Macbook Air vs. iPhone: A Multi-touch Mystery

Continuing my theme of Macbook Air trackpad related posts, today we're going to look at some intriguing differences in behavior between the trackpad and the device that made multi-touch all the rage -- the iPhone. The particular behavior I'm talking about is the swipe behavior in Preview.app. The behavior in Preview is obviously an attempt to mimic how the iPhone allows one to browse through all of the open documents in Preview. In this example we'll use a group of photos to exhibit both behaviors.

Let's start with the iPhone.

On the iPhone, the idea is that the user is reaching out and touching the photo, and "flicking" it to the left or right. So, let's say you reach out to the right side of a photo, and slide your finger to the left. The image then follows your finger, sliding off to the left, and the next image slides in from the right. This is pretty expected -- you have flicked the photo off the screen to the left, and it follows your finger off the edge of the screen. Even if you reach out and touch the middle of the photo and flick just a little bit to the left, the same expected behavior happens. You've grabbed the photo, pushed/flicked it off to the left, and a new image comes in from the right. Of course, the images aren't unlimited and if you attempt to do this when there is not a next image the image attempts to move off to the left, and then bounces back to show you that no image to the right exists, and that you are at the end. This all makes perfect sense, is pretty intuitive, and seems like the logical behavior to model the swipe behavior in Preview after, right?

Apparently not.

As an iPhone user, I approached the Macbook Air with a great bit of excitement. While the applications that currently support gestures don't exactly make me jump for joy, the potential for these gestures in third party applications is simply put, awesome. However, I'd at least expect some consistency between the two platforms.

Unfortunately, Preview falls short.

In Preview, swipes aren't as sophisticated, and in my opinion, not as well thought out as on the iPhone. Instead of the reaching out, touching, and flicking metaphors that work so well on the iPhone, swipes on the Macbook Air's trackpad simply move in the direction of the swipe rather uninterestingly. Sure, they animate nicely, taking full advantage of Core Animation, and when they reach the end of the set the image bounces back. However, Preview decides that reality, and thus platform parity, should fly out the window.

A swipe to the right in Preview, moves to the photo to the right. A swipe to the left in Preview, moves to the photo to the left. This is the opposite behavior you'd expect if you've ever used an iPhone, and sure enough, the opposite behavior I think you'd actually want. Using a multi-touch trackpad is not analogous to using the arrow keys. I'm not trying to arrow through my pictures, my mind is expecting a higher level experience -- I am reaching out and literally swiping through my photos, just like I might turn the pages of a book. Similarly if I rotate, or magnify my pictures, I'd be expecting the computer to act like I'm picking up a photo, and pulling the photo closer to me respectively, and indeed this is what happens.

Now then, it's possible that this functionality is actually intended. If we look at another application that implements multi-touch capability, the current behavior is actually correct. In Safari, moving to the right should in fact send us forward, and moving to the left, should send us backwards. That makes sense after using it a couple of times. There are thus two arguments that can be leveraged for the case of Preview's behavior. The first is system parity. Other applications act this way, thus, Preview should as well. I'm guessing that's the one they chose, and that's why it's implemented this way. I argue that is should be changed, because it just feels wrong. Even more so after you've used an iPhone for about two minutes. The second reason, is that Preview is not necessarily running a full screen context. Thus, the idea of flicking pictures isn't especially clear. However, I get the feeling that's exactly what they were attempting to mimic. When you reach the end of a set of photos, the image has a nice bounce effect, just like on the iPhone. However it bounces the wrong way! That's right, when you get to the end of a group of photos, and continue to scroll as if another photo should be there, the image slides to the right and then bounces back. This is completely wrong. Since the photo should be sliding off to the left, it should do so, and then bounce back, very similarly to how the iPhone works.

I think this ultimately shows one of the interesting aspects of these trackpads being integrated into our computers. It's very easy to get confused about how they should work. Multi-touch shouldn't be just an alternative way to arrow through things. It's an advanced and sophisticated input method, and requires programmers to really think about how users are going to interact with their computer when using gestures. Assuming Apple continues to integrate this technology into their laptops, we will soon be at a point where multi-touch is a big deal. Both platform parity and system parity need to be considered, but more importantly a great deal of thought needs to go into this process, and whether through guidance from the top as to how users should be expected to interact with the multi-touch trackpad, or through a standards system of our own, right now it's up to the developers using the technology to shape the way users use this technology.

All in all, there are far more iPhones and iPod touches around than Macbook Airs. Far more people are going to be used to using these devices, rather than a Macbook Air, and thus I think it's clear the paradigms we should strive to mimic.

Peter Hosey has pointed out, and I agree with him really, that Safari should mimic the iPhone behavior as well. After all, who doesn't want to flick through webpages?

Bugs have been filed on Preview and Safari: here and here.

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