joystick: initial state of throttle input is not detected #105676
Description
Tested versions
v4.5.dev.custom_build [689c503c5]
I believe this is present in all versions with joystick support.
System information
Godot v4.5.dev (689c503c5) - Arch Linux #1 SMP PREEMPT_DYNAMIC Mon, 07 Apr 2025 19:59:13 +0000 on X11 - X11 display driver, Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4070 (nvidia; 570.133.07) - AMD Ryzen 9 9950X 16-Core Processor (32 threads)
Issue description
Some joysticks have throttle controls - axis inputs which remain where you put them when you let go, rather than returning to a neutral position.
This means that when Godot starts up, it is quite reasonable for a throttle to actually be in a non-zero position. However, Godot does not know the position of the throttle until it actually moves.
On Linux, joysticks are accessed via the evdev interface at - typically - /dev/input/eventN. This interface does not provide a way to query the current state of the axes.
There is another interface at /dev/input/jsN which emits synthetic input events reflecting the current state of the axes when you open the device file.
Steps to reproduce
Having a joystick with a throttle, run print(Input.get_joy_axis(A, B) in a _process, where A and B are whatever's right for the throttle control. Until you move the throttle, it'll print 0.0, even if the throttle starts in a non-zero position.