touchpad: if a palm touch moves out of the edge zone within a timeout, unpalm

On small touchpads a touch that is intended to traverse much of the screen
width may start at the very edge, i.e. in the palm zone.
In that case, and if the touch moves out of the palm zone quickly enough, drop
the palm label and make it a normal touchpoint.

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

3 files changed, 40 insertions, 11 deletions

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 1325355c..830e9fee 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -148,7 +148,7 @@ tp_end_touch(struct tp_dispatch *tp, struct tp_touch *t)
 
 	t->dirty = true;
 	t->is_pointer = false;
-	t->is_palm = false;
+	t->palm.is_palm = false;
 	t->state = TOUCH_END;
 	t->pinned.is_pinned = false;
 	assert(tp->nfingers_down >= 1);
@@ -340,7 +340,7 @@ static int
 tp_touch_active(struct tp_dispatch *tp, struct tp_touch *t)
 {
 	return (t->state == TOUCH_BEGIN || t->state == TOUCH_UPDATE) &&
-		!t->is_palm &&
+		!t->palm.is_palm &&
 		!t->pinned.is_pinned && tp_button_touch_active(tp, t);
 }
 
@@ -360,11 +360,21 @@ tp_set_pointer(struct tp_dispatch *tp, struct tp_touch *t)
 }
 
 static void
-tp_palm_detect(struct tp_dispatch *tp, struct tp_touch *t)
+tp_palm_detect(struct tp_dispatch *tp, struct tp_touch *t, uint64_t time)
 {
-	/* once a palm, always a palm */
-	if (t->is_palm)
+	const int PALM_TIMEOUT = 200; /* ms */
+
+	/* If labelled a touch as palm, we unlabel as palm when
+	   we move out of the palm edge zone within the timeout.
+	 */
+	if (t->palm.is_palm) {
+		if (time < t->palm.time + PALM_TIMEOUT &&
+		    (t->x > tp->palm.left_edge && t->x < tp->palm.right_edge)) {
+			t->palm.is_palm = false;
+			tp_set_pointer(tp, t);
+		}
 		return;
+	}
 
 	/* palm must start in exclusion zone, it's ok to move into
 	   the zone without being a palm */
@@ -379,7 +389,8 @@ tp_palm_detect(struct tp_dispatch *tp, struct tp_touch *t)
 	    tp_button_is_inside_softbutton_area(tp, t))
 		return;
 
-	t->is_palm = true;
+	t->palm.is_palm = true;
+	t->palm.time = time;
 }
 
 static void
@@ -398,7 +409,7 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
 			continue;
 		}
 
-		tp_palm_detect(tp, t);
+		tp_palm_detect(tp, t, time);
 
 		tp_motion_hysteresis(tp, t);
 		tp_motion_history_push(t);
diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
index 689687ee..8255a1cd 100644
--- a/src/evdev-mt-touchpad.h
+++ b/src/evdev-mt-touchpad.h
@@ -103,7 +103,6 @@ struct tp_touch {
 	bool dirty;
 	bool fake;				/* a fake touch */
 	bool is_pointer;			/* the pointer-controlling touch */
-	bool is_palm;
 	int32_t x;
 	int32_t y;
 	uint64_t millis;
@@ -140,6 +139,11 @@ struct tp_touch {
 	struct {
 		enum tp_tap_touch_state state;
 	} tap;
+
+	struct {
+		bool is_palm;
+		uint32_t time; /* first timestamp if is_palm == true */
+	} palm;
 };
 
 struct tp_dispatch {
diff --git a/test/touchpad.c b/test/touchpad.c
index 672cbf9b..18427c1a 100644
--- a/test/touchpad.c
+++ b/test/touchpad.c
@@ -1302,17 +1302,31 @@ START_TEST(touchpad_palm_detect_at_top_corners)
 }
 END_TEST
 
-START_TEST(touchpad_palm_detect_palm_stays_palm)
+START_TEST(touchpad_palm_detect_palm_becomes_pointer)
 {
 	struct litest_device *dev = litest_current_device();
 	struct libinput *li = dev->libinput;
+	struct libinput_event *ev;
+	enum libinput_event_type type;
 
 	litest_drain_events(li);
 
 	litest_touch_down(dev, 0, 99, 50);
-	litest_touch_move_to(dev, 0, 99, 50, 0, 70, 5);
+	litest_touch_move_to(dev, 0, 99, 70, 0, 70, 5);
 	litest_touch_up(dev, 0);
 
+	libinput_dispatch(li);
+
+	ev = libinput_get_event(li);
+	ck_assert_notnull(ev);
+	do {
+		type = libinput_event_get_type(ev);
+		ck_assert_int_eq(type, LIBINPUT_EVENT_POINTER_MOTION);
+
+		libinput_event_destroy(ev);
+		ev = libinput_get_event(li);
+	} while (ev);
+
 	litest_assert_empty_queue(li);
 }
 END_TEST
@@ -1404,7 +1418,7 @@ int main(int argc, char **argv) {
 	litest_add("touchpad:palm", touchpad_palm_detect_at_edge, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add("touchpad:palm", touchpad_palm_detect_at_bottom_corners, LITEST_TOUCHPAD, LITEST_CLICKPAD);
 	litest_add("touchpad:palm", touchpad_palm_detect_at_top_corners, LITEST_TOUCHPAD, LITEST_TOPBUTTONPAD);
-	litest_add("touchpad:palm", touchpad_palm_detect_palm_stays_palm, LITEST_TOUCHPAD, LITEST_ANY);
+	litest_add("touchpad:palm", touchpad_palm_detect_palm_becomes_pointer, LITEST_TOUCHPAD, LITEST_ANY);
 	litest_add("touchpad:palm", touchpad_palm_detect_no_palm_moving_into_edges, LITEST_TOUCHPAD, LITEST_ANY);
 
 	return litest_run(argc, argv);