Re: [PATCH 7/7] elantech: average the two coordinates when 2 fingers

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Aug 02, 2010 at 01:22:15PM +0200, Henrik Rydberg wrote:
> On 08/02/2010 01:12 PM, Éric Piel wrote:
> 
> > Op 02-08-10 12:02, Henrik Rydberg schreef:
> >> On 08/02/2010 10:17 AM, Éric Piel wrote:
> >>
> >>> Op 01-08-10 15:57, Henrik Rydberg schreef:
> >>>> On 08/01/2010 01:28 PM, Éric Piel wrote:
> >>> :
> >>>>> I still think that for the very specific use case of scrolling when
> >>>>> pressing one finger and moving up and dow the other one, reporting the
> >>>>> average works better than the first finger. However, I guess this can be
> >>>>> considered just as a drawback of the ST protocol, and fixed in userspace
> >>>>> by using the MT protocol.
> >>>>>
> >>>>> What do you think? Does it look fine to you? Below is the code.
> >>>>
> >>>>
> >>>> I might have lost track of what problem needs to be solved. The current patch
> >>>> seems to implement tracking, but still does not solve the individual MT finger
> >>>> problem. And, it uses the same definition of ABS_X/Y as before. I was also under
> >>>> the impression that synaptics needs fixing, anyways. All of this taken together
> >>>> sadly suggests that this patch could just as well be reverted to the original
> >>>> one. Or? Alternatively, one could switch to the type B protocol, since no
> >>>> further tracking improvement is possible in userspace. The implementation is
> >>>> tidy and simple enough, I think.
> >>> Yes, you're right, the patch I've sent was still with the "average of
> >>> the 2 fingers", but I'm now willing to drop it. With the tracking, at
> >>> least we can keep sending info about a real finger and avoid jumps at
> >>> the transition 1->2, so reporting the first finger might have advantages
> >>> over reporting the average :-) The improvement for the test case can
> >>> just go to userspace.
> >>>
> >>> The tracking is still not so clever, so it's definitly not adapted to a
> >>> type B MT protocol (think transition 2->1).
> >>
> >>
> >> You need to add the tracking id and a couple of lines, but i do not see why the
> >> 2->1 transition would be treated any differently. The one-finger coordinate
> >> would be close to either position[0] or position[1], which would determine the
> >> tracking id to keep. Every time you add a finger you add a new tracking id. What
> >> is your planned support for three fingers?
> > Yes, yes, it's probably fairly easy to do some kind of tracking. But I
> > think that as long as the hardware does not provide such a thing, it's
> > better to do the minimum in kernel space, just enough to be meaningful,
> > and leave the rest to userspace.
> 
> 
> The implemented part could also be done in userspace. Going half-way just to
> circumvent buggy behavior in synaptics is really not a good idea.
> 

What synaptics you are talking about here? Userspace driver or the
in-kernel synaptics support? If the latter, then the device is not truly
multitouch device (latest versions of the hardware/firmware aside) as it
is capable of reportiong only one set of coordinates (X/Y) in addition
to number of fingers on the surface.

-- 
Dmitry
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