Even though I’m building with Qt 5.11, the pen input does not seem to register unless I force the use of this workaround which, according to the code, is meant for Qt 5.6.
I think the check was there because Qt::AA_SynthesizeMouseForUnhandledTabletEvents didn't exist in Qt before 5.7. But I'll just drop the check, the hack doesn't really hurt anything (except it's more code).
Even though I’m building with Qt 5.11, the pen input does not seem to register unless I force the use of this workaround which, according to the code, is meant for Qt 5.6.