The forthcoming OS X Lion has a few trackpad gesture changes. Here is a brief rundown of what looks interesting to me from a UX point of view. This is based on the WWDC presentation and Apple's web site (this page in particular). I'll update this after I've tried Lion myself. Update: Please see this follow-up post.
Reverse scrolling direction
Apple has reversed the vertical scrolling direction so that moving your fingers down on the trackpad will move the screen content down, rather than up, as currently happens. This is a change in the metaphor from "grabbing the scrollbar" to "grabbing the content." The latter metaphor is what Apple has used on the iPad and iPhone, which are direct-touch devices where manipulating the content directly is much more intuitive. Overall, Apple is making the notebook experience closer to the touchscreen experience so this change makes sense (and the scrollbar now hides so this aligns with that change too).
Apple is highlighting this new metaphor on their website:
"Multi-Touch gestures in OS X Lion make it feel as though you’re controlling your content more directly than ever before. So when you scroll down on your trackpad or Magic Mouse, your document scrolls down. When you scroll up, your web page scrolls up. When you swipe left, your photos move left."
Question: Will people get used to this? In the Lion previews there was a checkbox to toggle the direction -- is it still there?
Related: a post at the Human Factors blog about this topic: Scroll direction, touch screens, trackpads.
More fluid responses and animations -- "Gestures that feel real"
Again a carry-over of features like rubber-banding from iOS. Apple has done a better job than Windows PC makers to make their gestures respond smoothly and to use animations. This is no doubt partly a result of Apple's tighter control over applications and OS features. The touchpad gesture experience on Windows is influenced by at least three parties: Microsoft, the OEM, and the touchpad maker. As a result it's more difficult to refine the user experience of features like this.
Two-finger double-tap to zoom
This is another feature that will be familiar to iOS users. I'm curious whether this replaces or supplements the Control-scroll feature for screen zooming. And will the "intelligent" zooming feel right on a big screen? Zooming in to a tiny column of text could be a visually jarring.
In Snow Leopard, two-finger tap could be configured to do a secondary (right) click to bring up a context menu. Is this option still available in Lion? If so I'm curious how they got the two to co-exist well. One option would be to delay the single-tap response in order to determine if the user will do a double-tap; the double-tap action (zoom) would then cancel the single-tap action (context menu).
Different navigation gestures and their implications
Before Lion, three-finger swipe left or right meant navigate backwards or forward. In Lion there are two navigation gestures:
- Three-finger swipe left or right to move between full-screen apps.
- Two-finger swipe left or right to move between "web pages, documents, and more."
So two-finger swipe now seems like the main navigation gesture, and three-finger swipe is for the special case of full-screen applications. This raises a few questions about the usability:
- Will users keep this straight or will they end up swiping two fingers when they meant three and vice-versa? What will happen if they make this mistake? Hopefully nothing too disruptive.
- Would a modifier key have been more intuitive? For example -- swipe two fingers to navigate within the application; hold Control and swipe two fingers to navigate between applications.
- In Snow Leopard, Apple introduced the option of using three fingers for dragging instead of swiping. Is this option still there? I thought this was quite an interesting change because it promised to make dragging simpler and perhaps faster than the old, awkward "tap and a half" gesture. I tried it for a while and liked it, but I missed the three-finger navigation too much to stick with it.
- How well do two-finger swipe and two-finger horizontal scroll get along? Does the gesture engine do a good job of disambiguating between the two? Or is horizontal scrolling now limited or gone altogether? (Limited in the sense of perhaps having to start a scroll gesture vertically before going horizontally.)
- What about two-finger swipe and two-finger vertical scroll? One of the great things about Apple's current two-finger scroll is that if you're in a situation where only vertical and not horizontal scrolling is possible, you can be very relaxed about the angle at which you move your fingers to scroll. And people do often scroll vertically with their fingers moving at an angle of about 30 degrees above horizontal. Will some of these strokes now get mistaken for swipes? (And will some swipes be mistaken for scrolls?) That's the cost of introducing a new gesture into the same parameter space (in this case the space of two-finger strokes) -- the recognizer has to be more sophisticated about discriminating between gestures.
With all these questions I don't mean to doubt the usability of what Apple has done -- as I said I haven't even tried Lion yet. I assume they've done their usual great job. My intention here was just to highlight some of the usability questions I'd look to answer when implementing and testing these features.