[PATCH libinput] touchpad: make the hysteresis dependent on physical distance

[Bill Spitzak]

Can you set the "fake" resolution so that you get the same answer 
without having to check if it is fake?

It looks like setting tp->device->abs.absinfo_x/y->resolution to 
diagonal * 2 / DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR would avoid the if 
statement, and I would probably make everything that uses this 
resolution value "work" (in that they all scale the same).

>> On 12-06-15 08:09, Peter Hutterer wrote:
>>
>>> Some touchpads, e.g. the Cyapa in the Acer c720 have a small axis range
>>> ([0, 870], [0, 470]), so the diagonal/magic value yields a hysteresis
>>> margin
>>> of 1 device unit. On that device, that's one-tenth of a millimeter,
>>> causing
>>> pointer motion just by holding the finger.
>>>
>>> For touchpads that provide a physical resolution, set the hysteresis axes
>>> to
>>> 0.5mm and do away with the magic factor.
>>>
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1230441
>>>
>>> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
>>>
>>
>> Yes I think this is a good idea:
>>
>> Reviewed-by: Hans de Goede <hdegoede at redhat.com>
>>
>> Can you also ask the reporter of:
>>
>> https://bugs.freedesktop.org/show_bug.cgi?id=90590
>>
>> To test libinput/master once you've pushed this? It will likely
>> help with his problem too.
>>
>> Regards,
>>
>> Hans
>>
>>
>>
>>   ---
>>>    src/evdev-mt-touchpad.c | 16 ++++++++++++----
>>>    1 file changed, 12 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
>>> index 8c28ff7..e9870ad 100644
>>> --- a/src/evdev-mt-touchpad.c
>>> +++ b/src/evdev-mt-touchpad.c
>>> @@ -1495,10 +1495,18 @@ tp_init(struct tp_dispatch *tp,
>>>                                                         EV_ABS,
>>>                                                         ABS_MT_DISTANCE);
>>>
>>> -       tp->hysteresis_margin.x =
>>> -               diagonal / DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR;
>>> -       tp->hysteresis_margin.y =
>>> -               diagonal / DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR;
>>> +       if (device->abs.fake_resolution) {
>>> +               tp->hysteresis_margin.x =
>>> +                       diagonal / DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR;
>>> +               tp->hysteresis_margin.y =
>>> +                       diagonal / DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR;
>>> +       } else {
>>> +               int res_x = tp->device->abs.absinfo_x->resolution,
>>> +                   res_y = tp->device->abs.absinfo_y->resolution;
>>> +
>>> +               tp->hysteresis_margin.x = res_x/2;
>>> +               tp->hysteresis_margin.y = res_y/2;
>>> +       }
>>>
>>>          if (tp_init_accel(tp, diagonal) != 0)
>>>                  return -1;
>>>
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