Touchscreen filters / pressure detection

[Andy Green]

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Somebody in the thread at some point said:
| Andy Green wrote:
|> http://focus.ti.com/lit/an/sbaa155a/sbaa155a.pdf
|
| Thanks ! Very interesting. If we could get this to work, I think
| there would be lots of nice things one could do with it. E.g.,
| use drag with a light touch to move a cursor by a fraction of
| the relative distance.

I got the impression that it could be made to work, but that there may
be one or more "problem corners".  While the bulk of the display gave
either reasonable or very good "Z" resolution IIRC (allowing that the
scale varied in X and Y) there was one corner that only had a couple of
bits of this "Z" information possible for whatever reason.

Also it's not really telling you about lightness of touch directly but
area of contact.  That can be related but it is indirect.  What is was
really good for was telling you if it was a stylus, fingertip, amount of
finger, or thumb or even palm.

| Regarding uneven resistance, I also wonder how much touch screen
| parameters differ among devices.

At the time the X and Y is calibrated the Z could be as well as part of
the same touch actions.  But the math in the patch I sent appears to be
broken somehow because it's far from linearly scaled on X or Y for Z.

- -Andy
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