MIDI TrackPad

Transform your Apple Trackpad into a midi device (only Linux)

Requirements

• Linux
• Apple TrackPad
• evdev — sudo apt install libevdev-dev
• portmidi — sudo apt install libportmidi-dev

Building

git clone <this repo>
cd <this repo>
cmake -S . -B build
cmake --build build
./build/apps/miditrackpad # <--- executable here

Usage

1. Run the executable (NB. requires root privileges, eg. sudo)
2. Touch the trackpad (emits MIDI messages)

By default, the device axes emit standard MIDI keyboard actions

• X-Axis ⇒ (PB) Pitch Bend (after touch release, it resets to center)
• Y-Axis ⇒ (CC1) Control Change #1 (Modulation)
• Z-Axis ⇒ (CP) Channel Pressure (Aftertouch)

However, each axis may assign to any of the afforementioned MIDI actions (including none), and may optionally reset to center, after release.

Command line flags

./miditrackpad
    -l # list all evdev input and midi output devices
    -t <timeout-ms> # how long poll() should wait
    -i <evdev-input-device-id|device-path>
    -o <midi-output-device-id>
    -c <midi-channel> # [1-16]
    -x <PB|CC#|CP|OFF>[!] # configure MIDI actions on this axis
    -y <PB|CC#|CP|OFF>[!] #
    -z <PB|CC#|CP|OFF>[!] #

Examples:

# list all input and output devices
./miditrackpad -l

# translate events
# from input device 1
# to output device 2
# on MIDI channel 3
./miditrackpad -i /dev/input/event1 -o2 -c3

# or equivalently
./miditrackpad -i1 -o2 -c3

# or with custom axis assignment
# where:
#     x-axis emits Control Change 88, and resets to center
#     y-axis emits Control Change 89, and does NOT reset to center
#     z-axis emits Pitch Bend, and resets to center
./miditrackpad -i1 -o2 -c3 -xCC88! -yCC89 -zPB!