Playing with touch screen events

Andy Green andy at
Tue Oct 21 08:38:54 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| On Tue, 21 Oct 2008 03:55:48 +0100 Andy Green <andy at> babbled:
|> Hash: SHA1
|> Somebody in the thread at some point said:
|> |>
|> |
|> | IIUC this is listening to X events, but this has already been filtered
|> | through a driver that tries to reduce jitter and stuff.  What kind of
|> | info does the driver give?  Could it support multiple touches
|> | (e.g. pinch, two-finger scroll, ...)?
|> The only extra thing you can squeeze out of it is the area of the
|> contact to the touchscreen, so you can tell between stylus, fingernail,
|> thumb.  I also made a patch for this, but I was unable to get the
|> results normalized across the whole touchscreen surface.  It could tell
|> very well though in any given area about the contact size.
| do you have any raw data on your results? how was the "size" reported
| from touch point?)

It was reported as additional ABS_PRESSURE of the sample, so X and Y
were left alone.  That breaks X somehow so it needs changing to Z or
some other parallel attribute.

But I couldn't find the right formula to normalize the results across
the screen, they varied widely depending on which corner of the screen.

Here's the somewhat bitrotted patch with some noise stuff at the
beginning, if anyone is interested to move it on.  It applies over the
other patch mentioned earlier that does median filtering.

- -Andy
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