Florent THIERY fthiery at
Tue Apr 3 18:19:07 CEST 2007

> Tapping two fingers on and off on my Mac laptop (old G4 model) I can
> see behavior that matches this, although the pointer algorithm it uses
> is trying to figure out a single point.
> So we will not see clearly defined bounding box limits. The point will
> skate around within the limits depending on relative pressure.

> The first finger will set a clear start point, the second finger will
> make that point shoot off towards it, but it will not go all the way
> to the second touch. The effect should be to oscillate along the line
> between the two end points, and it wont return to the position of the
> first touch.

On my own touchpad (thinkpad), it's almost the same, except that if i
release the 1st finger, the cursor goes to the effective 2nd finger
position. And i'd add that the oscillation is pretty steady on mine:
almost none.

Which gives us 2 sure elements:
* the pointer won't come OUT of this box
* the displacement speed from point 1 (single finger) to point 2 is
constant, and hopefully will be detectable

> If we capture a clear single touch, and an average position of
> oscillation, then we can take the average oscillation to be the center
> of the bounding box, and project an estimate of the opposite corner
> where the second touch should be. With the right filtering and
> limiting algorithm it should be possible to get the effect we want.
> Challenges: In comparison with a true dual touch input device, its
> going to react more slowly as the algorithm will need to gather more
> data to decide where the pointer should be. Some of the faster moving
> single touch gestures may be hard to distinguish from multi touch.

You're totally right. What about adding this to the touchscreen
section in the wiki UI_Improvements ? ;)


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