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

[Daniel Stone]

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.

Cheers,
Daniel