Add HiDPI support

[Daniel Schürmann]

From Ubuntu Trusty and all other gtk 3.10 based distros, HIDPI settings will supported.

We should respect them in MIxxx as well.

https://blog.qt.digia.com/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/
https://wiki.archlinux.org/index.php/HiDPI

gsettings set org.gnome.settings-daemon.plugins.xsettings overrides "{ 'Gdk/WindowScalingFactor':<2>, 'Gdk/UnscaledDPI':<92160> }"

Related:
Bug #661717 Zoomable text size in library

[Daniel Schürmann (daschuer)]

Related: Bug #1249539

[Daniel Schürmann (daschuer)]

http://www.mixxx.org/forums/viewtopic.php?f=8&t=7098

[Daniel Schürmann (daschuer)]

HiDPI support has not creped to Qt 4 by now.

So there is only th poor man solution to hack up the legacy string parser to multiply all size values by 2.
The other solution would be to provide dedicated HiDPI skins.

I would prefer to hack up the legacy string parser, if one needs it very hard for 1.12
Later versions of Mixxx will probably base on Qt5 with library support for HiDPI.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[jus (jus)]

https://github.com/mixxxdj/mixxx/pull/1204

[Virgil (virgil-v)]

I would love to see it upgraded from "wishlist" as it makes Mixxx unusable on my portable device...

[Daniel Schürmann (daschuer)]

What are the specs of your mobile device?
Are you able to build the linked branch in #5?

[Virgil (virgil-v)]

My device is a surface book pro, with a 13,5" 3000*2000 display.

I'll try to build it, it is the first time however I do this, so bear with me as building an executable might take some time :)

[Daniel Schürmann (daschuer)]

If it runs windows, you can download a build from:
https://ci.appveyor.com/api/buildjobs/od5nt3v1p7o1q2pb/artifacts/mixxx-2.1.0-alpha-pre-master-PR1204-git6225-release-x64.msi

[Virgil (virgil-v)]

I did not know you could do this :p
And it works quite fine! A *2,5-3 option (or even a numeric one) could be interesting however it is now usable, hurray =)

[Be (be.ing)]

https://github.com/mixxxdj/mixxx/pull/1204

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7370