[Interest] Replacement for Qt4 QMatrix4x4?

[Matthew Woehlke]

So... after a full day of debugging, trying to port my Qt4 app to Qt5
and chase down a nasty case of stack clobbering, I discovered that the
problem is that QMatrix4x4 changed from qreal to float.

(Uh...why? I am not particularly amused by the loss of precision, nor
the extremely subtle incompatibility.)

Alas, there does not seem to be any feasible replacement in Qt. I can't
use QGenericMatrix because it can't be used to transform QPointF's, nor
can it be inverted, both of which are features I require. I *really*
don't want to throw out the precision of double, especially as I have
tons of other code that still uses double and would have to wade through
mountains of conversion warnings to do so.

Am I missing something, or do I need to drag in Eigen?

-- 
Matthew