Force feedback auto center implementation?

[Tyson Whitehead]

Would like to get disabling force feedback auto-centering working so
that trimming will work properly with force feedback devices in flight
simulators.

Currently the call to disable it is a stub

static HRESULT dinput_device_set_property( IDirectInputDevice8W
*iface, const GUID *guid,
                                           const DIPROPHEADER *header )
{
    ...
    case (DWORD_PTR)DIPROP_AUTOCENTER:
    {
        const DIPROPDWORD *value = (const DIPROPDWORD *)header;
        if (!(impl->caps.dwFlags & DIDC_FORCEFEEDBACK)) return
DIERR_UNSUPPORTED;
        if ( header->dwHow != DIPH_DEVICE) return DIERR_INVALIDPARAM;
        impl->vtbl->set_property( iface,
        FIXME( "DIPROP_AUTOCENTER stub!\n" );
        impl->autocenter = value->dwData;
        return DI_OK;
    }
    ...
}

After having looked through the wine, SDL, and kernel code and read up
on the force feedback HID physical interface device (PID) usage table
reports, I am guessing this was left as a stub because it doesn't fit
in with the current design of dipnut communicating with the backend
via HID reports. The issue being that auto centering, unlike
everything else, isn't part of the PID specification, so there isn't a
predefined report that can be used for this (see table 0x0f)

https://www.usb.org/document-library/hid-usage-tables-14

Although I am no wine or Windows code expert, I am guess this leaves
the following options

- leave it disabled in the backend and emulate it via a frontend spring effect
- abuse an existing HID report to communicate it
- add a WINE specific HID report to communicate it
- add a WINE specific IOCTL to communicate it

For the first option, I mean have the winebus backends disable it via
the kernel or an SDL call and then have the dinput layer enable
simulate it by adding a default spring effect. This then lets the
dinput frontend disable it again by removing or disabling its spring
effect. For the second one I mean something like reserve an effect ID
for specifying auto centering.

Both of these are inspired by the fact that from the kernel code, it
seems auto centering for HID devices is an undocumented use of the
first effect ID for a spring effect

https://github.com/torvalds/linux/blob/610a9b8f/drivers/hid/usbhid/hid-pidff...
https://github.com/torvalds/linux/blob/610a9b8f/drivers/hid/usbhid/hid-pidff...

Would be interesting in knowing what sort of implementation people
think would be best and acceptable for inclusion into wine?

Thanks!  Tyson