Enabling multitouch in input-evdev

Bradley T. Hughes bradley.hughes at nokia.com
Thu Jan 14 02:23:23 PST 2010

On 01/12/2010 12:03 PM, ext Peter Hutterer wrote:
>> So, first question: is my behavior the good one? (not being
>> compliant with Windows or MacOS)
> Short answer - no. Long answer - sort-of.
> Multitouch in X is currently limited by the lack of multitouch events in the
> protocol. What you put into evdev is a way around it to get multitouch-like
> features through a multipointer system. As Bradley said, it is likely better
> for the client-side to include the lot in a single event.  Since X
> essentially exists to make GUI applications easier (this may come as a
> surprise to many), I'd go with his stance.
> However, this is the harder bit and would require changing the driver, parts
> of the X servers's input system, the protocol and the libraries. It'd be
> about as wide-reaching as MPX though I hope that there is significantly less
> rework needed in the input subsystem now.

Why do you think it would require protocol changes? For the new event type? 
If I understand it correctly, events for devices can contain any number of 
valuators... is it possible to have x1,y1 x2,y2 x3,y3 and so-on?

 From what I can tell, there are a number of challenges that would require 
driver and server changes. In particular, being able to do collaborative 
work on a large multi-touch surface requires the driver (or server, not sure 
which makes most sense) to be able to somehow split the touch points between 
multiple windows. This is something that we had to do in Qt at least.

Bradley T. Hughes (Nokia-D-Qt/Oslo), bradley.hughes at nokia.com
Sandakervn. 116, P.O. Box 4332 Nydalen, 0402 Oslo, Norway

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