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 ? ;)
Florent
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