Re: [PATCH RESEND] USB HID: Add ID for eGalax Multitouch used in JooJoo tablet

[Chase Douglas <chase.douglas@canonical.com>]

On Tue, 2010-08-17 at 09:49 +0200, Stéphane Chatty wrote:
> Le 16 août 10 à 17:30, Henrik Rydberg a écrit :
> 
>   - the single touch emulation is highly device dependent. I was (and  
> still am) pretty proud of my choice of tracking the 'oldest' finger  
> on the panel: this turns multitouch panels into single touch panels  
> that are impervious to parasite touches. But the drawback is that  
> currently there is no generic method for this tracking: I used  
> whatever device-specific information I could use (order of fingers in  
> a message, tracking id, etc).

Stéphan,

Can you explain in more detail why you chose an 'oldest' finger approach
for single touch emulation? I wonder if it's the best mechanism. Take
the following example:

1. User touches with one finger and intends to drag an object on screen
2. User touches another finger down, either accidentally or
intentionally, while dragging the first finger
3. User releases first finger to end the drag
4. Object suddenly is dragged under the second finger

As I'm implementing support for the Magic Trackpad right now, I'm having
to figure out the best way to do single-touch emulation. What I'm
currently doing is converting the first finger touched for single-touch
emulation, and when that finger is released no single-touch emulation
can occur until all fingers have left the screen again.

This should hopefully become a moot point once everyone understands MT
input, but sadly we have to deal with the reality of X not being MT
aware quite yet :).

Thanks,

-- Chase

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