might find something here:
https://github.com/olilarkin/wdl-ol/pull/38
or my old retina implementation which i removed from next branch, can't remember the exact details
https://github.com/AlexHarker/wdl-ol...7c74b266982b62
bool isRetina = CGContextConvertSizeToDeviceSpace(pCGC, CGSizeMake(1,1)).width > 1.9;