Extra pointer motion with current git xf86-input-synaptics

[Magnus Kessler]

On Sunday 28 September 2008, Simon Thum wrote:
> Peter Hutterer wrote:
[...]
> > Check out GetPointerEvents in xserver/dix/getevents.c.
> >
> > We take valuator coordinates, scale them to screen coords based on the
> > axis information and then scale them back to device coords*.
> >
> > The screen coords are used to move the cursor and the scaling is done
> > based on the axis ranges. Hence the different acceleration when you
> > change the axis range to 0,-1 (in which case the screen coords are used
> > as axis ranges).
>
> To me, this case sounds like a rounding error piling up.
>
> What about:
>
> rescaleValuatorAxis(int coord, AxisInfoPtr from, AxisInfoPtr to,
>                      int defmax)
> {
>      [...]
>      return (int)(((float)(coord - fmin) + 0.5f) * (tmax - tmin + 1) /
>                   (fmax - fmin + 1)) + tmin;
> }
>
>
> in getevents.c. This may take out the trend you're observing.

Thanks, Simon. That change does indeed solve my problem.

For the record: By instrumenting the driver with xf86Msg calls as Peter 
suggested I have verified that the synaptics driver only calls 
xf86PostMotionEvent when the touchpad was actually touched. Yet I was 
seeing the cursor move even when xf86PostButtonEvent was called after 
clicking the physical buttons.

Cheers,

Magnus

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