Best way to visualize a 2D triangulation?

[bts]

You can drop the scene and use simple widget.

Just draw on the widget using paint event.
It will require less memory and may be even faster if done right, but it will require more work to implement.

In my test 1m polys in scene requires around 600mb of memory, when doing the same on a widget requires just ~90mb.

Qwt uses that technique and it works well.
Depends on what you need - you could try Qwt.

Thank you!

I'm new to Qwt, which classes do you have used for your test?