Since 5.2 /
QTBUG-30008 we have had Wacom support via the Wintab API, but not Windows Ink support, which is newer and probably going to supersede wintab eventually. Tablet Computers which use non-Wacom technologies (such as nTrig) do not ship with drivers that support the Wintab API, so they do not work with Qt.
There is some documentation here (and related links around)
and on 2017/04/26 I was chatting with someone on #krita who wants to write a library to support Windows Ink and maybe eventually turn it into a cross-platform library supporting stylus devices. He plans to use a permissive license so that we could potentially ship it with Qt as a third-party library. That will be here: https://github.com/darkuranium/libstylus
Whether that gets done or not, we need to support Windows Ink eventually. It appears to support all of the same features that we need to generate fully-populated QTabletEvents.