[PATCH libinput] touchpad: drop motion hysteresis

[Peter Hutterer]

Some older touchpad devices jitter a fair bit when a finger is resting on the
touchpad. That's why the hysteresis was introduced in the synaptics driver
back in 2011. However, the default value of the hysteresis in the synaptics
driver ended up being 0, even though the code looks like it's using a fraction
of the touchpad diagonal. When the hysteresis code was ported to libinput it
was eventually set to 0.5mm.

Turns out this is still too high and tiny finger motions are either
nonreactive or quite jumpy, making it hard to select small targets. Drop the
hysteresis by reducing its margin to 0. I'm leaving the code in place for now
because this will likely be needed for some devices.

https://bugs.freedesktop.org/show_bug.cgi?id=93503

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
 src/evdev-mt-touchpad.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index f249116..757c7c7 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -1957,7 +1957,6 @@ tp_init(struct tp_dispatch *tp,
 {
 	int width, height;
 	double diagonal;
-	int res_x, res_y;
 
 	tp->base.interface = &tp_interface;
 	tp->device = device;
@@ -1971,8 +1970,6 @@ tp_init(struct tp_dispatch *tp,
 	if (tp_init_slots(tp, device) != 0)
 		return -1;
 
-	res_x = tp->device->abs.absinfo_x->resolution;
-	res_y = tp->device->abs.absinfo_y->resolution;
 	width = device->abs.dimensions.x;
 	height = device->abs.dimensions.y;
 	diagonal = sqrt(width*width + height*height);
@@ -1981,8 +1978,8 @@ tp_init(struct tp_dispatch *tp,
 						       EV_ABS,
 						       ABS_MT_DISTANCE);
 
-	tp->hysteresis_margin.x = res_x/2;
-	tp->hysteresis_margin.y = res_y/2;
+	tp->hysteresis_margin.x = 0;
+	tp->hysteresis_margin.y = 0;
 
 	if (tp_init_accel(tp, diagonal) != 0)
 		return -1;
-- 
2.5.0