[PATCH synaptics] Don't count fingers twice when guessing distance (#48316)

[Peter Hutterer]

On Tue, Apr 10, 2012 at 05:24:26PM -0700, Chase Douglas wrote:
> On 04/10/2012 05:03 PM, Peter Hutterer wrote:
> > A finger may be closer than the required distance to more than one finger.
> > e.g. for fingers A, B, C, AC and BC could both trigger the check and count
> > C twice.
> 
> The above description actually results in the correct count for three
> touches. A better description would mention the case where AC, BC, and
> AB are all close enough to trigger the check, in which case we have too
> many fingers.

right, sorry, amended to:
   A finger may be closer than the required distance to more than one
   finger.e.g. for fingers A, B, C, AB, AC and BC may trigger the check and
   count C twice -resulting in a 4 finger click.

> > Avoid double-counting by marking those fingers already close enough to a
> > previous finger to avoid overcounting.
> > 
> > X.Org Bug 48316 <http://bugs.freedesktop.org/show_bug.cgi?id=48316>
> > 
> > Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> > ---
> >  src/synaptics.c |    9 ++++++++-
> >  1 files changed, 8 insertions(+), 1 deletions(-)
> > 
> > diff --git a/src/synaptics.c b/src/synaptics.c
> > index 918dc6f..0e10aeb 100644
> > --- a/src/synaptics.c
> > +++ b/src/synaptics.c
> > @@ -2624,7 +2624,9 @@ clickpad_guess_clickfingers(SynapticsPrivate *priv, struct SynapticsHwState *hw)
> >  {
> >      int nfingers = 0;
> >  #if HAVE_MULTITOUCH
> > +    int skip[SYNAPTICS_MAX_TOUCHES] = {0};
> >      int i, j;
> > +
> >      for (i = 0; i < hw->num_mt_mask - 1; i++) {
> >          ValuatorMask *f1;
> >  
> > @@ -2642,6 +2644,9 @@ clickpad_guess_clickfingers(SynapticsPrivate *priv, struct SynapticsHwState *hw)
> >                  hw->slot_state[j] == SLOTSTATE_CLOSE)
> >                  continue;
> >  
> > +            if (skip[j])
> > +                continue;
> > +
> >              f2 = hw->mt_mask[j];
> >  
> >              x1 = valuator_mask_get_double(f1, 0);
> > @@ -2655,8 +2660,10 @@ clickpad_guess_clickfingers(SynapticsPrivate *priv, struct SynapticsHwState *hw)
> >               * you'll need to find a touchpad that doesn't lie about it's
> >               * size. Good luck. */
> >              if (abs(x1 - x2) < (priv->maxx - priv->minx) * .3 &&
> > -                abs(y1 - y2) < (priv->maxy - priv->miny) * .3)
> > +                abs(y1 - y2) < (priv->maxy - priv->miny) * .3) {
> >                  nfingers++;
> > +                skip[j] = 1;
> > +            }
> >          }
> >      }
> >  #endif
> 
> I think we would get the same results if we merely added a "break;"
> after "nfingers++;". This would ensure we only increment the finger
> count once for each outer loop iteration. In the example, we would see
> AB, and BC, but not AC because we broke out of the inner loop after AB.

you can't guarantee that BC are close enough together when you see the first
match though. so for the case of physical B left of A left of C, you have AB
and AC being close but BC may not be. If you break after finding the AB
match, you'd skip the AC and get two-finger click only.

Cheers,
  Peter