Mac OS X: Best way to do runtime check for retina display?

Question

Given a Cocoa application which runs on Mac OS X 10.7 and later:

What is the best way to check, at runtime, if your app is currently running on a Mac with at least one retina display attached?

If checking for this sort of thing is just really wrong-headed, I fully welcome a well-reasoned explanation of why (and I will up-vote such answers if they are good).

But I'd still like to know :).

It seems likely you could just do a check specifically for the new Mac Book Pro "Retina" hardware (the only Mac which currently has a retina display), but I'd really prefer a more general/generic/future-proof way to check than this.

Ideally, I'd like to know how to detect the retina display, not the specific Mac model which currently happens to ship with a retina display.

Answer 1

If you really do need to do this, take a look at -[NSScreen backingScaleFactor]. But, this does seem wrong-headed, at least without knowing more about why you want to know.

While there is currently only one Mac with a Retina display, there may eventually be standalone displays that support Retina (and can be attached/detached at runtime) and you may be able to configure the built-in Retina display in 1x mode. Thus the answer to the question "is there a Retina display attached" can change at any time.

Rather, you may want to know if your content should be drawn with a given scale by using the -convert*ToBacking: methods or -[NSWindow backingScaleFactor]. For a ton more detail, watch the WWDC 2012 session video "Advanced Tips and Tricks for High Resolution on OS X" (when posted, hopefully within the next few weeks).

Answer 2

I just ran into an instance where I needed to detect if any screen was high resolution, this worked

float displayScale = 1;
    if ([[NSScreen mainScreen] respondsToSelector:@selector(backingScaleFactor)]) {
        NSArray *screens = [NSScreen screens];
        NSUInteger screenCount = screens.count
        for (int i = 0; i < screenCount; i++) {
            float s = [screens[i] backingScaleFactor];
            if (s > displayScale)
                displayScale = s;
        }
    }

Answer 3

Well, on iOS you use the UIScreen.scale property. If it returns 2.0, then you're on a device with a high resolution display. Otherwise you're on a low-resolution device.

So I'd imagine that on Mac OS you could use either -[NSScreen backingScaleFactor] or -[NSWindow backingScaleFactor].