[PATCH libinput 2/3] Implement support for pen barrel rotation

[Bill Spitzak]

You are right that the fact that it is along the pen is not obvious from 
"Z". However this is actually true of "X" and "Y" (one of them could be 
the angle in the plane defined by the other tilt).

Roll probably is good, but it still seems to me that Z is more common, 
also it looks like the evdev library is using "Z" from your code.

On 12/08/2014 03:24 PM, Peter Hutterer wrote:
> On Mon, Dec 08, 2014 at 12:13:17PM -0800, Bill Spitzak wrote:
>> Why not call it Z instead of TWIST?
>>
>> I'm pretty certain that is a common term for this movement, and that "twist"
>> is a rather strange term ("roll" is used more). And Z has the advantage that
>> it also implies that counter-clockwise is positive.
>
> my main issue with Z is that it's not immediately clear what it refers to in
> the context of a tablet. x/y is relative to the tablet itself, not the
> stylus, so Z could be interpreted to be the same. twist isn't though, it
> relates to the stylus rotation regardless of tilt.
>
> Having said, I do like the term roll, better than twist.
>
> Cheers,
>     Peter
>
>>
>> On 12/08/2014 09:59 AM, Jason Gerecke wrote:
>>
>>> --- a/src/libinput.h
>>> +++ b/src/libinput.h
>>> @@ -277,7 +277,8 @@ enum libinput_tablet_axis {
>>>   	LIBINPUT_TABLET_AXIS_PRESSURE = 3,
>>>   	LIBINPUT_TABLET_AXIS_TILT_X = 4,
>>>   	LIBINPUT_TABLET_AXIS_TILT_Y = 5,
>>> -	LIBINPUT_TABLET_AXIS_CNT = LIBINPUT_TABLET_AXIS_TILT_Y + 1
>>> +	LIBINPUT_TABLET_AXIS_TWIST = 6,
>>> +	LIBINPUT_TABLET_AXIS_CNT = LIBINPUT_TABLET_AXIS_TWIST + 1
>>>   };
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