Increasingly I get as whether MPX allows multi-touch. The answer is neither yes nor no.

There is a bit of confusion out there as to what constitutes multi-touch. The simple answer "deals with multiple touch points" isn't quite that simple.

What is "touch"? In user interfaces, it usually means being able to manipulate an object by touching a sensitive surface. This can be done indirectly (touchpad on the laptop) or directly (touch screens).

To the X server, whether it's direct or indirect manipulation is irrelevant. What does matter though is the data the touch-device provides. Many devices reduce the touch point to a simple x/y coordinate (e.g. Wacom tablets, most touchscreens in public places, and AFAIK even the iPhone do essentially that [1]). From the X server's point, there is no difference between a mouse and such a touch device. MPX is multi-point, i.e. if your device supports multiple touch points, or you have multiple such devices, you have already won. Use them. Write software for them.

But - and here's the big difference: some devices can detect the area of touch, rather than a single point. And here's where it gets interesting, as this allows gestures. Touch with a flat hand is different to the side of hand, is different to the thumb, is different to a finger. This is true "touch support", and by far not commonplace yet. One of the prominent examples that supports true multi-touch is MS Surface.

MPX doesn't do multi-touch. But it turns out that multi-point is the hard thing and multi-touch is quite easy (once you have multi-point) [2]. The only difference is that you have to get the information to the clients. The X server doesn't have appropriate events to send the data and last year, I dabbled with this for a few weeks [3]. The result were the BlobEvents [4], but that branch hasn't seen many updates since, mainly due to lack of time. It will come back, once I find the time to merge the blob branch into current master, clean it out, and get some public review.

But for now - multi-point. Not multi-touch.

[1] there are exceptions, some provide pressure on the point, wacom tablets provide tilt, etc.
[2] From a technical perspective. Semantically, it's quite hard to get it right.
[3] http://wearables.unisa.edu.au/mpx/?q=node/86
[4] http://wearables.unisa.edu.au/mpx/?q=node/88