[Bug 51922] HID joystick constant Force Feedback effect does not work

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=51922

--- Comment #15 from Rémi Bernon <rbernon at codeweavers.com> ---
(In reply to Ivo Ivanov from comment #14)
> Created attachment 71221 [details]
> winebus-fixes.patch
> 
> I remember that comment in the SDL code :)
> I got confused by it when I was writing a Linux FFB driver for a Fanatec
> device and found it on the net. Maybe they mean the 90 deg difference
> between polar and spherical. Anyway, it is visible from the SDL code that
> they just rescale the source polar coords to the Linux FF range.
> 

You're right, I've been so much confused by the comment that I even read the
code as if it was actually doing what it described, but it isn't...

> So your previous code was correct. I have reverted the lnxev part of the
> patch, and immediately the "set effect" output reports started showing the
> correct direction 0x2d similar to the other backends and Windows.
> 

What I'm still puzzled with is that the legacy dinput evdev backend we
previously had was using the same direction rotations as we are now. I wouldn't
trust it too much though, it's possible that it also got it wrong, or that the
inversion was indeed here in the Linux kernel, a long time ago.

> The FFB was still absent, though, so I looked at some captured usb traffic,
> and found two interesting things. The FF gain was set to 0 on the lnxev
> backend, and the duration field of the "set effect" report was 0x7fff on the
> both SDL and lnxev backends.
> 
> For the first issue appeared that FF_GAIN needed to be rescaled for the
> Linux FF range.
> 
> For the second issue, we pass correctly 0xffff for infinite duration, but
> Linux just clamps it to the max allowed value of 0x7fff, as it doesn't
> consider that value an infinite duration. The Linux FF uses 0 for that,
> while SDL uses SDL_HAPTIC_INFINITY.
> 
> So, attached patches that correct the issues. Tested thoroughly both the SDL
> and lnxev backends with various games - rFactor 2, Assetto Corsa
> Competizione, Automobilista 2, BeamNG, etc. The FFB worked properly and on
> par with hidraw and Windows.
> The only problem I could still spot is that the damper condition effect is
> very weak in comparison to hidraw and Windows. Assetto Corsa Competizione
> uses such effect when the car is stand still.
> 
> The patches are based on 3f6102080e632b9f4d8a97c0f0b1231fbd8e759b

Thanks for the fixes, they look right indeed.

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