Re: Touchpad problems with 2.6.11-rc2

[Vojtech Pavlik <vojtech@suse.cz>]

On Tue, Feb 01, 2005 at 11:41:48PM -0800, Pete Zaitcev wrote:
> On 30 Jan 2005 12:10:34 +0100, Peter Osterlund <petero2@telia.com> wrote:
> 
> > > - Slow motion of finger produces no motion, then a jump. So, it's very hard to
> > >   target smaller UI elements and some web links.
> > 
> > I see this too when I don't use the X touchpad driver. With the X
> > driver there is no problem. I think the problem is that mousedev.c in
> > the kernel has to use integer arithmetic, so probably small movements
> > are rounded off to 0. I'll try to come up with a fix for this.
> 
> Thanks for the hint. I tried various schemes and mathematical transformations
> and found one which gives unquestionably the best result, with smoothest, most
> precise and comfortable pointer movement:

Well, you removed the scaling to the touchpad resolution, which will
cause ALPS touchpad to be significantly slower than Synaptics touchpads.
Similarly, the screen size used to be taken into account, but probably
that was a mistake, since the value is usually left at default and
doesn't correspond to the real screen size.

> --- linux-2.6.11-rc2/drivers/input/mousedev.c	2005-01-22 14:54:14.000000000 -0800
> +++ linux-2.6.11-rc2-lem/drivers/input/mousedev.c	2005-02-01 23:20:19.000000000 -0800
> @@ -122,19 +122,19 @@ static void mousedev_touchpad_event(stru
>  	if (mousedev->touch) {
>  		switch (code) {
>  			case ABS_X:
> -				size = dev->absmax[ABS_X] - dev->absmin[ABS_X];
> -				if (size == 0) size = xres;
>  				fx(0) = value;
>  				if (mousedev->pkt_count >= 2)
> -					mousedev->packet.dx = ((fx(0) - fx(1)) / 2 + (fx(1) - fx(2)) / 2) * xres / (size * 2);
> +					mousedev->packet.dx = (value - fx(2)) / 2;
> +				else if (mousedev->pkt_count == 1)
> +					mousedev->packet.dx = value - fx(1);
>  				break;
>  
>  			case ABS_Y:
> -				size = dev->absmax[ABS_Y] - dev->absmin[ABS_Y];
> -				if (size == 0) size = yres;
>  				fy(0) = value;
>  				if (mousedev->pkt_count >= 2)
> -					mousedev->packet.dy = -((fy(0) - fy(1)) / 2 + (fy(1) - fy(2)) / 2) * yres / (size * 2);
> +					mousedev->packet.dy = (fy(2) - value) / 2;
> +				else if (mousedev->pkt_count == 1)
> +					mousedev->packet.dy = fy(1) - value;
>  				break;
>  		}
>  	}
> 
> I'm not kidding. Someone obviously outsmarted himself when programming this.
 
-- 
Vojtech Pavlik
SuSE Labs, SuSE CR