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

From: "Stéphane Chatty" <chatty@enac.fr>
To: Chase Douglas <chase.douglas@canonical.com>
Cc: Henrik Rydberg <rydberg@bitmath.org>,
	linux-input <linux-input@vger.kernel.org>
Subject: Re: [PATCH RESEND] USB HID: Add ID for eGalax Multitouch used in  JooJoo tablet
Date: Tue, 17 Aug 2010 13:34:00 +0200	[thread overview]
Message-ID: <FDB1F269-49AF-4985-BD0F-869D23833D2B@enac.fr> (raw)
In-Reply-To: <1282042502.13264.21.camel@mini>

Le 17 août 10 à 12:55, Chase Douglas a écrit :

> 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.

Yes, the debate is what to do when the 'actual oldest' finger is  
released: should the 'second oldest' take its place or should this be  
a release or should somthing else occur.

Some arguments in favour of the first option:
- My experience is that 'accidental' touches are transient.  
Therefore, the conjunction of having an accidental touch and a  
release is not very frequent.
  - At the opposite, on very large screens, it may sometimes be  
comfortable to "replace one finger with another", thus 'moving' the  
dragged object from one hand to the other.

More or less, the debate is about statistics and user experience  
design...

Cheers,

St.

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