louisswarren/promacro

Sending key presses using a gamepad isn't that hard

promacro

Sending key presses using a gamepad isn't that hard.

I use my gamepad to play games on an emulator, with the following macros:

1. Left trigger maps to space (fast-forward in the emulator)
2. When the right stick forward/back axis is not in the neutral position, mash (rapidly toggle) the x key.

After using various unstable programs to do this (which randomly crash while interacting with the GUI, or wipe my settings), I realised that this is actually very simple to implement myself (in Linux, at least).

Usage

First, note this is Linux-only.

If you want precisely the same macros that I use, and you own a Logitech F310, then you're good to go. There is no config file, because otherwise 90% of the code would be for handling the config file, and it would require some kind of domain-specific language that would not be able to handle every use case.

Instead, modify the code in promacro.c to do what you want! Here are some hints:

Interpreting joystick signals

/dev/input/js0 is the file handle for your joystick. To figure out what the input looks like, use xxd. In the case of the Logitech F310, each input signal is 8 bytes, so watching the output of xxd -c8 /dev/input/js0 as I pressed buttons allowed me to figure out what the input format is.

In my case, it was:

• 32 bits (little endian) of timestamp
• 16 bits (little endian two's complement) of button value
• 16 bits of button identifier

The identifier is button the event is for. For binary buttons, the value is 1 on press, 0 on release. For analogue buttons, the value ranges between -32768 and 32767, with 0 being neutral.

Sending key events

The keycodes you'll want to send are listed in <linux/input-event-codes.h> (i.e. located in /usr/include/linux/input-event-codes.h).