Life of Mouse Event

This document explains how mouse events are processed. The first section describes drivers, and subsequent sections work up the software stack.

Driver

Input Pipeline (src/ui/lib/input_pipeline/) watch_for_devices and add bindings based on device type to receive input report events and translate to Input Pipeline internal events, then more handlers in Input Pipeline.

MouseBinding receives sdk/fidl/fuchsia.input.report/ and convert them to mouse_binding::MouseEvent, then send to handlers in Input Pipeline.

Handlers in Input Pipeline process events in order:

ClickDragHandler translate events to RelativeMouseEvent if the event belongs to a click and drag sequence. It improves the disambiguation of click vs. drag events. We may need to revisit this handler when touchpad support is done.
PointerMotionScaleHandler scale the mouse movement based on scale factor. Scale factor is passed to PointerMotionScaleHandler when created.
MouseInjectHandler update_cursor_renderer (eg. position, visibility) and converts mouse_binding::MouseEvent to fuchsia.ui.pointerinjector.PointerSample and send to Scenic.

MouseInjector converts fuchsia.ui.pointerinjector.PointerSample to scenic_impl::input::InternalMouseEvent.

Most clients listen to fuchsia.ui.pointer.MouseEvent events. A special case is Carnelian Terminal.

When running under the graphical shell (Ermine), it uses fuchsia.ui.pointer, like other clients.
In modes that have minimal component topologies (e.g., virtcon/recovery), it runs directly on the display driver and reads fuchsia.input.report from the input driver.