Mobile world makes it a necessity to develop techniques to show information that, by nature, would need a larger display. For the carefree user this substantially means to be able to see hi-res images without renouncing to see details, to read a website not mobile-ready, or to look over a wide spreadsheet or some tables.

The problems of the scrolling bar

The touchscreen is a valid help in this situation, but the classic solution of the scrolling bar would force us to give up half the display to make it accessible to our huge finger tips, and if the scrollable element is much longer than display size it would mean having a bad time when trying to find a precise position (i.e.: a movement of 1mm on the display could mean 2cm of content). This is already difficult with a mouse on huge screens, if for example we’re scrolling a long document like a degree thesis.

Touch Scrolling

To avoid this problem, they resorted to direct scrolling technique, which is also much more natural and, if well designed (see below) much more comfortable. In practice, the scrolling happens as if we had a paper sheet on our smooth desk and made it slide with the finger.

The rougher implementation of this system is that for which the “sheet” (the content) slides on a “sticky” surface. Once lifted the finger, the contents stop immediately, granting precision but, in case of huge contents, slowness and discomfort like riding a bike with brakes pulled.

Inertial Touch Scrolling

The advanced implementation is instead the one in which the surface is slippery. If you give a fling to the contents, they will keep scrolling before your eyes until we stop them with the fingertip, or they stop because of the virtual drag of the surface, or we get to the edge. The advantage is that fine scrolling is still possible if we lift the finger while not moving.

But like with all the advanced things, other factors come in asking for attention.

The problems of Touch Scrolling

Primarily, all these touches might create some “misunderstandings”: if for example we’re visiting a site and by chance we stop a scrolling by putting our finger over a link, this touch shouldn’t be interpreted like a link click, or in brief we’ll start cursing who developed that thing, and our decision to use something else because this one is not a good one. This is not simple, because the touchscreen is all but perfect: it can’t tell two fast touches from a not very sharp one (a click is a click, but a touch can have different pressures), and one could get lost if the processor is under heavy load (in background or just showing contents). Moreover, it’s actually impossible to keep the finger steadily on a display spot, making it impossible to avoid the fling when lifting the finger, unless we don’t apply a speed/movement limit under which considering the finger still. In short, if you want to adopt this method, you have to afford the responsibilities it brings (I’m talking to the developers reading).

As a second point, there are different ways to manage the reach of the edge. The easiest way for the developer is to avoid at all any management: the scrolling is infinite and if we want we can scroll until contents are miles away. This method is not too much uncomfortable for the user if it’s a sticky scrolling, and could be used for your own advantage for example in a jigsaw puzzle where you’d have an infinite surface on which move the tiles, or if the surface is actually a sphere (see GoogleMaps). Another way could be: once reached the edge, the contents could just stop moving in that direction (maybe making the device vibrate – if you want to try this solution, we have implemented it in our game ParanoidDifferences), or bounce (a pretty strange solution). The most trendy solution seems to be the one where you simulate a spring mechanism, so that we’ll see the black background and “feel” more resistance to our dragging. Personally though, I find a bit unaesthetic (and a philosophical trouble) seeing this “nothing” behind, and I feel it’s a waste of time seeing the contents lazily sliding back to their place when I lift the finger. Moreover, if this “spring” is too soft, it’s not so straightforward to understand that’s the edge.

Another thought about smooth scrolling is that if the device can’t recreate a smooth enough sliding animation and jerks, this experience will become a pain aesthetically and practically, as you’ll never know at what point of the scrolling you are and if by stopping you really are where you want.

Salutations

So many and such are the variables to take in account when considering a scrolling method. Sometimes it’s just a matter of user’s tastes (that, sadly for developers, are the most important and unpredictable), sometimes not. Users shouldn’t be surprised, therefore, to find many apps with an uncomfortable scrolling, and should report the problems they have (if the developer is willing to listen to them!).