View Full Version : QTabletEvent instead of QTouchEvent

19th November 2013, 11:34
Hi everyone,

I'm trying to use a Cintiq 24HD screen (multi-touch + stylus tablet) under Ubuntu 12.04. Things work great on Windows 7 so far.
On Ubuntu on the other hand, I'm facing a few difficulties :
Since Qt4 doesn't handle it on Ubuntu, and only returns QMouseEvents, I tried with Qt5. By default, Qt5 had the same behavior as Qt4 on that point.

Following the guide I found there http://guide.x21.ch/2012/12/07/linux-multitouch/, things got a bit better : I now have QTabletEVents ! (tried with both Qt 5.0.0 and 5.1.1 SDKs, with identical results).

This is a good first step, but when I try the FingerPaint example from Qt, as well as my own app, nothing happens (of course, only TouchEvent are handled), and even worse : the app crashes as soon as I use a second finger with the following error : thus I can't use multi-touch.

1ASSERT: "dev" in file qxcbconnection_xi2.cpp, line 337

Multi-touch works on my machine, validated with https://wiki.ubuntu.com/Multitouch/Testing/

Every post i've found about that were posted quite a long time ago, and are the ones that helped me to get where I am now, so I figured there would probably be some changes since that time. I didn't find anything about receiving the wrong QEvent though.
So, is there something I'm missing there ? Is there any ubuntu touch/multitouch support yet ?

Thanks in advance :)

20th November 2013, 15:03
I managed to get TouchEvents to work by adding arguments on my qt app :

sudo ./fingerpaint -plugin evdevtouch:/dev/input/event9
(event9 being my wacom's "touch finger" device).
This way, Touch events are correctly interpreted.

However, I still have the second finger issue (i.e. the app crashes as soon as i use a second finger with the message displayed in my first post).
I tried removing wacom driver as suggested here ( https://bugs.launchpad.net/ubuntu/+source/xf86-input-wacom/+bug/901630 ) with no change in Qt's behavior.

Still looking for any advice or help or any link.

Thanks !

26th November 2013, 12:19
Small Bump

I still can't figure out what the issue is. I tried different versions of Qt (from 4.8 to 5.1), and all have the same behavior. I can't find any official documentation about using wacom tablets as touch device, and not that much either about using multi-touch devices with Qt. So far everything I found was quite hack-ish. It really looks like multi-touch under ubuntu is not very well supported, but I hope I'm just wrong on that point.

9th December 2013, 13:01
Hello again.

I would really appreciate if anyone who has been successfully using a muti-touch device on ubuntu using Qt would at least explain me how they managed to do it.

Thanks in advance.