backport of
r2aa9cf5badfcc978268a9bf06950942f27dfd366
Added cast to qreal, avoiding ftbfs due to
issue #758
More explanation here
https://wiki.debian.org/ArmEabiFixes
And on qt-project.org reference website:
"Typedef for double on all platforms except for those using CPUs with ARM architectures. On ARM-based platforms, qreal is a typedef for float for performance reasons."
