power-manager-button.c

    if ( xfpm_brightness_has_hw (button->priv->brightness) )
    {
        GdkPixbuf *pix;

        max_level = xfpm_brightness_get_max_level (button->priv->brightness);

        /* determine minimum value for slider */
        min_level = xfconf_channel_get_int (button->priv->channel,
                                            PROPERTIES_PREFIX BRIGHTNESS_SLIDER_MIN_LEVEL,
                                            -1);
        if (min_level == -1)
        {
            /* Some laptops (and mostly newer ones with intel graphics) can turn off the
             * backlight completely. If the user is not careful and sets the brightness
             * very low using the slider, he might not be able to see the screen contents
             * anymore. Brightness keys do not work on every laptop, so it's better to use
             * a safe default minimum level that the user can change via the settings
             * editor if desired.
             */
            min_level = (max_level > 100) ? SAFE_SLIDER_MIN_LEVEL : 0;
            xfconf_channel_set_int (button->priv->channel,
                                    PROPERTIES_PREFIX BRIGHTNESS_SLIDER_MIN_LEVEL,
                                    min_level);
        }

        mi = scale_menu_item_new_with_range (min_level, max_level, 1);

        /* attempt to load and display the brightness icon */
        pix = gtk_icon_theme_load_icon (gtk_icon_theme_get_default (),
                                       XFPM_DISPLAY_BRIGHTNESS_ICON,
                                       32,
                                       GTK_ICON_LOOKUP_GENERIC_FALLBACK,
                                       NULL);
        if (pix)
        {
            img = gtk_image_new_from_pixbuf (pix);
            gtk_image_menu_item_set_image (GTK_IMAGE_MENU_ITEM(mi), img);
        }

        scale_menu_item_set_description_label (SCALE_MENU_ITEM(mi), _("<b>Display brightness</b>"));

        /* range slider */
        button->priv->range = scale_menu_item_get_scale (SCALE_MENU_ITEM (mi));

        /* update the slider to the current brightness level */
        xfpm_brightness_get_level (button->priv->brightness, &current_level);
        gtk_range_set_value (GTK_RANGE(button->priv->range), current_level);

        g_signal_connect_swapped (mi, "value-changed", G_CALLBACK (range_value_changed_cb), button);
        g_signal_connect (mi, "scroll-event", G_CALLBACK (range_scroll_cb), button);
        g_signal_connect (menu, "show", G_CALLBACK (range_show_cb), button);

        gtk_widget_show_all (mi);
        gtk_menu_shell_append(GTK_MENU_SHELL(menu), mi);
    }

    /* Presentation mode checkbox */
    mi = gtk_check_menu_item_new_with_mnemonic (_("Presentation _mode"));
    gtk_widget_set_sensitive (mi, TRUE);
    gtk_widget_show (mi);
    gtk_menu_shell_append(GTK_MENU_SHELL(menu), mi);
    xfconf_g_property_bind(button->priv->channel,
                           PROPERTIES_PREFIX PRESENTATION_MODE,
                           G_TYPE_BOOLEAN, G_OBJECT(mi), "active");

    /* Power manager settings */
    mi = gtk_menu_item_new_with_mnemonic (_("_Power manager settings..."));
    gtk_widget_show(mi);
    gtk_menu_shell_append(GTK_MENU_SHELL(menu), mi);
    g_signal_connect(G_OBJECT(mi), "activate", G_CALLBACK(xfpm_preferences), NULL);

    gtk_menu_popup (GTK_MENU (menu),
                    NULL,
                    NULL,
#ifdef XFCE_PLUGIN
                    xfce_panel_plugin_position_menu,
#else
                    NULL,
#endif
                    button->priv->plugin,
                    0,
                    gtk_get_current_event_time ());
}