APIs existed for fractional scale and assets in early Mac OS X versions (10.4 I think). I remember building out 1.25, 1.5 and 2x assets for an application at the time. These were never to be shipped to consumers for a few reasons.
There were intractable issues with window spanning across displays with different scale factors. Ultimately this was resolved by not allowing window spanning on the platform anymore.
There were intractable issues with window spanning across displays with different scale factors. Ultimately this was resolved by not allowing window spanning on the platform anymore.