Ubuntu Wiki

• Launchpad Entry: desktop-lucid-xorg-multitouch

• Created: 2010-03-07

• Contributors: BryceHarrington, AndyWhitcroft

• Packages affected: linux, xserver-xorg-input-evdev, xserver-xorg-input-evtouch, xserver-xorg-input-wacom

• See also: Touchscreen Blueprint

Summary

Integrates low-level support for certain models of touchscreen devices and exposes basic multitouch functionality on them to allow Ubuntu to be used as a proving ground for multitouch and touch gesture experimentation.

The packages implementing this functionality will be staged in a PPA for evaluation. Depending on the outcome of the evaluation we may then move some or all into Lucid proper. They are currently being staged in this PPA: https://edge.launchpad.net/~xorg-edgers/+archive/multitouch/

Project Planning Information is also available.

Rationale

Ultimately, we'd like to ensure that Ubuntu works with the current generation of multitouch capable touch screens. We have looked at general touchscreen enablement previously in the Touchscreen blueprint, from low level driver support (which for regular touch is largely taken care of with -evdev and XI2) to configuration tools, window-manager functionality, and application support. Certainly, solving the entire breadth of the problem is well beyond what we can do for Lucid, but if we focus on a small subset of the fundamental problems at the lower levels, we can make some useful progress and establish a base from which the higher level implementation work can be done. Our goal is that Ubuntu can provide a solid foundation for experimentation in touch, multitouch, and touch gesture interfaces.

The subset which makes the most sense to focus on as the top priority is the intersection of hardware that can be supported with the -evdev driver, and with whom Canonical has some level of business relationship with in case we have questions (e.g. hardware the OEM team expects to be supporting in the coming year or so). Hopefully in enabling this specific hardware, there will be additional hardware that can trivially be enabled as low hanging fruit.

Overview

The intended stack would be (upside down):

• kernel driver (mine or others)
• /dev/input/eventX

• X.org evdev driver (the one patched by Benjamin, for instance)

• X.org MPX/XInput2 API
• multitouchd daemon
• Qt or GTK+ or other

The current status of the above stack is "multi-pointer only", that is multi-touch without any gesture recognition. There have been debates as to where to put gesture recognition in the stack. Very few people have worked on multitouch gestures.

Multitouch in X is currently limited by the lack of multitouch events in the protocol. Benjamin's patch is a way around it to get multitouch-like features through a multipointer system. Upstream (Peter Hutterer) has indicated a preference to seeing this done via a single-pointer, because then clients would need to deal with a single touch event, instead of one event for each finger. But there are pros and cons to each approach and it's not clear there is yet a consensus about this. See discussion on xorg-devel@ for more background.

Benjamin's patch makes some simplifying assumptions that may not address the full spectrum of possible multi-touch use cases. For instance, multi-user collaboration using inputs from multiple hands going to multiple windows that support both multi-pointer and multi-touch awareness. It is likely some significant API redesign beyond Benjamin's proposed patch would be needed to address all possible cases. Thus, clients which implement support on top of Benjamin's patch would likely need reimplementation for what eventually is officially adopted by upstream.

Kernel

Multitouch support first appears in any form in v2.6.30 bringing finger tracking to the events protocol. There does not appear to be any actual drivers supporting it at that point. In v2.6.31 the n-trig driver seems to have been converted over to expose multi-touch support (with appropriate firmware only). In v2.6.32 and v2.6.33 the support is apparently unchanged. A number of drivers appear to be merging in v2.6.34-rc1 as do a number of fixes for the existing n-trig driver.

The v2.6.34-rc1 HID drivers seems to support multitouch for the following devices:

It seems that to have any sort of support for multitouch at the kernel level we would need to backport the drivers from at least v2.6.34-rc1 to even get n-trig support in a workable state.

Required Changes

As of v2.6.34-rc1 the commits below seem to be required to get the foundations changed in HID to get the drivers we require for the common multi-touch devices listed above, note these have been selected by inspection and not as yet tested:

Tasks

See the blueprint whiteboard.