linux-kernel - Re: [PATCH] input: mt: Interface and MT

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Date:	Fri, 10 Dec 2010 21:01:34 +0100
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Ping Cheng <pinglinux@...il.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] input: mt: Interface and MT_TOOL documentation updates

On 12/10/2010 08:00 PM, Ping Cheng wrote:

> On Fri, Dec 10, 2010 at 10:13 AM, Henrik Rydberg <rydberg@...omail.se> wrote:
>>
>>> Can we make MT_TOOL_ENVELOPE cover a bit more cases by:
>>>
>>> 1. Removing ", and is only used for legacy hardware";
>>> 2. Adding "Or the number of contacts inside the bounding rectangle is
>>> reported if hardware provides the number but not the real contact
>>> positions" to the end of the paragraph.
>>
>> You might disagree, but "old" is still somewhat apt in this situation.
> 
> It's ok if we say the new type was inspired by legacy hardware. But
> saying that it "is only used for legacy hardware" closes the door for
> future development. That's not what we are trying to do, right?


Well, in a sense we are. I would agree that data aiming to provide gestures as a
2D transformation matrix can be handled quite well with two tracked points and a
finger count. However, a multitouch interface where users manipulate different
objects on the screen simultaneously is a different story.

> 
>> How would you suggest we report the number of fingers?
> 
> I guess if we want to make it generic, we could have something like
> ABS_MT_NUM_CONTACTS to go with MT_TOOL_ENVELOPE. Clients, such as
> synaptics touchpads, that only care about the number of contacts
> inside the envelope don't need to process the contact positions even
> when they are reported. This also resolve the potential that
> BTN_TOOL_QUADTAP is not enough to tell us how many contacts are on the
> surface.


I really would like to avoid adding a new way to solve an old problem, in
particular given the statement above. Adding something like BTN_TOOL_QUINTAP
would hurt a little bit, but not nearly as much.

> 
> Maybe we should also tell the clients whether they are going to get
> the contact positions or not.


I may not understand what you mean here, but if you are referring to an up-front
declaration of what MT_TOOL types are to be expected, we did discuss this
before, without any conclusion. Perhaps it is relevant to outline why this would
be important.

Thanks,
Henrik
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