Re: [PATCH v3] Documentation: Add evdev type and code definitions

[Chris Bagwell]

On Thu, Mar 24, 2011 at 2:45 PM, Chase Douglas
<chase.douglas@xxxxxxxxxxxxx> wrote:
> On 03/24/2011 02:44 PM, Chris Bagwell wrote:
>> Looking good.  Minor comments at end.
>>
>> On Thu, Mar 24, 2011 at 12:44 PM, Chase Douglas
>> <chase.douglas@xxxxxxxxxxxxx> wrote:
>>> +Touchscreens:
>>> +----------
>>> +ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
>>> +used to report when a touch is active on the screen.
>>> +BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported. BTN_TOOL_<name> events
>>> +should be reported where possible.
>>
>> Does the real button event restriction solve something?  I know
>> majority of touchscreens are not sending a button today but usually
>> there is a button on the touchscreen frame that I'd image at least
>> some devices hooking it up to touchscreen interface.
>>
>> stylus+touchscreen combo devices are surely going to want to do this.
>
> Perhaps this should be more clearly for touchscreen-only devices (not
> tablets or a mix). The problem we end up seeing is drivers who use
> BTN_LEFT because they want a touch to generate a primary button press in
> X. I want to prevent people from doing this.

Oh, yes.  We do not want that for sure.  I thought you were talking
about "real" buttons and not something from a touch.  I would have
gotten it on first read if it said "BTN_* must not be reported as a
result of active touch."

>
> I believe mixed devices are hard to detect between tablets and
> stylus+touchscreen right now, as evidenced by the X evdev driver not
> handling the former by default while wacom is often used for the latter.
> However, with the device properties a userspace driver should be able to
> tell the two apart.
>
> I'll rename this guideline: Touchscreens without stylus tools. Any issues?

I think either original name or new name is fine.  The above intent
doesn't change even on combo devices.

>
>>> +
>>> +Trackpads:
>>> +----------
>>> +Legacy trackpads that only provide relative position information must report
>>> +events like mice described above.
>>> +
>>> +Trackpads that provide absolute touch position must report ABS_{X,Y} for the
>>> +location of the touch. BTN_TOUCH should be used to report when a touch is active
>>> +on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
>>> +be used to report the number of touches active on the trackpad.
>>
>> How about a Tablet?
>>
>> Something like:
>>
>> Tablets:
>> --------
>>
>> BTN_TOOL_<name> events must be reported when a stylus or other tool is
>> active on tablet.  ABS_{X,Y} must be reported with the location of the
>> tool. BTN_TOUCH should be used to report when the tool is in contact
>> with the tablet. BTN_{STYLUS,STLUS2} should be used to report buttons
>> on tool itself and BTN_{LEFT,MIDDLE,RIGHT,1,2,etc} should be used to
>> report buttons on tablet.
>
> Thanks for the addition! I'll add it in and add you on a SOB line if
> that's alright with you.

Sure thing.

Chris

>
>> Some tablets send ABS_PRESSURE with no BTN_TOUCH (why I said should
>> instead of must).  Probably this is not worth mentioning here?
>
> Yeah, I'd leave that off as I think we want to set the guidelines to use
> BTN_TOUCH.
>
> Thanks,
>
> -- Chase
>
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