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Every Xfce panel plugin is required to reimplement UI, which makes writing basic plugins more difficult and leads to UI inconsistencies.

There is a need for a generic plugin that provides basic UI (icon, label(s), menu, etc., see below) and allows the plugin writer to implement only data collection logic.

Question: should this mechanism allow independent applications communicate with the plugin (e.g. via dbus) and display “indicators” on the panel (that's how indicator plugin works)? Even if such functionality is not needed now, it may be necessary if the panel is used in a non-X environment (one that does not support widget embedding). So far, this page assumes that this feature is not needed. — Andrzej 2013/03/19 00:00

Basic Architecture

The plugin should be partitioned into two components:

  • a library implementing UI consisting of one or more(?) buttons (called monitor-UI),
  • a plugin implementing monitoring logic (called monitor-logic).

The panel should not assume that monitor-logic is implemented as e.g. a library written in C. In the future, this could be used for writing monitor plugins in scripting languages.

Preferably, the library should provide a base class of a monitor-logic object, with some virtual functions populated.

Note: I had started some months ago a skeleton of a gobject monitor plugin, intending to merge all monitors inside it, and using libgtop & upower for data collection. See http://rhaalovely.net/cgit/xfce4-monitor-plugin/. — Landry Breuil 2013/03/18 22:05



  • The plugin should be visible in the “Add New Items” panel dialog as a separate item (i.e. not as a monitor-UI plugin that can be later configured to load some module). To populate the list of plugins the plugin should provide (via a .desktop file?):
    • A user readable and translatable name,
    • A user readable and translatable description,
    • Version number, if not hard to do or a lot of additional work — Harald Judt 2013/03/19 16:10
    • An icon (32px, dnd size) — Andrzej 2013/03/18 10:36
      • Icon-name. The item dialog show dnd size icons (32px) — Nick Schermer 2013/03/18 09:49
  • Monitor-logic should not call any UI operations directly, i.e. it should not have no direct access to XfcePanelPlugin object.
    • Perhaps we should allow creating generic Gtk objects for configuration UI?
  • Monitor-UI should provide following features to the Monitor-logic object:
    • One or more (?) panel buttons logically grouped together and sorted. Each of them displaying at least one of following:
      • An icon.
        • The icon should be provided by Monitor-logic, and Monitor-logic should be able to enable, disable or swap the icon at any time.
        • Should come in multiple sizes and/or .svg format to fit different panel sizes.
          • This means, if possible, Monitor-logic should not use Pixbuf objects as they do not scale well.
        • Monitor-UI should scale the icon in a single panel row size.
        • For UI consistency we should recommend every plugin to have an icon (but probably better not to make it mandatory via API).
      • One or more (?) text labels (not GtkLabel objects, though).
        • The text label should be provided by Monitor-logic.
        • Should be translatable when it makes sense,
        • (should support Pango markup?)
        • (what about custom widgets like the weather plugin's scrollbox? how would these be handled?) — Harald Judt 2013/03/19 16:31
      • If icon and labels are shown, Monitor-UI should arrange them in one of the following layouts:
        • Stacked vertically - icon at the top, labels below. In this case, all objects should be centered.
        • Horizontal grouping - icon on the left, on the right a vertical stack of labels. In this mode, all objects should be aligned left.
          • In this mode, the plugin could default to a “small” representation, assuming that all labels fit in a single row. — Andrzej 2013/03/18 10:36
        • Perhaps this should be configurable at the panel level, not in each plugin separately.
      • If only labels are shown, they should be stacked vertically and centered.
      • If only icon and is shown, it should be treated as a “small” plugin.
    • For each button, Monitor-UI should provide a default action, configured by Monitor-logic, that, when the button is clicked, does one of following:
      • Calls a specified callback in Monitor-logic.
      • Opens a menu specified (but not created) by Monitor-logic. (How to specify the menu? Glade?)
        • Should this menu be merged with the context-menu of the plugin instead? This is what plugins do at the moment, and frees them to use LMB click for other purposes (indicator plugin makes these menus separate, though). — Andrzej 2013/03/18 10:50
      • Displays a popup with a range widget (e.g. for setting audio volume)
      • Displays a popup with a text entry field.
    • For each button, Monitor-UI should provide a tooltip information, consisting of: — Andrzej 2013/03/18 10:50
      • An icon,
      • A (pango formatted?) label.
  • Provide a standard XfcePanelPlugin context menu shown when right mouse button is clicked.
  • If “About” is clicked, Monitor-UI should display a dialog box with following information:
    • “About” should only be visible if requested by Monitor-logic.
      • There can be a set function to enable about (like xfce_panel_plugin_menu_show_about) and a vfunc/signal to show the about dialog (gtk_show_about_dialog is easy enough). — Nick Schermer 2013/03/18 09:53
        • Or we can build in at least a basic “About” dialog in the base class. BTW, one more problem with a “set_” function is that it would add a circular dependency between Monitor_logic and Monitor_UI (otherwise, there is no need for Monitor_logic to include Monitor_UI header). — Andrzej 2013/03/18 10:36
    • Icon, name and description displayed in the “Add New Items” dialog box.
      • Extracted from the desktop file, no need to set that twice. — Nick Schermer 2013/03/18 09:53
        • Which object should do the extraction, Monitor-UI or Monitor-logic? The latter may be useful if there is any processing to do on these strings (is there?). — Andrzej 2013/03/18 10:46
    • Copyright, as provided by the Monitor-logic.
    • A detail description, as provided by Monitor-logic.
      • Also in the about dialog, short description in the .desktop file.
    • A list of authors to populate “Credits”, as provided by Monitor-logic.
      • See about dialog.
    • A text of the license to populate “License”, as provided by Monitor-logic.
      • Can also be displayed in the about dialog.
  • If “Properties” is clicked, Monitor-UI should call a specified callback in Monitor-logic.
    • “Properties” should only be visible if requested by Monitor-logic.
    • Note: this assumes that Monitor-logic would then display a config dialog, which would require it to perform some UI operations. (any better solution?)
      • Maybe it should always provide basic appearance settings, so user can configure this (the backend is only responsible for the data, not the display). When building the dialog the plugin can populate its own frame/box for additional settings that are required for the data collection. — Nick Schermer 2013/03/18 09:53
        • Yes, appearance settings could be handled directly by Monitor-UI, but what about settings related to the actual function of the plugin? (e.g. location in weather plugin) — Andrzej 2013/03/18 10:36
        • This part sounds tricky; Alternatively, how about only creating an abstract “template” plugin that does all the basics but is supposed to be extended by the plugin developer? — Harald Judt 2013/03/19 16:28
      • Basic appearance settings could simply be provided by an entry in the context menu. I'd somehow rather associate this with the panel, or with the genericness of the plugin, e.g. font size, font color. — Harald Judt 2013/03/19 16:25


  • For each button, Monitor-UI should provide a secondary action.
    • Same features as for primary action.
  • For each button, Monitor-UI should provide mouse scroll actions.
    • When mouse wheel is turned, a specified callback in Monitor-logic should be called along with the direction of scrolling.
  • For each button (only if Icon is shown?) Monitor-UI should provide a “progress-bar” widget.
    • Monitor-logic should be able to specify whether to enable/disable it and what value to display (in % or so)
    • (Monitor-UI should draw the “progress-bar” on top of the icon, so that it is visible even if only icon is shown).
  • Monitor-UI or panel should generate periodic (configurable?) events for polling external events that are then propagated to Monito-logic objects. Doing this centrally in one place, reduces the number of CPU wake-ups.
    • The idea is nice and I thought about that too some time ago, but then there are plugins that update their widgets quite frequently and more frequently than others, so the questions here are more like: “Is it worth all the engineering? Does it really make a noticeable difference?” Maybe it makes a difference in powersave mode, if such a mode is planned. But how big are the gains in reality? One positive side-effect would be that all plugins update at once, which might perhaps look better and less chaotic, I'm not sure. On the other hand, could it lead to bad effects when all plugins update at the same time (jerkiness,…)? I'm all in for a central place to configure or enable general powersave mode, however. But then the plugins themselves might need to decide how to implement powersaving. — Harald Judt 2013/03/19 21:25
  • Decision needed: Font size and color selectable in the panel or in the plugin? — Harald Judt 2013/03/19 16:10
  • A recommendation: we should avoid “setters”, “updaters” etc. in Monitor-logic API in favor of “getters” and signals - this makes both sides of the API deal with only its own tasks.
  • Currently without a use-case, but perhaps be useful: Support reacting to external signals, e.g. via D-Bus? — Harald Judt 2013/03/19 16:18
  • Not sure this belongs here, but… as an alternative to making a plugin “small”, could it somehow be achieved that a plugin can occupy more than one row but still have the “small” properties and so share space with another plugin? — Harald Judt 2013/03/19 21:13

UI mockups

Horizontal panel

Deskbar mode

Vertical panel

Sample API

Monitor UI

Monitor-UI API would be visible to the panel.

Monitor logic

Monitor-logic API would be visible to a plugin developer.

class XfceMonitor extends GObject
    list of XfceMonitorButton
    has_about() // should "About" info be required 
    get_name() // or taken from .desktop?
    get_plugin_icon() // ditto
    get_desciption() // ditto
    get_credits() // perhaps hardcoded
    get_license() // ditto
    has_properties() // for config dialog
    properties_clicked() // show a config dialog from XfceMonitor object(?)
                         // ideally, this should be handled by XfceMonitorUI object instead
                         // (like "About") but that would require describing the dialog somehow
                         // (glade?)
    signal monitor_button_added(button)
    signal monitor_button_removed(button)
    signal monitor_buttons_reordered

class XfceMonitorButton extends GObject
    list of text_labels
    signal icon_changed()
    signal label_list_changed()
    //primary action
    get_primary_action_type() // returns enum: None, Callback, Menu, Range, TextField
    signal primary_menu_changed()
    primary_action_range_changed (percentage)
    primary_action_text_entered (text)
    //secondary action
    get_secondary_action_type() // returns enum: None, Callback, Menu, Range, TextField
    signal secondary_menu_changed()
    secondary_action_range_changed (percentage)
    secondary_action_text_entered (text)
    //tooltip --- // Andrzej 2013/03/18 10:58//
    get_tooltip_icon() //optional(?), return NULL if there is no icon
    signal tooltip_changed()
    //mouse wheel event
    //progress bar
    signal progress_bar_changed() // either value or visibility
    // polling mechanism
    get_poll_interval() // returns interval in # of seconds
    signal poll_interval_changed() //changed interval or polling enabled/disabled