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

[Dave Airlie]

On Fri, Nov 22, 2013 at 6:41 PM, Gerd Hoffmann <address@hidden> wrote:
>   Hi,
>
>> > While thinking about this:  A completely different approach to tackle
>> > this would be to implement touchscreen emulation.  So we don't have a
>> > single usb-tablet, but multiple (one per display) touch input devices.
>> > Then we can simply route absolute input events from this display as-is
>> > to that touch device and be done with it.  No need to deal with
>> > coordinate transformations in qemu, the guest will deal with it.
>>
>> This is a nice dream, except you'll find the guest won't deal with it
>> very well, and you'll have all kinds of guest scenarios to link up
>> that touchscreen a talks to monitor a etc.
>
> Ok, scratch the idea then.
>
> I don't have personal experience with this,
> no touch capable displays here.

Hmm I think we get to unscratch this idea,

After looking into this a bit more I think we probably do need
something outside the gpu to handle this.

The problem is that there are two scenarios for a GPU multi-head,

a) one resource - two outputs, the second output has an offset to
scanout into the resource
b) two resources - two outputs, both outputs have a 0,0 into their
respective resources.

So the GPU doesn't have this information in all cases on what the
input device configuration should be,
Neither do we have anyway in the guests to specify this relationship
at the driver level.

So I think we probably do need treat multi-head windows as separate
input devices, and/or have
an agent in the guest to do the right thing by configuring multiple
input devices to map to multiple outputs.

I suppose spice must do something like this already, maybe they can
tell me more.

Dave.