HighDPI / retina support

[jf---]

I managed to trick traitsui into using high-dpi settings and observe that enaml does not take high-dpi (retina) screens into account. I know its debatable whether to what extent enaml should take care of providing these settings, so curious to have your view on this.

http://blog.qt.digia.com/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/

[sccolbert]

There's lots of bugs with Qt4's hidpi scaling on OSX. Even more troublesome are the hacks I had to use for thing like DockArea to make it user-stylable. The Qt stylesheet and resource api's are woefully insufficient for building an api around, and make supporting hidpi very difficult.

I haven't dug into Qt5, but support may be better there. I will revisit this once we move to Qt5.

Qt also has other problems on OSX which i've reported, but they are not yet fixed: https://bugreports.qt-project.org/browse/QTBUG-29212 https://bugreports.qt-project.org/browse/QTBUG-30762

My primary deployment platform is also Window 7 and 8, so that gets the most attention and testing.