They want you to open a window and build a widget inside the window. The APIs for rendering to a byte buffer and injecting bogus input events seem kinda weak. If I make my own toolkit, I'll focus on that first. I don't want such a huge part of the app to be an untestable I/O leaf.
And, Win32 has a whole separate subsystem for unit testing UIs. Read more here: Win32 -> "UI Automation Test Library"
Man, there is so much damn misinformation about Qt on HN. It is tiring. I don't understand the source of this misinformation. Part of it probably stems from their various licensing mishaps over the years that seeded a bunch of FUD. It's a ridiculously good cross-platform UI library. KDE would not exist without it! I don't work for them, but I have used the toolkit for years. Nothing beats it. Yes, it is huge, but it does everything you could ever need.
Maybe I didn't check the docs closely, maybe it's better in Qt6. I stopped working on GUIs a while back.
Fwiw HTML and xaml were just as bad for that.
Also, Qt4 was last released in 2011. That was nearly 12 years ago. Maybe... try again?
Also, you can Google: qt widget without window border
Plenty of hits.
The real issue, in my opinion - as someone who's worked in a litany of UI systems and built my own UI frameworks and libraries: it's a lot of frankly boring as shit work that everyone gets into and then drops like a rock once the dopamine rush of implementing basic widgets wears off.
(Then you add on that the number of people who know the big three (Cocoa/Win-whatever-they-use-now/GTK-or-QT) really well is a much smaller pool)