Re: Questions about the documentation/specification of Linux ForceFeedback input.h

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Anssi Hannula]

15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
> Hi everyone,

Hi!

> 
> If you receive my mail, it is either because you:
> - are listed under the MAINTAINERS for "/include/uapi/linux/input.h":
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS#n4410
> - are listed as an author of "/Documentation/input/ff.txt" or of
> "/Documentation/input/interactive.fig"
> 
> In the process of testing the new driver (ff-memless-next) Michal
> (CC-ed) is working on, this allowed me to gain more insight in the
> internal workings of Linux FF. That's why I decided to review the
> userspace code that currently uses most of Linux FF functionality:
> Wine's DInput translation layer (and eventually SDL2.)
> Trying to get everything correct, I noticed both
> "/include/uapi/linux/input.h" and "/Documentation/input/ff.txt"
> provide not enough information for the following things:
> 
> 1)
> The real meaning of 'directions', declared in
> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
> :
>     "Direction of the effect" is encoded as follows: ...
> But it is not clear whether 'direction of the effect' means either:
> - positive direction of the force the user should apply to counteract
> the force that the joystick applies; or
> - positive direction of the force applied by joystick
> From my intuition, I think the latter is (silently?) meant by input.h
> If you're interested why this is so important, I attached a document
> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
> translation layer between DInput and Linux input is to be written.

>From input.h:
 * Direction of the effect is encoded as follows:
 *      0 deg -> 0x0000 (down)
 *      90 deg -> 0x4000 (left)
 *      180 deg -> 0x8000 (up)
 *      270 deg -> 0xC000 (right)

The directions in parantheses are the direction of applied force.

However, there is actually a 1:1 mapping between DInput polar
coordinates and our direction parameter; DInput polar coordinates have 0
deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
match our values due to the reverse definition.

Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
different definitions of Carts: For DInput you use -1 = north, but for
Linux +1 = up, while you use -1 = west/left for both. This causes the
1st and 3rd entries on both of the Mapping tables to be reversed. When
that is fixed, the table #2 shows the correct result.

> 2)
> It is not clear how to create a FF effect with infinite duration
> (replay.length):
> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L966
> Only the following is written about duration values in general:
> "All duration values are expressed in ms. Values above 32767 ms
> (0x7fff) should not be used and have unspecified results."
> Michal solved this by associating replay.length==0 for infinite, which
> makes sense since otherwise the effect would not have been started
> anyway.

Infinite duration can be achieved with length = 0.

> 3)
> Many Linux FF effect parameters don't have a clear explanation of the
> allowed range, and their corresponding meaning at the extrema.
> Here I list the ones that need more explanation, also take a look at
> "interactive.fig" in the kernel documentation (but also included as
> attachment):
> - left_saturation and right_saturation; and

left_saturation = maximum force on the negative ("left") side of the
center point
right_saturation = same for positive side

0x0 => no force,
0xFFFF => maximum force.

> - deadband

The range from center point wherein the effect has no effect, with
0x0 => no dead band
0xFFFF => dead band encompassing the entire axis, effect not active
anywhere.

Assuming center offset of 0, though. Not sure how the currently
supported devices interpret 0xFFFF with non-zero center offset, i.e. if
the effect is then still active in the extreme opposite end of the axis.
You wrote below that this is indeed the case with DInput, so it is
highly likely this is how the devices handle it as well.


> They all have __u16 types, but "/include/uapi/linux/input.h" does not
> say what the maximum values are.
> I'm doing a proposal to define and document this (in the Linux kernel)
> in the following way, also take a look at my attachment
> "interactiveAlteredWithRanges.svg" for the modified version:
>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>         Because the maximal value of the saturation bound can be only
> half of the total range covered by the max negative to max positive
> bounds.
>         And also because they are related to some form of force, and
> all other forms of force magnitude in Linux FF have a maximum value of
> 0x7FFF

I'm not really convinced that the different range from the other
magnitude values is a reason enough to change the definition here.

>     Max Range of {deadband} = 0xFFFF
>         This is a bit harder to explain:
>         - First, I would suggest to alter the deadband definition in
> figure "interactive.fig":
>             I would define deadband as going from a deadband-bound to
> the center (BTW, This is how MSDN defines it: "In other words, the
> condition is not active between lOffset minus lDeadBand and lOffset
> plus lDeadBand."),
>             instead of from a deadband-bound to the other deadband-bound.
>                 => Same spec as in DInput.

With 0xFFFF being the maximum deadband with center offset 0, it does not
matter if deadband is defined as range from center or total width,
maximum is 0xFFFF in both cases.

>         - Now, knowing that ff_condition_effect->center is __s16:
>             The worst case scenario is that "center = -32768" or
> "center = +32767" while still wanting to cover the whole region (this
> is actually not possible with DInput's specs: in that case, they can
> only cover half of the total region):
>             Then, to keep the scale of "center" and "deadband" the
> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF

Interesting idea. However, if this is not possible in DInput, this means
the devices will likely not support it either, since they are using the
DInput effect model (as are we).


I tried to confirm this with my SWFF2 device, but either it has stopped
working properly or, more likely, there is a regression in the kernel...
no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
requests don't seem to go through properly).


> I expect we will have to add/document the answers to my questions in
> the appropriate file "/include/uapi/linux/input.h" or
> "/Documentation/input/ff.txt", so that other userspace developers (and
> maybe also kernel devs) don't face the same ambiguities.
> 
> 
> Thank you very much for your time,

Thanks for looking into this.

> Elias
> 


-- 
Anssi Hannula

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

On Sat, Feb 15, 2014 at 3:05 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
> 15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
>> Hi everyone,
>
> Hi!
>
>>
>> If you receive my mail, it is either because you:
>> - are listed under the MAINTAINERS for "/include/uapi/linux/input.h":
>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS#n4410
>> - are listed as an author of "/Documentation/input/ff.txt" or of
>> "/Documentation/input/interactive.fig"
>>
>> In the process of testing the new driver (ff-memless-next) Michal
>> (CC-ed) is working on, this allowed me to gain more insight in the
>> internal workings of Linux FF. That's why I decided to review the
>> userspace code that currently uses most of Linux FF functionality:
>> Wine's DInput translation layer (and eventually SDL2.)
>> Trying to get everything correct, I noticed both
>> "/include/uapi/linux/input.h" and "/Documentation/input/ff.txt"
>> provide not enough information for the following things:
>>
>> 1)
>> The real meaning of 'directions', declared in
>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
>> :
>>     "Direction of the effect" is encoded as follows: ...
>> But it is not clear whether 'direction of the effect' means either:
>> - positive direction of the force the user should apply to counteract
>> the force that the joystick applies; or
>> - positive direction of the force applied by joystick
>> From my intuition, I think the latter is (silently?) meant by input.h
>> If you're interested why this is so important, I attached a document
>> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
>> translation layer between DInput and Linux input is to be written.
>
> From input.h:
>  * Direction of the effect is encoded as follows:
>  *      0 deg -> 0x0000 (down)
>  *      90 deg -> 0x4000 (left)
>  *      180 deg -> 0x8000 (up)
>  *      270 deg -> 0xC000 (right)
>
> The directions in parantheses are the direction of applied force.

Alright, thanks! That is invaluable information, maybe it should be
added to input.h .
It will avoid a lot of confusion for former DInput devs.

>
> However, there is actually a 1:1 mapping between DInput polar
> coordinates and our direction parameter; DInput polar coordinates have 0
> deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
> match our values due to the reverse definition.
>
> Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
> different definitions of Carts: For DInput you use -1 = north, but for
> Linux +1 = up, while you use -1 = west/left for both.

So I assume you agree that I got the DInput part right? ((0, -1) = north)

Then my mistake lies in the assumption that (0, +1) = up, so I should
flip the y-axis to correct the Linux part.
I'll explain how I originally derived the Linux part:
Michal documented (in "ff-memless-next.txt") the Linux directions in
the following way:
"
Direction of the effect's force translates to Cartesian coordinates system
as follows:
  Direction = 0: Down
  Direction (0; 16384): 3rd quadrant
  Direction = 16384: Left
  Direction (16385; 32768): 2nd quadrant
  Direction = 32768: Up
  Direction (32769; 49152): 1st quadrant
  Direction = 49152: Right
  Direction (49153; 65535) :4th quadrant
  Direction = 65565: Down
"
For a Cartesian coordinates system:
- The (-1, 0)-axis (=-x) is the intersection of 3rd quadrant and 2nd
quadrant => Left
- The (0, +1)-axis (=+y) is the intersection of 2nd quadrant and 1st
quadrant => Up
- The (+1, 0)-axis (=+x) is the intersection of 1st quadrant and 4th
quadrant => Right
- The (0, -1)-axis (=-y) is the intersection of 4th quadrant and 3rd
quadrant => Down

Michal's approach seems logical to me, if he made a mistake, it's
caused by the lack of documentation of input.h : it should mention
what axes (-x, +x, -y or +y) the words (left, right, down and up)
correspond with.

So, which interpretation is the right one?
(I did not find anything in the Linux documentation that states "there
is actually a 1:1 mapping between DInput polar coordinates and our
direction parameter")

> This causes the
> 1st and 3rd entries on both of the Mapping tables to be reversed. When
> that is fixed, the table #2 shows the correct result.
>
>> 2)
>> It is not clear how to create a FF effect with infinite duration
>> (replay.length):
>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L966
>> Only the following is written about duration values in general:
>> "All duration values are expressed in ms. Values above 32767 ms
>> (0x7fff) should not be used and have unspecified results."
>> Michal solved this by associating replay.length==0 for infinite, which
>> makes sense since otherwise the effect would not have been started
>> anyway.
>
> Infinite duration can be achieved with length = 0.

Thanks! This has to be documented.

>
>> 3)
>> Many Linux FF effect parameters don't have a clear explanation of the
>> allowed range, and their corresponding meaning at the extrema.
>> Here I list the ones that need more explanation, also take a look at
>> "interactive.fig" in the kernel documentation (but also included as
>> attachment):
>> - left_saturation and right_saturation; and
>
> left_saturation = maximum force on the negative ("left") side of the
> center point
> right_saturation = same for positive side
>
> 0x0 => no force,
> 0xFFFF => maximum force.

OK, thanks for giving the definition. I think these things can be
understood from "interactive.fig", so there's no need to write
additional doc about this topic.

>
>> - deadband
>
> The range from center point wherein the effect has no effect

Notice this contradicts with "interactive.fig", this figure defines
'deadband' as bound-to-bound, not as center-to-bound (as with DInput).

> , with
> 0x0 => no dead band
> 0xFFFF => dead band encompassing the entire axis, effect not active
> anywhere.
>
> Assuming center offset of 0, though. Not sure how the currently
> supported devices interpret 0xFFFF with non-zero center offset, i.e. if
> the effect is then still active in the extreme opposite end of the axis.
> You wrote below that this is indeed the case with DInput, so it is
> highly likely this is how the devices handle it as well.

Careful, here there's a catch:
    I did not write that in DInput "if deadband == maxValue(deadband)
with non-zero center offset, then the effect is still active in the
extreme opposite end of the axis.",
    I wrote that in DInput "if deadband == maxValue(deadband) with
maximum non-zero center offset, then the effect can only cover half of
the total region". For reference: maxValue(deadband)=10000

Now I'm proposing to let DInput maxValue(deadband) correspond to linux
deadband 0x7FFF.
And still allowing linux deadband to be maximal 0xFFFF => two times
the maximum range of DInput

>
>
>> They all have __u16 types, but "/include/uapi/linux/input.h" does not
>> say what the maximum values are.
>> I'm doing a proposal to define and document this (in the Linux kernel)
>> in the following way, also take a look at my attachment
>> "interactiveAlteredWithRanges.svg" for the modified version:
>>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>>         Because the maximal value of the saturation bound can be only
>> half of the total range covered by the max negative to max positive
>> bounds.
>>         And also because they are related to some form of force, and
>> all other forms of force magnitude in Linux FF have a maximum value of
>> 0x7FFF
>
> I'm not really convinced that the different range from the other
> magnitude values is a reason enough to change the definition here.

After reviewing this mail, I totally agree with you, sorry for that.

>
>>     Max Range of {deadband} = 0xFFFF
>>         This is a bit harder to explain:
>>         - First, I would suggest to alter the deadband definition in
>> figure "interactive.fig":
>>             I would define deadband as going from a deadband-bound to
>> the center (BTW, This is how MSDN defines it: "In other words, the
>> condition is not active between lOffset minus lDeadBand and lOffset
>> plus lDeadBand."),
>>             instead of from a deadband-bound to the other deadband-bound.
>>                 => Same spec as in DInput.
>
> With 0xFFFF being the maximum deadband with center offset 0, it does not
> matter if deadband is defined as range from center or total width,
> maximum is 0xFFFF in both cases.

Indeed, because (assume applying 0xFFFF linux deadband with center offset 0):
a) If DInput maxValue(deadband)=10000 (=half of the total region) maps
to 0x7FFF in the Linux case (=my proposal) if linux deadband is
defined as range from center:
    the driver will clamp {0 + 0xFFFF =approx 0 + 2 * 0x7FFF} to
0x7FFF for both left as right side of center => Total region is
covered by the deadband.
b) If DInput maxValue(deadband)=10000 (=half of the total region) maps
to 0x7FFF in the Linux case (=my proposal) if linux deadband is
defined as total width:
    the driver will set {0 + 0xFFFF / 2 =approx 0 + 0x7FFF} for both
left as right side of center => Total region is covered by the
deadband.

If we define linux deadband as range from center, like a), the Linux
FF API can represent more variations of conditional effects than
DInput can (and also with greater resolution), and thus becomes
superior in that aspect.
We will have to do the clamping anyway for devices that only accept
left and right deadband bounds, i.e. Logitech wheels.
For devices that only accept a single deadband value, like your SWFF2
as you mentioned below, the linux deadband would only need to be
shifted "<< 1" before being send to the device, if they accept u16 and
work exactly like DInput (range from center, and
maxValue(deadband)=half of total region).

>
>>         - Now, knowing that ff_condition_effect->center is __s16:
>>             The worst case scenario is that "center = -32768" or
>> "center = +32767" while still wanting to cover the whole region (this
>> is actually not possible with DInput's specs: in that case, they can
>> only cover half of the total region):
>>             Then, to keep the scale of "center" and "deadband" the
>> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF
>
> Interesting idea. However, if this is not possible in DInput, this means
> the devices will likely not support it either, since they are using the
> DInput effect model (as are we).

This is no problem, use "<< 1" as mentioned above.

>
>
> I tried to confirm this with my SWFF2 device, but either it has stopped
> working properly or, more likely, there is a regression in the kernel...
> no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
> requests don't seem to go through properly).
>
>
>> I expect we will have to add/document the answers to my questions in
>> the appropriate file "/include/uapi/linux/input.h" or
>> "/Documentation/input/ff.txt", so that other userspace developers (and
>> maybe also kernel devs) don't face the same ambiguities.
>>
>>
>> Thank you very much for your time,
>
> Thanks for looking into this.
>
>> Elias
>>
>
>
> --
> Anssi Hannula

Elias

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Anssi Hannula]

15.02.2014 14:14, Elias Vanderstuyft kirjoitti:
> On Sat, Feb 15, 2014 at 3:05 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>> 15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
>>> Hi everyone,
>>
>> Hi!
>>
>>>
>>> If you receive my mail, it is either because you:
>>> - are listed under the MAINTAINERS for "/include/uapi/linux/input.h":
>>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS#n4410
>>> - are listed as an author of "/Documentation/input/ff.txt" or of
>>> "/Documentation/input/interactive.fig"
>>>
>>> In the process of testing the new driver (ff-memless-next) Michal
>>> (CC-ed) is working on, this allowed me to gain more insight in the
>>> internal workings of Linux FF. That's why I decided to review the
>>> userspace code that currently uses most of Linux FF functionality:
>>> Wine's DInput translation layer (and eventually SDL2.)
>>> Trying to get everything correct, I noticed both
>>> "/include/uapi/linux/input.h" and "/Documentation/input/ff.txt"
>>> provide not enough information for the following things:
>>>
>>> 1)
>>> The real meaning of 'directions', declared in
>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
>>> :
>>>     "Direction of the effect" is encoded as follows: ...
>>> But it is not clear whether 'direction of the effect' means either:
>>> - positive direction of the force the user should apply to counteract
>>> the force that the joystick applies; or
>>> - positive direction of the force applied by joystick
>>> From my intuition, I think the latter is (silently?) meant by input.h
>>> If you're interested why this is so important, I attached a document
>>> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
>>> translation layer between DInput and Linux input is to be written.
>>
>> From input.h:
>>  * Direction of the effect is encoded as follows:
>>  *      0 deg -> 0x0000 (down)
>>  *      90 deg -> 0x4000 (left)
>>  *      180 deg -> 0x8000 (up)
>>  *      270 deg -> 0xC000 (right)
>>
>> The directions in parantheses are the direction of applied force.
> 
> Alright, thanks! That is invaluable information, maybe it should be
> added to input.h .
> It will avoid a lot of confusion for former DInput devs.
> 
>>
>> However, there is actually a 1:1 mapping between DInput polar
>> coordinates and our direction parameter; DInput polar coordinates have 0
>> deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
>> match our values due to the reverse definition.
>>
>> Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
>> different definitions of Carts: For DInput you use -1 = north, but for
>> Linux +1 = up, while you use -1 = west/left for both.
> 
> So I assume you agree that I got the DInput part right? ((0, -1) = north)

I guess so.

> Then my mistake lies in the assumption that (0, +1) = up, so I should
> flip the y-axis to correct the Linux part.
> I'll explain how I originally derived the Linux part:
> Michal documented (in "ff-memless-next.txt") the Linux directions in
> the following way:
> "
> Direction of the effect's force translates to Cartesian coordinates system
> as follows:
>   Direction = 0: Down
>   Direction (0; 16384): 3rd quadrant
>   Direction = 16384: Left
>   Direction (16385; 32768): 2nd quadrant
>   Direction = 32768: Up
>   Direction (32769; 49152): 1st quadrant
>   Direction = 49152: Right
>   Direction (49153; 65535) :4th quadrant
>   Direction = 65565: Down
> "

The above is correct.

> For a Cartesian coordinates system:
> - The (-1, 0)-axis (=-x) is the intersection of 3rd quadrant and 2nd
> quadrant => Left
> - The (0, +1)-axis (=+y) is the intersection of 2nd quadrant and 1st
> quadrant => Up
> - The (+1, 0)-axis (=+x) is the intersection of 1st quadrant and 4th
> quadrant => Right
> - The (0, -1)-axis (=-y) is the intersection of 4th quadrant and 3rd
> quadrant => Down

Not sure why you've arbitrarily chosen reverse definition of Y axis
here, when all DInput and Linux joysticks, mouses, etc. have -y as "up".

> Michal's approach seems logical to me, if he made a mistake, it's
> caused by the lack of documentation of input.h : it should mention
> what axes (-x, +x, -y or +y) the words (left, right, down and up)
> correspond with.

Well, the "left", "right", "down", "up" correspond to directions from
the user perspective. I don't think that is ambigiuous at all, as I
don't see how you could consider "down" to be away from user?

I'm not against more documentation if it helps, though.

> So, which interpretation is the right one?

The one where the directions provided in input.h match physical
direction of the force effect from user perspective on a 2-axis joystick
device.

> (I did not find anything in the Linux documentation that states "there
> is actually a 1:1 mapping between DInput polar coordinates and our
> direction parameter")

It is not stated explicitely, it just naturally follows.

1. Both use a clock-wise direction.
1. DInput direction definition is reversed, as they use the "counteract"
direction. We can flip to correct.
2. DInput direction has 0 = up/north, we have 0 = down/south,
   i.e. the exact opposite, so we must flip the direction.

DInput direction = flipped(flipped(Linux direction))
                 = Linux direction

>> This causes the
>> 1st and 3rd entries on both of the Mapping tables to be reversed. When
>> that is fixed, the table #2 shows the correct result.
>>
>>> 2)
>>> It is not clear how to create a FF effect with infinite duration
>>> (replay.length):
>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L966
>>> Only the following is written about duration values in general:
>>> "All duration values are expressed in ms. Values above 32767 ms
>>> (0x7fff) should not be used and have unspecified results."
>>> Michal solved this by associating replay.length==0 for infinite, which
>>> makes sense since otherwise the effect would not have been started
>>> anyway.
>>
>> Infinite duration can be achieved with length = 0.
> 
> Thanks! This has to be documented.
> 
>>
>>> 3)
>>> Many Linux FF effect parameters don't have a clear explanation of the
>>> allowed range, and their corresponding meaning at the extrema.
>>> Here I list the ones that need more explanation, also take a look at
>>> "interactive.fig" in the kernel documentation (but also included as
>>> attachment):
>>> - left_saturation and right_saturation; and
>>
>> left_saturation = maximum force on the negative ("left") side of the
>> center point
>> right_saturation = same for positive side
>>
>> 0x0 => no force,
>> 0xFFFF => maximum force.
> 
> OK, thanks for giving the definition. I think these things can be
> understood from "interactive.fig", so there's no need to write
> additional doc about this topic.
> 
>>
>>> - deadband
>>
>> The range from center point wherein the effect has no effect
> 
> Notice this contradicts with "interactive.fig", this figure defines
> 'deadband' as bound-to-bound, not as center-to-bound (as with DInput).

There is no difference between those definitions that I can see:

                       Axis range
|------------------------------------------------------|

Definition from interactive.fig, bound-to-bound:
0x0:
|--------------------------X---------------------------|
0x8000 (covers half of the end-to-end area):
|------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
0xFFFF:
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|

Center-to-bound definition:
0x0:
|--------------------------X---------------------------|
0x8000 (covers half of the center-to-end area):
|------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
0xFFFF:
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|


>> , with
>> 0x0 => no dead band
>> 0xFFFF => dead band encompassing the entire axis, effect not active
>> anywhere.
>>
>> Assuming center offset of 0, though. Not sure how the currently
>> supported devices interpret 0xFFFF with non-zero center offset, i.e. if
>> the effect is then still active in the extreme opposite end of the axis.
>> You wrote below that this is indeed the case with DInput, so it is
>> highly likely this is how the devices handle it as well.
> 
> Careful, here there's a catch:
>     I did not write that in DInput "if deadband == maxValue(deadband)
> with non-zero center offset, then the effect is still active in the
> extreme opposite end of the axis.",
>     I wrote that in DInput "if deadband == maxValue(deadband) with
> maximum non-zero center offset, then the effect can only cover half of
> the total region". For reference: maxValue(deadband)=10000

I don't see the difference in those statements here. Note that deadband
is the area where the effect is *not* active.

> Now I'm proposing to let DInput maxValue(deadband) correspond to linux
> deadband 0x7FFF.
> And still allowing linux deadband to be maximal 0xFFFF => two times
> the maximum range of DInput
> 
>>
>>
>>> They all have __u16 types, but "/include/uapi/linux/input.h" does not
>>> say what the maximum values are.
>>> I'm doing a proposal to define and document this (in the Linux kernel)
>>> in the following way, also take a look at my attachment
>>> "interactiveAlteredWithRanges.svg" for the modified version:
>>>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>>>         Because the maximal value of the saturation bound can be only
>>> half of the total range covered by the max negative to max positive
>>> bounds.
>>>         And also because they are related to some form of force, and
>>> all other forms of force magnitude in Linux FF have a maximum value of
>>> 0x7FFF
>>
>> I'm not really convinced that the different range from the other
>> magnitude values is a reason enough to change the definition here.
> 
> After reviewing this mail, I totally agree with you, sorry for that.
> 
>>
>>>     Max Range of {deadband} = 0xFFFF
>>>         This is a bit harder to explain:
>>>         - First, I would suggest to alter the deadband definition in
>>> figure "interactive.fig":
>>>             I would define deadband as going from a deadband-bound to
>>> the center (BTW, This is how MSDN defines it: "In other words, the
>>> condition is not active between lOffset minus lDeadBand and lOffset
>>> plus lDeadBand."),
>>>             instead of from a deadband-bound to the other deadband-bound.
>>>                 => Same spec as in DInput.
>>
>> With 0xFFFF being the maximum deadband with center offset 0, it does not
>> matter if deadband is defined as range from center or total width,
>> maximum is 0xFFFF in both cases.
> 
> Indeed, because (assume applying 0xFFFF linux deadband with center offset 0):
> a) If DInput maxValue(deadband)=10000 (=half of the total region) maps
> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
> defined as range from center:
>     the driver will clamp {0 + 0xFFFF =approx 0 + 2 * 0x7FFF} to
> 0x7FFF for both left as right side of center => Total region is
> covered by the deadband.
> b) If DInput maxValue(deadband)=10000 (=half of the total region) maps
> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
> defined as total width:
>     the driver will set {0 + 0xFFFF / 2 =approx 0 + 0x7FFF} for both
> left as right side of center => Total region is covered by the
> deadband.
> 
> If we define linux deadband as range from center, like a), the Linux
> FF API can represent more variations of conditional effects than
> DInput can (and also with greater resolution), and thus becomes
> superior in that aspect.

Can you provide any example effect parameters on your proposed system
that would not be possible on DInput?

If I understood correctly, what you are saying is an effect like this
(percentages in parantheses are from left extreme of the axis to right
extreme of the axis):
sat_left = 0xFFFF
sat_right = 0xFFFF
coeff_left = 0x4000
coeff_right = -0x4000
center = 0x6000   (87.5% point)
deadband (your definition) = 0xA000
     (62.5% of full area from 87.5% point to either direction, i.e.
      25%..150% => (clamping) 25%..100%)

So that deadband can reach further left than it would be with DInput
definition (which maxes at 0x7FFF of your definition, which would not
reach the 25% mark at the left side).

However, from what I can see, you can achieve the exact same effect with
these parameters (DInput deadband definition):
sat_left = 0xFFFF
sat_right = 0x0000
coeff_left = 0x4000
coeff_right = 0x0000
center = 0x0000 (50% point)
deadband (DInput/ours) = 0x8000 (50% total area, or 50% of
center-to-end, so it reaches 25%..75%)

On the left side, the effect is exactly the same as before with same
parameters (sat 0xffff, coeff 0x4000, starts at 25% point).

On the right side the parameters differ, but the end-result is the same,
there is no effect at all:
- In the first example, the right side is fully in deadband area,
  causing the effect to have zero effect.
- In my variant with our definition, the right side has zero saturation,
  causing the effect to have zero effect.


So the present definitions (and DInput definitions) can achieve the same
effects as your proposed definitions, unless I'm missing something,
making the change unneeded.

> We will have to do the clamping anyway for devices that only accept
> left and right deadband bounds, i.e. Logitech wheels.
> For devices that only accept a single deadband value, like your SWFF2
> as you mentioned below, the linux deadband would only need to be
> shifted "<< 1" before being send to the device, if they accept u16 and
> work exactly like DInput (range from center, and
> maxValue(deadband)=half of total region).

I'm not sure what you are trying to accomplish with "<< 1" here. If the
device can't accept the deadband you want, left-shifting wouldn't fix that.

>>
>>>         - Now, knowing that ff_condition_effect->center is __s16:
>>>             The worst case scenario is that "center = -32768" or
>>> "center = +32767" while still wanting to cover the whole region (this
>>> is actually not possible with DInput's specs: in that case, they can
>>> only cover half of the total region):
>>>             Then, to keep the scale of "center" and "deadband" the
>>> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF
>>
>> Interesting idea. However, if this is not possible in DInput, this means
>> the devices will likely not support it either, since they are using the
>> DInput effect model (as are we).
> 
> This is no problem, use "<< 1" as mentioned above.
> 
>>
>>
>> I tried to confirm this with my SWFF2 device, but either it has stopped
>> working properly or, more likely, there is a regression in the kernel...
>> no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
>> requests don't seem to go through properly).
>>
>>
>>> I expect we will have to add/document the answers to my questions in
>>> the appropriate file "/include/uapi/linux/input.h" or
>>> "/Documentation/input/ff.txt", so that other userspace developers (and
>>> maybe also kernel devs) don't face the same ambiguities.
>>>
>>>
>>> Thank you very much for your time,
>>
>> Thanks for looking into this.
>>
>>> Elias
>>>
>>
>>
>> --
>> Anssi Hannula
> 
> Elias
> 


-- 
Anssi Hannula

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

On Sat, Feb 15, 2014 at 3:04 PM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
> 15.02.2014 14:14, Elias Vanderstuyft kirjoitti:
>> On Sat, Feb 15, 2014 at 3:05 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>>> 15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
>>>> Hi everyone,
>>>
>>> Hi!
>>>
>>>>
>>>> If you receive my mail, it is either because you:
>>>> - are listed under the MAINTAINERS for "/include/uapi/linux/input.h":
>>>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS#n4410
>>>> - are listed as an author of "/Documentation/input/ff.txt" or of
>>>> "/Documentation/input/interactive.fig"
>>>>
>>>> In the process of testing the new driver (ff-memless-next) Michal
>>>> (CC-ed) is working on, this allowed me to gain more insight in the
>>>> internal workings of Linux FF. That's why I decided to review the
>>>> userspace code that currently uses most of Linux FF functionality:
>>>> Wine's DInput translation layer (and eventually SDL2.)
>>>> Trying to get everything correct, I noticed both
>>>> "/include/uapi/linux/input.h" and "/Documentation/input/ff.txt"
>>>> provide not enough information for the following things:
>>>>
>>>> 1)
>>>> The real meaning of 'directions', declared in
>>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
>>>> :
>>>>     "Direction of the effect" is encoded as follows: ...
>>>> But it is not clear whether 'direction of the effect' means either:
>>>> - positive direction of the force the user should apply to counteract
>>>> the force that the joystick applies; or
>>>> - positive direction of the force applied by joystick
>>>> From my intuition, I think the latter is (silently?) meant by input.h
>>>> If you're interested why this is so important, I attached a document
>>>> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
>>>> translation layer between DInput and Linux input is to be written.
>>>
>>> From input.h:
>>>  * Direction of the effect is encoded as follows:
>>>  *      0 deg -> 0x0000 (down)
>>>  *      90 deg -> 0x4000 (left)
>>>  *      180 deg -> 0x8000 (up)
>>>  *      270 deg -> 0xC000 (right)
>>>
>>> The directions in parantheses are the direction of applied force.
>>
>> Alright, thanks! That is invaluable information, maybe it should be
>> added to input.h .
>> It will avoid a lot of confusion for former DInput devs.
>>
>>>
>>> However, there is actually a 1:1 mapping between DInput polar
>>> coordinates and our direction parameter; DInput polar coordinates have 0
>>> deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
>>> match our values due to the reverse definition.
>>>
>>> Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
>>> different definitions of Carts: For DInput you use -1 = north, but for
>>> Linux +1 = up, while you use -1 = west/left for both.
>>
>> So I assume you agree that I got the DInput part right? ((0, -1) = north)
>
> I guess so.
>
>> Then my mistake lies in the assumption that (0, +1) = up, so I should
>> flip the y-axis to correct the Linux part.
>> I'll explain how I originally derived the Linux part:
>> Michal documented (in "ff-memless-next.txt") the Linux directions in
>> the following way:
>> "
>> Direction of the effect's force translates to Cartesian coordinates system
>> as follows:
>>   Direction = 0: Down
>>   Direction (0; 16384): 3rd quadrant
>>   Direction = 16384: Left
>>   Direction (16385; 32768): 2nd quadrant
>>   Direction = 32768: Up
>>   Direction (32769; 49152): 1st quadrant
>>   Direction = 49152: Right
>>   Direction (49153; 65535) :4th quadrant
>>   Direction = 65565: Down
>> "
>
> The above is correct.
>
>> For a Cartesian coordinates system:
>> - The (-1, 0)-axis (=-x) is the intersection of 3rd quadrant and 2nd
>> quadrant => Left
>> - The (0, +1)-axis (=+y) is the intersection of 2nd quadrant and 1st
>> quadrant => Up
>> - The (+1, 0)-axis (=+x) is the intersection of 1st quadrant and 4th
>> quadrant => Right
>> - The (0, -1)-axis (=-y) is the intersection of 4th quadrant and 3rd
>> quadrant => Down
>
> Not sure why you've arbitrarily chosen reverse definition of Y axis
> here,

I really tried to derive the above in a non-arbitrary manner, here you
can verify why I 'chose' the +y axis as the intersection of 2nd
quadrant and 1st quadrant:
    http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg
And because you said that the part about directions in
"ff-memless-next.txt" is correct, it follows that Up (which lies
between the 2nd quadrant and 1st quadrant) corresponds with +y
direction.
I hope this makes sense.

> when all DInput and Linux joysticks, mouses, etc. have -y as "up".

Alright, I did not know that, at least not for Linux. Where in the
Linux documentation can I find this?

>
>> Michal's approach seems logical to me, if he made a mistake, it's
>> caused by the lack of documentation of input.h : it should mention
>> what axes (-x, +x, -y or +y) the words (left, right, down and up)
>> correspond with.
>
> Well, the "left", "right", "down", "up" correspond to directions from
> the user perspective.

That makes sense.

> I don't think that is ambigiuous at all, as I
> don't see how you could consider "down" to be away from user?

Yes, that's true. But it does not say to which axes (and polarity) they map.

>
> I'm not against more documentation if it helps, though.
>
>> So, which interpretation is the right one?
>
> The one where the directions provided in input.h match physical
> direction of the force effect from user perspective on a 2-axis joystick
> device.

That's a nice explanation! For the doc, also add to what axis each
direction corresponds to.

>
>> (I did not find anything in the Linux documentation that states "there
>> is actually a 1:1 mapping between DInput polar coordinates and our
>> direction parameter")
>
> It is not stated explicitely, it just naturally follows.
>
> 1. Both use a clock-wise direction.
> 1. DInput direction definition is reversed, as they use the "counteract"
> direction. We can flip to correct.
> 2. DInput direction has 0 = up/north, we have 0 = down/south,
>    i.e. the exact opposite, so we must flip the direction.
>
> DInput direction = flipped(flipped(Linux direction))
>                  = Linux direction

Alright, now I understand how it works.
But: the thing I wrote about the Cartesian coordinates system (the +y
axis lies between 2nd quadrant and 1st quadrant) is mathematically
correct (see referenced link to wiki), so, to fix the only
contradiction left, we will have to change the explanation about
directions in "ff-memless-next.txt" to the following text:
"
Direction of the effect's force translates to Cartesian coordinates system
as follows:
  Direction = 0: Down: +y
  Direction (0; 16384): 2nd quadrant
  Direction = 16384: Left: -x
  Direction (16385; 32768): 3th quadrant
  Direction = 32768: Up: -y
  Direction (32769; 49152): 4rd quadrant
  Direction = 49152: Right: +x
  Direction (49153; 65535) :1st quadrant
  Direction = 65565: Down: +y
"
As you can see, I only changed the quadrants (and added axes for
convenience), now they agree to
"http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg", and
to input.h , so everyone should be happy :)
Can you confirm the modification is correct?

>
>>> This causes the
>>> 1st and 3rd entries on both of the Mapping tables to be reversed. When
>>> that is fixed, the table #2 shows the correct result.
>>>
>>>> 2)
>>>> It is not clear how to create a FF effect with infinite duration
>>>> (replay.length):
>>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L966
>>>> Only the following is written about duration values in general:
>>>> "All duration values are expressed in ms. Values above 32767 ms
>>>> (0x7fff) should not be used and have unspecified results."
>>>> Michal solved this by associating replay.length==0 for infinite, which
>>>> makes sense since otherwise the effect would not have been started
>>>> anyway.
>>>
>>> Infinite duration can be achieved with length = 0.
>>
>> Thanks! This has to be documented.
>>
>>>
>>>> 3)
>>>> Many Linux FF effect parameters don't have a clear explanation of the
>>>> allowed range, and their corresponding meaning at the extrema.
>>>> Here I list the ones that need more explanation, also take a look at
>>>> "interactive.fig" in the kernel documentation (but also included as
>>>> attachment):
>>>> - left_saturation and right_saturation; and
>>>
>>> left_saturation = maximum force on the negative ("left") side of the
>>> center point
>>> right_saturation = same for positive side
>>>
>>> 0x0 => no force,
>>> 0xFFFF => maximum force.
>>
>> OK, thanks for giving the definition. I think these things can be
>> understood from "interactive.fig", so there's no need to write
>> additional doc about this topic.
>>
>>>
>>>> - deadband
>>>
>>> The range from center point wherein the effect has no effect
>>
>> Notice this contradicts with "interactive.fig", this figure defines
>> 'deadband' as bound-to-bound, not as center-to-bound (as with DInput).
>
> There is no difference between those definitions that I can see:
>
>                        Axis range
> |------------------------------------------------------|
>
> Definition from interactive.fig, bound-to-bound:
> 0x0:
> |--------------------------X---------------------------|
> 0x8000 (covers half of the end-to-end area):
> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
> 0xFFFF:
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|

Alright, agreed with this part: deadband units or dimensions are the
same as the ones of the center offset parameter.

>
> Center-to-bound definition:
> 0x0:
> |--------------------------X---------------------------|
> 0x8000 (covers half of the center-to-end area):
> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
> 0xFFFF:
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|

Ah, I see, this is where we disagree: now you're not working with the
same units or dimensions as the ones of the center offset parameter:
you have multiplied them by a factor 2 (that's where my "<< 1" came
from, for going from my definition to your definition).

This is my proposal of how it could be:

Center-to-bound definition (same dimensions as center offset parameter):
0x0:
|--------------------------X---------------------------|
0x4000 (covers half of the center-to-end area):
|------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
0x8000 (covers whole the center-to-end area):
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
0xC000:
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)
0xFFFF:
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)

>
>
>>> , with
>>> 0x0 => no dead band
>>> 0xFFFF => dead band encompassing the entire axis, effect not active
>>> anywhere.
>>>
>>> Assuming center offset of 0, though. Not sure how the currently
>>> supported devices interpret 0xFFFF with non-zero center offset, i.e. if
>>> the effect is then still active in the extreme opposite end of the axis.
>>> You wrote below that this is indeed the case with DInput, so it is
>>> highly likely this is how the devices handle it as well.
>>
>> Careful, here there's a catch:
>>     I did not write that in DInput "if deadband == maxValue(deadband)
>> with non-zero center offset, then the effect is still active in the
>> extreme opposite end of the axis.",
>>     I wrote that in DInput "if deadband == maxValue(deadband) with
>> maximum non-zero center offset, then the effect can only cover half of
>> the total region". For reference: maxValue(deadband)=10000
>
> I don't see the difference in those statements here.

There is, when assuming same dimensions as center offset parameter.
Otherwise, you're right.

> Note that deadband
> is the area where the effect is *not* active.

I know, that's why it's called *dead*-band ;)

>
>> Now I'm proposing to let DInput maxValue(deadband) correspond to linux
>> deadband 0x7FFF.
>> And still allowing linux deadband to be maximal 0xFFFF => two times
>> the maximum range of DInput
>>
>>>
>>>
>>>> They all have __u16 types, but "/include/uapi/linux/input.h" does not
>>>> say what the maximum values are.
>>>> I'm doing a proposal to define and document this (in the Linux kernel)
>>>> in the following way, also take a look at my attachment
>>>> "interactiveAlteredWithRanges.svg" for the modified version:
>>>>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>>>>         Because the maximal value of the saturation bound can be only
>>>> half of the total range covered by the max negative to max positive
>>>> bounds.
>>>>         And also because they are related to some form of force, and
>>>> all other forms of force magnitude in Linux FF have a maximum value of
>>>> 0x7FFF
>>>
>>> I'm not really convinced that the different range from the other
>>> magnitude values is a reason enough to change the definition here.
>>
>> After reviewing this mail, I totally agree with you, sorry for that.
>>
>>>
>>>>     Max Range of {deadband} = 0xFFFF
>>>>         This is a bit harder to explain:
>>>>         - First, I would suggest to alter the deadband definition in
>>>> figure "interactive.fig":
>>>>             I would define deadband as going from a deadband-bound to
>>>> the center (BTW, This is how MSDN defines it: "In other words, the
>>>> condition is not active between lOffset minus lDeadBand and lOffset
>>>> plus lDeadBand."),
>>>>             instead of from a deadband-bound to the other deadband-bound.
>>>>                 => Same spec as in DInput.
>>>
>>> With 0xFFFF being the maximum deadband with center offset 0, it does not
>>> matter if deadband is defined as range from center or total width,
>>> maximum is 0xFFFF in both cases.
>>
>> Indeed, because (assume applying 0xFFFF linux deadband with center offset 0):
>> a) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>> defined as range from center:
>>     the driver will clamp {0 + 0xFFFF =approx 0 + 2 * 0x7FFF} to
>> 0x7FFF for both left as right side of center => Total region is
>> covered by the deadband.
>> b) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>> defined as total width:
>>     the driver will set {0 + 0xFFFF / 2 =approx 0 + 0x7FFF} for both
>> left as right side of center => Total region is covered by the
>> deadband.
>>
>> If we define linux deadband as range from center, like a), the Linux
>> FF API can represent more variations of conditional effects than
>> DInput can (and also with greater resolution), and thus becomes
>> superior in that aspect.
>
> Can you provide any example effect parameters on your proposed system
> that would not be possible on DInput?

Sure:

Center-to-bound definition (same dimensions as center offset parameter):
Assume center offset is set to the maximum non-zero value +32767
0x0:
|-----------------------------------------------------X|
0x4000 (covers a quarter of the end-to-end area):
|----------------------------------------XXXXXXXXXXXXXX|
0x8000 (covers half of the end-to-end area):
|---------------------------XXXXXXXXXXXXXXXXXXXXXXXXXXX|
0xC000 (covers three quarters of the end-to-end area):
|-------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
0xFFFF (covers whole the end-to-end area):
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|

>
> If I understood correctly, what you are saying is an effect like this
> (percentages in parantheses are from left extreme of the axis to right
> extreme of the axis):
> sat_left = 0xFFFF
> sat_right = 0xFFFF
> coeff_left = 0x4000
> coeff_right = -0x4000
> center = 0x6000   (87.5% point)
> deadband (your definition) = 0xA000
>      (62.5% of full area from 87.5% point to either direction, i.e.
>       25%..150% => (clamping) 25%..100%)
>
> So that deadband can reach further left than it would be with DInput
> definition (which maxes at 0x7FFF of your definition, which would not
> reach the 25% mark at the left side).

Exactly.

>
> However, from what I can see, you can achieve the exact same effect with
> these parameters (DInput deadband definition):
> sat_left = 0xFFFF
> sat_right = 0x0000
> coeff_left = 0x4000
> coeff_right = 0x0000
> center = 0x0000 (50% point)
> deadband (DInput/ours) = 0x8000 (50% total area, or 50% of
> center-to-end, so it reaches 25%..75%)
>
> On the left side, the effect is exactly the same as before with same
> parameters (sat 0xffff, coeff 0x4000, starts at 25% point).
>
> On the right side the parameters differ, but the end-result is the same,
> there is no effect at all:
> - In the first example, the right side is fully in deadband area,
>   causing the effect to have zero effect.
> - In my variant with our definition, the right side has zero saturation,
>   causing the effect to have zero effect.
>
>
> So the present definitions (and DInput definitions) can achieve the same
> effects as your proposed definitions, unless I'm missing something,
> making the change unneeded.

Agreed.

But the benefit could be to make the user application less complex,
since otherwise, when a special case like the one you mentioned above
(with deadband larger than half of the total region), they would also
need to change the saturation values. This is not really a problem
when the conditional effect is a 'static' one (i.e. center and
deadband do not change over time), but it might come in handy for
'dynamic' conditional effects.

Although honestly I think that situation is extremely rare, so I'm OK
with it if we leave the current definition as is.
And now I realize that for devices that require the deadband paramater
to be passed explicitly (and use the present definition) like SWFF2,
this either would not work, or would require additional (and maybe
complex) kernel driver code, which is not what we want.

So, I agree to leave its definition unchanged, sorry for the discussion ;)
I just have to be sure about this to improve Wine's DInput translation layer.

>
>> We will have to do the clamping anyway for devices that only accept
>> left and right deadband bounds, i.e. Logitech wheels.
>> For devices that only accept a single deadband value, like your SWFF2
>> as you mentioned below, the linux deadband would only need to be
>> shifted "<< 1" before being send to the device, if they accept u16 and
>> work exactly like DInput (range from center, and
>> maxValue(deadband)=half of total region).
>
> I'm not sure what you are trying to accomplish with "<< 1" here. If the
> device can't accept the deadband you want, left-shifting wouldn't fix that.

See above about the factor 2.

>
>>>
>>>>         - Now, knowing that ff_condition_effect->center is __s16:
>>>>             The worst case scenario is that "center = -32768" or
>>>> "center = +32767" while still wanting to cover the whole region (this
>>>> is actually not possible with DInput's specs: in that case, they can
>>>> only cover half of the total region):
>>>>             Then, to keep the scale of "center" and "deadband" the
>>>> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF
>>>
>>> Interesting idea. However, if this is not possible in DInput, this means
>>> the devices will likely not support it either, since they are using the
>>> DInput effect model (as are we).
>>
>> This is no problem, use "<< 1" as mentioned above.
>>
>>>
>>>
>>> I tried to confirm this with my SWFF2 device, but either it has stopped
>>> working properly or, more likely, there is a regression in the kernel...
>>> no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
>>> requests don't seem to go through properly).
>>>
>>>
>>>> I expect we will have to add/document the answers to my questions in
>>>> the appropriate file "/include/uapi/linux/input.h" or
>>>> "/Documentation/input/ff.txt", so that other userspace developers (and
>>>> maybe also kernel devs) don't face the same ambiguities.
>>>>
>>>>
>>>> Thank you very much for your time,
>>>
>>> Thanks for looking into this.
>>>
>>>> Elias
>>>>
>>>
>>>
>>> --
>>> Anssi Hannula
>>
>> Elias
>>
>
>
> --
> Anssi Hannula

Elias

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Anssi Hannula]

15.02.2014 22:32, Elias Vanderstuyft kirjoitti:
> On Sat, Feb 15, 2014 at 3:04 PM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>> 15.02.2014 14:14, Elias Vanderstuyft kirjoitti:
>>> On Sat, Feb 15, 2014 at 3:05 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>>>> 15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
[...]
>>>>> 1)
>>>>> The real meaning of 'directions', declared in
>>>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
>>>>> :
>>>>>     "Direction of the effect" is encoded as follows: ...
>>>>> But it is not clear whether 'direction of the effect' means either:
>>>>> - positive direction of the force the user should apply to counteract
>>>>> the force that the joystick applies; or
>>>>> - positive direction of the force applied by joystick
>>>>> From my intuition, I think the latter is (silently?) meant by input.h
>>>>> If you're interested why this is so important, I attached a document
>>>>> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
>>>>> translation layer between DInput and Linux input is to be written.
>>>>
>>>> From input.h:
>>>>  * Direction of the effect is encoded as follows:
>>>>  *      0 deg -> 0x0000 (down)
>>>>  *      90 deg -> 0x4000 (left)
>>>>  *      180 deg -> 0x8000 (up)
>>>>  *      270 deg -> 0xC000 (right)
>>>>
>>>> The directions in parantheses are the direction of applied force.
>>>
>>> Alright, thanks! That is invaluable information, maybe it should be
>>> added to input.h .
>>> It will avoid a lot of confusion for former DInput devs.
>>>
>>>>
>>>> However, there is actually a 1:1 mapping between DInput polar
>>>> coordinates and our direction parameter; DInput polar coordinates have 0
>>>> deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
>>>> match our values due to the reverse definition.
>>>>
>>>> Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
>>>> different definitions of Carts: For DInput you use -1 = north, but for
>>>> Linux +1 = up, while you use -1 = west/left for both.
>>>
>>> So I assume you agree that I got the DInput part right? ((0, -1) = north)
>>
>> I guess so.
>>
>>> Then my mistake lies in the assumption that (0, +1) = up, so I should
>>> flip the y-axis to correct the Linux part.
>>> I'll explain how I originally derived the Linux part:
>>> Michal documented (in "ff-memless-next.txt") the Linux directions in
>>> the following way:
>>> "
>>> Direction of the effect's force translates to Cartesian coordinates system
>>> as follows:
>>>   Direction = 0: Down
>>>   Direction (0; 16384): 3rd quadrant
>>>   Direction = 16384: Left
>>>   Direction (16385; 32768): 2nd quadrant
>>>   Direction = 32768: Up
>>>   Direction (32769; 49152): 1st quadrant
>>>   Direction = 49152: Right
>>>   Direction (49153; 65535) :4th quadrant
>>>   Direction = 65565: Down
>>> "
>>
>> The above is correct.
>>
>>> For a Cartesian coordinates system:
>>> - The (-1, 0)-axis (=-x) is the intersection of 3rd quadrant and 2nd
>>> quadrant => Left
>>> - The (0, +1)-axis (=+y) is the intersection of 2nd quadrant and 1st
>>> quadrant => Up
>>> - The (+1, 0)-axis (=+x) is the intersection of 1st quadrant and 4th
>>> quadrant => Right
>>> - The (0, -1)-axis (=-y) is the intersection of 4th quadrant and 3rd
>>> quadrant => Down
>>
>> Not sure why you've arbitrarily chosen reverse definition of Y axis
>> here,
> 
> I really tried to derive the above in a non-arbitrary manner, here you
> can verify why I 'chose' the +y axis as the intersection of 2nd
> quadrant and 1st quadrant:
>     http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg
> And because you said that the part about directions in
> "ff-memless-next.txt" is correct, it follows that Up (which lies
> between the 2nd quadrant and 1st quadrant) corresponds with +y
> direction.
> I hope this makes sense.
> 
>> when all DInput and Linux joysticks, mouses, etc. have -y as "up".
> 
> Alright, I did not know that, at least not for Linux. Where in the
> Linux documentation can I find this?

I don't think it is explicitely said either. I guess one could say it is
"standard industry practice" (not limited to input, by the way, with
e.g. in images the pixel row and column values are increasing right and
down, not right and up).

I don't oppose more explicit documentation, though.

>>
>>> Michal's approach seems logical to me, if he made a mistake, it's
>>> caused by the lack of documentation of input.h : it should mention
>>> what axes (-x, +x, -y or +y) the words (left, right, down and up)
>>> correspond with.
>>
>> Well, the "left", "right", "down", "up" correspond to directions from
>> the user perspective.
> 
> That makes sense.
> 
>> I don't think that is ambigiuous at all, as I
>> don't see how you could consider "down" to be away from user?
> 
> Yes, that's true. But it does not say to which axes (and polarity) they map.
> 
>>
>> I'm not against more documentation if it helps, though.
>>
>>> So, which interpretation is the right one?
>>
>> The one where the directions provided in input.h match physical
>> direction of the force effect from user perspective on a 2-axis joystick
>> device.
> 
> That's a nice explanation! For the doc, also add to what axis each
> direction corresponds to.
> 
>>
>>> (I did not find anything in the Linux documentation that states "there
>>> is actually a 1:1 mapping between DInput polar coordinates and our
>>> direction parameter")
>>
>> It is not stated explicitely, it just naturally follows.
>>
>> 1. Both use a clock-wise direction.
>> 1. DInput direction definition is reversed, as they use the "counteract"
>> direction. We can flip to correct.
>> 2. DInput direction has 0 = up/north, we have 0 = down/south,
>>    i.e. the exact opposite, so we must flip the direction.
>>
>> DInput direction = flipped(flipped(Linux direction))
>>                  = Linux direction
> 
> Alright, now I understand how it works.
> But: the thing I wrote about the Cartesian coordinates system (the +y
> axis lies between 2nd quadrant and 1st quadrant) is mathematically
> correct (see referenced link to wiki), so, to fix the only
> contradiction left, we will have to change the explanation about
> directions in "ff-memless-next.txt" to the following text:
> "
> Direction of the effect's force translates to Cartesian coordinates system
> as follows:
>   Direction = 0: Down: +y
>   Direction (0; 16384): 2nd quadrant
>   Direction = 16384: Left: -x
>   Direction (16385; 32768): 3th quadrant
>   Direction = 32768: Up: -y
>   Direction (32769; 49152): 4rd quadrant
>   Direction = 49152: Right: +x
>   Direction (49153; 65535) :1st quadrant
>   Direction = 65565: Down: +y
> "
> As you can see, I only changed the quadrants (and added axes for
> convenience), now they agree to
> "http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg", and
> to input.h , so everyone should be happy :)
> Can you confirm the modification is correct?

I think so.

However, assigning quadrants here is a bit confusing to me here with the
non-mathematical-traditional reversed Y axis. I.e. my first instinct is
that the upper-right quadrant is the first one, while it is not the case
here...

But if it helps...


>>
>>>> This causes the
>>>> 1st and 3rd entries on both of the Mapping tables to be reversed. When
>>>> that is fixed, the table #2 shows the correct result.
[...]
>>>>> 3)
>>>>> Many Linux FF effect parameters don't have a clear explanation of the
>>>>> allowed range, and their corresponding meaning at the extrema.
>>>>> Here I list the ones that need more explanation, also take a look at
>>>>> "interactive.fig" in the kernel documentation (but also included as
>>>>> attachment):
>>>>> - left_saturation and right_saturation; and
>>>>
>>>> left_saturation = maximum force on the negative ("left") side of the
>>>> center point
>>>> right_saturation = same for positive side
>>>>
>>>> 0x0 => no force,
>>>> 0xFFFF => maximum force.
>>>
>>> OK, thanks for giving the definition. I think these things can be
>>> understood from "interactive.fig", so there's no need to write
>>> additional doc about this topic.
>>>
>>>>
>>>>> - deadband
>>>>
>>>> The range from center point wherein the effect has no effect
>>>
>>> Notice this contradicts with "interactive.fig", this figure defines
>>> 'deadband' as bound-to-bound, not as center-to-bound (as with DInput).
>>
>> There is no difference between those definitions that I can see:
>>
>>                        Axis range
>> |------------------------------------------------------|
>>
>> Definition from interactive.fig, bound-to-bound:
>> 0x0:
>> |--------------------------X---------------------------|
>> 0x8000 (covers half of the end-to-end area):
>> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
>> 0xFFFF:
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
> 
> Alright, agreed with this part: deadband units or dimensions are the
> same as the ones of the center offset parameter.
> 
>>
>> Center-to-bound definition:
>> 0x0:
>> |--------------------------X---------------------------|
>> 0x8000 (covers half of the center-to-end area):
>> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
>> 0xFFFF:
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
> 
> Ah, I see, this is where we disagree: now you're not working with the
> same units or dimensions as the ones of the center offset parameter:
> you have multiplied them by a factor 2 (that's where my "<< 1" came
> from, for going from my definition to your definition).

Yes, the center offset and deadband are in "relative" units, so due to
the different value range the scales differ by a factor of 2.

I agree it is a bit unfortunate the scales do not match, but IMHO not a
totally hopeless situation.

> This is my proposal of how it could be:
> 
> Center-to-bound definition (same dimensions as center offset parameter):
> 0x0:
> |--------------------------X---------------------------|
> 0x4000 (covers half of the center-to-end area):
> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
> 0x8000 (covers whole the center-to-end area):
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
> 0xC000:
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)
> 0xFFFF:
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)

Yes, this I understood.

>>
>>
>>>> , with
>>>> 0x0 => no dead band
>>>> 0xFFFF => dead band encompassing the entire axis, effect not active
>>>> anywhere.
>>>>
>>>> Assuming center offset of 0, though. Not sure how the currently
>>>> supported devices interpret 0xFFFF with non-zero center offset, i.e. if
>>>> the effect is then still active in the extreme opposite end of the axis.
>>>> You wrote below that this is indeed the case with DInput, so it is
>>>> highly likely this is how the devices handle it as well.
>>>
>>> Careful, here there's a catch:
>>>     I did not write that in DInput "if deadband == maxValue(deadband)
>>> with non-zero center offset, then the effect is still active in the
>>> extreme opposite end of the axis.",
>>>     I wrote that in DInput "if deadband == maxValue(deadband) with
>>> maximum non-zero center offset, then the effect can only cover half of
>>> the total region". For reference: maxValue(deadband)=10000
>>
>> I don't see the difference in those statements here.
> 
> There is, when assuming same dimensions as center offset parameter.
> Otherwise, you're right.

Right.

>> Note that deadband
>> is the area where the effect is *not* active.
> 
> I know, that's why it's called *dead*-band ;)
> 
>>
>>> Now I'm proposing to let DInput maxValue(deadband) correspond to linux
>>> deadband 0x7FFF.
>>> And still allowing linux deadband to be maximal 0xFFFF => two times
>>> the maximum range of DInput
>>>
>>>>
>>>>
>>>>> They all have __u16 types, but "/include/uapi/linux/input.h" does not
>>>>> say what the maximum values are.
>>>>> I'm doing a proposal to define and document this (in the Linux kernel)
>>>>> in the following way, also take a look at my attachment
>>>>> "interactiveAlteredWithRanges.svg" for the modified version:
>>>>>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>>>>>         Because the maximal value of the saturation bound can be only
>>>>> half of the total range covered by the max negative to max positive
>>>>> bounds.
>>>>>         And also because they are related to some form of force, and
>>>>> all other forms of force magnitude in Linux FF have a maximum value of
>>>>> 0x7FFF
>>>>
>>>> I'm not really convinced that the different range from the other
>>>> magnitude values is a reason enough to change the definition here.
>>>
>>> After reviewing this mail, I totally agree with you, sorry for that.
>>>
>>>>
>>>>>     Max Range of {deadband} = 0xFFFF
>>>>>         This is a bit harder to explain:
>>>>>         - First, I would suggest to alter the deadband definition in
>>>>> figure "interactive.fig":
>>>>>             I would define deadband as going from a deadband-bound to
>>>>> the center (BTW, This is how MSDN defines it: "In other words, the
>>>>> condition is not active between lOffset minus lDeadBand and lOffset
>>>>> plus lDeadBand."),
>>>>>             instead of from a deadband-bound to the other deadband-bound.
>>>>>                 => Same spec as in DInput.
>>>>
>>>> With 0xFFFF being the maximum deadband with center offset 0, it does not
>>>> matter if deadband is defined as range from center or total width,
>>>> maximum is 0xFFFF in both cases.
>>>
>>> Indeed, because (assume applying 0xFFFF linux deadband with center offset 0):
>>> a) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>>> defined as range from center:
>>>     the driver will clamp {0 + 0xFFFF =approx 0 + 2 * 0x7FFF} to
>>> 0x7FFF for both left as right side of center => Total region is
>>> covered by the deadband.
>>> b) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>>> defined as total width:
>>>     the driver will set {0 + 0xFFFF / 2 =approx 0 + 0x7FFF} for both
>>> left as right side of center => Total region is covered by the
>>> deadband.
>>>
>>> If we define linux deadband as range from center, like a), the Linux
>>> FF API can represent more variations of conditional effects than
>>> DInput can (and also with greater resolution), and thus becomes
>>> superior in that aspect.
>>
>> Can you provide any example effect parameters on your proposed system
>> that would not be possible on DInput?
> 
> Sure:
> 
> Center-to-bound definition (same dimensions as center offset parameter):
> Assume center offset is set to the maximum non-zero value +32767
> 0x0:
> |-----------------------------------------------------X|
> 0x4000 (covers a quarter of the end-to-end area):
> |----------------------------------------XXXXXXXXXXXXXX|
> 0x8000 (covers half of the end-to-end area):
> |---------------------------XXXXXXXXXXXXXXXXXXXXXXXXXXX|
> 0xC000 (covers three quarters of the end-to-end area):
> |-------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
> 0xFFFF (covers whole the end-to-end area):
> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|

I meant a complete set of effect parameters that will cause an effect
not possible with the DInput definitions, like I provided below. Your
above example seems to be the same case I covered below in my example,
in which case you can simply move the center point left a bit and use a
zero right-side saturation value, without needing a large deadband value.

>>
>> If I understood correctly, what you are saying is an effect like this
>> (percentages in parantheses are from left extreme of the axis to right
>> extreme of the axis):
>> sat_left = 0xFFFF
>> sat_right = 0xFFFF
>> coeff_left = 0x4000
>> coeff_right = -0x4000
>> center = 0x6000   (87.5% point)
>> deadband (your definition) = 0xA000
>>      (62.5% of full area from 87.5% point to either direction, i.e.
>>       25%..150% => (clamping) 25%..100%)
>>
>> So that deadband can reach further left than it would be with DInput
>> definition (which maxes at 0x7FFF of your definition, which would not
>> reach the 25% mark at the left side).
> 
> Exactly.
> 
>>
>> However, from what I can see, you can achieve the exact same effect with
>> these parameters (DInput deadband definition):
>> sat_left = 0xFFFF
>> sat_right = 0x0000
>> coeff_left = 0x4000
>> coeff_right = 0x0000
>> center = 0x0000 (50% point)
>> deadband (DInput/ours) = 0x8000 (50% total area, or 50% of
>> center-to-end, so it reaches 25%..75%)
>>
>> On the left side, the effect is exactly the same as before with same
>> parameters (sat 0xffff, coeff 0x4000, starts at 25% point).
>>
>> On the right side the parameters differ, but the end-result is the same,
>> there is no effect at all:
>> - In the first example, the right side is fully in deadband area,
>>   causing the effect to have zero effect.
>> - In my variant with our definition, the right side has zero saturation,
>>   causing the effect to have zero effect.
>>
>>
>> So the present definitions (and DInput definitions) can achieve the same
>> effects as your proposed definitions, unless I'm missing something,
>> making the change unneeded.
> 
> Agreed.
> 
> But the benefit could be to make the user application less complex,
> since otherwise, when a special case like the one you mentioned above
> (with deadband larger than half of the total region), they would also
> need to change the saturation values. This is not really a problem
> when the conditional effect is a 'static' one (i.e. center and
> deadband do not change over time), but it might come in handy for
> 'dynamic' conditional effects.

True. Though it will likely not outweigh the benefit of using the same
definition as DInput.


> Although honestly I think that situation is extremely rare, so I'm OK
> with it if we leave the current definition as is.
> And now I realize that for devices that require the deadband paramater
> to be passed explicitly (and use the present definition) like SWFF2,
> this either would not work, or would require additional (and maybe
> complex) kernel driver code, which is not what we want.
> 
> So, I agree to leave its definition unchanged, sorry for the discussion ;)
> I just have to be sure about this to improve Wine's DInput translation layer.

No problem with the discussion, better too much discussion than not
enough :)

As you've seen, the effect model should very closely match the DInput
model (as that is what the devices tend to support), mostly just the
units are different (our units use the 16-bit range as a whole, i.e.
there are no out-of-range values).

If you have any specific suggestions (patches preferred, otherwise this
ends up further from the head of my TODO list :) ) to improve docs,
those would be welcome.


>>> We will have to do the clamping anyway for devices that only accept
>>> left and right deadband bounds, i.e. Logitech wheels.
>>> For devices that only accept a single deadband value, like your SWFF2
>>> as you mentioned below, the linux deadband would only need to be
>>> shifted "<< 1" before being send to the device, if they accept u16 and
>>> work exactly like DInput (range from center, and
>>> maxValue(deadband)=half of total region).
>>
>> I'm not sure what you are trying to accomplish with "<< 1" here. If the
>> device can't accept the deadband you want, left-shifting wouldn't fix that.
> 
> See above about the factor 2.
> 
>>
>>>>
>>>>>         - Now, knowing that ff_condition_effect->center is __s16:
>>>>>             The worst case scenario is that "center = -32768" or
>>>>> "center = +32767" while still wanting to cover the whole region (this
>>>>> is actually not possible with DInput's specs: in that case, they can
>>>>> only cover half of the total region):
>>>>>             Then, to keep the scale of "center" and "deadband" the
>>>>> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF
>>>>
>>>> Interesting idea. However, if this is not possible in DInput, this means
>>>> the devices will likely not support it either, since they are using the
>>>> DInput effect model (as are we).
>>>
>>> This is no problem, use "<< 1" as mentioned above.
>>>
>>>>
>>>>
>>>> I tried to confirm this with my SWFF2 device, but either it has stopped
>>>> working properly or, more likely, there is a regression in the kernel...
>>>> no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
>>>> requests don't seem to go through properly).
>>>>
>>>>
>>>>> I expect we will have to add/document the answers to my questions in
>>>>> the appropriate file "/include/uapi/linux/input.h" or
>>>>> "/Documentation/input/ff.txt", so that other userspace developers (and
>>>>> maybe also kernel devs) don't face the same ambiguities.
>>>>>
>>>>>
>>>>> Thank you very much for your time,
>>>>
>>>> Thanks for looking into this.
>>>>
>>>>> Elias
>>>>>
>>>>
>>>>
>>>> --
>>>> Anssi Hannula
>>>
>>> Elias
>>>
>>
>>
>> --
>> Anssi Hannula
> 
> Elias
> 


-- 
Anssi Hannula

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

On Sun, Feb 16, 2014 at 12:04 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
> 15.02.2014 22:32, Elias Vanderstuyft kirjoitti:
>> On Sat, Feb 15, 2014 at 3:04 PM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>>> 15.02.2014 14:14, Elias Vanderstuyft kirjoitti:
>>>> On Sat, Feb 15, 2014 at 3:05 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>>>>> 15.02.2014 01:28, Elias Vanderstuyft kirjoitti:
> [...]
>>>>>> 1)
>>>>>> The real meaning of 'directions', declared in
>>>>>> http://lxr.free-electrons.com/source/include/uapi/linux/input.h#L1113
>>>>>> :
>>>>>>     "Direction of the effect" is encoded as follows: ...
>>>>>> But it is not clear whether 'direction of the effect' means either:
>>>>>> - positive direction of the force the user should apply to counteract
>>>>>> the force that the joystick applies; or
>>>>>> - positive direction of the force applied by joystick
>>>>>> From my intuition, I think the latter is (silently?) meant by input.h
>>>>>> If you're interested why this is so important, I attached a document
>>>>>> "DInputVsLinuxDirections.txt" that tries to explain the dilemma if a
>>>>>> translation layer between DInput and Linux input is to be written.
>>>>>
>>>>> From input.h:
>>>>>  * Direction of the effect is encoded as follows:
>>>>>  *      0 deg -> 0x0000 (down)
>>>>>  *      90 deg -> 0x4000 (left)
>>>>>  *      180 deg -> 0x8000 (up)
>>>>>  *      270 deg -> 0xC000 (right)
>>>>>
>>>>> The directions in parantheses are the direction of applied force.
>>>>
>>>> Alright, thanks! That is invaluable information, maybe it should be
>>>> added to input.h .
>>>> It will avoid a lot of confusion for former DInput devs.
>>>>
>>>>>
>>>>> However, there is actually a 1:1 mapping between DInput polar
>>>>> coordinates and our direction parameter; DInput polar coordinates have 0
>>>>> deg = up, 90 deg = right, etc, so they are exactly flipped and therefore
>>>>> match our values due to the reverse definition.
>>>>>
>>>>> Looking at your DInputVsLinuxDirections.txt, you seem to have mixed
>>>>> different definitions of Carts: For DInput you use -1 = north, but for
>>>>> Linux +1 = up, while you use -1 = west/left for both.
>>>>
>>>> So I assume you agree that I got the DInput part right? ((0, -1) = north)
>>>
>>> I guess so.
>>>
>>>> Then my mistake lies in the assumption that (0, +1) = up, so I should
>>>> flip the y-axis to correct the Linux part.
>>>> I'll explain how I originally derived the Linux part:
>>>> Michal documented (in "ff-memless-next.txt") the Linux directions in
>>>> the following way:
>>>> "
>>>> Direction of the effect's force translates to Cartesian coordinates system
>>>> as follows:
>>>>   Direction = 0: Down
>>>>   Direction (0; 16384): 3rd quadrant
>>>>   Direction = 16384: Left
>>>>   Direction (16385; 32768): 2nd quadrant
>>>>   Direction = 32768: Up
>>>>   Direction (32769; 49152): 1st quadrant
>>>>   Direction = 49152: Right
>>>>   Direction (49153; 65535) :4th quadrant
>>>>   Direction = 65565: Down
>>>> "
>>>
>>> The above is correct.
>>>
>>>> For a Cartesian coordinates system:
>>>> - The (-1, 0)-axis (=-x) is the intersection of 3rd quadrant and 2nd
>>>> quadrant => Left
>>>> - The (0, +1)-axis (=+y) is the intersection of 2nd quadrant and 1st
>>>> quadrant => Up
>>>> - The (+1, 0)-axis (=+x) is the intersection of 1st quadrant and 4th
>>>> quadrant => Right
>>>> - The (0, -1)-axis (=-y) is the intersection of 4th quadrant and 3rd
>>>> quadrant => Down
>>>
>>> Not sure why you've arbitrarily chosen reverse definition of Y axis
>>> here,
>>
>> I really tried to derive the above in a non-arbitrary manner, here you
>> can verify why I 'chose' the +y axis as the intersection of 2nd
>> quadrant and 1st quadrant:
>>     http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg
>> And because you said that the part about directions in
>> "ff-memless-next.txt" is correct, it follows that Up (which lies
>> between the 2nd quadrant and 1st quadrant) corresponds with +y
>> direction.
>> I hope this makes sense.
>>
>>> when all DInput and Linux joysticks, mouses, etc. have -y as "up".
>>
>> Alright, I did not know that, at least not for Linux. Where in the
>> Linux documentation can I find this?
>
> I don't think it is explicitely said either. I guess one could say it is
> "standard industry practice" (not limited to input, by the way, with
> e.g. in images the pixel row and column values are increasing right and
> down, not right and up).
>
> I don't oppose more explicit documentation, though.
>
>>>
>>>> Michal's approach seems logical to me, if he made a mistake, it's
>>>> caused by the lack of documentation of input.h : it should mention
>>>> what axes (-x, +x, -y or +y) the words (left, right, down and up)
>>>> correspond with.
>>>
>>> Well, the "left", "right", "down", "up" correspond to directions from
>>> the user perspective.
>>
>> That makes sense.
>>
>>> I don't think that is ambigiuous at all, as I
>>> don't see how you could consider "down" to be away from user?
>>
>> Yes, that's true. But it does not say to which axes (and polarity) they map.
>>
>>>
>>> I'm not against more documentation if it helps, though.
>>>
>>>> So, which interpretation is the right one?
>>>
>>> The one where the directions provided in input.h match physical
>>> direction of the force effect from user perspective on a 2-axis joystick
>>> device.
>>
>> That's a nice explanation! For the doc, also add to what axis each
>> direction corresponds to.
>>
>>>
>>>> (I did not find anything in the Linux documentation that states "there
>>>> is actually a 1:1 mapping between DInput polar coordinates and our
>>>> direction parameter")
>>>
>>> It is not stated explicitely, it just naturally follows.
>>>
>>> 1. Both use a clock-wise direction.
>>> 1. DInput direction definition is reversed, as they use the "counteract"
>>> direction. We can flip to correct.
>>> 2. DInput direction has 0 = up/north, we have 0 = down/south,
>>>    i.e. the exact opposite, so we must flip the direction.
>>>
>>> DInput direction = flipped(flipped(Linux direction))
>>>                  = Linux direction
>>
>> Alright, now I understand how it works.
>> But: the thing I wrote about the Cartesian coordinates system (the +y
>> axis lies between 2nd quadrant and 1st quadrant) is mathematically
>> correct (see referenced link to wiki), so, to fix the only
>> contradiction left, we will have to change the explanation about
>> directions in "ff-memless-next.txt" to the following text:
>> "
>> Direction of the effect's force translates to Cartesian coordinates system
>> as follows:
>>   Direction = 0: Down: +y
>>   Direction (0; 16384): 2nd quadrant
>>   Direction = 16384: Left: -x
>>   Direction (16385; 32768): 3th quadrant
>>   Direction = 32768: Up: -y
>>   Direction (32769; 49152): 4rd quadrant
>>   Direction = 49152: Right: +x
>>   Direction (49153; 65535) :1st quadrant
>>   Direction = 65565: Down: +y
>> "
>> As you can see, I only changed the quadrants (and added axes for
>> convenience), now they agree to
>> "http://en.wikipedia.org/wiki/File:Cartesian_coordinates_2D.svg", and
>> to input.h , so everyone should be happy :)
>> Can you confirm the modification is correct?
>
> I think so.
>
> However, assigning quadrants here is a bit confusing to me here with the
> non-mathematical-traditional reversed Y axis. I.e. my first instinct is
> that the upper-right quadrant is the first one, while it is not the case
> here...

I totally understand your confusion about the quadrants: Michal seems
so have meant the 'quadrants' that can be seen in the text about
directions in "input.h", which are different of the classical
mathematical Cartesian coordinate system. I probably should ask Michal
to clearify that in the doc of "ff-memless-next.txt".

>
> But if it helps...
>
>
>>>
>>>>> This causes the
>>>>> 1st and 3rd entries on both of the Mapping tables to be reversed. When
>>>>> that is fixed, the table #2 shows the correct result.
> [...]
>>>>>> 3)
>>>>>> Many Linux FF effect parameters don't have a clear explanation of the
>>>>>> allowed range, and their corresponding meaning at the extrema.
>>>>>> Here I list the ones that need more explanation, also take a look at
>>>>>> "interactive.fig" in the kernel documentation (but also included as
>>>>>> attachment):
>>>>>> - left_saturation and right_saturation; and
>>>>>
>>>>> left_saturation = maximum force on the negative ("left") side of the
>>>>> center point
>>>>> right_saturation = same for positive side
>>>>>
>>>>> 0x0 => no force,
>>>>> 0xFFFF => maximum force.
>>>>
>>>> OK, thanks for giving the definition. I think these things can be
>>>> understood from "interactive.fig", so there's no need to write
>>>> additional doc about this topic.
>>>>
>>>>>
>>>>>> - deadband
>>>>>
>>>>> The range from center point wherein the effect has no effect
>>>>
>>>> Notice this contradicts with "interactive.fig", this figure defines
>>>> 'deadband' as bound-to-bound, not as center-to-bound (as with DInput).
>>>
>>> There is no difference between those definitions that I can see:
>>>
>>>                        Axis range
>>> |------------------------------------------------------|
>>>
>>> Definition from interactive.fig, bound-to-bound:
>>> 0x0:
>>> |--------------------------X---------------------------|
>>> 0x8000 (covers half of the end-to-end area):
>>> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
>>> 0xFFFF:
>>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
>>
>> Alright, agreed with this part: deadband units or dimensions are the
>> same as the ones of the center offset parameter.
>>
>>>
>>> Center-to-bound definition:
>>> 0x0:
>>> |--------------------------X---------------------------|
>>> 0x8000 (covers half of the center-to-end area):
>>> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
>>> 0xFFFF:
>>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
>>
>> Ah, I see, this is where we disagree: now you're not working with the
>> same units or dimensions as the ones of the center offset parameter:
>> you have multiplied them by a factor 2 (that's where my "<< 1" came
>> from, for going from my definition to your definition).
>
> Yes, the center offset and deadband are in "relative" units, so due to
> the different value range the scales differ by a factor of 2.
>
> I agree it is a bit unfortunate the scales do not match, but IMHO not a
> totally hopeless situation.
>
>> This is my proposal of how it could be:
>>
>> Center-to-bound definition (same dimensions as center offset parameter):
>> 0x0:
>> |--------------------------X---------------------------|
>> 0x4000 (covers half of the center-to-end area):
>> |------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX------------|
>> 0x8000 (covers whole the center-to-end area):
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
>> 0xC000:
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)
>> 0xFFFF:
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| (clamped)
>
> Yes, this I understood.
>
>>>
>>>
>>>>> , with
>>>>> 0x0 => no dead band
>>>>> 0xFFFF => dead band encompassing the entire axis, effect not active
>>>>> anywhere.
>>>>>
>>>>> Assuming center offset of 0, though. Not sure how the currently
>>>>> supported devices interpret 0xFFFF with non-zero center offset, i.e. if
>>>>> the effect is then still active in the extreme opposite end of the axis.
>>>>> You wrote below that this is indeed the case with DInput, so it is
>>>>> highly likely this is how the devices handle it as well.
>>>>
>>>> Careful, here there's a catch:
>>>>     I did not write that in DInput "if deadband == maxValue(deadband)
>>>> with non-zero center offset, then the effect is still active in the
>>>> extreme opposite end of the axis.",
>>>>     I wrote that in DInput "if deadband == maxValue(deadband) with
>>>> maximum non-zero center offset, then the effect can only cover half of
>>>> the total region". For reference: maxValue(deadband)=10000
>>>
>>> I don't see the difference in those statements here.
>>
>> There is, when assuming same dimensions as center offset parameter.
>> Otherwise, you're right.
>
> Right.
>
>>> Note that deadband
>>> is the area where the effect is *not* active.
>>
>> I know, that's why it's called *dead*-band ;)
>>
>>>
>>>> Now I'm proposing to let DInput maxValue(deadband) correspond to linux
>>>> deadband 0x7FFF.
>>>> And still allowing linux deadband to be maximal 0xFFFF => two times
>>>> the maximum range of DInput
>>>>
>>>>>
>>>>>
>>>>>> They all have __u16 types, but "/include/uapi/linux/input.h" does not
>>>>>> say what the maximum values are.
>>>>>> I'm doing a proposal to define and document this (in the Linux kernel)
>>>>>> in the following way, also take a look at my attachment
>>>>>> "interactiveAlteredWithRanges.svg" for the modified version:
>>>>>>     Max Range of {right_saturation and left_saturation} = 0x7FFF
>>>>>>         Because the maximal value of the saturation bound can be only
>>>>>> half of the total range covered by the max negative to max positive
>>>>>> bounds.
>>>>>>         And also because they are related to some form of force, and
>>>>>> all other forms of force magnitude in Linux FF have a maximum value of
>>>>>> 0x7FFF
>>>>>
>>>>> I'm not really convinced that the different range from the other
>>>>> magnitude values is a reason enough to change the definition here.
>>>>
>>>> After reviewing this mail, I totally agree with you, sorry for that.
>>>>
>>>>>
>>>>>>     Max Range of {deadband} = 0xFFFF
>>>>>>         This is a bit harder to explain:
>>>>>>         - First, I would suggest to alter the deadband definition in
>>>>>> figure "interactive.fig":
>>>>>>             I would define deadband as going from a deadband-bound to
>>>>>> the center (BTW, This is how MSDN defines it: "In other words, the
>>>>>> condition is not active between lOffset minus lDeadBand and lOffset
>>>>>> plus lDeadBand."),
>>>>>>             instead of from a deadband-bound to the other deadband-bound.
>>>>>>                 => Same spec as in DInput.
>>>>>
>>>>> With 0xFFFF being the maximum deadband with center offset 0, it does not
>>>>> matter if deadband is defined as range from center or total width,
>>>>> maximum is 0xFFFF in both cases.
>>>>
>>>> Indeed, because (assume applying 0xFFFF linux deadband with center offset 0):
>>>> a) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>>>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>>>> defined as range from center:
>>>>     the driver will clamp {0 + 0xFFFF =approx 0 + 2 * 0x7FFF} to
>>>> 0x7FFF for both left as right side of center => Total region is
>>>> covered by the deadband.
>>>> b) If DInput maxValue(deadband)=10000 (=half of the total region) maps
>>>> to 0x7FFF in the Linux case (=my proposal) if linux deadband is
>>>> defined as total width:
>>>>     the driver will set {0 + 0xFFFF / 2 =approx 0 + 0x7FFF} for both
>>>> left as right side of center => Total region is covered by the
>>>> deadband.
>>>>
>>>> If we define linux deadband as range from center, like a), the Linux
>>>> FF API can represent more variations of conditional effects than
>>>> DInput can (and also with greater resolution), and thus becomes
>>>> superior in that aspect.
>>>
>>> Can you provide any example effect parameters on your proposed system
>>> that would not be possible on DInput?
>>
>> Sure:
>>
>> Center-to-bound definition (same dimensions as center offset parameter):
>> Assume center offset is set to the maximum non-zero value +32767
>> 0x0:
>> |-----------------------------------------------------X|
>> 0x4000 (covers a quarter of the end-to-end area):
>> |----------------------------------------XXXXXXXXXXXXXX|
>> 0x8000 (covers half of the end-to-end area):
>> |---------------------------XXXXXXXXXXXXXXXXXXXXXXXXXXX|
>> 0xC000 (covers three quarters of the end-to-end area):
>> |-------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
>> 0xFFFF (covers whole the end-to-end area):
>> |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
>
> I meant a complete set of effect parameters that will cause an effect
> not possible with the DInput definitions, like I provided below. Your
> above example seems to be the same case I covered below in my example,
> in which case you can simply move the center point left a bit and use a
> zero right-side saturation value, without needing a large deadband value.

Indeed, it's always possible to find a set of parameters in DInput to
match the same result as with using any parameters with the deadband
of my proposal.

>
>>>
>>> If I understood correctly, what you are saying is an effect like this
>>> (percentages in parantheses are from left extreme of the axis to right
>>> extreme of the axis):
>>> sat_left = 0xFFFF
>>> sat_right = 0xFFFF
>>> coeff_left = 0x4000
>>> coeff_right = -0x4000
>>> center = 0x6000   (87.5% point)
>>> deadband (your definition) = 0xA000
>>>      (62.5% of full area from 87.5% point to either direction, i.e.
>>>       25%..150% => (clamping) 25%..100%)
>>>
>>> So that deadband can reach further left than it would be with DInput
>>> definition (which maxes at 0x7FFF of your definition, which would not
>>> reach the 25% mark at the left side).
>>
>> Exactly.
>>
>>>
>>> However, from what I can see, you can achieve the exact same effect with
>>> these parameters (DInput deadband definition):
>>> sat_left = 0xFFFF
>>> sat_right = 0x0000
>>> coeff_left = 0x4000
>>> coeff_right = 0x0000
>>> center = 0x0000 (50% point)
>>> deadband (DInput/ours) = 0x8000 (50% total area, or 50% of
>>> center-to-end, so it reaches 25%..75%)
>>>
>>> On the left side, the effect is exactly the same as before with same
>>> parameters (sat 0xffff, coeff 0x4000, starts at 25% point).
>>>
>>> On the right side the parameters differ, but the end-result is the same,
>>> there is no effect at all:
>>> - In the first example, the right side is fully in deadband area,
>>>   causing the effect to have zero effect.
>>> - In my variant with our definition, the right side has zero saturation,
>>>   causing the effect to have zero effect.
>>>
>>>
>>> So the present definitions (and DInput definitions) can achieve the same
>>> effects as your proposed definitions, unless I'm missing something,
>>> making the change unneeded.
>>
>> Agreed.
>>
>> But the benefit could be to make the user application less complex,
>> since otherwise, when a special case like the one you mentioned above
>> (with deadband larger than half of the total region), they would also
>> need to change the saturation values. This is not really a problem
>> when the conditional effect is a 'static' one (i.e. center and
>> deadband do not change over time), but it might come in handy for
>> 'dynamic' conditional effects.
>
> True. Though it will likely not outweigh the benefit of using the same
> definition as DInput.
>
>
>> Although honestly I think that situation is extremely rare, so I'm OK
>> with it if we leave the current definition as is.
>> And now I realize that for devices that require the deadband paramater
>> to be passed explicitly (and use the present definition) like SWFF2,
>> this either would not work, or would require additional (and maybe
>> complex) kernel driver code, which is not what we want.
>>
>> So, I agree to leave its definition unchanged, sorry for the discussion ;)
>> I just have to be sure about this to improve Wine's DInput translation layer.
>
> No problem with the discussion, better too much discussion than not
> enough :)
>
> As you've seen, the effect model should very closely match the DInput
> model (as that is what the devices tend to support), mostly just the
> units are different (our units use the 16-bit range as a whole, i.e.
> there are no out-of-range values).
>
> If you have any specific suggestions (patches preferred, otherwise this
> ends up further from the head of my TODO list :) ) to improve docs,
> those would be welcome.

Alright, when I find enough spare time, I will bundle all additional
documentation and propose it as a patch.

>
>
>>>> We will have to do the clamping anyway for devices that only accept
>>>> left and right deadband bounds, i.e. Logitech wheels.
>>>> For devices that only accept a single deadband value, like your SWFF2
>>>> as you mentioned below, the linux deadband would only need to be
>>>> shifted "<< 1" before being send to the device, if they accept u16 and
>>>> work exactly like DInput (range from center, and
>>>> maxValue(deadband)=half of total region).
>>>
>>> I'm not sure what you are trying to accomplish with "<< 1" here. If the
>>> device can't accept the deadband you want, left-shifting wouldn't fix that.
>>
>> See above about the factor 2.
>>
>>>
>>>>>
>>>>>>         - Now, knowing that ff_condition_effect->center is __s16:
>>>>>>             The worst case scenario is that "center = -32768" or
>>>>>> "center = +32767" while still wanting to cover the whole region (this
>>>>>> is actually not possible with DInput's specs: in that case, they can
>>>>>> only cover half of the total region):
>>>>>>             Then, to keep the scale of "center" and "deadband" the
>>>>>> same, "deadband = 65535" = +32767 - -32768 = 0xFFFF
>>>>>
>>>>> Interesting idea. However, if this is not possible in DInput, this means
>>>>> the devices will likely not support it either, since they are using the
>>>>> DInput effect model (as are we).
>>>>
>>>> This is no problem, use "<< 1" as mentioned above.
>>>>
>>>>>
>>>>>
>>>>> I tried to confirm this with my SWFF2 device, but either it has stopped
>>>>> working properly or, more likely, there is a regression in the kernel...
>>>>> no time to debug now, though, so added to my TODO (HID_REQ_GET_REPORT
>>>>> requests don't seem to go through properly).
>>>>>
>>>>>
>>>>>> I expect we will have to add/document the answers to my questions in
>>>>>> the appropriate file "/include/uapi/linux/input.h" or
>>>>>> "/Documentation/input/ff.txt", so that other userspace developers (and
>>>>>> maybe also kernel devs) don't face the same ambiguities.
>>>>>>
>>>>>>
>>>>>> Thank you very much for your time,
>>>>>
>>>>> Thanks for looking into this.
>>>>>
>>>>>> Elias
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Anssi Hannula
>>>>
>>>> Elias
>>>>
>>>
>>>
>>> --
>>> Anssi Hannula
>>
>> Elias
>>
>
>
> --
> Anssi Hannula

Elias

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

On Sun, Feb 16, 2014 at 12:04 AM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
> 15.02.2014 22:32, Elias Vanderstuyft kirjoitti:
>> On Sat, Feb 15, 2014 at 3:04 PM, Anssi Hannula <anssi.hannula@iki.fi> wrote:
>>>
>>> However, from what I can see, you can achieve the exact same effect with
>>> these parameters (DInput deadband definition):
>>> sat_left = 0xFFFF
>>> sat_right = 0x0000
>>> coeff_left = 0x4000
>>> coeff_right = 0x0000
>>> center = 0x0000 (50% point)
>>> deadband (DInput/ours) = 0x8000 (50% total area, or 50% of
>>> center-to-end, so it reaches 25%..75%)
>>>
>>> On the left side, the effect is exactly the same as before with same
>>> parameters (sat 0xffff, coeff 0x4000, starts at 25% point).
>>>
>>> On the right side the parameters differ, but the end-result is the same,
>>> there is no effect at all:
>>> - In the first example, the right side is fully in deadband area,
>>>   causing the effect to have zero effect.
>>> - In my variant with our definition, the right side has zero saturation,
>>>   causing the effect to have zero effect.
>>>
>>>
>>> So the present definitions (and DInput definitions) can achieve the same
>>> effects as your proposed definitions, unless I'm missing something,
>>> making the change unneeded.

Today, I noticed something strange: an explicit saturation of zero in
DInput (or at least using the most recent driver for my Logitech MOMO
wheel), appears to be transformed to max saturation! (This is why I
chose to quote your "sat_right = 0x0000" part, however that's not the
point I want to make in this mail)

E.g:
    pos_sat = 10000    ->    Max saturation send to device
    pos_sat =  5000    ->    Half saturation send to device
    ...
    pos_sat =     1    ->    Zero saturation send to device (because
it appears to be rounded to zero)
    pos_sat =     0    ->    Max saturation send to device (?!)

Also interesting is that the FEdit tool (from MS DirectX SDK) sets all
'saturation' values to zero by default. This is not the case for the
'coefficient' values: they are set to maximum. The resulting default
conditional force generates a maxed out conditional effect on my MOMO
wheel.
The weird thing is, that MSDN does not explicitly say anything about
this: http://msdn.microsoft.com/en-us/library/windows/desktop/microsoft.directx_sdk.reference.dicondition%28v=vs.85%29.aspx
"dwPositiveSaturation:
    Maximum force output on the positive side of the offset, in the
range from 0 through 10,000.
    If the device does not support force saturation, the value of this
member is ignored.
"

So, my question is:
    - Should Wine's translation layer convert a 0 dinput saturation to
max linux saturation?
    - or Should the Linux FF drivers send a max saturation command
when the linux saturation equals zero?
    - or Should we forget about this? (but that will result Wine's
behaviour to be different from Windows', at least for my MOMO wheel (I
don't have another capable (non-Logitech?) wheel to test it with))

Best regards,
Elias

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

Another question:
There is written on /include/uapi/linux/input.h:1058 :
    "@phase: 'horizontal' shift"
where 'horizontal' most likely means time dimension, not phase of the
waveform, right?


Elias

Re: Questions about the documentation/specification of Linux ForceFeedback input.h

[Elias Vanderstuyft]

On Wed, Feb 19, 2014 at 7:54 PM, Elias Vanderstuyft <elias.vds@gmail.com> wrote:
> Today, I noticed something strange: an explicit saturation of zero in
> DInput (or at least using the most recent driver for my Logitech MOMO
> wheel), appears to be transformed to max saturation! (This is why I
> chose to quote your "sat_right = 0x0000" part, however that's not the
> point I want to make in this mail)
>
> E.g:
>     pos_sat = 10000    ->    Max saturation send to device
>     pos_sat =  5000    ->    Half saturation send to device
>     ...
>     pos_sat =     1    ->    Zero saturation send to device (because
> it appears to be rounded to zero)
>     pos_sat =     0    ->    Max saturation send to device (?!)
>
> Also interesting is that the FEdit tool (from MS DirectX SDK) sets all
> 'saturation' values to zero by default. This is not the case for the
> 'coefficient' values: they are set to maximum. The resulting default
> conditional force generates a maxed out conditional effect on my MOMO
> wheel.
> The weird thing is, that MSDN does not explicitly say anything about
> this: http://msdn.microsoft.com/en-us/library/windows/desktop/microsoft.directx_sdk.reference.dicondition%28v=vs.85%29.aspx
> "dwPositiveSaturation:
>     Maximum force output on the positive side of the offset, in the
> range from 0 through 10,000.
>     If the device does not support force saturation, the value of this
> member is ignored.
> "
>
> So, my question is:
>     - Should Wine's translation layer convert a 0 dinput saturation to
> max linux saturation?
>     - or Should the Linux FF drivers send a max saturation command
> when the linux saturation equals zero?
>     - or Should we forget about this? (but that will result Wine's
> behaviour to be different from Windows', at least for my MOMO wheel (I
> don't have another capable (non-Logitech?) wheel to test it with))
>

On Thu, Feb 20, 2014 at 9:52 AM, Elias Vanderstuyft <elias.vds@gmail.com> wrote:
> Another question:
> There is written on /include/uapi/linux/input.h:1058 :
>     "@phase: 'horizontal' shift"
> where 'horizontal' most likely means time dimension, not phase of the
> waveform, right?
>

Hi Anssi,

Any thoughts about my previous 2 mails' questions?
(I just need be sure of these things to finish my Wine FF patchset,
however, if you don't have time, no problem, it can wait for some time)

Best regards,
Elias