#21 Cannot calibrate joystick

[Anonymous]

I've calibrated joystick using jscalibrator utility
from libjsw (it's USB Logitech WingmanAttack 2, seen
properly in /dev/js0), unfortunately when I start any
game that has joystick option, player goes left and no
other moves are possible (on Jet Set Willy player can
jump when I press the button)

Paul

[Fredrick Meunier]

🤖 Repo Assist investigation complete.

Root cause identified: the do_axis() function in ui/uijoystick.c (the libjsw joystick backend) has no deadzone threshold. It checks position == 0.0 — any non-zero axis value, even tiny hardware drift, is treated as a directional input. This causes constant "left" movement and blocks all other directional inputs.

The SDL1 (ui/sdl/sdljoystick.c) and SDL2 (ui/sdl2/sdl2_joystick_internal.c) backends correctly implement a ±16384 deadzone, which explains why building with SDL instead of libjsw works around the issue.

Proposed fix: add a configurable deadzone threshold to do_axis() in ui/uijoystick.c, similar to the SDL backends. A default of ~0.25 (on libjsw's normalised [-1.0, 1.0] range) would be analogous to the SDL ±16384 threshold. A --joystick-deadzone setting would let users tune this.

Files involved:

• ui/uijoystick.c — do_axis() at line ~242 (needs deadzone)
• ui/sdl/sdljoystick.c — reference implementation with deadzone
• ui/sdl2/sdl2_joystick_internal.c — reference implementation with deadzone

[Sergio Baldoví]

Proposed fix sounds good, but libjsw is unmaintained and no longer distributed in linux distributions (except Gentoo IIRC).

I suggest dropping libjsw support and use SDL to handle joysticks.

[Fredrick Meunier]

Thanks, sounds very sensible. I'll drop libjsw for the next release unless someone beats me to it.

[Fredrick Meunier]

Now done. Please let me know if any configuration is broken. [5dad7a]

[Paul Osmialowski]

Thanks for finalizing this. I'm surprised that this has been handled after so many decades. Meanwhile, I got myself an USB adapter for Atari-compatible DB9 joysticks, it's recognized by SDL as a hat device, and the hat devices don't need any calibration. Fuse works with it just fine.