Re: [PATCH] input: mt: Add an envelope tool type

[Ping Cheng]

On Wed, Dec 8, 2010 at 3:58 PM, Dmitry Torokhov
<dmitry.torokhov@xxxxxxxxx> wrote:
> On Wed, Dec 08, 2010 at 03:43:51PM -0800, Ping Cheng wrote:
>> On Wed, Dec 8, 2010 at 9:43 AM, Chase Douglas
>> <chase.douglas@xxxxxxxxxxxxx> wrote:
>> > On 12/07/2010 03:29 AM, Henrik Rydberg wrote:
>> >> Some touch devices are capable of detecting the envelope or hull
>> >> of the touches, but not the touches themselves. This patch adds
>> >> the MT_TOOL_ENVELOPE touch type to be used for such devices.
>> >>
>> >> Signed-off-by: Henrik Rydberg <rydberg@xxxxxxxxxxx>
>> >> ---
>> >> Hi all,
>> >>
>> >> This patch represents an MT solution for those devices that can detect
>> >> and report some effects of dual touch, but cannot report individual
>> >> contacts. Synaptics and elantech are two examples. Having the drivers
>> >> report the bounding rectangle of the touches is useful in userland,
>> >> since the information makes it possible to implement zooming
>> >> gestures. At the same time, it would be confusing to send these
>> >> envelope points as fingers, since they clearly are not. As a remedy,
>> >> introduce MT_TOOL_ENVELOPE, which tells applications that care about
>> >> details that these are not real fingers, at the same time as it allows
>> >> gesture applications based on MT data to function without
>> >> modification.
>> >
>> > Is it assumed that the envelop has only two touches comprising it? Or is
>> > it any number of touches? If it's any number of touches, how does one
>> > know how many touches it is?
>>
>> Those are good questions. Specifying how many touches are in the
>> envelop makes sense. It also covers rectangle as a special case of
>> envelop.
>
> I have a feeling that trying to accomodate non-rectangular,

No, we are not talking about non-rectangular shape here. Envelop is
always a rectangle. By rectangle above, I meant 2 touches.

An envelop that includes number of touches offers us more information
than a rectangle does.

Ping

> more than 2 point shapes without using native MT data is over-engineering the
> problem... Do we have examples other than older generation Elantechs and
> Synaptics that need envelope notion?
>
> --
> Dmitry
>
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