[RFC XI 2.1 - xf86-input-evdev 2/3] Add experimental XI 2.1 multitouch support

Peter Hutterer peter.hutterer at who-t.net
Thu Dec 9 17:29:31 PST 2010

On Mon, Dec 06, 2010 at 09:41:48AM -0800, Chase Douglas wrote:
> On 12/05/2010 10:41 PM, Peter Hutterer wrote:
> > if the kernel can send it through one device, we can handle it, right?
> > if both are sent through the same axes (and need a serial or something to
> > differentiate like the wacom drivers) then yes, they need to be split up
> > into multiple devices.
> I think we're in agreement about what we can handle. We should be able
> to handle whatever the kernel sends us. But I feel that it's impossible
> to have a kernel device that sends touch information through the same
> properties for different surfaces. Thus, we don't need per-axis touch modes.

it's much easier for the kernel to add new information to the event
interface that it is for us to change the protocol. the initial MT protocol
didn't have pressure, for example, no tracking ID (IIRC), etc. all these
have been added since, while we were stuck with the same protocol version.
how hard would it be to add REL_MT_POSITION_X to the kernel and have devices
send events?

so unless you're _sure_ that in two or three years time we won't have
devices with multiple modes I'd say add a per-valuator flag. Worst case,
it's always 0 or 1 for all valuators for the forseeable future.


> To push towards a resolution to this issue, Peter, Ping, do you still
> feel we will need per-axis touch modes? If you do, then I could use more
> detail on how such a device would be defined through the evdev or touch
> class interface. Maybe I'm missing something obvious?

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