Re: [Qemu-devel] console muti-head some more design input

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > With absolute pointer events the whole thing becomes a bit more tricky
> > as we have to map input from multiple displays (QemuConsoles) to a
> > single absolute pointing device (usb tablet).  This is what Dave wants
> > the screen layout for.  I still think the input layer is the place to do
> > this transformation.
> 
> We solve this problem in our UI now. It's not enough to know the 
> offsets. You also need to know all the resolutions - the display window, 
> the guest, and the device coordinate system of the virtual pointing 
> device (we use a PV event ring instead of a USB tablet).
> 
> If your UI can scale the guest output, that means you need to also store 
> the UI's window geometry in the QemuConsole to get the math right.

qemu input layer uses a 0 -> 0x7fff range for absolute coordinates.  So
your ui code has to transform the pointer position to that, considering
window scaling if needed, then pass it to the input code.  Inout code
passes it on to the input device, which again will scale it to the
dimensions of the usb-tablet / pv device / whatever.

For multihead support we need the additional step to transform (display,
phys-x, phys-y) to (virtual-x, virtual-y) using the screen layout.  IMO
the input layer should to that.  Quite some changes are need to handle
that, but the input layer needs some love anyway.

cheers,
  Gerd