OLPC: pen tablet

Zephaniah E. Hull warp at aehallh.com
Wed May 16 13:54:04 EDT 2007

It looks like the Wiki is going to need some updating, however.

The Pen Tablet portion of the touchpad appears to X as an extended input
device which can be in absolute or relative mode, and which reports
core events.

The absolute/relative mode switch simply controls if the driver
translates absolute coordinate input to relative output, and is an
XInput control.

Coordinate data from the device can be read either simply by watching
the core pointer (perhaps not ideal for this case), or by opening the
device with XInput (with XGrabDevice and friends).

The latter case may be what you're looking for there, that gives you the
PT input, but leaves the user free to move the core pointer around to
hit buttons and such.

Let me know if you need more information, or more detailed information,
or if this doesn't work.

Zephaniah E. Hull.

On Wed, May 16, 2007 at 04:46:07PM +0200, Andre Schmeisser wrote:
> Hi,
> I have a question regarding the OLPC and someone on #olpc told me you
> were probably the right one to ask.
> I want to do some stroke recognition on the pen tablet, but first I have
> to somehow read input from it.
> I'd be glad if you could provide me with any info/references/hints on
> how to do that.
> From #olpc:
> (10:37:32) topspin84: Hi there, can anyone help me?
> (10:37:50) topspin84: I need to know how to read input from the
> tablet/touchpad. The wiki page
> (http://wiki.laptop.org/go/Getting_started_programming#Touchpad) doesn't
> have any info on this.
> (10:38:23) Mitch_Bradley: the touchpad part just looks like a mouse
> (10:40:05) topspin84: Ok, how would you know the difference between the
> two parts then, if that's possible?
> (10:41:51) topspin84: Say you want to read some stylus input, but don't
> want to interpret the mouse moving up to the close button.
> (10:42:20) Mitch_Bradley: At the hardware level, when you press down
> with a stylus, the device sends a code that says that tablet data is
> available.  The driver then tells the device to switch to tablet mode.
> (10:43:03) Mitch_Bradley: When no tablet data has arrived for a period
> of time, something like half a second, the driver tells the device to
> resume touchpad mode.
> (10:43:30) Mitch_Bradley: How those events get reported up through the
> various layers of the input system is beyond me.
> (10:44:43) topspin84: I need to access that in Python and/or C, any
> hints where to start looking for?
> (10:45:24) Mitch_Bradley: sorry, I just don't know.  Mercury is the
> person who knows.
> (10:45:50) topspin84: OK, thanks.
> (11:08:34) Mitch_Bradley: you could email him  "Zephaniah E. Hull"
> <Warp at debian.org>

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