multitouch + audio feedback linux dev -> XO-2?

Nate Ridderman nate.ridderman at
Mon Jan 26 20:40:33 EST 2009

On Mon, Jan 26, 2009 at 7:22 PM, Nirav Patel <olpc at> wrote:

> 1) Are there any existing hooks/systems for Linux for multi-touch?
>> That's the only proper way you can get a virtual keyboard to work for
>> a double-touchscreen clamshell device (the feasibility of which is not
>> sold to me because of the power consumption of running a 2nd screen vs
>> a keyboard, and mostly mostly mostly the lack of haptic feedback from
>> a virtual keyboard).
> Peter Hutterer has been working on Multi-Pointer X for several years.
> It is getting pretty usable, judging by the Youtube videos.

Jim Gettys put together a synopsis of multi-touch input for XO-2 in
September -

2) Audio feedback
>> A big problem with touch-screen/virtual keyboards is lack of haptic
>> feedback (and haptic feedback would probably eat batteries a lot). A
>> standardized/universal audio mapping to keyboard keys similar to
>> QWERTY, Dvorak or Braille would help solve this.
I have some insight into this topic from experience in the cell phone
industry. There are several ways to do haptic responses: linear vibrators,
piezo-electric elements, speakers. Localized haptics are best (the vibration
comes from the area on the screen that has been touched), but that's still
an emerging technology. The challenge with your idea is latency. For
applications like typing, the haptic response must happen very quickly to
trick the brain into thinking it is related to the press. I think I've heard
the number 25 ms before, but don't quote me on that. A quick google search
couldn't confirm or deny this. I did find an interesting paper ( that stated
100-200 ms was the limit, but I don't think the results apply to typing. The
game in their experiment took a second to complete, which is way longer than
a keystroke takes. If you don't care about typing repeatedly, the latency is
less important. But for typing quickly with a  limit of 25 ms, it will be
hard to interrupt the processor, load a sound file, and play it in time. A
dedicated microprocessor might be up to the task though.

Also, I'm not sure if a speaker would draw significantly less power than a
piezo or linear vibrator. I don't remember hard numbers for either use case.

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