Hi,
all I know is that the $.screens command returns an array of objects for all available screens.
Try
for (var i = 0; i < $.screens.length; i++) {
$.writeln ("Screen " + i);
$.writeln ("top: " + $.screens[i].top);
$.writeln ("left: " + $.screens[i].left);
$.writeln ("bottom: " + $.screens[i].bottom);
$.writeln ("right: " + $.screens[i].right);
}
As I don't have a retina display to test this, I'd be interested to know what the above returns.
Dpi information is not included, so you would have to map the typical resolutions of higher res displays and assume they're not super-big