[PATCH libinput 4/4] touchpad: reset the motion history on significant negative pressure changes

[Peter Hutterer]

Resetting the motion history has the side-effect of swallowing movements, we
don't calculate deltas until we have 4 motion events. During a finger release,
we're likely to get a large pressure change between two events, resetting the
motion history prevents the cursor from jumping on release.

The value of 7 found by trial-and-error, tested on the T440 and T450 hardware.
The absolute value is highly variable but recordings show that the pressure
changes only by 1 or 2 units during normal interaction. Higher pressure
changes are during finger position changes but since those should not cause a
jump anyway, we tend to win there too.

Currently only enabled for negative pressure changes, let's see how we go with
that.

https://bugs.freedesktop.org/show_bug.cgi?id=94379

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
 src/evdev-mt-touchpad.c |  4 ++++
 src/evdev-mt-touchpad.h |  1 +
 test/litest.c           | 38 +++++++++++++++++++++++++++-----------
 test/litest.h           |  7 +++++++
 test/touchpad.c         |  2 +-
 5 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index e16aecb..0640974 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -335,6 +335,7 @@ tp_process_absolute(struct tp_dispatch *tp,
 			tp_end_sequence(tp, t, time);
 		break;
 	case ABS_MT_PRESSURE:
+		t->pressure_delta = e->value - t->pressure;
 		t->pressure = e->value;
 		t->dirty = true;
 		tp->queued |= TOUCHPAD_EVENT_OTHERAXIS;
@@ -946,6 +947,9 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
 		if (!t->dirty)
 			continue;
 
+		if (t->pressure_delta < -7)
+			tp_motion_history_reset(t);
+
 		tp_thumb_detect(tp, t, time);
 		tp_palm_detect(tp, t, time);
 
diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
index 1f05a03..d1dae83 100644
--- a/src/evdev-mt-touchpad.h
+++ b/src/evdev-mt-touchpad.h
@@ -154,6 +154,7 @@ struct tp_touch {
 	uint64_t millis;
 	int distance;				/* distance == 0 means touch */
 	int pressure;
+	int pressure_delta;
 
 	struct {
 		/* A quirk mostly used on Synaptics touchpads. In a
diff --git a/test/litest.c b/test/litest.c
index f679652..1d729ef 100644
--- a/test/litest.c
+++ b/test/litest.c
@@ -1494,23 +1494,39 @@ litest_touch_move_extended(struct litest_device *d,
 }
 
 void
+litest_touch_move_to_extended(struct litest_device *d,
+			      unsigned int slot,
+			      double x_from, double y_from,
+			      double x_to, double y_to,
+			      struct axis_replacement *axes,
+			      int steps, int sleep_ms)
+{
+	for (int i = 0; i < steps - 1; i++) {
+		litest_touch_move_extended(d, slot,
+					   x_from + (x_to - x_from)/steps * i,
+					   y_from + (y_to - y_from)/steps * i,
+					   axes);
+		if (sleep_ms) {
+			libinput_dispatch(d->libinput);
+			msleep(sleep_ms);
+			libinput_dispatch(d->libinput);
+		}
+	}
+	litest_touch_move_extended(d, slot, x_to, y_to, axes);
+}
+
+void
 litest_touch_move_to(struct litest_device *d,
 		     unsigned int slot,
 		     double x_from, double y_from,
 		     double x_to, double y_to,
 		     int steps, int sleep_ms)
 {
-	for (int i = 0; i < steps - 1; i++) {
-		litest_touch_move(d, slot,
-				  x_from + (x_to - x_from)/steps * i,
-				  y_from + (y_to - y_from)/steps * i);
-		if (sleep_ms) {
-			libinput_dispatch(d->libinput);
-			msleep(sleep_ms);
-			libinput_dispatch(d->libinput);
-		}
-	}
-	litest_touch_move(d, slot, x_to, y_to);
+	litest_touch_move_to_extended(d, slot,
+				      x_from, y_from,
+				      x_to, y_to,
+				      NULL,
+				      steps, sleep_ms);
 }
 
 static int
diff --git a/test/litest.h b/test/litest.h
index e854210..c218361 100644
--- a/test/litest.h
+++ b/test/litest.h
@@ -403,6 +403,13 @@ litest_touch_move_to(struct litest_device *d,
 		     double x_from, double y_from,
 		     double x_to, double y_to,
 		     int steps, int sleep_ms);
+void
+litest_touch_move_to_extended(struct litest_device *d,
+			      unsigned int slot,
+			      double x_from, double y_from,
+			      double x_to, double y_to,
+			      struct axis_replacement *axes,
+			      int steps, int sleep_ms);
 
 void
 litest_touch_move_two_touches(struct litest_device *d,
diff --git a/test/touchpad.c b/test/touchpad.c
index 4651b7a..a58b337 100644
--- a/test/touchpad.c
+++ b/test/touchpad.c
@@ -3594,7 +3594,7 @@ START_TEST(touchpad_thumb_edgescroll)
 	libinput_dispatch(li);
 	litest_assert_only_typed_events(li, LIBINPUT_EVENT_POINTER_AXIS);
 
-	litest_touch_move_to(dev, 0, 99, 55, 99, 70, 10, 0);
+	litest_touch_move_to_extended(dev, 0, 99, 55, 99, 70, axes, 10, 0);
 
 	litest_assert_only_typed_events(li, LIBINPUT_EVENT_POINTER_AXIS);
 }
-- 
2.5.0