Re: PATCH: Fix "invisible wall" problem with relative mouse mode

[Anthony Liguori <anthony codemonkey ws>]

Daniel P. Berrange wrote:
> On Tue, Feb 24, 2009 at 08:25:33AM -0600, Anthony Liguori wrote:
>   
> > Daniel P. Berrange wrote:
> >     
> > > A number of bugs have conspired together to make relative mouse mode not
> > > work very well. The core problem is that when using the relative mode the
> > > mouse pointer will appear to hit an "invisible wall" before the true edge
> > > of the screen.
> > >
> > > The problems start occur when we do the mouse grab and fall out from 
> > > that...
> > >
> > > - We passed our window as the "confine-to" arg for the gdk_pointer_grab.
> > >   This meant that the client desktop pointer would stop moving / 
> > >   generating
> > >   events when we hit the edge of our window. In relative mode we need to
> > >   get continuous events no matter where the pointer is, since we're after
> > >   relative changes, not absolute coords.
> > >  
> > >       
> > What is supposed to fix this is auto warping.  If you detect that you're 
> > close to the edge of the screen, it should warp you toward the center of 
> > the window.
> >
> > When I first implemented this, I observed that confining the pointer to 
> > the desktop instead of the window merely made the problem harder to 
> > reproduce.  You still stop getting pointer events if the mouse hits the 
> > edge of the screen so under the right circumstances, you'll still hit a 
> > wall.
> >
> > The warping was supposed to be the proper fix although apparently it's 
> > not working well enough.
> >     
>
> The warping *does* in fact work perfectly, but only if you allow the mouse
> to move  outside the VNC window. So this patch should enable the behaviour 
> you originally intended. If we confined the pointer to just the VNC 
> window, then we would have to change the warping code to watch for hitting
> the edge of the VNC widget instead of edge of the screen. 
>
> To test this was actually working, I tweaked the grab so that the local
> cursor was not hidden while grabbed - this lets you see when it hits
> the edge and that it warps back away from it
>   
>         if (x == 0) x += 200;
>         if (y == 0) y += 200;
>         if (x == (gdk_screen_get_width(screen) - 1)) x -= 200;
>         if (y == (gdk_screen_get_height(screen) - 1)) y -= 200;

This looks like a bug to me, no?  Shouldn't it be using the window 
sizes?  I'm not sure what I was thinking with this one...

If we just changed it to use the window width/height, shouldn't that 
also fix the problem?

Regards,

Anthony Liguori