Improve responsiveness of touchpads by reducing the motion history.

0001-touchpad-only-use-the-last-two-coordinates-for-delta.patch

@@ -0,0 +1,62 @@
+From e288c3045d0c582ee19e85cbe11529dc374d4bbf Mon Sep 17 00:00:00 2001
+From: Peter Hutterer <peter.hutterer@who-t.net>
+Date: Mon, 21 Nov 2016 08:39:47 +1000
+Subject: [PATCH libinput] touchpad: only use the last two coordinates for
+ delta calculation
+
+Taking the last 4 points means factoring in a coordinate that may be more than
+40ms in the past - or even more when the finger moves slowly and we don't get
+events for a while. This makes the pointer more sluggish and slower to catch up
+with what the finger is actually doing.
+
+We already have the motion hysteresis as a separate item to prevent jumps (and
+thus adds some delay to the movement), the calculation over time doesn't
+provide enough benefit to justify the sluggish pointer.
+
+Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
+---
+ src/evdev-mt-touchpad.c | 20 +++++---------------
+ 1 file changed, 5 insertions(+), 15 deletions(-)
+
+diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
+index d72cb19..7b8514c 100644
+--- a/src/evdev-mt-touchpad.c
++++ b/src/evdev-mt-touchpad.c
+@@ -262,29 +262,19 @@ tp_end_sequence(struct tp_dispatch *tp, struct tp_touch *t, uint64_t time)
+ 	tp_end_touch(tp, t, time);
+ }
+ 
+-static double
+-tp_estimate_delta(int x0, int x1, int x2, int x3)
+-{
+-	return (x0 + x1 - x2 - x3) / 4.0;
+-}
+-
+ struct normalized_coords
+ tp_get_delta(struct tp_touch *t)
+ {
+ 	struct device_float_coords delta;
+ 	const struct normalized_coords zero = { 0.0, 0.0 };
+ 
+-	if (t->history.count < TOUCHPAD_MIN_SAMPLES)
++	if (t->history.count <= 1)
+ 		return zero;
+ 
+-	delta.x = tp_estimate_delta(tp_motion_history_offset(t, 0)->x,
+-				    tp_motion_history_offset(t, 1)->x,
+-				    tp_motion_history_offset(t, 2)->x,
+-				    tp_motion_history_offset(t, 3)->x);
+-	delta.y = tp_estimate_delta(tp_motion_history_offset(t, 0)->y,
+-				    tp_motion_history_offset(t, 1)->y,
+-				    tp_motion_history_offset(t, 2)->y,
+-				    tp_motion_history_offset(t, 3)->y);
++	delta.x = tp_motion_history_offset(t, 0)->x -
++		  tp_motion_history_offset(t, 1)->x;
++	delta.y = tp_motion_history_offset(t, 0)->y -
++		  tp_motion_history_offset(t, 1)->y;
+ 
+ 	return tp_normalize_delta(t->tp, delta);
+ }
+-- 
+2.9.3
+

libinput.spec

@@ -5,7 +5,7 @@
 
 Name:           libinput
 Version:        1.5.1
-Release:        1%{?gitdate:.%{gitdate}git%{gitversion}}%{?dist}
+Release:        2%{?gitdate:.%{gitdate}git%{gitversion}}%{?dist}
 Summary:        Input device library
 
 License:        MIT
@@ -18,6 +18,8 @@ Source2:        commitid
 Source0:        http://www.freedesktop.org/software/libinput/libinput-%{version}.tar.xz
 %endif
 
+Patch01:        0001-touchpad-only-use-the-last-two-coordinates-for-delta.patch
+
 BuildRequires:  git
 BuildRequires:  autoconf automake libtool pkgconfig
 BuildRequires:  libevdev-devel
@@ -94,6 +96,9 @@ find $RPM_BUILD_ROOT -name '*.la' -delete
 
 
 %changelog
+* Tue Nov 22 2016 Peter Hutterer <peter.hutterer@redhat.com> 1.5.1-2
+- Improve responsiveness of touchpads by reducing the motion history.
+
 * Fri Nov 11 2016 Peter Hutterer <peter.hutterer@redhat.com> 1.5.1-1
 - libinput 1.5.1