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

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Date:	Wed, 14 Mar 2007 20:04:32 +0200
From:	Anssi Hannula <anssi.hannula@...il.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	johann deneux <johann.deneux@...il.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	linux-input@...ey.karlin.mff.cuni.cz
Subject: Re: FF layer restrictions [Was: [PATCH 1/1] Input: add sensable phantom
 driver]

Jiri Slaby wrote:
> Dmitry Torokhov napsal(a):
>> On 3/13/07, Jiri Slaby <jirislaby@...il.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.

Interesting. What kind of device is that? i.e. what is the third
direction value?

>>>> 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.

I don't like the idea of a driver-specific "raw" effect, I'd rather add
real effect types.

> 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.

Wine and BZflag come to mind, though I think the support is quite
limited in both.

-- 
Anssi Hannula

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