High DPI issues

[David Edmundson]

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

There are branches being merged in for 5.4. They affect QWidgets too.

Everything is based around a devicePixelRatio.
As I understand it, you write code as though you have pixels on a
normal 96dpi screen; but then there's a scaling factor for high DPI
skills which converts to screen pixels.

This can be overridden by an env variable.

It's always better to work closer with upstream than to roll your own thing.