A MIDI piano-roll visualizer written in Odin using Raylib.

Resonance loads Standard MIDI Files and renders them as a falling-note piano roll with real-time audio playback via sine-wave synthesis. The MIDI parser is written from scratch — no external MIDI libraries.

• Odin compiler (the vendor:raylib bindings ship with Odin, so Raylib needs no separate install)
• A desktop OS with OpenGL (developed on Linux / Arch)

# Run directly (compiles to a temp binary, then runs)
odin run .

# …optionally with a file to load on startup
odin run . -- song.mid

# Or build a standalone binary
odin build . -out:resonance
./resonance song.mid

Once the window is open, drag and drop any .mid file onto it to load it. A summary of the parsed file (format, division, tracks, note counts, tempo) is printed to the console — handy for verifying the parser against real files.

Two example files are included:

odin run . -- assets/demo.mid    # 2-track melody + chords (good first look)
odin run . -- assets/sample.mid  # minimal 2-note file

Playback loops automatically at the end. The speed multiplier changes tempo, not pitch.

The MIDI parser has a unit-test suite (hand-built byte streams covering tempo meta events, running status, note-on-velocity-0, SMPTE division, and malformed headers):

odin test .

resonance/
├── main.odin        # entry point, playback engine, controls
├── midi.odin        # MIDI binary parser (Format 0 & 1)
├── midi_test.odin   # parser unit tests
├── timeline.odin    # tick→seconds tempo map, note + event extraction
├── piano_roll.odin  # falling-note rendering + 88-key keyboard
├── audio.odin       # sine-wave synthesis + polyphonic mixing
├── ui.odin          # BPM display, speed/pause overlay, progress bar
└── assets/
    ├── demo.mid     # 2-track melody + chords
    └── sample.mid   # minimal 2-note file

• MIDI parser — Format 0/1, variable-length quantities, running status, note on/off, velocity, delta/absolute ticks, tempo & meta events, SysEx
• Piano-roll renderer — falling note blocks, 88-key keyboard, per-octave shading
• Multi-track rendering — one color per track, layered
• Audio playback — sine-wave synthesis (equal temperament, A4 = 440 Hz), polyphonic mixing
• Playback controls — 0.5×/1×/2× speed, pause/resume, BPM display
• Drag-and-drop loading at runtime

MIT