To fix to the Mac OSX error in the histogram region rendering:
set QApplication.setGraphicsSystem('raster') before the QApplication is created. But this is not possible from a QGIS plugin;
alternatively, use a RemoteGraphicsView to run in a parallel process and on this one set the Graphics System.
However, there's also a bug with the remote view in recent OSX (10.8 - 10.10): https://groups.google.com/forum/#!topic/pyqtgraph/_vSSyrm7AHE
For now I ignore the rendering error as it only affects Mac OS, but must try an alternative selection method to overcome the problem.
User can switch those lines on/off.
To fix to the Mac OSX error in the histogram region rendering:
set QApplication.setGraphicsSystem('raster') before the QApplication is created. But this is not possible from a QGIS plugin; alternatively, use a RemoteGraphicsView to run in a parallel process and on this one set the Graphics System. However, there's also a bug with the remote view in recent OSX (10.8 - 10.10): https://groups.google.com/forum/#!topic/pyqtgraph/_vSSyrm7AHE
For now I ignore the rendering error as it only affects Mac OS, but must try an alternative selection method to overcome the problem. User can switch those lines on/off.