Re: Mixed "pen" and multitouch input devices

[Chase Douglas <chasedouglas@gmail.com>]

On 03/18/2012 11:39 PM, Henrik Rydberg wrote:
>> The proper way to send events through evdev when there are two different
>> "tools" (pen and touch) is to use BTN_TOOL_*. In your example above, it
>> would be:
>>
>> # finger touch (Note lack of tool, it's assumed to be finger)
>>     ABS_MT_SLOT 0
>>     ABS_MT_TRACKING_ID 42
>>     ABS_MT_POSITION_X finger_x
>>     ABS_MT_POSITION_Y finger_y
>>     SYN_MT_REPORT
>>     ABS_X finger_x
>>     ABS_Y finger_y
>>     SYN_REPORT
>> # finger release
>>     ABS_MT_SLOT 0
>>     ABS_MT_TRACKING_ID -1
>>     SYN_REPORT
>> # pen motion
>>     BTN_TOOL_PEN 1
>>     ABS_X pen_x
>>     ABS_Y pen_y
>>     SYN_REPORT
>> # finger touch begin
>>     ABS_MT_SLOT 0
>>     ABS_MT_TRACKING_ID 42
>>     ABS_MT_POSITION_X finger_x
>>     ABS_MT_POSITION_Y finger_y
>>     SYN_MT_REPORT
>>     BTN_TOOL_PEN 0
>>     ABS_X finger_x
>>     ABS_Y finger_y
>>     SYN_REPORT
>> etc.
>>
>> Then, xf86-input-evdev ignores ABS_{X,Y} events when there is no
>> BTN_TOOL_* active.
> 
> On the subject how pen and touch could work going forward, the MT
> protocol is prepared to deal with tool type per slot. It makes a lot
> of sense to move away from the above example, towards a fully parallel
> representation of pen and touch data. Today's multitouch interfaces
> are really tremendously restrictive; I am looking forward to the day
> when one does not need to worry about touching or resting on a surface
> in order to operate it.
> 
> In short, why not make xf86-input-evdev aware of MT_TOOL_TYPE?

There's no reason it can't be made aware. The question is whether you
want to create separate X input devices, or annotate events with the
tool type. No one has really bothered looking into it outside of wacom
devices, but my understanding is that wacom is a big special cased
situation due to historical reasons anyway.

If we merely annotate events by setting valuator values, that's a
trivial change that may even be already supported out of the box.
Splitting the evdev device into multiple X input devices is also
possible, since xf86-input-wacom does it, but would require a large
refactoring of xf86-input-evdev.

-- Chase