Input pipeline library {#input-pipeline-library}
Overview {#overview}
The input pipeline library tracks available input devices, manages device state, and allows the session to register handlers for events.
An input pipeline runs alongside session. It is preconfigured to support a set of input devices. This will be configurable by the session in the future.
The input pipeline 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.
Input pipeline {#input-pipeline}
An input pipeline manages [InputDeviceBindings][glossary.InputDeviceBinding] and [InputHandlers][glossary.InputHandler].
- An
InputDeviceBindingrepresents a connection to a physical input device (e.g. mouse, keyboard). - An
InputHandlerrepresents a client of [InputEvents][glossary.InputEvent].
An input pipeline routes input from physical devices to various clients by doing the following:
- Detects and binds to new input devices as they appear in
/dev/class/input-report. - Propagates
InputEvents throughInputHandlers.
Session authors are responsible for setting up input pipelines. More details on how can be found in [input_pipeline.rs].
InputDeviceBinding {#input-device-binding}
An InputDeviceBinding does the following:
- Connects to an [InputReport][glossary.InputReport] file located at
/dev/class/input-report/XXX. - Generates
InputEvents from the [InputDeviceDescriptor][glossary.InputDeviceDescriptor] and incomingInputReports.
The input pipeline creates and owns InputDeviceBindings as new input
peripherals are connected to a device.
InputHandler {#input-handler}
When an InputHandler receives an InputEvent, it does at least one of the
following:
- Forwards the
InputEventto the relevant client component. - Outputs a vector of
InputEvents for the nextInputHandlerto process.
InputHandlers must satisfy at least one of these conditions, but otherwise
their implementation details can vary.
The developer guide includes an
[example implementation of an InputHandler][example-input-handler].
glossary.InputDeviceBinding /glossary/README.md#InputHandler glossary.InputEvent /glossary/README.md#InputReport glossary.InputDeviceDescriptor /src/ui/lib/input_pipeline/src/input_pipeline.rs example-input-handler