Fwd: Re: Openmoko Bug #1194: Touchscreen Jitter

Andy Green andy at openmoko.com
Wed Jun 18 16:31:28 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| On 18.06.2008 00:44, Andy Green wrote:
|> So if the "selfselection" of samples from the firehose don't make it a
|> nonsense to look at it this way, it means we get excursions in the first
|> coordinate of up to +/- 20% at about 10% probability.
|> What we could do is refuse to accept samples too far outside a running
|> average into the average reported back to userspace....
| Beware of that approach. While it would be doable, it is certainly not
| always obvious how to do it correctly. If the stylus is moved too fast,
| all new samples will be outside the cleaned running average. So if you
| compare against the cleaned running average, fast movements will result
| in a hang of the fast-moving axis. If you compare against the uncleaned
| running average, similar stuff can happen and some really strong
| measurement errors will hang the axis with the errors.

Yes I found this already for real... it gave +/- 1 jitter mostly
(sometimes +/-2), but reacted badly to fast drag.

I tried a second approach which doesn't have that behaviour.  I will
post the patch in a minute so people can try it / and/or meddle with the
heuristic themselves, I doubt that it is optimal.

- -Andy
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