Touchscreen requirements

[imm]

>> I'd rather keep tracking the first touches and ignore additional  
>> ones. Then accidental touches wouldn't interrupt the current  
>> interaction.
>
> Interesting point.

On an experimental multi-touch "kiosk" we were working on (and which  
came to nothing in the end), we found that it was pretty easy to run  
out of "touches" (we could only reliably detect 3 or 4 at the time)  
and that the users were less confused if we kept the "established"  
touches and ignored the new ones.

But... That was for our main app. We also had a few toy applications  
to play with this new h/w, one of which was a sort of music keyboard  
thing. Using that, it turned out that it was better to handle the new  
touches and discard the old ones when we ran out, as the users  
expected to hear a new sound when they added a new touch and didn't  
seem to be too phased by a previous sound disappearing.

So, in summary, erm, it depends...

For a "conventional" UI application (if such a thing exists on a  
multi-touch tablet), I think keeping the established touches is better.

But if you are doing some sort of dynamic, interactive UI, then maybe  
discarding the oldest first is what the users would expect.

Just some experiences to consider.

I don't know the answer.