REAPER Trackpad Engine — MIDI smooth scrolling build

Native macOS extension that makes a MacBook trackpad substantially more natural in REAPER’s Arrange view and MIDI editor.

This repository is a downstream fork of duanebeatzz/ReaperTrackpadEngine. It preserves the upstream source history and publishes the tested Apple Silicon release builds made for this fork.

What v3.6 MIDI changes

• Two-finger scrolling pans the Arrange view as in the established Trackpad Engine build.
• Inside the piano roll, two-finger horizontal and vertical scrolling are handled as precise viewport motion.
• Pinch-to-zoom in the MIDI editor is anchored at the mouse cursor instead of REAPER’s edit/play cursor.
• MIDI pinch sensitivity is reduced relative to the preceding experimental build.
• The extension restores REAPER’s previous horizontal-zoom preference when it unloads.

REAPER’s MIDI editor still scrolls vertically in native note-row steps. That is a REAPER viewport limitation; this build does not add a fake visual interpolation layer.

Requirements

• macOS on Apple Silicon (M1/M2/M3/M4 and later)
• REAPER for macOS
• ReaPack and the js_ReaScriptAPI extension, installed through ReaPack

js_ReaScriptAPI is required for the smooth MIDI viewport scrolling. If it is absent, the extension intentionally leaves MIDI input to stock REAPER rather than interfering with it.

Install

1. In the latest release, download reaper-trackpadengine-v3.6-midi-arm64.zip.

2. Quit REAPER completely (⌘Q), not merely close its window.

3. Unzip the download and copy reaper_trackpadengine.dylib to:

   ~/Library/Application Support/REAPER/UserPlugins/
   

4. If Finder asks, replace the older file of the same name.

5. Start REAPER again.

Install js_ReaScriptAPI

1. Install ReaPack if it is not already present, then restart REAPER.
2. Choose Extensions → ReaPack → Browse packages.
3. Search for js_ReaScriptAPI, install it, then restart REAPER once more.

Update / remove

• Update: quit REAPER, replace the same .dylib, start REAPER again.
• Remove: quit REAPER and delete reaper_trackpadengine.dylib from the UserPlugins folder. REAPER will return to its normal trackpad behaviour.

Verify the download

The release includes SHA256SUMS.txt. In Terminal, from the unzipped release folder:

shasum -a 256 reaper_trackpadengine.dylib

For v3.6 MIDI the expected hash is:

cee7dab6c28c76646e54c5a228afe7d04270d7ab328aa0d8120c9b193f74b65c

Compatibility and scope

This first downstream release is specifically built for arm64 macOS. It is not an Intel build and has not been tested on Windows or Linux. It uses REAPER internals and js_ReaScriptAPI, so test it on a copy of an important project before relying on it in a critical session.

The project is not affiliated with Cockos.

Source and reproducibility

The source tree preserves the upstream project. The exact downstream changes used for this release are kept as an ordered, reviewable patch series in patches/. The published binary was built after applying that series; a plain upstream-source build does not by itself reproduce v3.6 MIDI.

Credits

Upstream project: duanebeatzz/ReaperTrackpadEngine.

This fork’s MIDI scrolling and cursor-anchored pinch work were developed as a downstream modification. See CHANGELOG.md for the release-specific behaviour.