linux-kernel - Re: [PATCH v3 11/13] HID: hid-multitouch: support for hovering devices

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Message-ID: <20121113180453.GA3622@polaris.bitmath.org>
Date:	Tue, 13 Nov 2012 19:04:53 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 11/13] HID: hid-multitouch: support for hovering
 devices

Hi Benjamin,

> > Why [-1,1] here?
> 
> At first, I only used [0,1]. However, it's still the same problem with
> the information being kept between the touches:
> if you start an application after having touched your device, you
> normally have to ask for the different per-touche states to get x, y,
> distance, pressure, etc...
> However, this is not much mandatory because the protocol in its
> current form ensures that you will get the new states of the axes when
> a new touch occurs.

Right, the stateful communication requires a full state read after
opening the deivce, although in most cases this is not really
necessary. This is no different for ABS_MT_DISTANCE, of course.

> ABS_MT_DISTANCE is a little bit different here because the protocol
> guarantees that once you get the "not in range" state through
> tracking_id == -1, distance should be 1.
> When the new touch of the very same slot occurs, you also have the
> guarantee that distance is at 1 too.

ABS_MT_DISTANCE is just another attribute of the slot, so it really is
no different.

> So basically, if you don't ask for the slot states, you will never get
> that very first distance.

Which will not be important either; as long as the slot is unused, it
does not matter what the attributes of that slot are.

> I know that it's a user-space problem, but honestly, I don't want to
> fix several user-space problems when we could fix it through the
> protocol.
> 
> I can see 2 solutions:
> - set the range to: [0,1] and still sending -1 (or 2) for the invalid
> distance value (if it's not clamped)
> - set the range to: [0,2] and having: 0 for touch, 1 for hovering, and
> 2 for not in range
> 
> Does that make sense?

I just do not see what problem you want to solve here.

Thanks,
Henrik
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