I have a full-screen app in kiosk mode that runs on qt 5.13.2 (Qt compiled from source). Up until 1 week ago, it displayed just fine. Then, I did an apt dist-upgrade and I now get horizontal lines and gobbley-goop:

enter image description here

However, I can hack around this by changing the "virtual terminal" using chvt:

sudo chvt 1
./launch_app &
sleep 10s
sudo chvt 7

Then it launches fine (it's working):

enter image description here

What is different between launching in virtual terminal 7 while in virtual terminal 7 vs launching in virtual terminal 7 while in virtual terminal 1 and then changing to virtual terminal 7? I understand it is different, but I have no clue where to start looking in the Qt code base or on the pi raspbian system about how these launching modes are different.

FYI, other programs don't have this issue, so it could be the way Qt interacts with X-windows. I get the same behavior when I switch back to an older version of the app that uses the platform default qt 5.11.3. Something changed in the last couple of weeks with the pi platform. I'm sorry to be so vague. Normally sudo apt upgrade works just fine. Where should I look?


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