Processing & multitouch

I wasn’t supposed to be doing this today, but:

Multitouch support on Linux seems much simpler with a different library than SMT that I was unsuccessfully tryin last year. “Simple Touch” actually “just works” via evdev library. The only thing that was needed was to supply the right event device from /dev/input and also make it readable and writable for normal user.

Find out which event device is your touch screen:

Above you see that id of the touch-screen is 11. Which means we have to allow access to /dev/input/event11.

Alternatively (and perhaps much more reliably) one should check the contents of /dev/input/by-id/

You can see that the touch-screen reports to be device “../event5”.

Simple Touch library is available from the Tools menu in Processing, but also here:

In Processing there is couple of examples for Simple Touch library, but the essence for a successful start is

1) list devices

will output something like

Touch-screen (event11) has [3] index, so to open this device you finally use

It seems also to be possible to do just this:

and the following also works:

This opens the door for writing multitouch interfaces in Processing, which however means a lot more work. For now it seems a good way to go with writing control GUI in SuperCollider, but eventually, the Processing possibility seems like very interesting and inviting.

So a final complete working example for my machine is this:

multitouch with dual head/monitor Xorg

Having a multi-touch monitor (DELL P2314T) together with another non-multi-touch output confuses (in my case) the pointer maping – in other words, the pointer (mouse) is not where you touch the screen.

1) Make sure the touch screen is the leftmost monitor. Seems like offset-ing the pointer with xinput does not work (and something is buggy here), but scaling does. Actually that is not entirely true: offseting works with xinput, but in the case of multi-touch screen not being left-most the pointer is thrown to the rightmost pixel on X-axis the moment it’s supposed to appear on the multi-touch screen (this is true only for MT input, not for the actual mouse). If the touch-screen the leftmost, there’s no need to do offset, just proper scaling.

2) use xinput’s “Coordinate Transformation Matrix” to ‘remap’ it correctly:


and here’s a simple /etc/X11/xorg.conf: