Date: Wed, 2 Feb 2005 23:58:05 +0100 (CET)
From: Peter Osterlund <petero2@telia.com>
To: Pete Zaitcev <zaitcev@redhat.com>
Cc: vojtech@suse.cz, linux-kernel@vger.kernel.org, dtor_core@ameritech.net
Subject: Re: Touchpad problems with 2.6.11-rc2
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On Wed, 2 Feb 2005, Pete Zaitcev wrote:

> On 02 Feb 2005 21:57:39 +0100, Peter Osterlund <petero2@telia.com> wrote:
>
> > Please try this patch instead. It works well with my alps touchpad. (I
> > don't have a synaptics touchpad.) It does the following:
> >
> > * Compensates for the lack of floating point arithmetic by keeping
> >   track of remainders from the integer divisions.
> > * Removes the xres/yres scaling so that you get the same speed in the
> >   X and Y directions even if your screen is not square.
> > * Sets scale factors so that the speed for synaptics and alps should
> >   be equal to each other and equal to the synaptics speed from 2.6.10.
>
> Thanks a lot, Peter. I think I like the result even better than the one
> after the simple-minded removal that I posted. It's possible that when
> I accepted the case of (pktcount == 1) it hurt smoothness.
>
> Do you think it makes sense to zero fractions when pktcount is dropped?

In practice I don't think it will make any significant difference. What
the code should do depends on what you want to happen if you move the
mouse pointer 1/2 pixel with one finger stroke, then move it another 1/2
pixel with a second stroke. The patch I posted will move the pointer one
pixel in this case and your code will move it 0 pixels. (The X driver does
not reset the fractions, but that doesn't of course mean that it's the
only right thing to do.)

> Also, I think the extra unary minus is uncoth.

The code was written like that to emphasize the fact that X and Y use the
same formula, with the only difference that the kernel Y axis is mirrored
compared to the touchpad Y axis.

It didn't make any difference for the generated assembly code though,
using gcc 3.4.2 from Fedora Core 3.

> +	enum {  FRACTION_DENOM = 100 };

The enum is much nicer than my #define.

-- 
Peter Osterlund - petero2@telia.com
http://web.telia.com/~u89404340
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