Archive for June, 2010

Getting multitouch to just work

Wednesday, June 9th, 2010

There are many things going on in this field, from the recent merge of the xi2 branch into GTK+ master (yay!) to the ongoing effort in Xorg to support multitouch devices.

I’ve worked myself in a proposal to the evdev driver so it deals with multitouch devices as a set of XI2 devices (in GTK+ world, this means each finger would be represented by a GdkDevice), only one finger is able to send core events, while the others only get to send XI2 events, this seems pretty much in line with Peter’s thoughts on multitouch support

I also have a few patches in the xi2-playground branch that understand these semantics and basically make multitouch work out of the box.

So, if you have a multitouch device that’s understood by the linux kernel, these are the ingredients:

Voilá! xinput list should tell something like:


⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ N-Trig MultiTouch id=12 [slave pointer (2)]
⎜ ...
⎣ Virtual core keyboard id=3 [master keyboard (2)]
...
∼ N-Trig MultiTouch touchpoint 0 id=13 [floating slave]
∼ N-Trig MultiTouch touchpoint 1 id=14 [floating slave]
∼ N-Trig MultiTouch touchpoint 2 id=15 [floating slave]
∼ N-Trig MultiTouch touchpoint 3 id=16 [floating slave]

And the GTK+ tests in tests/multidevice/ should just work, providing at the same time a single-touch device feeling to applications unaware of XI2 or multiple devices.

Guadec
If you find this subject interesting, don’t miss my guadec talk! where I’ll be talking about multitouch in GTK+ and what applications can do to support it.