Brightness updates not reflected in slider

[kylecorry31]

Distribution (run cat /etc/os-release): NAME="Pop!_OS" VERSION="18.04 LTS" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Pop!_OS 18.04 LTS" VERSION_ID="18.04" HOME_URL="https://system76.com/pop" SUPPORT_URL="http://support.system76.com" BUG_REPORT_URL="https://github.com/pop-os/pop/issues" PRIVACY_POLICY_URL="https://system76.com/privacy" VERSION_CODENAME=bionic UBUNTU_CODENAME=bionic

Related Application and/or Package Version (run apt policy $PACKAGE NAME): system76-power: Installed: 0.0.1~1526005757~18.04~1222310 Candidate: 0.0.1~1526005757~18.04~1222310 Version table: *** 0.0.1~1526005757~18.04~1222310 776 776 http://ppa.launchpad.net/system76/pop/ubuntu bionic/main amd64 Packages 100 /var/lib/dpkg/status

Issue/Bug Description: When switching power states and the brightness changes, the slider in the menu does not change.

Steps to reproduce (if you know): Start in high power mode. Turn brightness to 100%, toggle to another power mode. The brightness will change but the slider will not change in the user menu.

Expected behavior: The slider should reflect the current brightness level.

Other Notes: gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.freedesktop.DBus.Properties.Set org.gnome.SettingsDaemon.Power.Screen Brightness ""

Sets the brightness, where XX is the percent from 0 to 100.

[jackpot51]

This seems like a bug in GNOME Settings Daemon, assuming the brightness only changes from within GNOME Settings Daemon.

To have this power daemon work outside of GNOME, it uses the /sys/class/backlight API to control backlights. GNOME Settings Daemon should probably watch this for changes.

Since the likelihood of changing GNOME Settings Daemon to do this is low, I will look into sending the new brightness information through the DBUS API if it is available, as a temporary workaround.

[mmstick]

Documentation on the DBUS API is scarce. Here's a dump from gdbus.

node /org/gnome/SettingsDaemon/Power {
  interface org.freedesktop.DBus.Properties {
    methods:
      Get(in  s interface_name,
          in  s property_name,
          out v value);
      GetAll(in  s interface_name,
             out a{sv} properties);
      Set(in  s interface_name,
          in  s property_name,
          in  v value);
    signals:
      PropertiesChanged(s interface_name,
                        a{sv} changed_properties,
                        as invalidated_properties);
    properties:
  };

  interface org.freedesktop.DBus.Introspectable {
    methods:
      Introspect(out s xml_data);
    signals:
    properties:
  };

  interface org.freedesktop.DBus.Peer {
    methods:
      Ping();
      GetMachineId(out s machine_uuid);
    signals:
    properties:
  };

  interface org.gnome.SettingsDaemon.Power.Screen {
    methods:
      StepUp(out i new_percentage,
             out i output_id);
      StepDown(out i new_percentage,
               out i output_id);
    signals:
    properties:
      readwrite i Brightness = 50;
  };

  interface org.gnome.SettingsDaemon.Power.Keyboard {
    methods:
      StepUp(out i new_percentage);
      StepDown(out i new_percentage);
      Toggle(out i new_percentage);
    signals:
      BrightnessChanged(i brightness,
                        s source);
    properties:
      readwrite i Brightness = 0;
  };
};

It seems that in order to control brightness, you have to use the Brightness property.

Checking if it exists

gdbus introspect --session --dest org.gnome.SettingsDaemon.Power \
    --object-path /org/gnome/SettingsDaemon/Power \
        || echo SettingsDaemon.Power does not exist

Getting Brightness

dbus-send --session --print-reply \
    --dest="org.gnome.SettingsDaemon.Power" \
    /org/gnome/SettingsDaemon/Power \
    org.freedesktop.DBus.Properties.Get \
    string:org.gnome.SettingsDaemon.Power.Screen \
    string:Brightness

Setting Brightness

dbus-send --session --print-reply \
    --dest="org.gnome.SettingsDaemon.Power" \
    /org/gnome/SettingsDaemon/Power \
    org.freedesktop.DBus.Properties.Set \
    string:org.gnome.SettingsDaemon.Power.Screen \
    string:Brightness \
    variant:int32:${PERCENT}

[jackpot51]

Thanks Michael, I think that is enough information to figure this out