[RFC] Multi-Touch (MT) support - arbitration or not

[Ping Cheng]

On Sat, Nov 6, 2010 at 8:53 AM, Michal Suchanek <hramrach at centrum.cz> wrote:
>
> As a tablet user, not X developer I don't think it is desirable and
> expected to register pen touch and finger touch together as a
> multitouch. That is, if I wanted to trigger a multitouch feature I
> would use fingers, not pen and finger. While it would be technically
> possible to use the pen touch and finger touch together to trigger
> multitouch I don't think it makes much sense.
>
> Also it is a good idea to turn off (single) touch when pen is in
> proximity because it is quite easy to accidentally touch the surface
> while moving the pen.
>
> This means that the protocol that sends abs events from pen when in
> proximity and from finger otherwise would work well.
>
> However, there is one feature that makes sort of sense and does not
> work when touch is completely off. It might be possible to use touch
> for button and pen for moving the cursor. I tried to use the pad
> button on my Bamboo together with pen motion for right drags and it
> seems somewhat easier than using the pen button.

Thank you for sharing your thoughts. This is the kind of "third party"
feedback that I wished for. So, you do see the value of reporting and
using both MT and pen data simultaneously.

> So I would say that protocol that allows events from both pen and
> touch at the same time is desirable in the long run but with some
> options to filter the events when both pen and touch are used
> together.
>
> This gives basically three options
>
> 1) leave as is, turn off touch when pen is in proximity
>
> 2) report everything by kernel, put some filter on the touch events in
> the  X driver (which defaults to killing most touch stuff when pen is
> in proximity)
>
> 3) the same as above but put the filter in the kernel driver
>
>
> 2 or 3 is more flexible as people with some special uses can just turn
> off the filter and get all events.

Then, which option, 2 or 3, do you prefer? To share where I am with
you: I am 60% with option 2 and 40% with 3 (I was 100% with 3 before)

> WRT X ease of development I would suggest that the same device should
> never report different events based on pen proximity. Either the
> device is in some "compatibility mode" and reports only one pointer as
> per 1 or there are two separate pointers and they are just reported
> out of proximity when the pointer positioning is not desirable (ie
> when pen is out or when touch is off due to pen being in).
>
> If somebody wants to have multitouch combining two different pointers
> there is nothing stopping them, either with P&T pen and touch pointers
> or completely unrelated devices.

We'll take care of this step once we know how to report the data.

Ping