SKILL.md
REAPER JSFX MIDI Processing
Patterns for MIDI utility plugins including note processing, arpeggiators, chord generators, and CC manipulation.
Requires: [reaper-jsfx-core](../reaper-jsfx-core/SKILL.md) for language fundamentals.
Rules
| Rule | Description |
|---|---|
| [midi-basics](./rules/midi-basics.md) | MIDI message structure, receive/send, SysEx handling |
| [midi-transform](./rules/midi-transform.md) | Note transposition, velocity scaling, CC mapping |
| [midi-generate](./rules/midi-generate.md) | Arpeggiators, sequencers, chord generators |
| [midi-routing](./rules/midi-routing.md) | Multi-bus routing, channel filtering, splitting |
Official Documentation
Key Principles
1. MIDI-Only Plugin Structure
desc:MIDI Utility
tags:midi
in_pin:none
out_pin:none
@block
while(midirecv(offset, msg1, msg2, msg3)) (
// Process and forward
midisend(offset, msg1, msg2, msg3);
);2. Always Forward or Handle All Messages
@block
while(midirecv(offset, msg1, msg2, msg3)) (
status = msg1 & $xF0;
status == $x90 || status == $x80 ? (
// Process notes
process_note(offset, msg1, msg2, msg3);
) : (
// Pass through everything else unchanged
midisend(offset, msg1, msg2, msg3);
);
);3. Preserve Timing
@block
// Use original offset for timing-critical events
while(midirecv(offset, msg1, msg2, msg3)) (
// Transform but keep original offset
midisend(offset, new_msg1, new_msg2, new_msg3);
);Quick Reference
| Use Case | Rule |
|---|---|
| Understanding MIDI | [midi-basics](./rules/midi-basics.md) |
| Transpose / Velocity | [midi-transform](./rules/midi-transform.md) |
| Arpeggiator | [midi-generate](./rules/midi-generate.md) |
| Channel Filter | [midi-routing](./rules/midi-routing.md) |