On Wed, Feb 22, 2012 at 04:24:25PM +0100, Henrik Rydberg wrote: > > > I see the problem. However, ignoring it will just move the problem > > > forward to another bug report, will it not? Hysteresis is a slam dunk > > > here. In addition, since the low-pressure state is bound to be > > > transitional (soon to be followed by a real num_fingers==1 package), > > > simply skipping such packages might be a better option. > > > > In practice, we don't actually see the profile sensor pad sending one > > low-z finger, and one high-z finger. In the case where one finger is > > solidly on the pad, and another finger is hovering, lifting, or > > alighting, the pad sends 2 high-z fingers, with one of them having a > > completely wrong x or y coordinate. > > Urgh. > > > The two reported z-values are > > nearly, but not exactly, identical. I can't think of good fix for > > this, other than adding finger tracking and filtering out via > > 'moved-too-far-too-fast', where possible, and I'd prefer that this be > > handled in userspace. > > It sounds like the z value in the second packet carries zero > information. If that were true, the fact that the patch is effective > suggests the semi-mt slot reporting could follow BTN_TOUCH, more or > less. In doing so, you would also obtain hysteresis automatically. > > > The 1-low-z && 1-high-z case that we are > > discussing here isn't actually ever triggered; either both fingers are > > high-z, or neither are. > > I suspect it depends a bit on the values of low-z and hi-z, > respectively? Otherwise, there really is no information in that extra > packet. > > > The real usefulness of this patch is filtering out the 1-low-z-finger > > and 2-low-z fingers cases. > > > > As for the hypothetical 1-finger-hi, 1-finger-low case, which I asked > > Chung-yih to add because it seemed like a good idea in theory... > > > > Yes, I think you have a good point. Thanks to evdev's stateful > > nature, simply skipping the (1-strong,1-weak) packet might actually > > work better than forcing num_fingers == 0. > > > > For cases where a second finger is temporarily reporting low-z because > > it is arriving or leaving, evdev would just lock the (1 or 2 initial) > > fingers in their current position until the transition is over, and > > then start reporting the new number of fingers at their new positions. > > > > For cases where there is one high-z finger, and a hovering thumb or > > palm triggers 2-finger reporting temporarily (without ever going above > > the threshold), the original finger will get frozen in its current > > position until the hovering finger is no longer detected, and then > > snap to its new position. This might cause strange sudden jumps, but > > that seems unavoidable. > > A lot of things seem unavoidable with this hardware. :-) > > > I'm not sure hysteresis is a "slam dunk"... in fact, I don't see how > > it would help much. But, it is hard to argue against adding the > > functionality, since the hysteresis window can be made arbitrarily > > small. Perhaps if you are inclined, you can elaborate on why you > > think it is important. > > The most striking effect is the ability to better retain a > drag. Although the statement was made in light of possible > (1-strong,1-weak) packets, it should help in the 2-weak case too. The bigger question is why is this needed in kernel. The original hysteresis with BTN_TOUCH was done for sole benefit of mousedev so that we could allow somewhat better transition from standard PS/2 mode into native Synaptics mode with absolute coordinates at time when barely anyone had Synaptics X driver installed. This was, what, 10 years ago? Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
