13.06.2014 15:22, Gabriele Mazzotta wrote:
It appears that 71652fe ("Ignore motion the first X ms after a
clickpad click") is not enough to prevent unwanted cursor jumps when
two different fingers are used to respectively move the cursor and
click. The jumps are due to the small delay between the actual click and
the moment the finger is placed on the clickpad. Because of this delay,
the two events are sometimes seen as independent from each other and
since the finger detection happens first, the motion is not ignored.
Add a constraint on the distance covered to prevent jumps.
The difference between two detections along the x axis has to be
smaller than 1/4 of the clickpad width and smaller than 1/4 of the
height along the y axis.
See also https://bugs.freedesktop.org/show_bug.cgi?id=76722 for a
similar bug in libinput. In that case, though, I was able to trace it to
a touchpad firmware bug.
Signed-off-by: Gabriele Mazzotta <[email protected]>
---
This patch was tested on a Dell XPS13 9333. I don't know if 1/4 of the
width and 1/4 of the height are good constraints, on my laptop I couldn't
notice any side effect even with stricter constraints.
In my patch for libinput (see the attachment to
http://lists.freedesktop.org/archives/wayland-devel/2014-March/013935.html)
I used 1/8 of the diagonal.
src/synaptics.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/src/synaptics.c b/src/synaptics.c
index 32edce5..b9da62c 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -3233,6 +3233,9 @@ HandleState(InputInfoPtr pInfo, struct SynapticsHwState
*hw, CARD32 now,
buttons |= tap_mask;
}
+ if (para->clickpad && abs(dx) > priv->maxx/4 && abs(dy) > priv->maxy/4)
+ ignore_motion = TRUE;
+
I'd say this is sufficient to fix the original bug that you see.
However, when jumps result from the (*cough* Sony *cough*) hardware
failing to see that the new touch point in fact belongs to a different
finger, just ignoring motion may or may not be sufficient. Are there any
tap-related or other gestures that may be affected by the wrong
assumption that there were no finger-up/finger-down events in the middle
(i.e. that it is the same finger)?
--
Alexander E. Patrakov
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