Re: FF layer restrictions [Was: [PATCH 1/1] Input: add sensable phantom driver]

From: Jiri Slaby <jirislaby@gmail.com>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Jiri Slaby <jirislaby@gmail.com>,
	johann deneux <johann.deneux@gmail.com>,
	Linux kernel mailing list <linux-kernel@vger.kernel.org>,
	linux-input@atrey.karlin.mff.cuni.cz,
	Anssi Hannula <anssi.hannula@gmail.com>
Subject: Re: FF layer restrictions [Was: [PATCH 1/1] Input: add sensable phantom driver]
Date: Wed, 14 Mar 2007 17:43:18 +0100	[thread overview]
Message-ID: <45F82626.8000108@gmail.com> (raw)
In-Reply-To: <d120d5000703140802jb48bc74tbbe7ee2b120b1798@mail.gmail.com>

Dmitry Torokhov napsal(a):
> On 3/13/07, Jiri Slaby <jirislaby@gmail.com> wrote:
>> Why did you remove all Cced people? Anyway I filtered some of them out
>>
>> johann deneux napsal(a):
>> > You are right, the direction in ff_effect is meant to be an angle.
>> > A dirty solution would be to use the 16 bits as two 8-bits angles. Or
>>
>> That would be a problem as I need 3x 16bits.
>>
>> > maybe we should change the API. I don't think there are many
>> > applications using force feedback yet, so maybe that should be ok?
>> >
>> > If we change the API, we should remove the assumption that a device has
>> > at most two axes to render effects. We could for instance have a
>> > magnitude argument for each axis which is capable of rendering effects.
>> > That might be necessary even for more common gaming devices like racing
>> > wheels: One can think pedals could also be capable of force feedback
>> > some day, not just the steering wheel.
>>
>> I can do that, but in that case, I need to know how people (especially
>> those
>> input one) want me to do...
>>
> 
> Since we have no idea how many programs (if any) are using force
> feedback interface I would be wary of changing existing effcets and

I definitely agree.

> rather add new set of 3D effects.

I was thinking about having "raw" (e.g. FF_RAW) effect, which would be only
X "axes"/entries of u32, where X is about 10 for future use and simply
posting these values further to HW (maybe after clamping or driver specific
processing) from this array. This seems to be augmentation of FF_CONSTANT
but the fact, it doesn't compute forces from direction.

Also yet another one such as FF_VECTOR or FF_3D could be considered as one
posibility, but it's still the same -- to have no more than 3 entries to
pass forces...

> Do we have any idea if there any users of FF out there?

At least me :). I'm using it for wheel and joystick in modules for locally
developped multiplatform virtual reality system.

regards,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E