touchpad: implement edge-based basic palm detection

A large part of palm events are situated on the far edges of the touchpad. In
a test run on a T440s while typing a long email all but 2 touch points were
located in the outer ~5% of the touchpad. Define a 5% exclusion zone on the
left and right edges in which new touchpoint is automatically assigned to be a
palm.

A finger may move into that exclusion zone without being marked as palm, it
just can't start in one.

On clickpads, the exclusion zone does not extend into the software buttons.

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

src/evdev-mt-touchpad-buttons.c

@@ -733,3 +733,9 @@ tp_button_touch_active(struct tp_dispatch *tp, struct tp_touch *t)
 {
 	return t->button.state == BUTTON_STATE_AREA;
 }
+
+bool
+tp_button_is_inside_softbutton_area(struct tp_dispatch *tp, struct tp_touch *t)
+{
+	return is_inside_top_button_area(tp, t) || is_inside_bottom_button_area(tp, t);
+}

src/evdev-mt-touchpad.c

@@ -148,6 +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->state = TOUCH_END;
 	t->pinned.is_pinned = false;
 	assert(tp->nfingers_down >= 1);
@@ -339,6 +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->pinned.is_pinned && tp_button_touch_active(tp, t);
 }
 
@@ -357,6 +359,29 @@ tp_set_pointer(struct tp_dispatch *tp, struct tp_touch *t)
 		t->is_pointer = true;
 }
 
+static void
+tp_palm_detect(struct tp_dispatch *tp, struct tp_touch *t)
+{
+	/* once a palm, always a palm */
+	if (t->is_palm)
+		return;
+
+	/* palm must start in exclusion zone, it's ok to move into
+	   the zone without being a palm */
+	if (t->state != TOUCH_BEGIN ||
+	    (t->x > tp->palm.left_edge && t->x < tp->palm.right_edge))
+		return;
+
+	/* don't detect palm in software button areas, it's
+	   likely that legitimate touches start in the area
+	   covered by the exclusion zone */
+	if (tp->buttons.is_clickpad &&
+	    tp_button_is_inside_softbutton_area(tp, t))
+		return;
+
+	t->is_palm = true;
+}
+
 static void
 tp_process_state(struct tp_dispatch *tp, uint64_t time)
 {
@@ -373,6 +398,8 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
 			continue;
 		}
 
+		tp_palm_detect(tp, t);
+
 		tp_motion_hysteresis(tp, t);
 		tp_motion_history_push(t);
 
@@ -702,6 +729,23 @@ tp_init_scroll(struct tp_dispatch *tp)
 	return 0;
 }
 
+static int
+tp_init_palmdetect(struct tp_dispatch *tp,
+		   struct evdev_device *device)
+{
+	int width;
+
+	width = abs(device->abs.absinfo_x->maximum -
+		    device->abs.absinfo_x->minimum);
+
+	/* palm edges are 5% of the width on each side */
+	tp->palm.right_edge = device->abs.absinfo_x->maximum - width * 0.05;
+	tp->palm.left_edge = device->abs.absinfo_x->minimum + width * 0.05;
+
+	return 0;
+}
+
+
 static int
 tp_init(struct tp_dispatch *tp,
 	struct evdev_device *device)
@@ -738,6 +782,9 @@ tp_init(struct tp_dispatch *tp,
 	if (tp_init_buttons(tp, device) != 0)
 		return -1;
 
+	if (tp_init_palmdetect(tp, device) != 0)
+		return -1;
+
 	return 0;
 }
 

src/evdev-mt-touchpad.h

@@ -103,6 +103,7 @@ 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;
@@ -202,6 +203,11 @@ struct tp_dispatch {
 		struct libinput_timer timer;
 		enum tp_tap_state state;
 	} tap;
+
+	struct {
+		int32_t right_edge;
+		int32_t left_edge;
+	} palm;
 };
 
 #define tp_for_each_touch(_tp, _t) \
@@ -242,4 +248,7 @@ tp_button_handle_state(struct tp_dispatch *tp, uint64_t time);
 int
 tp_button_touch_active(struct tp_dispatch *tp, struct tp_touch *t);
 
+bool
+tp_button_is_inside_softbutton_area(struct tp_dispatch *tp, struct tp_touch *t);
+
 #endif

test/touchpad.c

@@ -1241,6 +1241,117 @@ START_TEST(touchpad_tap_default)
 }
 END_TEST
 
+START_TEST(touchpad_palm_detect_at_edge)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+
+	litest_drain_events(li);
+
+	litest_touch_down(dev, 0, 99, 50);
+	litest_touch_move_to(dev, 0, 99, 50, 99, 70, 5);
+	litest_touch_up(dev, 0);
+
+	litest_assert_empty_queue(li);
+
+	litest_touch_down(dev, 0, 5, 50);
+	litest_touch_move_to(dev, 0, 5, 50, 5, 70, 5);
+	litest_touch_up(dev, 0);
+}
+END_TEST
+
+START_TEST(touchpad_palm_detect_at_bottom_corners)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+
+	/* Run for non-clickpads only: make sure the bottom corners trigger
+	   palm detection too */
+	litest_drain_events(li);
+
+	litest_touch_down(dev, 0, 99, 95);
+	litest_touch_move_to(dev, 0, 99, 95, 99, 99, 10);
+	litest_touch_up(dev, 0);
+
+	litest_assert_empty_queue(li);
+
+	litest_touch_down(dev, 0, 5, 95);
+	litest_touch_move_to(dev, 0, 5, 95, 5, 99, 5);
+	litest_touch_up(dev, 0);
+}
+END_TEST
+
+START_TEST(touchpad_palm_detect_at_top_corners)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+
+	/* Run for non-clickpads only: make sure the bottom corners trigger
+	   palm detection too */
+	litest_drain_events(li);
+
+	litest_touch_down(dev, 0, 99, 5);
+	litest_touch_move_to(dev, 0, 99, 5, 99, 9, 10);
+	litest_touch_up(dev, 0);
+
+	litest_assert_empty_queue(li);
+
+	litest_touch_down(dev, 0, 5, 5);
+	litest_touch_move_to(dev, 0, 5, 5, 5, 9, 5);
+	litest_touch_up(dev, 0);
+}
+END_TEST
+
+START_TEST(touchpad_palm_detect_palm_stays_palm)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+
+	litest_drain_events(li);
+
+	litest_touch_down(dev, 0, 99, 50);
+	litest_touch_move_to(dev, 0, 99, 50, 0, 70, 5);
+	litest_touch_up(dev, 0);
+
+	litest_assert_empty_queue(li);
+}
+END_TEST
+
+START_TEST(touchpad_palm_detect_no_palm_moving_into_edges)
+{
+	struct litest_device *dev = litest_current_device();
+	struct libinput *li = dev->libinput;
+	struct libinput_event *ev;
+	enum libinput_event_type type;
+
+	/* moving non-palm into the edge does not label it as palm */
+	litest_drain_events(li);
+
+	litest_touch_down(dev, 0, 50, 50);
+	litest_touch_move_to(dev, 0, 50, 50, 99, 50, 5);
+
+	litest_drain_events(li);
+
+	litest_touch_move_to(dev, 0, 99, 50, 99, 90, 5);
+	libinput_dispatch(li);
+
+	type = libinput_next_event_type(li);
+	do {
+
+		ck_assert_int_eq(type, LIBINPUT_EVENT_POINTER_MOTION);
+		ev = libinput_get_event(li);
+		libinput_event_destroy(ev);
+
+		type = libinput_next_event_type(li);
+		libinput_dispatch(li);
+	} while (type != LIBINPUT_EVENT_NONE);
+
+	litest_touch_up(dev, 0);
+	libinput_dispatch(li);
+	litest_assert_empty_queue(li);
+}
+END_TEST
+
 int main(int argc, char **argv) {
 
 	litest_add("touchpad:motion", touchpad_1fg_motion, LITEST_TOUCHPAD, LITEST_ANY);
@@ -1290,5 +1401,11 @@ int main(int argc, char **argv) {
 
 	litest_add("touchpad:scroll", touchpad_2fg_scroll, LITEST_TOUCHPAD, LITEST_SINGLE_TOUCH);
 
+	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_no_palm_moving_into_edges, LITEST_TOUCHPAD, LITEST_ANY);
+
 	return litest_run(argc, argv);
 }