D-Bus-examples.md

@@ -108,6 +108,46 @@ sudo gdbus call --system \
 
 See [this thread](https://forums.puri.sm/t/phone-call-api/8433) for context.
 
+### Getting/Setting Screen Brightness
+
+Introspect the GNOME Settings daemon to see what interfaces are available:
+```
+gdbus introspect --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power
+```
+
+The `org.gnome.SettingsDaemon.Power.Screen` interface is relevant:
+```
+  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 = 29;
+  };
+```
+
+Get all properties related to the screen:
+```
+gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.freedesktop.DBus.Properties.GetAll org.gnome.SettingsDaemon.Power.Screen
+```
+This should return something like the following:
+```
+({'Brightness': <29>},)
+```
+
+The brightness can be individually read:
+```
+gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.freedesktop.DBus.Properties.Get org.gnome.SettingsDaemon.Power.Screen Brightness
+```
+
+It can also be set:
+```
+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 '<30>'
+```
+
 ## Using Applications to Provide Services
 
 GNOME applications run using the `--gapplication-service` command line option will expose the [org.freedesktop.Application](https://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#dbus) interface on the session bus. This can be accessed to launch the application and request that it open files specified with URIs. The parameters of the API are explained by [this GApplication D-Bus APIs document](https://wiki.gnome.org/Projects/GLib/GApplication/DBusAPI) which refers to a different interface but which seems to overlap with the freedesktop interface.