this sounds cool! is it a code from jqplot itself? will it clash if we later upgrade to latest jqplot? maybe it can be included upstream... Cheers

I opened a ticket in trac: http://dev.piwik.org/trac/ticket/4389#comment:1

Basically the issue is that the upstream version hasn't applied this fix yet and there's been no reelase of jqPlot since march. There are three tickets about this currently open: https://bitbucket.org/cleonello/jqplot/issues?q=retina

The code in this PR is basically the fix proposed in one of those tickets. For now I suggest we maintain this ourselves and hope that jqPlot picks up the issue upstream.

Tried to test it with Chromes new mobile device emulation feature but didn't see a big difference. Maybe it is better visible on an actual retina device? Will merge...