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

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@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 67828bd..b58a6ca 100644 (file)
--- 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 (file)
--- 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 */