Re: [Qemu-devel] [PATCH 7/9] spice: add mouse

[Anthony Liguori]

On 08/20/2010 09:03 AM, Gerd Hoffmann wrote:
>   Hi,
>
> > > Again this is libspice interface (and I think also wire protocol), so
> > > I can't change it. I can convert dz into some button_mask bits before
> > > calling kbd_mouse_event, but looking at the vnc code it seems qemu
> > > expects the mouse wheel events being passed via dz not button_state.
> >
> > That's unfortunate but understood. Is Spice considered a stable API/wire
> > protocol at this point?
>
> Yes.  There are version numbers though, so we can add new messages and 
> use them in case both server and client are new enough.  Unfortunaly 
> this makes the keyboard f*ckup only slightly less messy as we'll have 
> to support both old+new way for compatibility reasons.  Oh well.

One of the things to consider is that we only emulate a 2-axis 5 button 
mouse.  Buttons one through three are bits in button_state and buttons 
4/5 are represented through dz.  My mouse IRL is actually a 9 button mouse.

We encode buttons 4/5 as a -1, 0, 1 in dz which corresponds to 10, 00, 
and 11.  We cannot represent 11 with dz which corresponds to having 
buttons 4 and 5 pressed simultaneously.  Most mice have a scroll wheel 
for 4/5 but there's no strict requirement that that's the case.

So in terms of building a long term stable wire protocol, you'd be much 
better off using button_mask to encode buttons 4/5 because it's just a 
matter of time before we drop the dz hack in qemu.

Regards,

Anthony Liguori

> cheers,
>   Gerd