[Development] Move math3d from QtGui to QtCore

[Laszlo Papp]

> I understand it's useful for you, but other people who might use the
> functionality said it isn't and they'd need more. That means I've got a single
> use-case to consider (yours) and I'm not convinced that this is worth the
> moving.

Like I said, we agreed about that, you are totally against moving any
of these things into QtCore. Right, but why are you actually blocking
moving out of QtGui? If it is not in QtCore, it needs to be in a new
Playground module. You were asking about eigen, but I did not really
get the question. Using eigen for managing some coordinates sounds
utterly overkill.

BR,
Laszlo Papp

PS.: Not to mention, I had a question about QPointF3D into QtCore.