X Server MultiTouch Support

Dylan McCall dylanmccall at gmail.com
Sun Jul 15 18:29:36 CEST 2007

In my opinion, multitouch on a phone is rather pointless unless that phone's
screen is big. To do it, you need to either touch the screen with two
fingers at once (which is very uncomfortable if you want any kind of
control), or you need both hands oriented to touch the screen (which is
uncomfortable). Doing so also blocks almost the entire screen. Note that
none of the iPhone commercials showcase this multitouch functionality,
probably because it blocks so much of the screen and requires uncomfortable
operation (often leading to one dropping the thing).
Just about the only application for multitouch for a phone like this is the
keyboard, and even that seems a bit odd to me since people don't usually
press two keys at once.
Am I missing something, like a tendency to have one's fingers on a key for a
moment after pressing, while the other is being pressed?

For other two-touch gestures that require specific motions, what Simon
mentions is entirely possible on most single touch screens. It is possible
to determine, with some accuracy, how many points are touching the screen.
The point reported by the touch screen is actually the point directly
between the two touch points. (This is controlled by the pressure of either
touch, which can make for some pretty fancy tricks already).

Now, some fancy mathematics stuff later, and you have two-fingered gestures.
First finger can be assumed to not move, so when a second finger appears the
position of the two can be figured out. Most multitouch gestures work with
the first finger not moving anyway, so it is hardly a sacrifice.
The method works pretty well, though it could be worrying bringing it out of
a test scenario and into an actual released "final" product, since it's all
rather imprecise. With some calibration, wide-spread testing, and some
assumptions, it could be quite nice.

Just detecting "gesture mode" could be a simple matter of figuring out how
many touch points there are (some multitouch demos for the Nintendo DS do
this really well!). With that, simple linear gestures such as the two
fingered scrolling gesture could be really nice and easy (as with track
pads; move both fingers vertically to scroll vertically, etc.). Touching
with two fingers to do the same as a double click also springs to mind.

I, for one, would be happy to see a gesture replace that scroll wheel on the
left side of the interface!

-Dylan McCall

On 7/15/07, Simon <simon.xhz at gmail.com> wrote:
> > Well I don't know what so cool about multi-touch screen on a phone
> unless
> > for scaling images and webpages. So maybe just implementing a gesture to
> do
> > that function, no need for a full blown implementation of a multi-touch
> > support. unless i'm not getting something...
> I'm not sure if it is related, but on a mac, you can hold one finger
> still and move the other up to down to have the screen be scrolled
> (like the scroll button on a mouse).
> And that is killer, things get relative to touches!
> Simon
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