WestonTouchScreenIssues

Issues with Touch Screen Input when using Weston

Prior to version 1.7 of the Weston compositor touch screen events are incorrectly dispatched in some configurations, rendering Qt unresponsive to touch events.

Problem Description

Qt relies on touch frame events that indicate discrete sampling windows of touch devices to implement reliable multi touch support. Unfortunately several releases of the Weston reference compositor fail to send out these events correctly.

The issue is present in the Weston evdev input backend until its removal in Weston 1.7. In the libinput backend the same issue is fixed in Weston 1.5. The table below summarizes the situation.

Weston Release	Weston Input Backend	Incorrect Touch Frame Delivery
Weston 1.4	evdev	yes
	libinput	Backend not available
Weston 1.5	evdev	yes
	libinput
Weston 1.6	evdev	yes
	libinput
Weston 1.7	evdev	Backend not available
	libinput
Weston 1.8	evdev	Backend not available
	libinput

For situations where using a recent version of Weston or switching to the libinput backend is not possible, we provide a patch for Weston's evdev backend. The patch is included in Qt For Device Creation in releases made after 2015-08-20, but for convenience also provided separately here.