[PATCH] touchpad: reset motion history when nfingers changes on semi-mt pads

Mon Jul 21 16:34:59 PDT 2014

On Mon, Jul 21, 2014 at 03:25:47PM +0200, Hans de Goede wrote:
> On semi-mt touchpads the reported position of the first finger down may
> jump when the pad switches from st to mt mode. When this happens a large
> delta gets seen on the first finger at the same time the second fingers
> is first seen down, causing a spurious 2 finger scroll event.
>> Reset the motion history when nfingers changes on semi-mt pads to avoid this.
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>

I don't seem to have any good recordings here that show the SEMI_MT jumps.
Any chance you can get one and add a test device for this?
ACK to the patch, but this is really something I'd like to see a specific
test case for so we know what we're fixing here. plus, adding a semi-mt
device to the test suite means we can figure out if everything else works
fine with it.
Cheers,
 Peter
> ---
> src/evdev-mt-touchpad.c | 8 ++++++++
> src/evdev-mt-touchpad.h | 2 ++
> 2 files changed, 10 insertions(+)
>> diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
> index b0520c7..315c531 100644
> --- a/src/evdev-mt-touchpad.c
> +++ b/src/evdev-mt-touchpad.c
> @@ -406,6 +406,11 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
>> 	for (i = 0; i < tp->ntouches; i++) {
> 		t = tp_get_touch(tp, i);
> +
> +		/* semi-mt finger postions may "jump" when nfingers changes */
> +		if (tp->semi_mt && tp->nfingers_down != tp->old_nfingers_down)
> +			tp_motion_history_reset(t);
> +
> 		if (i >= tp->real_touches && t->state != TOUCH_NONE) {
> 			t->x = first->x;
> 			t->y = first->y;
> @@ -454,6 +459,7 @@ tp_post_process_state(struct tp_dispatch *tp, uint64_t time)
> 		t->dirty = false;
> 	}
>> +	tp->old_nfingers_down = tp->nfingers_down;
> 	tp->buttons.old_state = tp->buttons.state;
>> 	tp->queued = TOUCHPAD_EVENT_NONE;
> @@ -668,6 +674,8 @@ tp_init_slots(struct tp_dispatch *tp,
> 		tp->has_mt = false;
> 	}
>> +	tp->semi_mt = libevdev_has_property(device->evdev, INPUT_PROP_SEMI_MT);
> +
> 	ARRAY_FOR_EACH(max_touches, m) {
> 		if (libevdev_has_event_code(device->evdev,
> 					 EV_KEY,
> diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
> index af6a3a3..83edf4f 100644
> --- a/src/evdev-mt-touchpad.h
> +++ b/src/evdev-mt-touchpad.h
> @@ -152,8 +152,10 @@ struct tp_dispatch {
> 	struct evdev_dispatch base;
> 	struct evdev_device *device;
> 	unsigned int nfingers_down;		/* number of fingers down */
> +	unsigned int old_nfingers_down;		/* previous no fingers down */
> 	unsigned int slot;			/* current slot */
> 	bool has_mt;
> +	bool semi_mt;
>> 	unsigned int real_touches;		/* number of slots */
> 	unsigned int ntouches;			/* no slots inc. fakes */
> -- 
> 2.0.1
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