[PATCH] Touch: Fix duplicate TouchBegin selection with virtual devices

[Peter Hutterer]

On Sun, Oct 07, 2012 at 12:07:01PM +1100, Daniel Stone wrote:
> Hi,
> 
> On 7 October 2012 01:58, Chase Douglas <chase.douglas at ubuntu.com> wrote:
> > Sorry for the delay, I've been trying to think about this to come up
> > with a cogent argument.
> >
> > I don't like the idea of overlapping selections being allowed. There
> > are two ways to handle an overlapping selection:
> >
> > * Only deliver to one of the selections. Which do you pick? Will the
> > unpicked client be annoyed (i.e. will the developer be confounded when
> > his application fails to receive touch events, and is this a problem)?
> >
> > * Deliver to both selections. This could cause multiple responses to a
> > single physical action, which I have always found troubling.
> >
> > I don't think either is a great approach. I would prefer to lock it
> > down so there cannot be any overlap. Are there use cases that require
> > the ability for overlapping selections that I may not be aware of?
> 
> At the time, I remember making the argument that we should allow
> overlapping selections, but only for the generic
> XIAllDevices/XIAllMasterDevices.  The reasoning was basically that
> toolkits etc want to select on those to avoid having to track device
> addition/removal (with all the inherent race conditions), and if
> someone else selects on just one device, that would break the whole
> thing.  I don't particularly mind either way tho.

correct, that is the reason why XI2 treates the virtual devices separately
and I think we need to do the same for touch devices too.

Cheers,
   Peter