how to design a tablet driver?

Kevin Oberman oberman at
Thu Mar 6 10:52:22 PST 2008

> From: "Daniel O'Connor" <doconnor at>
> Date: Thu, 6 Mar 2008 19:09:50 +1030
> Sender: owner-freebsd-current at
> On Thu, 6 Mar 2008, Chuck Robey wrote:
> > My current project is making a usb driver for my "Superpen" WP8060
> > Tablet. It's a cheaper version of the better known Wacom Tablet,
> > which i couldn't afford for my use in Gimp.  I figure, I better ask
> > myu questions here, because they don't really bear so much on usb as
> > they bear upon the basic architecture of a mouselike drvice that must
> > be absolute, not relative, in approach.
> I would say that you should report the physical size of the tablet, and 
> then report movement in terms of real physical units. You could do all 
> this in fixed point 32 bit ints and then have an enum which says what 
> units it's reporting in (tenths of a millimetre, or whatever).
> After that it's up to the client to do the right thing. Passing screen 
> size to the display drive seems like a gross hack liable to much 
> breakage.
> All this said I suspect that this problem has already been solved by 
> other tablet drivers so I'd look there. Not to mention that there 
> should already be a protocol for tablets that goes between the kernel 
> and X (or from an X driver that opens ugen and speaks to the rest of X)
> > OK, that means that I have to know the graphic point size (is there a
> > Well, if it does, then it also means that I need to find the
> > absoluite point size of whatever screen you're playing with, no
> > matter if I'm talking about an X11 screen or a screen from a vty.  I
> > mean, vty's use mice now, isn't it possible for use a tablet on a
> > vtyt also?  OR, extra possibility, maybe if we're in a non-X11
> > environment, fall back to a relative use, and only go to absolute
> > when you go to X11.  If I have too much trouble getting and keeping
> > an idea of the screen size oout of X11, I could do that.
> Personally, I'd forget about vty's unless you want to do mouse emulation 
> stuff there.. I imagine it would be a pretty major rearchitecting of 
> sysmouse, moused etc etc.. Too hard to for too little reward :)
> > I'm suggesting this because I'm very, very confused as to how I would
> > figure out what the screen size is for a vty.  If I gotta do a
> > absolute gig on a bty, then I gotta find some way to ask the size of
> > the cry, and get me driver in the list of those to be notified if the
> > size of a vty changes.
> As above - basically "don't bother".
> > Please, if you have any comment, feel free to interrupt all over me,
> > sir! The sooner I get some of this, the sooner that really cheap
> > (~$60) 8"X6" tablet is ours, especially for Gimp.
> Wow, pretty nice :)
> I might see if I can grab one..

$49.99 at ThinkGeek. or

They are both ThinkGeek, but you might already be set up to order
through Amazon. I' prefer ordering through ThinkGeek, since I see no
reason for Amazon to get a cut. (If you own Amazon stock, your opinion
may differ.)
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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