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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.


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.

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
Weston 1.6 evdev yes
Weston 1.7 evdev Backend not available
Weston 1.8 evdev Backend not available