Hi Daniel, Chase, On Wed, Jun 29, 2011 at 6:32 PM, Chase Douglas <chase.douglas@xxxxxxxxxxxxx> wrote: > On 06/29/2011 11:07 AM, Daniel Stone wrote: >> Hi Chase, >> >> On Wed, Jun 29, 2011 at 11:02:53AM +0100, Chase Douglas wrote: >>> In the older "profile" devices, we got essentially the bounding box of >>> all touches. This allows us to detect pinch gestures between the two >>> most extreme touches when there are three touches on the touchpad. >> >> This isn't necessarily true for all pads. If you look at Derek's >> patchset from a couple of weeks ago, it was for a profile sensor which >> had the same reporting behaviour. Internally, the touchpad could track >> many fingers, but would always report the first (in SGM packet) and most >> recent (in AGM packet) fingers. You could fake a bounding-box >> calculation, but it would be the bounding box of fingers 0 and n, rather >> than the bounding box of all fingers. > > Are we really sure that Derek's trackpad was a profile device? I mean > *really* sure. Because if Synaptics is putting out two different devices > that are identical in protocol but behave differently, then that's a > *big* problem for us gesture developers :). > > I would be surprised if a profile device were providing the first and > third touch locations as opposed to the bounding box because then > there's no difference between it and this new "image sensor" device type. I agree with Chase, the 0:n box behavior sounds more like image sensor than profile sensor. However, as I just mentioned in the previous email, I have looked at a profile sensor that tries to report first and second finger positions, not a bounding box. In any case, the result is: You end up computing (usually) a 0:1 "bounding box", with n >= 2 fingers on the pad. I say usually because it is pretty easy to confuse the finger tracking of a profile sensor. >>> The above description makes it sound like we will no longer have a >>> bounding box of touches. According to the description, if I put four >>> fingers down in a square formation and then touch a fifth finger in the >>> middle of the square, I will only see the locations of one corner and >>> the middle of the square. This would make meaningful gesture detection >>> beyond two touches nearly impossible. Is this really how the touchpad >>> works, or is the above description not quite right? >> >> Yes, I believe that's how the touchpad works. It would be nice to get >> all fingers, but unfortunately PS/2 doesn't give us enough bandwidth to >> do that. > > If this is true for these new image devices, then we'll need to set a > different property bit other than SEMI_MT (maybe FIRST_LAST_MT? I'm not > good with names :). I'm thinking we should disable gesture support for > these trackpads in uTouch when there are more than two touches because > we can't be sure what is going on in any meaningful way. The bounding > box is more useful than this, which is really sad. > > -- Chase This is exactly what this patch set does by defining the T5R2 property. It is very challenging to support any 3+ finger gestures with a touchpad that only reports two fingers... whether it is semi-mt or T5R2. You must always make an assumption about where those hidden fingers are. But, that's a problem for userspace... :) -Daniel -- 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
