evdev: workaround for missing ABS_X/Y on multitouch devices (mostly Android)

[Colin Macdonald]

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On 25/06/14 02:39, Peter Hutterer wrote:
> it's doable, and with libevdev fairly simple nowadays, we'd only
> have to call libevdev_set_abs_info() and be done with it. Send a
> patch and I'll merge this.

First attempt at a patch attached.  Works for me on an Android
device but haven't yet tested on a normal bit of hardware.

I used libevdev_enable_event_code() to create ABS_X with a copy
libevdev_get_abs_info() from ABS_MT_POSITION_X (etc, following the
mt_axis_mapping table in the code).

Older applications (XFCE window manager for one) don't get drags but
perhaps this is b/c they expect actual ABS_X,Y events.

I also get some pretty ominous warnings, but I'm not sure if they
are related or not!

libevdev error in sanitize_event: BUG: Device "sec_touchscreen"
received a double tracking ID 21 in slot 1.
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 1
(EE) [dix] touchscreen: unable to find touch point 1
(EE) [dix] touchscreen: unable to find touch point 1
(EE) [dix] touchscreen: unable to find touch point 1
(EE) [dix] touchscreen: unable to find touch point 1
(EE) [dix] touchscreen: unable to find touch point 1
libevdev error in sanitize_event: BUG: Device "sec_touchscreen"
received a double tracking ID 22 in slot 0.
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 0
(EE) [dix] touchscreen: unable to find touch point 0
libevdev error in sanitize_event: BUG: Device "sec_touchscreen"
received a double tracking ID 24 in slot 3.
(EE) [dix] touchscreen: unable to find touch point 3
(EE) [dix] touchscreen: unable to find touch point 3
(EE) [dix] touchscreen: unable to find touch point 3
(EE) [dix] touchscreen: unable to find touch point 3
[dix] EventToCore: Not implemented yet
[dix] EventToCore: Not implemented yet

In case you prefer not to apply this as is, I'm working in "noabsx"
branch on https://github.com/cbm755/xf86-input-evdev/

Colin
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