docs: add newer, cut down and commented panel.js from GNOME Shell 48.2

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// My annotated and cut down js/ui/panel.js from gnome-shell/48.2.
// All annotations are what I guessed, interpreted and copied while reading the
// code and comparing to other panel.js versions and might be wrong. They are
// prefixed with "Annotation:" to indicate that they're my comments, not
// comments that orginally existed.
// Taken from: https://gitlab.gnome.org/GNOME/gnome-shell/-/blob/48.2/js/ui/panel.js
// On: 2025-06-08
// License: This code is licensed under GPLv2.
// Taken from: https://gitlab.gnome.org/GNOME/gnome-shell/-/blob/48.2/js/ui/sessionMode.js
// On: 2025-06-08
// License: This code is licensed under GPLv2.
// I'm using the word "item" to refer to the thing, which gets added to the top
// (menu)bar / panel, where an item has a role/name and an indicator.
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import Clutter from 'gi://Clutter';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import GObject from 'gi://GObject';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import St from 'gi://St';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import * as CtrlAltTab from './ctrlAltTab.js';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import * as PopupMenu from './popupMenu.js';
import * as PanelMenu from './panelMenu.js';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import * as Main from './main.js';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
import {DateMenuButton} from './dateMenu.js';
import {ATIndicator} from './status/accessibility.js';
import {InputSourceIndicator} from './status/keyboard.js';
import {DwellClickIndicator} from './status/dwellClick.js';
import {ScreenRecordingIndicator, ScreenSharingIndicator} from './status/remoteAccess.js';
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for this
// Extension.
// Of note (for PANEL_ITEM_IMPLEMENTATIONS):
// const AppMenuButton = [...]
// const ActivitiesButton = [...]
// const QuickSettings = [...]
const PANEL_ITEM_IMPLEMENTATIONS = {
'activities': ActivitiesButton,
'appMenu': AppMenuButton,
'quickSettings': QuickSettings,
'dateMenu': DateMenuButton,
'a11y': ATIndicator,
'keyboard': InputSourceIndicator,
'dwellClick': DwellClickIndicator,
'screenRecording': ScreenRecordingIndicator,
'screenSharing': ScreenSharingIndicator,
};
export const Panel = GObject.registerClass(
class Panel extends St.Widget {
// Annotation: Initializes the top (menu)bar / panel.
// Does relevant stuff like:
// - Defining this._leftBox, this._centerBox and this._rightBox.
// - Finally calling this._updatePanel().
// Compared to panel_47.rc_2024-09-12.js: connectObject instead of connect
// gets used, which shouldn't be relevant for this extension.
_init() {
super._init({
name: 'panel',
reactive: true,
});
this.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
this._sessionStyle = null;
this.statusArea = {};
this.menuManager = new PopupMenu.PopupMenuManager(this);
this._leftBox = new St.BoxLayout({name: 'panelLeft'});
this.add_child(this._leftBox);
this._centerBox = new St.BoxLayout({name: 'panelCenter'});
this.add_child(this._centerBox);
this._rightBox = new St.BoxLayout({name: 'panelRight'});
this.add_child(this._rightBox);
this.connect('button-press-event', this._onButtonPress.bind(this));
this.connect('touch-event', this._onTouchEvent.bind(this));
Main.overview.connectObject('showing',
() => this.add_style_pseudo_class('overview'),
this);
Main.overview.connectObject('hiding',
() => this.remove_style_pseudo_class('overview'),
this);
Main.layoutManager.panelBox.add_child(this);
Main.ctrlAltTabManager.addGroup(this,
_('Top Bar'), 'shell-focus-top-bar-symbolic',
{sortGroup: CtrlAltTab.SortGroup.TOP});
Main.sessionMode.connectObject('updated',
this._updatePanel.bind(this),
this);
global.display.connectObject('workareas-changed',
() => this.queue_relayout(),
this);
this._updatePanel();
}
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for
// this Extension.
// Annotation: Gets called by this._init() to populate the top (menu)bar /
// panel initially.
//
// It does the following relevant stuff:
// - Calls this._hideIndicators()
// - Calls this._updateBox() for this._leftBox, this._centerBox and
// this._rightBox with panel.left, panel.center and panel.right to
// populate the boxes with items defined in panel.left, panel.center and
// panel.right.
//
// panel.left, panel.center and panel.right get set via the line let panel
// = Main.sessionMode.panel, which uses the panel of Mains (js/ui/main.js)
// instance of SessionMode (js/ui/sessionMode.js).
//
// And in js/ui/sessionMode.js (48.2, 2025-06-08) you have different modes
// with different panel configuration. For example the "user" mode with:
// panel: {
// left: ['activities'],
// center: ['dateMenu'],
// right: ['screenRecording', 'screenSharing', 'dwellClick', 'a11y', 'keyboard', 'quickSettings'],
// }
//
// This way this function populates the top (menu)bar / panel with the
// default stuff you see on a fresh Gnome.
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
_updatePanel() {
let panel = Main.sessionMode.panel;
this._hideIndicators();
this._updateBox(panel.left, this._leftBox);
this._updateBox(panel.center, this._centerBox);
this._updateBox(panel.right, this._rightBox);
if (panel.left.includes('dateMenu'))
Main.messageTray.bannerAlignment = Clutter.ActorAlign.START;
else if (panel.right.includes('dateMenu'))
Main.messageTray.bannerAlignment = Clutter.ActorAlign.END;
// Default to center if there is no dateMenu
else
Main.messageTray.bannerAlignment = Clutter.ActorAlign.CENTER;
if (this._sessionStyle)
this.remove_style_class_name(this._sessionStyle);
this._sessionStyle = Main.sessionMode.panelStyle;
if (this._sessionStyle)
this.add_style_class_name(this._sessionStyle);
}
// Annotation: This function hides all items, which are in the top (menu)bar
// panel and in PANEL_ITEM_IMPLEMENTATIONS.
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
_hideIndicators() {
for (let role in PANEL_ITEM_IMPLEMENTATIONS) {
let indicator = this.statusArea[role];
if (!indicator)
continue;
indicator.container.hide();
}
}
// Annotation: This function takes a role (of an item) and returns a
// corresponding indicator, if either of two things are true:
// - The indicator is already in this.statusArea.
// Then it just returns the indicator by using this.statusArea.
// - The role is in PANEL_ITEM_IMPLEMENTATIONS.
// Then it creates a new indicator, adds it to this.statusArea and returns
// it.
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
_ensureIndicator(role) {
let indicator = this.statusArea[role];
if (!indicator) {
let constructor = PANEL_ITEM_IMPLEMENTATIONS[role];
if (!constructor) {
// This icon is not implemented (this is a bug)
return null;
}
indicator = new constructor(this);
this.statusArea[role] = indicator;
}
return indicator;
}
// Annotation: This function takes a list of items (or rather their roles)
// and adds the indicators of those items to a box (like this._leftBox)
// using this._ensureIndicator() to get the indicator corresponding to the
// given role.
// So only items with roles this._ensureIndicator() knows, get added.
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
_updateBox(elements, box) {
let nChildren = box.get_n_children();
for (let i = 0; i < elements.length; i++) {
let role = elements[i];
let indicator = this._ensureIndicator(role);
if (indicator == null)
continue;
this._addToPanelBox(role, indicator, i + nChildren, box);
}
}
// Annotation: This function adds the given item to the specified top
// (menu)bar / panel box and connects to "destroy" and "menu-set" events.
//
// It takes the following arguments:
// - role: The name of the item to add.
// - indicator: The indicator of the item to add.
// - position: Where in the box to add the item.
// - box: The box to add the item to.
// Can be one of the following:
// - this._leftBox
// - this._centerBox
// - this._rightBox
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
_addToPanelBox(role, indicator, position, box) {
let container = indicator.container;
container.show();
let parent = container.get_parent();
if (parent)
parent.remove_child(container);
box.insert_child_at_index(container, position);
this.statusArea[role] = indicator;
let destroyId = indicator.connect('destroy', emitter => {
delete this.statusArea[role];
emitter.disconnect(destroyId);
});
indicator.connect('menu-set', this._onMenuSet.bind(this));
this._onMenuSet(indicator);
}
// Annotation: This function allows you to add an item to the top (menu)bar
// / panel.
// While per default it adds the item to the status area (the right box of
// the top bar), you can specify the box and add the item to any of the
// three boxes of the top bar.
// To add an item to the top bar, you need to give its role and indicator.
//
// This function takes the following arguments:
// - role: A name for the item to add.
// - indicator: The indicator for the item to add (must be an instance of
// PanelMenu.Button).
// - position: Where in the box to add the item.
// - box: The box to add the item to.
// Can be one of the following:
// - "left": referring to this._leftBox
// - "center": referring to this._centerBox
// - "right": referring to this._rightBox
// These boxes are what you see in the top bar as the left, right and
// center sections.
//
// Finally this function just calls this._addToPanelBox() for the actual
// work, so it basically just makes sure the input to this._addToPanelBox()
// is correct.
//
// Compared to panel_47.rc_2024-09-12.js: Nothing changed.
addToStatusArea(role, indicator, position, box) {
if (this.statusArea[role])
throw new Error(`Extension point conflict: there is already a status indicator for role ${role}`);
if (!(indicator instanceof PanelMenu.Button))
throw new TypeError('Status indicator must be an instance of PanelMenu.Button');
position ??= 0;
let boxes = {
left: this._leftBox,
center: this._centerBox,
right: this._rightBox,
};
let boxContainer = boxes[box] || this._rightBox;
this.statusArea[role] = indicator;
this._addToPanelBox(role, indicator, position, boxContainer);
return indicator;
}
// Of note:
// _onMenuSet(indicator) { [...] }
// Annotation: [...] Cut out bunch of stuff here, which isn't relevant for
// this Extension.
});