[Interest] Slow touchscreen (eGalax) response in QML using evdevtouch plugin and eglfs platform

Georgije Bosiger gbosiger at gmail.com
Tue May 27 12:06:22 CEST 2014

Hi Phil

Thank you for pointing out this aspect of the problem. I will try to check
if events are slowed down. However I know that device is faster than what I
can see in QtQuick because I also tested the device with "ts_test"
application from tslib and the input was much more responsive there. Also
by using the mouse in QtQuick I discovered that the problem is not in the
graphics performance.

I was also able to compile releases 5.2.0 and 5.3.0 of Qt library for my
embedded system and it is a lot better now - much faster than in 5.1.0,
there is no obvious difference between 5.2.0 and 5.3.0. Input reading is
still a bit slow but at least acceptable. Now also "flick resize" from
touchinteraction demos works nicely.

Maybe it would also make sense to try to read touch input using tslib
instead of evdevtouch and see if there is a difference. I also noticed that
elements like flickable or just plain dragging of a rectangle work great,
but adding some functionality to drag like displaying the position using
"onPositionChanged" slows things down. Maybe I should consider using some
different way of updating...

Best regards,

2014-05-27 10:30 GMT+02:00 Phil Hannent <phil at hannent.co.uk>:

> Hi,
> I have had experience with touch screens. The best place to start in my
> view is looking at the number of events and their frequency from the
> device. In my experience some equipment slows down the number of events it
> generates as you perform more complex/faster movements.
> I was working on something similar a year ago:
> http://stackoverflow.com/questions/11509140/touchscreen-sample-rate-for-human-interface-device
> Regards
> Phil
> On 23 May 2014 15:14, Georgije Bosiger <gbosiger at gmail.com> wrote:
>> Hi,
>> I have an embedded linux device with AM335x CPU on which I am running QML
>> applications using the eglfs platform. The Qt library version is 5.1. For
>> the input I have a touch panel with usb egalax controller that is used by
>> the evdevtouch plugin. Input works, but the problem is in performance. Only
>> slow movements are followed - on faster movements the position is updated
>> only on stop.
>> This behaviour can be seen even by simple QML app that writes the
>> coordinates on the screen. I have no problem if I use the mouse. If I run
>> the "ts_test" from tslib the touch screen works fine, so I guess the reason
>> is not in the driver.
>> Has anyone experienced a similar issue or has a clue what can be done?
>> _______________________________________________
>> Interest mailing list
>> Interest at qt-project.org
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