[PATCH libinput 2/2] evdev-mt-touchpad: Switch to smooth simple acceleration code from filter.c

[Hans de Goede]

The old touchpad accel code was clamping touchpad acceleration between
0.2 and 0.4, and on the test devices I have the constant_factor ended up
such that in practice the accel was almost always 0.2, so rather then having
a velocity based acceleration curve, in essence it was just always using an
acceleration of 0.2 .

This commit introduces actual velocity based acceleration based on the
recently added smooth simple acceleration code from filter.c .

Before feeding motion events to filter.c, they first get adjusted for touchpad
resolution and size, based on the diagonal-size in units see the large comment
added to tp_init_accel() for details.

While at it rename's tp_init_accel's dispatch parameter from touchpad to tp
to be consistent with all other functions.

Since the acceleration is also used for scrolling also adjust the scroll
start threshold for these changes.

Note that switching to the smooth simple accel code, as an added bonus gives
the tp code an accel profile with a threshold and a speed parameter, which
is exactly what is needed for the upcoming configuration interface support.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 src/evdev-mt-touchpad.c | 75 ++++++++++++++++++++++++++-----------------------
 src/evdev-mt-touchpad.h |  4 ---
 2 files changed, 40 insertions(+), 39 deletions(-)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 9e858f1..0e43586 100644
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -28,9 +28,7 @@
 
 #include "evdev-mt-touchpad.h"
 
-#define DEFAULT_CONSTANT_ACCEL_NUMERATOR 100
-#define DEFAULT_MIN_ACCEL_FACTOR 0.20
-#define DEFAULT_MAX_ACCEL_FACTOR 0.40
+#define DEFAULT_SIZE_ACCEL_NUMERATOR 1200.0
 #define DEFAULT_HYSTERESIS_MARGIN_DENOMINATOR 700.0
 
 static inline int
@@ -46,27 +44,6 @@ tp_hysteresis(int in, int center, int margin)
 		return center + diff + margin;
 }
 
-static double
-tp_accel_profile(struct motion_filter *filter,
-		 void *data,
-		 double velocity,
-		 uint64_t time)
-{
-	struct tp_dispatch *tp =
-		(struct tp_dispatch *) data;
-
-	double accel_factor;
-
-	accel_factor = velocity * tp->accel.constant_factor;
-
-	if (accel_factor > tp->accel.max_factor)
-		accel_factor = tp->accel.max_factor;
-	else if (accel_factor < tp->accel.min_factor)
-		accel_factor = tp->accel.min_factor;
-
-	return accel_factor;
-}
-
 static inline struct tp_motion *
 tp_motion_history_offset(struct tp_touch *t, int offset)
 {
@@ -464,11 +441,11 @@ tp_post_twofinger_scroll(struct tp_dispatch *tp, uint64_t time)
 
 	tp_filter_motion(tp, &dx, &dy, time);
 
-	/* Require at least three px scrolling to start */
-	if (dy <= -3.0 || dy >= 3.0)
+	/* Require at least five px scrolling to start */
+	if (dy <= -5.0 || dy >= 5.0)
 		tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_SCROLL_VERTICAL);
 
-	if (dx <= -3.0 || dx >= 3.0)
+	if (dx <= -5.0 || dx >= 5.0)
 		tp->scroll.direction |= (1 << LIBINPUT_POINTER_AXIS_SCROLL_HORIZONTAL);
 
 	if (dy != 0.0 &&
@@ -695,22 +672,50 @@ calculate_scale_coefficients(struct tp_dispatch *tp)
 }
 
 static int
-tp_init_accel(struct tp_dispatch *touchpad, double diagonal)
+tp_init_accel(struct tp_dispatch *tp, double diagonal)
 {
 	struct motion_filter *accel;
 
-	calculate_scale_coefficients(touchpad);
+	calculate_scale_coefficients(tp);
+
+	/*
+	 * Not all touchpads report the same amount of units/mm (resolution).
+	 * Besides resolution we also want to take the touchpad size into
+	 * account, on a small touchpad we want to report a bigger pointer
+	 * motion per mm moved.
+	 *
+	 * The kernel reports touchpad resolution only for a subset of all
+	 * supported touchpads, and without resolution info it is impossible
+	 * to calculate the physical size, so we cannot use either.
+	 *
+	 * Since physical-size == resolution * size-in-units, we end up with
+	 * a scaling formula which has resolution as a factor in both
+	 * the numerator and denominator, so we can simply leave resolution
+	 * out of the formula and scale only by size-in-units.
+	 *
+	 * Example 1: A small touchpad with a high resultion needs to have
+	 * events scaled up for its size, and scaled down for its resolution.
+	 * This touchpad has small-physical-size * high-amount-units/mm =
+	 * average-size-in-units.
+	 *
+	 * Example 2: A small touchpad with a low resolution needs to have
+	 * events scaled up twice once for its small size, once for its low
+	 * res. This touchpad has small-physical-size * low-amount-units/mm =
+	 * quite-low-size-in-units.
+	 *
+	 * Scaling events by average-size-in-units / touchpad-size-in-units
+	 * will result in the desired scaling in both cases.
+	 */
 
-	touchpad->accel.constant_factor =
-		DEFAULT_CONSTANT_ACCEL_NUMERATOR / diagonal;
-	touchpad->accel.min_factor = DEFAULT_MIN_ACCEL_FACTOR;
-	touchpad->accel.max_factor = DEFAULT_MAX_ACCEL_FACTOR;
+	tp->accel.x_scale_coeff *= DEFAULT_SIZE_ACCEL_NUMERATOR / diagonal;
+	tp->accel.y_scale_coeff *= DEFAULT_SIZE_ACCEL_NUMERATOR / diagonal;
 
-	accel = create_pointer_accelator_filter(tp_accel_profile);
+	accel = create_pointer_accelator_filter(
+			pointer_accel_profile_smooth_simple);
 	if (accel == NULL)
 		return -1;
 
-	touchpad->filter = accel;
+	tp->filter = accel;
 
 	return 0;
 }
diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
index 7afb3c4..051a7eb 100644
--- a/src/evdev-mt-touchpad.h
+++ b/src/evdev-mt-touchpad.h
@@ -152,10 +152,6 @@ struct tp_dispatch {
 	struct motion_filter *filter;
 
 	struct {
-		double constant_factor;
-		double min_factor;
-		double max_factor;
-
 		double x_scale_coeff;
 		double y_scale_coeff;
 	} accel;
-- 
2.0.0