Viewer and editor crashing on other than primary monitor

[CarryNL]

First of all: I'm on Windows 10 Pro build 1903, three monitors attached to one video card, Calibre running on the primary monitor.

For a while now (not really sure how long but somewhere in 2019, I think) the Calibre editor has been crashing when I try to edit an epub. I couldn't figure out what caused it as no logs were written and no entries in the system or application event logs were to be found. I don't use the editor very often so after a while I just forgot about it and was slightly annoyed when I tried to edit a book and re-discovered it didn't work. And, to make it more of a puzzle, there were times when it did work...

After updating to 4.9.0 the Calibre viewer occasionally crashed when trying to open an epub but opening the epub on my mobile phone (in Aldiko) or my kobo Aura never showed a problem. Also, no logs or event messages in Windows. This was a bit more annoying as I sometimes like to read from my computer but I could manage without it. The most annoying part was that the crashes were so random as the same book would sometimes open and sometimes it wouldn't.

Today I finally managed to reproduce the problem with both viewer and editor. If I try to open either of them and move my mouse to my secondary or tertiary monitor, the viewer or editor will be opened on the monitor my mouse is over and ends up non-responsive. As long as I make sure to hover over something on my primary monitor, the chosen program opens without any problem and I can read or edit my ebook without any problem. Just to be clear: I'm not clicking anywhere so the active focus should be either the Calibre GUI on my primary monitor or the Explorer window on my primary monitor from where I started the viewer or editor, as far as I know. But for some reason, the monitor where the viewer or editor opens is determined by the location of my mouse.

I dragged Calibre GUI to another monitor to see if that would change anything but nope, still the same behaviour. If my mouse isn't hovering over my primary monitor, viewer or editor open on the monitor my mouse is over and end up unresponsive.

Is this something that is 'by design' or at least 'to be expected'? Can I influence the behaviour by locking viewer and editor to never open anywhere else but my primary monitor no matter where my mouse is? Or is my system just a special snowflake that should be left alone as it's doing the best it can?

[kovidgoyal]

This will be a Qt WebEngine issue (the library calibre uses to render HTML). You cn probably workaround it by forcing it to use software rendering, see https://doc.qt.io/qt-5/qtwebengine-debugging.html

[CarryNL]

Thanks! I'll ask the resident technical person (aka husband ) to look into that

[Celebi]

Please, how and where can this be set?

[DNSB]

Easiest way would be to open File Explorer. Right click on My PC, click on Properties Click on the Advanced system settings. Click on Environment Variables tab. At this point, you either click on New under User variables for username or New under System variables. My preference is User.

Enter QTWEBENGINE_CHROMIUM_FLAGS as the variable name
Enter --disable-gpu as the variable value.
Click OK.

At least that is what I get from the instructions on the web page Kovid Goyal posted.

[Celebi]

Thank you. Even though it did not help to solve the problem, at least I learned something new.