How to check if your touch screen is really sending touch events

I've had this problem twice in the last year, I'm testing something related to touch in my laptop and I'm stuck trying to figure out if it's my code that is wrong or if my screen is misconfigured and it's only sending mouse events.

Thanks to Shawn of Qt fame for having helped me the two times and explained me how to test if my screen is sending touch events, I'm writing this blog so i don't forget and ask him a third time :D

First step is figuring out the xinput id of the touch screen of my laptop

tsdgeos@yoga:~:$ xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ Wacom Co.,Ltd. Pen and multitouch sensor Finger id=9 [slave pointer (2)]
⎜ ↳ ETPS/2 Elantech TrackPoint id=13 [slave pointer (2)]
⎜ ↳ ETPS/2 Elantech Touchpad id=14 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Sleep Button id=8 [slave keyboard (3)]
↳ Wacom Co.,Ltd. Pen and multitouch sensor Pen id=10 [slave keyboard (3)]
↳ Integrated Camera id=11 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=12 [slave keyboard (3)]
↳ ThinkPad Extra Buttons id=15 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]

In this case would be id=9

Then you can do

tsdgeos@yoga:~:$ xinput test-xi2 9

and if the output contains RawTouchBegin and RawTouchEnd events, it means that the screen is correctly sending touch events :)

Next you probably want to check if Qt actually is seeing those events, for that there's a few ready to use demos in the qtdeclarative source code, so I would do

tsdgeos@yoga:~:$ qml qt5/qtdeclarative_58/examples/quick/touchinteraction/multipointtouch/multiflame.qml

And after putting my five fingers on the screen I would see

So all is good, the bug is my code and not in Qt or the configuration of my touch screen :D

Big day in poppler-land

Today in Poppler:
* Poppler 0.57 got released
* We agreed to stop supporting openjpeg 1.x at the end of the year
* We agreed to stop supporting Qt 4.x at the end of the year
* We merged the better_object branch

The last one is the one that is really big, since it introduces a big rework of the Object class, a central component to Poppler. Object is much used like a QVariant, i.e. it can hold various kind of data inside and you can pass it around.

Unfortunately the Object implementation we inherited from xpdf was kind of hard to use, having to basically do the memory management by hand. i.e. destroying the object was not enough to free the memory, you had to call free() on it.

Thanks to C++11 now we have an implementation with move semantics that greatly simplifies the use of Object and will hopefully make for less memory management mistakes.

Let's hope we didn't break anything in the process though :D