The input library tracks available input devices, manages device state, and allows session to register handlers for events.
The session creates an input pipeline that is configured for the specific product. First the session decides which types of input devices the input pipeline should support. Then the session registers input handlers for input events. The input library provides implementations for common input handlers, such as Scenic and input method editors (IME). After the session instantiates components that consume input, the input pipeline directly sends input events to those components through the registered input handlers.
An input pipeline manages InputDeviceBindings
and InputHandlers
.
InputDeviceBinding
represents a connection to a physical input device (e.g. mouse, keyboard).InputHandler
represents a client of InputEvents
.An input pipeline routes input from physical devices to various clients. An input pipeline does the following:
/dev/class/input-report
.InputEvents
through InputHandlers
.Session authors are responsible for setting up input pipelines. More details on how can be found in input_pipeline.rs.
An InputDeviceBinding
does the following:
InputReport
file located at /dev/class/input-report/XXX
.InputEvents
from the DeviceDescriptor
and incoming InputReports
.The input pipeline creates and owns InputDeviceBindings
as new input peripherals are connected to a device.
When an InputHandler
receives an InputEvent
, it does at least one of the following:
InputEvent
to the relevant client component.InputEvents
for the next InputHandler
to process.InputHandlers
must satisfy at least one of these conditions, but otherwise their implementation details can vary.
In the following example, if the MouseHandler
detects a mouse-typed input event, the handler sends the event to Scenic and returns an empty vector. On all other types of input events, the MouseHandler
returns a vector containing the InputEvent
for the next InputHandler
to process.
#[async_trait] impl InputHandler for MouseHandler { async fn handle_input_event( &mut self, input_event: InputEvent, ) -> Vec<InputEvent> { match input_event { InputEvent { device_event: InputDeviceEvent::Mouse(mouse_event), device_descriptor: InputDeviceDescriptor::Mouse(mouse_descriptor), } => { // ... Handler specific details self.send_events_to_scenic(...)).await; vec![] // InputEvent is consumed because it was sent to Scenic } _ => vec![input_event], // InputEvent is returned for the next InputHanlder } } }