Oops, sorry. I really must sleep more. I replied with a libinput patch
to a synaptics patch.
As I no longer use synaptics and don't want to figure out whether the
code there allows to say "this is a new finger", I just slap an ACK on
the original patch.
16.09.2014 08:57, Alexander E. Patrakov wrote:
16.09.2014 07:08, Peter Hutterer wrote:
Touchpads are limited by a fixed sampling rate (usually 80Hz). Some
finger
changes may happen too fast for this sampling rate, resulting in two
distinct
event sequences:
* finger 1 up and finger 2 down in the same EV_SYN frame. Synaptics
sees one
finger down before and after and the changed coordinates
* finger 1 up and finger 2 down _between_ two EV_SYN frames. Synaptics
sees one
touchpoint move from f1 position to f2 position.
That move causes a large cursor jump. The former could be solved (with
difficulty) by adding fake EV_SYN handling after releasing touchpoints
but
that won't fix the latter case.
Hello.
Thanks for recognizing the problem and opting for a simple criterion for
detecting such jumps.
However, AFAICS, the patch just discards the motion without telling the
FSM that it is in fact a new touch. So it may be bad for gestures.
Attached is a patch that I use to work around this issue since July that
does attempt to tell the FSM about a different finger.
So as a solution for now limit the finger movement to 20mm per event.
Tests on a T440 and an x220 showed that this is just above what a
reasonable
finger movement would trigger. If a movement is greater than that
limit, reset
it to 0/0.
On devices without resolution, use 0.25 the touchpad's diagonal instead.
I have no objection to the resolution-aware threshold. My patch doesn't
have it, but you can obviously replace the heuristic there with your
version.
Signed-off-by: Peter Hutterer <[email protected]>
---
See the git repo below for a simple script to verify valid movement
deltas
on your device if you feel like it:
https://github.com/whot/input-data-analysis/tree/master/touchpad-max-delta
Max I got was 9mm on the x220 and 17mm on the T440s but the latter was
really ripping the cursor around the screen beyond what I'd deem useful.
src/synaptics.c | 33 +++++++++++++++++++++++++++++++++
src/synapticsstr.h | 2 ++
2 files changed, 35 insertions(+)
diff --git a/src/synaptics.c b/src/synaptics.c
index 2e3ad0c..756751d 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -780,6 +780,23 @@ set_default_parameters(InputInfoPtr pInfo)
pars->resolution_vert = 1;
}
+ /* Touchpad sampling rate is too low to detect all movements.
+ A user may lift one finger and put another one down within the
same
+ EV_SYN or even between samplings so the driver doesn't notice
at all.
+
+ We limit the movement to 20 mm within one event, that is more
than
+ recordings showed is needed (17mm on a T440).
+ */
+ if (pars->resolution_horiz > 1 &&
+ pars->resolution_vert > 1)
+ pars->maxDeltaMM = 20;
+ else {
+ /* on devices without resolution set the vector length to
0.25 of
+ the touchpad diagonal */
+ pars->maxDeltaMM = diag * 0.25;
+ }
+
+
/* Warn about (and fix) incorrectly configured
TopEdge/BottomEdge parameters */
if (pars->top_edge > pars->bottom_edge) {
int tmp = pars->top_edge;
@@ -2229,6 +2246,13 @@ get_delta(SynapticsPrivate *priv, const struct
SynapticsHwState *hw,
*dy = integral;
}
+/* Vector length, but not sqrt'ed, we only need it for comparison */
+static inline double
+vlenpow2(double x, double y)
+{
+ return x * x + y * y;
+}
+
/**
* Compute relative motion ('deltas') including edge motion.
*/
@@ -2238,6 +2262,7 @@ ComputeDeltas(SynapticsPrivate * priv, const
struct SynapticsHwState *hw,
{
enum MovingState moving_state;
double dx, dy;
+ double vlen;
int delay = 1000000000;
dx = dy = 0;
@@ -2283,6 +2308,14 @@ ComputeDeltas(SynapticsPrivate * priv, const
struct SynapticsHwState *hw,
out:
priv->prevFingers = hw->numFingers;
+ vlen = vlenpow2(dx/priv->synpara.resolution_horiz,
+ dy/priv->synpara.resolution_vert);
+
+ if (vlen > priv->synpara.maxDeltaMM * priv->synpara.maxDeltaMM) {
+ dx = 0;
+ dy = 0;
+ }
+
*dxP = dx;
*dyP = dy;
diff --git a/src/synapticsstr.h b/src/synapticsstr.h
index 4bd32ac..75f52d5 100644
--- a/src/synapticsstr.h
+++ b/src/synapticsstr.h
@@ -226,6 +226,8 @@ typedef struct _SynapticsParameters {
int area_left_edge, area_right_edge, area_top_edge,
area_bottom_edge; /* area coordinates absolute */
int softbutton_areas[4][4]; /* soft button area coordinates, 0
=> right, 1 => middle , 2 => secondary right, 3 => secondary middle
button */
int hyst_x, hyst_y; /* x and y width of hysteresis box */
+
+ int maxDeltaMM; /* maximum delta movement (vector
length) in mm */
} SynapticsParameters;
struct _SynapticsPrivateRec {
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