Summary. This document explains the design of the display ownership.
Fuchsia's input is sometimes multiplexed between two subsystems: the graphics subsystem, which is managed by Scenic, and the virtcon, the virtual console. Scenic sets aside a kernel Event that it uses to signal whether it owns the display or not. This Event can be obtained by calling fuchsia.ui.scenic/Scenic.GetDisplayOwnershipEvent.
The display ownership does not obtain the kernel Event that signals display ownership from Scenic itself. Rather, the client code for the input pipeline library is expected to obtain this Event first, and pass it down to the constructor function DisplayOwnership::new.
This means that the display ownership does not tolerate Scenic restarts as written today.
When the display ownership detects that the display ownership has been lost, it marks all events that it subsequently sees as handled. This makes all the input pipeline stages downstream see, but ignore the event. This way we ensure that effectively the input events are forwarded either to the clients of the input pipeline, or to the virtcon, but not both.