Touchpad stylus mode

[Zephaniah E. Hull]

On Sat, Mar 17, 2007 at 11:16:36PM -0400, Albert Cahalan wrote:
> On 3/17/07, Zephaniah E. Hull <warp at aehallh.com> wrote:
> >On Sat, Mar 17, 2007 at 09:08:30PM -0400, Albert Cahalan wrote:
> >> Bert Freudenberg and Jim Gettys had the right idea on March 7th.
> >> It goes something like this:
> >>
> >> a. Mode switches do not move the pointer.
> >
> >Mode switches themselves do not move the pointer, however the only way
> >to trigger a GS to PT switch is to put a stylus on the unit, immediately
> >after switching to PT mode we get coordinate data for the stylus, which
> >does cause the pointer to move.
> 
> So, from the user's view, mode switches DO move the pointer.
> That is generally defective as a user interface.

It is also the nature of a absolute device in X for there to be a 1:1
mapping between a point on the touchpad, and a point on the screen.

> BTW, I'd rather you didn't use "GS" and "PT", especially without
> explaining them. I can deal with resistive/capacitive I think, if
> I'm right that the middle thing is capacitive.

Sorry about that, I can't keep resistive/capacitive straight in my head,
and all the documentation from ALPS refers to it as the GS and the PT,
GS being the Glide Sensor (for use with a finger), and PT being the Pen
Tablet (for use with a stylus).
> 
> The stylus device is not shaped properly to cover the whole screen.
> Distortion would be very bad. Cropping it would work OK, but would
> waste 2/3 of the device. Unless you have some fantastic new idea,
> the stylus device's screen mapping needs to be able to move.

Agreed, however as previously mentioned in this thread, this requires
XInput protocol changes which are still in the X.org git tree.  Along
with xf86-input-evdev changes.
> 
> Mode switches can be disorienting and surprising. There are a
> number of things that can be done to deal with that:
> 
> Upon mode switch to stylus mode, one might draw an outline of
> the stylus device on the screen.

An outline of the stylus drawing area would be useful, however that is
the wrong point to draw it, IMHO.
> 
> Preventing sudden pointer movement on mode switch is critical.
> To the raw stylus data, subtract the initial (post-mode-switch)
> stylus data and add the pre-mode-switch screen location.

That roughly describes how we use the GS as a relative device, it is
useful for moving the cursor around for use on menus, however the PT
sensor is there for use with drawing, that _absolutely_ requires that
there be jumps when you lift the stylus and move it to another point on
the touchpad.

Please keep in mind, the GS sensor is not usable at all while in PT
mode, and the only indication that we have that we may wish to go back
to GS mode is the device indicating that there is no longer a stylus
touching the touchpad.  Thus, every lift and move to another position is
going to involve a mode switch to GS, then a mode switch to PT.

Thus, according to everything I know about how absolute devices are
used, you very strongly want a jump when you put the stylus down on the
unit, it's pretty much the definition of what an absolute device is.


Now, what I would suggest is either a button on the keyboard, or
something accessable through the frame, to bring up an outline of the PT
area, and cause the GS input to move that outline around.  The support
for this is not all there, however I really do believe that this is
going to be the optimal route if we do not wish to stretch the PT over
the whole screen.

The protocol support for moving the area around is in the X.org git
tree, however at the moment nothing ties into it.

Zephaniah E. Hull.

-- 
	  1024D/E65A7801 Zephaniah E. Hull <warp at aehallh.com>
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I've always taken the position that if you can't find anything bad  to
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it. I also agree with you about the advocacy. AHS. ASS.
  -- Shmuel (Seymour J.) Metz in the Scary Devil Monastery.
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