportedModes.includes(Main.sessionMode.parentMode)) {
+            this._dismissMessage();
+            return;
+        }
+
+        if (Main.sessionMode.currentMode === 'unlock-dialog') {
+            const dialog = Main.screenShield._dialog;
+            if (!this._settings.get_boolean('show-when-locked')) {
+                if (dialog._clock.visible) {
+                    this._dismissMessage();
+                    return;
+                }
+            }
+
+            if (!this._settings.get_boolean('show-when-unlocking')) {
+                if (!dialog._clock.visible) {
+                    this._dismissMessage();
+                    return;
+                }
+            }
+        }
+
+        const heading = this._settings.get_string('message-heading');
+        const body = this._settings.get_string('message-body');
+
+        if (!heading && !body) {
+            this._dismissMessage();
+            return;
+        }
+
+        if (!this._message) {
+            this._message = new HeadsUpMessage.HeadsUpMessage(heading, body);
+
+            this._message.connect('notify::allocation', this._adaptSessionForMessage.bind(this));
+            this._message.connect('clicked', this._onMessageClicked.bind(this));
+        }
+
+        this._message.reactive = true;
+        this._message.track_hover = true;
+
+        this._message.setHeading(heading);
+        this._message.setBody(body);
+
+        if (!Main.sessionMode.hasWindows) {
+            this._message.track_hover = false;
+            this._message.reactive = false;
+        }
+    }
+
+    _onMessageClicked() {
+        if (!Main.sessionMode.hasWindows)
+          return;
+
+        this._watchForIdle();
+        this._messageInhibitedUntilIdle = true;
+        this._updateMessage();
+    }
+
+    _dismissMessage() {
+        if (!this._message) {
+            return;
+        }
+
+        this._message.visible = false;
+        this._message.destroy();
+        this._message = null;
+        this._resetMessageTray();
+        this._resetLoginDialog();
+    }
+
+    _resetMessageTray() {
+        if (!Main.messageTray)
+            return;
+
+        if (this._updateMessageTrayId) {
+            global.stage.disconnect(this._updateMessageTrayId);
+            this._updateMessageTrayId = 0;
+        }
+
+        if (this._messageTrayConstraint) {
+            Main.messageTray.remove_constraint(this._messageTrayConstraint);
+            this._messageTrayConstraint = null;
+        }
+    }
+
+    _alignMessageTray() {
+        if (!Main.messageTray)
+            return;
+
+        if (!this._message || !this._message.visible) {
+            this._resetMessageTray()
+            return;
+        }
+
+        if (this._updateMessageTrayId)
+            return;
+
+        this._updateMessageTrayId = global.stage.connect('before-update', () => {
+            if (!this._messageTrayConstraint) {
+                this._messageTrayConstraint = new HeadsUpConstraint({ primary: true });
+
+                Main.layoutManager.panelBox.bind_property('visible',
+                    this._messageTrayConstraint, 'active',
+                    GObject.BindingFlags.SYNC_CREATE);
+
+                Main.messageTray.add_constraint(this._messageTrayConstraint);
+            }
+
+            const panelBottom = Main.layoutManager.panelBox.y + Main.layoutManager.panelBox.height;
+            const messageBottom = this._message.y + this._message.height;
+
+            this._messageTrayConstraint.offset = messageBottom - panelBottom;
+            global.stage.disconnect(this._updateMessageTrayId);
+            this._updateMessageTrayId = 0;
+        });
+    }
+
+    _resetLoginDialog() {
+        if (!Main.sessionMode.isGreeter)
+            return;
+
+        if (!Main.screenShield || !Main.screenShield._dialog)
+            return;
+
+        const dialog = Main.screenShield._dialog;
+
+        if (this._authPromptAllocatedId) {
+            dialog.disconnect(this._authPromptAllocatedId);
+            this._authPromptAllocatedId = 0;
+        }
+
+        if (this._updateLoginDialogId) {
+            global.stage.disconnect(this._updateLoginDialogId);
+            this._updateLoginDialogId = 0;
+        }
+
+        if (this._loginDialogConstraint) {
+            dialog.remove_constraint(this._loginDialogConstraint);
+            this._loginDialogConstraint = null;
+        }
+    }
+
+    _adaptLoginDialogForMessage() {
+        if (!Main.sessionMode.isGreeter)
+            return;
+
+        if (!Main.screenShield || !Main.screenShield._dialog)
+            return;
+
+        if (!this._message || !this._message.visible) {
+            this._resetLoginDialog()
+            return;
+        }
+
+        const dialog = Main.screenShield._dialog;
+
+        if (this._updateLoginDialogId)
+            return;
+
+        this._updateLoginDialogId = global.stage.connect('before-update', () => {
+        let messageHeight = this._message.y + this._message.height;
+            if (dialog._logoBin.visible)
+                messageHeight -= dialog._logoBin.height;
+
+            if (!this._logindDialogConstraint) {
+                this._loginDialogConstraint = new HeadsUpConstraint({ primary: true });
+                dialog.add_constraint(this._loginDialogConstraint);
+            }
+
+            this._loginDialogConstraint.offset = messageHeight;
+
+            global.stage.disconnect(this._updateLoginDialogId);
+            this._updateLoginDialogId = 0;
+        });
+    }
+
+    _adaptSessionForMessage() {
+        this._alignMessageTray();
+
+        if (Main.sessionMode.isGreeter) {
+            this._adaptLoginDialogForMessage();
+            if (!this._authPromptAllocatedId) {
+                const dialog = Main.screenShield._dialog;
+                this._authPromptAllocatedId = dialog._authPrompt.connect('notify::allocation', 
this._adaptLoginDialogForMessage.bind(this));
+            }
+        }
+    }
+}
+
+function init() {
+    return new Extension();
+}
diff --git a/extensions/heads-up-display/headsUpMessage.js b/extensions/heads-up-display/headsUpMessage.js
new file mode 100644
index 0000000..87a8c8b
--- /dev/null
+++ b/extensions/heads-up-display/headsUpMessage.js
@@ -0,0 +1,170 @@
+const { Atk, Clutter, GLib, GObject, Pango, St } = imports.gi;
+const Layout = imports.ui.layout;
+const Main = imports.ui.main;
+const Signals = imports.signals;
+
+var HeadsUpMessageBodyLabel = GObject.registerClass({
+}, class HeadsUpMessageBodyLabel extends St.Label {
+    _init(params) {
+        super._init(params);
+
+        this._widthCoverage = 0.75;
+        this._heightCoverage = 0.25;
+
+        this._workAreasChangedId = global.display.connect('workareas-changed', 
this._getWorkAreaAndMeasureLineHeight.bind(this));
+    }
+
+    _getWorkAreaAndMeasureLineHeight() {
+        if (!this.get_parent())
+            return;
+
+        this._workArea = Main.layoutManager.getWorkAreaForMonitor(Main.layoutManager.primaryIndex);
+
+        this.clutter_text.single_line_mode = true;
+        this.clutter_text.line_wrap = false;
+
+        this._lineHeight = super.vfunc_get_preferred_height(-1)[0];
+
+        this.clutter_text.single_line_mode = false;
+        this.clutter_text.line_wrap = true;
+    }
+
+    vfunc_parent_set(oldParent) {
+        this._getWorkAreaAndMeasureLineHeight();
+    }
+
+    vfunc_get_preferred_width(forHeight) {
+        const maxWidth = this._widthCoverage * this._workArea.width
+
+        let [labelMinimumWidth, labelNaturalWidth] = super.vfunc_get_preferred_width(forHeight);
+
+        labelMinimumWidth = Math.min(labelMinimumWidth, maxWidth);
+        labelNaturalWidth = Math.min(labelNaturalWidth, maxWidth);
+
+        return [labelMinimumWidth, labelNaturalWidth];
+    }
+
+    vfunc_get_preferred_height(forWidth) {
+        const labelHeightUpperBound = this._heightCoverage * this._workArea.height;
+        const numberOfLines = Math.floor(labelHeightUpperBound / this._lineHeight);
+        this._numberOfLines = Math.max(numberOfLines, 1);
+
+        const maxHeight = this._lineHeight * this._numberOfLines;
+
+        let [labelMinimumHeight, labelNaturalHeight] = super.vfunc_get_preferred_height(forWidth);
+
+        labelMinimumHeight = Math.min(labelMinimumHeight, maxHeight);
+        labelNaturalHeight = Math.min(labelNaturalHeight, maxHeight);
+
+        return [labelMinimumHeight, labelNaturalHeight];
+    }
+
+    destroy() {
+        if (this._workAreasChangedId) {
+            global.display.disconnect(this._workAreasChangedId);
+            this._workAreasChangedId = 0;
+        }
+
+        super.destroy();
+    }
+});
+
+var HeadsUpMessage = GObject.registerClass({
+}, class HeadsUpMessage extends St.Button {
+    _init(heading, body) {
+        super._init({
+            style_class: 'message',
+            accessible_role: Atk.Role.NOTIFICATION,
+            can_focus: false,
+            opacity: 0,
+        });
+
+        Main.layoutManager.addChrome(this, { affectsInputRegion: true });
+
+        this.add_style_class_name('heads-up-display-message');
+
+        this._panelAllocationId = Main.layoutManager.panelBox.connect('notify::allocation', 
this._alignWithPanel.bind(this));
+        this.connect('notify::allocation', this._alignWithPanel.bind(this));
+
+        const contentsBox = new St.BoxLayout({ style_class: 'heads-up-message-content',
+                                               vertical: true,
+                                               x_align: Clutter.ActorAlign.CENTER });
+        this.add_actor(contentsBox);
+
+        this.headingLabel = new St.Label({ style_class: 'heads-up-message-heading',
+                                           x_expand: true,
+                                           x_align: Clutter.ActorAlign.CENTER });
+        this.setHeading(heading);
+        contentsBox.add_actor(this.headingLabel);
+        this.contentsBox = contentsBox;
+
+        this.bodyLabel = new HeadsUpMessageBodyLabel({ style_class: 'heads-up-message-body',
+                                                       x_expand: true,
+                                                       y_expand: true });
+        contentsBox.add_actor(this.bodyLabel);
+
+        this.setBody(body);
+    }
+
+    vfunc_parent_set(oldParent) {
+        this._alignWithPanel();
+    }
+
+    _alignWithPanel() {
+        if (this._afterUpdateId)
+            return;
+
+        this._afterUpdateId = global.stage.connect('before-update', () => {
+            let x = Main.panel.x;
+            let y = Main.panel.y + Main.panel.height;
+
+            x += Main.panel.width / 2;
+            x -= this.width / 2;
+            x = Math.floor(x);
+            this.set_position(x,y);
+            this.opacity = 255;
+
+            global.stage.disconnect(this._afterUpdateId);
+            this._afterUpdateId = 0;
+        });
+    }
+
+    setHeading(text) {
+        if (text) {
+            const heading = text ? text.replace(/\n/g, ' ') : '';
+            this.headingLabel.text = heading;
+            this.headingLabel.visible = true;
+        } else {
+            this.headingLabel.text = text;
+            this.headingLabel.visible = false;
+        }
+    }
+
+    setBody(text) {
+        this.bodyLabel.text = text;
+        if (text) {
+            this.bodyLabel.visible = true;
+        } else {
+            this.bodyLabel.visible = false;
+        }
+    }
+
+    destroy() {
+        if (this._panelAllocationId) {
+            Main.layoutManager.panelBox.disconnect(this._panelAllocationId);
+            this._panelAllocationId = 0;
+        }
+
+        if (this._afterUpdateId) {
+            global.stage.disconnect(this._afterUpdateId);
+            this._afterUpdateId = 0;
+        }
+
+        if (this.bodyLabel) {
+            this.bodyLabel.destroy();
+            this.bodyLabel = null;
+        }
+
+        super.destroy();
+    }
+});
diff --git a/extensions/heads-up-display/meson.build b/extensions/heads-up-display/meson.build
new file mode 100644
index 0000000..40c3de0
--- /dev/null
+++ b/extensions/heads-up-display/meson.build
@@ -0,0 +1,8 @@
+extension_data += configure_file(
+  input: metadata_name + '.in',
+  output: metadata_name,
+  configuration: metadata_conf
+)
+
+extension_sources += files('headsUpMessage.js', 'prefs.js')
+extension_schemas += files(metadata_conf.get('gschemaname') + '.gschema.xml')
diff --git a/extensions/heads-up-display/metadata.json.in b/extensions/heads-up-display/metadata.json.in
new file mode 100644
index 0000000..e7ab71a
--- /dev/null
+++ b/extensions/heads-up-display/metadata.json.in
@@ -0,0 +1,11 @@
+{
+"extension-id": "@extension_id@",
+"uuid": "@uuid@",
+"gettext-domain": "@gettext_domain@",
+"name": "Heads-up Display Message",
+"description": "Add a message to be displayed on screen always above all windows and chrome.",
+"original-authors": [ "rstrode redhat com" ],
+"shell-version": [ "@shell_current@" ],
+"url": "@url@",
+"session-modes":  [ "gdm", "lock-screen", "unlock-dialog", "user" ]
+}
diff --git a/extensions/heads-up-display/org.gnome.shell.extensions.heads-up-display.gschema.xml 
b/extensions/heads-up-display/org.gnome.shell.extensions.heads-up-display.gschema.xml
new file mode 100644
index 0000000..ea1f377
--- /dev/null
+++ b/extensions/heads-up-display/org.gnome.shell.extensions.heads-up-display.gschema.xml
@@ -0,0 +1,54 @@
+<schemalist gettext-domain="gnome-shell-extensions">
+  <schema id="org.gnome.shell.extensions.heads-up-display"
+          path="/org/gnome/shell/extensions/heads-up-display/">
+    <key name="idle-timeout" type="u">
+      <default>30</default>
+      <summary>Idle Timeout</summary>
+      <description>
+        Number of seconds until message is reshown after user goes idle.
+      </description>
+    </key>
+    <key name="message-heading" type="s">
+      <default>""</default>
+      <summary>Message to show at top of display</summary>
+      <description>
+        The top line of the heads up display message.
+      </description>
+    </key>
+    <key name="message-body" type="s">
+      <default>""</default>
+      <summary>Banner message</summary>
+      <description>
+        A message to always show at the top of the screen.
+      </description>
+    </key>
+    <key name="show-on-login-screen" type="b">
+      <default>true</default>
+      <summary>Show on login screen</summary>
+      <description>
+        Whether or not the message should display on the login screen
+      </description>
+    </key>
+    <key name="show-when-locked" type="b">
+      <default>false</default>
+      <summary>Show on screen shield</summary>
+      <description>
+        Whether or not the message should display when the screen is locked
+      </description>
+    </key>
+    <key name="show-when-unlocking" type="b">
+      <default>false</default>
+      <summary>Show on unlock screen</summary>
+      <description>
+        Whether or not the message should display on the unlock screen.
+      </description>
+    </key>
+    <key name="show-when-unlocked" type="b">
+      <default>false</default>
+      <summary>Show in user session</summary>
+      <description>
+        Whether or not the message should display when the screen is unlocked.
+      </description>
+    </key>
+  </schema>
+</schemalist>
diff --git a/extensions/heads-up-display/prefs.js b/extensions/heads-up-display/prefs.js
new file mode 100644
index 0000000..a7106e0
--- /dev/null
+++ b/extensions/heads-up-display/prefs.js
@@ -0,0 +1,194 @@
+
+/* Desktop Icons GNOME Shell extension
+ *
+ * Copyright (C) 2017 Carlos Soriano <csoriano redhat com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+const { Gio, GObject, Gdk, Gtk } = imports.gi;
+const ExtensionUtils = imports.misc.extensionUtils;
+const Gettext = imports.gettext.domain('gnome-shell-extensions');
+const _ = Gettext.gettext;
+const N_ = e => e;
+const cssData = `
+   .no-border {
+       border: none;
+   }
+
+   .border {
+       border: 1px solid;
+       border-radius: 3px;
+       border-color: #b6b6b3;
+       box-shadow: inset 0 0 0 1px rgba(74, 144, 217, 0);
+       background-color: white;
+   }
+
+   .margins {
+       padding-left: 8px;
+       padding-right: 8px;
+       padding-bottom: 8px;
+   }
+
+   .contents {
+       padding: 20px;
+   }
+
+   .message-label {
+       font-weight: bold;
+   }
+`;
+
+var settings;
+
+function init() {
+    settings = ExtensionUtils.getSettings("org.gnome.shell.extensions.heads-up-display");
+    const cssProvider = new Gtk.CssProvider();
+    cssProvider.load_from_data(cssData);
+
+    const display = Gdk.Display.get_default();
+    Gtk.StyleContext.add_provider_for_display(display, cssProvider, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION);
+}
+
+function buildPrefsWidget() {
+    ExtensionUtils.initTranslations();
+
+    const contents = new Gtk.Box({
+        orientation: Gtk.Orientation.VERTICAL,
+        spacing: 10,
+        visible: true,
+    });
+
+    contents.append(buildSwitch('show-when-locked', _("Show message when screen is locked")));
+    contents.append(buildSwitch('show-when-unlocking', _("Show message on unlock screen")));
+    contents.append(buildSwitch('show-when-unlocked', _("Show message when screen is unlocked")));
+    contents.append(buildSpinButton('idle-timeout', _("Seconds after user goes idle before reshowing 
message")));
+    contents.get_style_context().add_class("contents");
+
+    const outerMessageBox = new Gtk.Box({
+        orientation: Gtk.Orientation.VERTICAL,
+        spacing: 5,
+        visible: true,
+    });
+    contents.append(outerMessageBox);
+
+    const messageLabel = new Gtk.Label({
+        label: 'Message',
+        halign: Gtk.Align.START,
+        visible: true,
+    });
+    messageLabel.get_style_context().add_class("message-label");
+    outerMessageBox.append(messageLabel);
+
+    const innerMessageBox = new Gtk.Box({
+        orientation: Gtk.Orientation.VERTICAL,
+        spacing: 0,
+        visible: true,
+    });
+    innerMessageBox.get_style_context().add_class("border");
+    outerMessageBox.append(innerMessageBox);
+
+    innerMessageBox.append(buildEntry('message-heading', _("Message Heading")));
+    innerMessageBox.append(buildTextView('message-body', _("Message Body")));
+    return contents;
+}
+
+function buildTextView(key, labelText) {
+    const textView = new Gtk.TextView({
+        accepts_tab: false,
+        visible: true,
+        wrap_mode: Gtk.WrapMode.WORD,
+    });
+
+    settings.bind(key, textView.get_buffer(), 'text', Gio.SettingsBindFlags.DEFAULT);
+
+    const scrolledWindow = new Gtk.ScrolledWindow({
+        hexpand: true,
+        vexpand: true,
+        visible: true,
+    });
+    const styleContext = scrolledWindow.get_style_context();
+    styleContext.add_class("margins");
+
+    scrolledWindow.set_child(textView);
+    return scrolledWindow;
+}
+function buildEntry(key, labelText) {
+    const entry = new Gtk.Entry({
+        placeholder_text: labelText,
+        visible: true,
+    });
+    const styleContext = entry.get_style_context();
+    styleContext.add_class("no-border");
+    settings.bind(key, entry, 'text', Gio.SettingsBindFlags.DEFAULT);
+
+    entry.get_settings()['gtk-entry-select-on-focus'] = false;
+
+    return entry;
+}
+
+function buildSpinButton(key, labelText) {
+    const hbox = new Gtk.Box({
+        orientation: Gtk.Orientation.HORIZONTAL,
+        spacing: 10,
+        visible: true,
+    });
+    const label = new Gtk.Label({
+        hexpand: true,
+        label: labelText,
+        visible: true,
+        xalign: 0,
+    });
+    const adjustment = new Gtk.Adjustment({
+        value: 0,
+        lower: 0,
+        upper: 2147483647,
+        step_increment: 1,
+        page_increment: 60,
+        page_size: 60,
+    });
+    const spinButton = new Gtk.SpinButton({
+        adjustment: adjustment,
+        climb_rate: 1.0,
+        digits: 0,
+        max_width_chars: 3,
+        visible: true,
+        width_chars: 3,
+    });
+    settings.bind(key, spinButton, 'value', Gio.SettingsBindFlags.DEFAULT);
+    hbox.append(label);
+    hbox.append(spinButton);
+    return hbox;
+}
+
+function buildSwitch(key, labelText) {
+    const hbox = new Gtk.Box({
+        orientation: Gtk.Orientation.HORIZONTAL,
+        spacing: 10,
+        visible: true,
+    });
+    const label = new Gtk.Label({
+        hexpand: true,
+        label: labelText,
+        visible: true,
+        xalign: 0,
+    });
+    const switcher = new Gtk.Switch({
+        active: settings.get_boolean(key),
+    });
+    settings.bind(key, switcher, 'active', Gio.SettingsBindFlags.DEFAULT);
+    hbox.append(label);
+    hbox.append(switcher);
+    return hbox;
+}
diff --git a/extensions/heads-up-display/stylesheet.css b/extensions/heads-up-display/stylesheet.css
new file mode 100644
index 0000000..9303446
--- /dev/null
+++ b/extensions/heads-up-display/stylesheet.css
@@ -0,0 +1,32 @@
+.heads-up-display-message {
+    background-color: rgba(0.24, 0.24, 0.24, 0.80);
+    border: 1px solid black;
+    border-radius: 6px;
+    color: #eeeeec;
+    font-size: 11pt;
+    margin-top: 0.5em;
+    margin-bottom: 0.5em;
+    padding: 0.9em;
+}
+
+.heads-up-display-message:insensitive {
+    background-color: rgba(0.24, 0.24, 0.24, 0.33);
+}
+
+.heads-up-display-message:hover {
+    background-color: rgba(0.24, 0.24, 0.24, 0.2);
+    border: 1px solid rgba(0.0, 0.0, 0.0, 0.5);
+    color: #4d4d4d;
+    transition-duration: 250ms;
+}
+
+.heads-up-message-heading {
+    height: 1.75em;
+    font-size: 1.25em;
+    font-weight: bold;
+    text-align: center;
+}
+
+.heads-up-message-body {
+    text-align: center;
+}
diff --git a/meson.build b/meson.build
index 8f2afda..79e529a 100644
--- a/meson.build
+++ b/meson.build
@@ -36,6 +36,7 @@ classic_extensions = [
 default_extensions = classic_extensions
 default_extensions += [
   'drive-menu',
+  'heads-up-display',
   'screenshot-window-sizer',
   'windowsNavigator',
   'workspace-indicator'