[PATCH libinput] tablet: add a fuzz-filter to avoid spamming callers with subpixel updates

[Peter Hutterer]

On Mon, Apr 11, 2016 at 06:43:15PM -0700, Jason Gerecke wrote:
> On Mon, Apr 11, 2016 at 5:17 PM, Peter Hutterer
> <peter.hutterer at who-t.net> wrote:
> > This is especially a problem for the cursor tool which can be legitimately
> > left on the tablet. It wobbles by a couple of device units, resulting in
> > continuous axis updates to the caller. Pre-filter any of these events by the
> > axis' fuzz value so we don't even process them.
> >
> > For ABS_DISTANCE which doesn't have a fuzz we hard-code a minimum fuzz of 2.
> > This should eventually land in the udev hwdb though.
> >
> 
> Bikeshed: s/udev hwdb/kernel/ (and poke Ping and I with a stick) since
> the lack of fuzz isn't a huge issue but is still something that should
> be fixed?

changed the commit message. And I've acquired an appropriately sized stick
for poking :)

> 
> Reviewed-by: Jason Gerecke <jason.gerecke at wacom.com>

thanks!

Cheers,
   Peter

> 
> > https://bugs.freedesktop.org/show_bug.cgi?id=94892
> >
> > Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> > ---
> >  src/evdev-tablet.c | 35 +++++++++++++++++++++++++++++++++++
> >  src/evdev-tablet.h |  2 ++
> >  2 files changed, 37 insertions(+)
> >
> > diff --git a/src/evdev-tablet.c b/src/evdev-tablet.c
> > index 84563a8..be828d9 100644
> > --- a/src/evdev-tablet.c
> > +++ b/src/evdev-tablet.c
> > @@ -112,6 +112,36 @@ tablet_device_has_axis(struct tablet_dispatch *tablet,
> >         return has_axis;
> >  }
> >
> > +static inline bool
> > +tablet_filter_axis_fuzz(const struct tablet_dispatch *tablet,
> > +                       const struct evdev_device *device,
> > +                       const struct input_event *e,
> > +                       enum libinput_tablet_tool_axis axis)
> > +{
> > +       int delta, fuzz;
> > +       int current, previous;
> > +
> > +       previous = tablet->prev_value[axis];
> > +       current = e->value;
> > +       delta = previous - current;
> > +
> > +       fuzz = libevdev_get_abs_fuzz(device->evdev, e->code);
> > +
> > +       /* ABS_DISTANCE doesn't have have fuzz set and causes continuous
> > +        * updates for the cursor/lens tools. Add a minimum fuzz of 2, same
> > +        * as the xf86-input-wacom driver
> > +        */
> > +       switch (e->code) {
> > +       case ABS_DISTANCE:
> > +               fuzz = max(2, fuzz);
> > +               break;
> > +       default:
> > +               break;
> > +       }
> > +
> > +       return abs(delta) <= fuzz;
> > +}
> > +
> >  static void
> >  tablet_process_absolute(struct tablet_dispatch *tablet,
> >                         struct evdev_device *device,
> > @@ -137,6 +167,11 @@ tablet_process_absolute(struct tablet_dispatch *tablet,
> >                         break;
> >                 }
> >
> > +               tablet->prev_value[axis] = tablet->current_value[axis];
> > +               if (tablet_filter_axis_fuzz(tablet, device, e, axis))
> > +                       break;
> > +
> > +               tablet->current_value[axis] = e->value;
> >                 set_bit(tablet->changed_axes, axis);
> >                 tablet_set_status(tablet, TABLET_AXES_UPDATED);
> >                 break;
> > diff --git a/src/evdev-tablet.h b/src/evdev-tablet.h
> > index 880d523..d12c675 100644
> > --- a/src/evdev-tablet.h
> > +++ b/src/evdev-tablet.h
> > @@ -55,6 +55,8 @@ struct tablet_dispatch {
> >         unsigned char changed_axes[NCHARS(LIBINPUT_TABLET_TOOL_AXIS_MAX + 1)];
> >         struct tablet_axes axes;
> >         unsigned char axis_caps[NCHARS(LIBINPUT_TABLET_TOOL_AXIS_MAX + 1)];
> > +       int current_value[LIBINPUT_TABLET_TOOL_AXIS_MAX + 1];
> > +       int prev_value[LIBINPUT_TABLET_TOOL_AXIS_MAX + 1];
> >
> >         /* Only used for tablets that don't report serial numbers */
> >         struct list tool_list;
> > --
> > 2.5.5
> >
>