We have some platform specific improvements as well as support for new platforms and compilers coming with Qt 5.9. Especially macOS is receiving many improvements, as we are updating the macOS platform plugin in order to support modern and future features of the operating system, especially on the graphics side. 

http://blog.qt.io/blog/2017/02/22/qt-roadmap-for-2017/

Qt 5.9对Mac的图形显示有许多改进