You remind me when microsoft was claiming that bash was hard and as example did some crazy obfuscated bash scripts, rather than just doing them the sane way.
If you're doing a GUI, you have no reason to be doing canvas manually.
What? Even with QT you often have to use a painter and draw what you want more or less. You also need a canvas to display anything that is visualisation related. In any case it doesn't matter, as I said, scrolling is just as easy on the web as it is on QT. my point was more general, if you want to do anything custom it's easier to do in JS than with QT. Even using the multiple tools QT offers to customize the view (the painters, canvases, 3d widgets, etc)
You're just showing me you've never dune as much as an hello world using QT. Which is completely fine, but don't paint yourself as knowing what you're talking about.
If you're doing a GUI, you have no reason to be doing canvas manually.