[PATCH synaptics] Limit the movement to 20 mm per event
Hans de Goede
hdegoede at redhat.com
Tue Sep 16 00:20:10 PDT 2014
Hi,
On 09/16/2014 03:08 AM, 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.
>
> 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.
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
Looks good to me:
Reviewed-by: Hans de Goede <hdegoede at redhat.com>
Regards,
Hans
> ---
> 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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