BACKENDS: SDL: cursor drifting for game controller

[beaumanvienna]

scummvm version: upstream
where: main screen

This is fixing the issue for me: backends/events/sdl/sdl-events.cpp

bool SdlEventSource::handleJoyAxisMotion(SDL_Event &ev, Common::Event &event) {

event.type = Common::EVENT_JOYAXIS_MOTION;
event.joystick.axis = ev.jaxis.axis;

if (abs(ev.jaxis.value) > 4000)

event.joystick.position = ev.jaxis.value >> 1;

else

event.joystick.position = 0;

return true;

}

[sev-]

This bug would be nice to get fixed before the release.

[digitall]

I think reading this code that it is implementing a fixed "deadband" for the joystick axis to prevent small zero offsets on the hardware causing drifts.

This would be applied at ​https://github.com/scummvm/scummvm/blob/master/backends/events/sdl/sdl-events.cpp#L823

However, I think that this is very hardware dependent and if this is implemented, it will be necessary to allow the deadband to be configured between 0 i.e. disabled and up to say around 4000. It is also usual to offset the deadband to avoid the startup jerk i.e. sudden 0 to 4000 transition with current code.

P.S. Had to do this kind of code for my "day job" a fair bit..

[digitall]

​https://en.wikipedia.org/wiki/Deadband for reference.

[digitall]

​https://wiki.libsdl.org/SDL_JoyAxisEvent and ​https://wiki.libsdl.org/SDL_JoystickGetAxis have some notes on this i.e. "The value returned by SDL_JoystickGetAxis() is a signed integer (-32768 to 32767) representing the current position of the axis. It may be necessary to impose certain tolerances on these values to account for jitter."