title: Adding support for retina displays (HiDPI) to an existing Qt4 application
body: <p>What do I need to do to upgrade an existing Qt4 application to work with retina displays on OS X?</p>
  <p>The Qt blog says that Qt 4.8 &quot;has good support, and backports of some of the Qt 5 patches are available&quot;:</p>
  <p><a href="https://www.qt.io/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11" rel="nofollow noreferrer">https://www.qt.io/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11</a></p>
  <p>I've added the following to <code>Info.plist</code> which seems to work. The text and buttons are no longer pixelated.</p>
  <pre><code>&lt;key&gt;NSPrincipalClass&lt;/key&gt;
  &lt;string&gt;NSApplication&lt;/string&gt;
  &lt;key&gt;NSHighResolutionCapable&lt;/key&gt;
  &lt;string&gt;True&lt;/string&gt;
  </code></pre>
  <p>What I'm struggling with is getting the icons/pixmaps to render nicely. I've created the UI using Qt Designer. I don't see how to get the application to recognise the @2x icons.</p>
  <p>The application I want to upgrade is written in C++ (<a href="https://github.com/qgis/QGIS" rel="nofollow noreferrer">https://github.com/qgis/QGIS</a>), but I've also been testing with Python (PyQt4). The QPixamp instance doesn't seem to have a <code>setDevicePixelRatio</code> method.</p>
  <p>I'm running OS X (10.9.4), with Qt 4.8 installed via Homebrew.</p>