We support devicePixelRatio, but currently only on OSX and iOS (Android is missing: QTBUG-38250). Also we do not yet correctly handle that topic in all of our code, see QTBUG-38127.

In some cases, I want to chose between devicePixelRatio-awareness and none. Also, I want to be able to "simulate" any devicePixelRatio on the Desktop.
Web developers seem to have that possibility by defining target-densitydpi like:

<meta name="viewport" content="target-densitydpi=device-dpi" />

Imho, it would be very useful if devicePixelRatio could be set/overridden in an application, be it via Api or environment variable. If that has to happen in the first line of code in my main() function, I am still happy