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

[Ping Cheng]

On Sun, Nov 7, 2010 at 8:30 AM, Daniel Stone <daniel at fooishbar.org> wrote:
>> The existing solution for single touch events is to arbitrate touch
>> when pen is in prox. This is based on the assumption that we do not
>> want to have two cursors competing on the screen.
>
> What do you mean by 'arbitrate' here? I guess you're talking about which
> events should send ABS_[XY]?

It means ignoring touch data when pen is in prox.

>> 1.     Arbitrate all touch data in the kernel.
>>
>> This is the simplest solution for device driver developers. But I do
>> not feel it is end user and userland client friendly.
>>
>> [...]
>>
>> 3.    Report first finger touch as ABS_X/Y events when pen is not in prox;
>>        Report pen data as ABS_X/Y events when there is no finger touch;
>>        Report touch data as MT_TOOL_TOUCH and pen data as MT_TOOL_PEN
>> events when both pen and touch data are received. No ABS_X/Y are
>> reported when pen and tocuh or multi-touch data are received.
>>
>> I feel this one makes sense to userland since pen can be considered as
>> another touch.
>
> I'd say that either #1 or #3 is the best idea here, simply because they
> seem to be the most straightforward, and thus easier to support.

There are two major difference between #

> Assuming that xf86-input-wacom will track the state itself and decide
> (using whatever criteria) which events should send core x/y motion, then
> all you need to do with ABS_[XY] is just make a best effort to have it
> more or less work for dumb userspace clients.