Hi all, Remember when I said the kernel interface for multitouch is all rather stable and good? Well, it turns out that there is a new proposal to modify it [1]. I had not been following the linux-input mailing list where it is being discussed, but I am now :). Here's a summary of the proposal:
Currently, any time a single property of a single multitouch event (say the pressure of one touch) changes, all of the current multitouch data is sent again. If you have 10 fingers touching a screen, this will generate a lot of data. The problem is that since there is no mechanism to tell the userspace which touch changed, we have to send all the data again. It would also be nice to have more explicit touch tracking exposed through the kernel <-> userspace interface. The proposal is to send ABS_SLOT events to distinguish between touches. The kernel and the userspace layers will maintain state for the input device. When one property of a touch changes, the kernel will explicitly send an ABS_SLOT event to describe which "slot" (i.e. which touch) the property change refers to. Slots will have a dynamically generated ID assigned to them when a touch begins, and the ID will be relinquished for reuse when a touch ends. Note that all this depends on the driver supporting touch tracking. For drivers that do not support touch tracking, the current protocol will be used (no ABS_SLOT events, and all data sent anytime one piece of data changes). Peter Hutterer, one of the X.org maintainers, has been following the discussion, so hopefully the new protocol will be integrated into any current X.org multitouch work. There have been a few revisions of patches to implement this support, so it appears that it could be committed to the linux-input tree sometime soon. However, it will not land in 2.6.35, which is the kernel we will ship with 10.10. If we are inclined, we can look into backporting the patch into our Maverick kernel. However, since the protocol is not backwards compatible, we will need to ensure we provide all the proper support in userspace for both use cases where touch tracking is and is not provided by the driver. P.S.: As the multitouch list seems to be private, I'm only CC'ing the internal kernel team list. -- Chase [1] http://www.spinics.net/lists/linux-input/msg08835.html _______________________________________________ Mailing list: https://launchpad.net/~multi-touch-dev Post to : [email protected] Unsubscribe : https://launchpad.net/~multi-touch-dev More help : https://help.launchpad.net/ListHelp
