Re: [Xen-devel] [PATCH 1/3] Add Summagraphics Tablet emulation

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Keir Fraser wrote:
> On 15 Mar 2006, at 23:22, Dugger, Donald D wrote:
>
> > Yes, the 3 patches are independent so you can apply them as you wish.
> >
> > I'm not sure what your concern is about the touchpad patch.  There was
> > code to emulate a touchpad in the code but it was all wrong and didn't
> > work, I basically had to re-do all of the touchpad code to get this to
> > work.
> Why is it not possible to translate from absolute coordinates provided 
> by VNC into deltas required for PS/2 mouse emulation? Do you end up 
> with accumulating absolute error?
There are two issues, the first is acceleration.  Most guests scale 
relative coordinates by some factor which is usually configuration so 
you can control the "speed" of the mouse.
The second is that you have no idea where the mouse starts out at or 
when it gets warped so even if you knew the acceleration you would 
always be at a fixed offset from the absolute cursor.
Since coordinates are only passed when the mouse is within the bounding 
box of the VNC window, you end up with unreachable portions of the 
screen depending on you're offset.
Regards,

Anthony Liguori
>  -- Keir
>
>
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