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

On Thu, Mar 24, 2011 at 2:45 PM, Chase Douglas
[off-list ref] wrote:

On 03/24/2011 02:44 PM, Chris Bagwell wrote:

quoted

Looking good.  Minor comments at end.

On Thu, Mar 24, 2011 at 12:44 PM, Chase Douglas
[off-list ref] wrote:

quoted

+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.

quoted

quoted

+
+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

quoted

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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