[PATCH libinput] touchpad: Drop the scroll direction lock, increase threshold instead

[Peter Hutterer]

The direction lock was intended to avoid erroneous horizontal scroll events
when scrolling vertically (and vice versa). Some testing on my touchpad here
shows that it is too easy to accidentally lock the direction when no lock is
intended (e.g. moving around an image). And quite hard to figure out what a
pure vertical gesture is.

I get movements from 90 degrees to 70 degrees for something my brain would
consider vertical scrolling. Depending on the hand position, the fingers
actually perform a slight curve, not a straight line.

Hence - drop the direction lock, but increase the threshold a little. It
doesn't totally avoid horizontal scroll events but keeps them minimal.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
Ok, I give up. I thought I could find a simple way of locking the scroll
directions but I ran out of time and the simplest approach didn't work that
greatly.

This patch replaces 5 and 6 of this series (the ones I never pushed)

 src/evdev-mt-touchpad.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 26d5f7d..466cf5e 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -463,21 +463,18 @@ tp_post_twofinger_scroll(struct tp_dispatch *tp, uint64_t time)
 
 	tp_filter_motion(tp, &dx, &dy, time);
 
-	if (tp->scroll.state == SCROLL_STATE_NONE) {
-		/* Require at least one px scrolling to start */
-		if (dx <= -1.0 || dx >= 1.0) {
-			tp->scroll.state = SCROLL_STATE_SCROLLING;
-			tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_HORIZONTAL_SCROLL);
-		}
-
-		if (dy <= -1.0 || dy >= 1.0) {
-			tp->scroll.state = SCROLL_STATE_SCROLLING;
-			tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_VERTICAL_SCROLL);
-		}
-
-		if (tp->scroll.state == SCROLL_STATE_NONE)
-			return;
+	/* Require at least three px scrolling to start */
+	if (dy <= -3.0 || dy >= 3.0) {
+		tp->scroll.state = SCROLL_STATE_SCROLLING;
+		tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_VERTICAL_SCROLL);
 	}
+	if (dx <= -3.0 || dx >= 3.0) {
+		tp->scroll.state = SCROLL_STATE_SCROLLING;
+		tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_HORIZONTAL_SCROLL);
+	}
+
+	if (tp->scroll.state == SCROLL_STATE_NONE)
+		return;
 
 	/* Stop spurious MOTION events at the end of scrolling */
 	tp_for_each_touch(tp, t)
-- 
1.9.3