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The Secret Life of Applets
In the current model, life is simple: we have an AppletManager and we have
Applets.
In this world, Applets exist as separate processes running in the background
on a user's desktop environment, parallel to the actual G13 Configurator
process. These applets are generally expected to be running all the time, and
maintain their registration status with the AppletManager via D-Bus.
When the configurator is running, the AppletManager is expected to be exposed
via D-Bus under the well-known bus name of com.theonelab.g13.AppletManager
(name subject to change), and Applets are expected to try to register to this
object as soon as they can.
Applet Lifecycle
During normal operation, Applets are mostly sleeping in the background,
waiting for one of their three exposed methods to be called by the
AppletManager. They don't render until told to by one of these methods, and
once they are called, then the applet can Present new frames periodically to
the AppletManager for display on the G13's LCD.
In essence, each Applet runs in the background, until it is made the
foreground applet by the user. Once there, it can push frames all it likes,
until it receives an Unpresent call from the AppletManager, in which case
then it's pushed into the background again. Further Present calls will fail
once this happens.
AppletManager
The AppletManager is a simple object that exposes two methods via D-Bus:
Register and Present, while the Applets are expected to expose three
endpoints for the AppletManager to call periodically: Present, Unpresent,
KeyPressed and KeyReleased.
Present and Unpresent
These two methods essentially control the "foreground"/"background"-ness of the
applet. Present tells the applet it has moved into the foreground, and it
needs to return the first frame it plans to render immediately.
Unpresent, on the other hand, tells the applet it is now in the background,
and it should stop rendering.
KeyPressed and KeyReleased
These two methods tell the applet which of the L1-L4 keys has been pressed. They
will only fire after the Present call has been made.