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touchpad: only use the last two coordinates for delta calculation

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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>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
This commit is contained in:
Peter Hutterer 2016-11-21 08:39:47 +10:00
parent ab83c8e626
commit cfdaaa32a7
1 changed files with 5 additions and 15 deletions
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20
src/evdev-mt-touchpad.c
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@ -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);
}