New approach to multitouch using DIDs and bitmasked events

[Chase Douglas]

On Mon, 2010-07-05 at 12:26 -0400, Rafi Rubin wrote:
> >> Just one small point, if you do make these DIDs look more pointer nodes, and we
> >> can come up with some way to associate them with a more classical device, I'd
> >> like to see the magic mouse and others also abandon valuators and switch to
> >> children of the normal mouse.  That just seems to me like a more consistent and
> >> easier to support approach.
> >
> > DIDs cannot be associated with traditional X pointers, even though they
> > may send motion events through XI2. However, in the mixed mode patches I
> > I made, we can support the magic mouse as a non-DID because it has a
> > traditional pointer. In this instance, it is assumed that the touch
> > surface is more of an augmentation of the pointer instead of as a
> > pointing device itself. Thus, we can attach the device to a master
> > pointer and clients can grab it.
> 
> Since, I seem to have missed some of the nuance of this discussion, I'd like to 
> ask for clarification.  If the mt events are coming down axes that core ignores, 
> why make the distinction?

I'm not sure I follow your question completely. I've rephrased your
question to what I think you mean and answered it.

If X core ignores MT valuators, why bother with DIDs?

(Even this doesn't quite make sense once you understand the answer)

The problem comes from the fact that the first two valuators of a
pointer device are assumed by the server to be the X and Y pointer
coordinates (relative or absolute). If a device is pure multitouch (i.e.
not a magicmouse), we still want the first two valuators to be the X and
Y coordinates of each touch, but we don't want them to be handled by the
server as though they were traditional X core motion events. Otherwise,
we'd have the following:

Event: (from touch 0)
	X
	Y
	Slot ID
Event: (from touch 1)
	X
	Y
	Slot ID

If these were passed through X core, the server would think the mouse
pointer is flickering back and forth between the two touch coordinates.
The solution is to "float" the input device so it's not tied to a master
pointer.

The reason we can't pass DIDs as XI1 events is because an XI1 client
also doesn't see "floating" input devices that aren't attached to master
pointers. Only XI2 can see events from "floating" input devices.

Now, in the magicmouse case, X core does ignore MT valuators. However,
in this case we actually have a real pointing device giving valid
relative pointer coordinates through X core. It's very much a different
type of device, compared to a pure multitouch touchpad, with a separate
set of meanings attached to pointer and touch coordinates.

-- Chase