Re: touchscreen calibration again

On Tue, 04 May 2004 18:04:57 +0200
Koen Kooi <koen_at_vestingbar.nl> wrote:

> Another observation when playing with opie-drawpad (gpe still does
> nothing): When i draw "horizontal" (along the short side of the screen,
> nearby the buttons) lines they end up looking like L shaped lines.
> Screenshot attached. It looks like the first read from the ts is correct
> and then it jumps down for some reason.
That's a known problem with touchscreens. The roots of the problem is that the
pen position is sampled with substantial errors when the pressure is low. Try
to draw horizontal lines with little pressure and you should observe largely
biased segments of the line.

A possible solution would be to
a) Drop first, say, three samples after the pen down event.
b) Drop three samples before the pen up event. This would require to delay
emiting samples to userspace, say keep them in a FIFO.

--
Greetings,
   Andrew