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

[Ping Cheng <pinglinux@gmail.com>]

On Wed, Dec 8, 2010 at 9:43 AM, Chase Douglas
<chase.douglas@canonical.com> 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@euromail.se>
>> ---
>> 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.

Ping

> How are the envelop shape and position determined?
>
> I think the idea is good, I just don't have enough information to
> understand how the tool type is supposed to be used. This has been an
> issue with many evdev properties, so I'm hoping we can provide more
> detailed documentation this time around :).
>
> -- Chase
> --
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