Macropad4s

A Scala Native application for intercepting and handling input events from programmable macro keyboards (macropads).

This project demonstrates how to use Scala Native to directly interact with Linux input devices at a low level, enabling custom keyboard shortcuts and device control without relying on proprietary manufacturer software.

Features

• Direct Linux input device access using Scala Native and ioctl system calls
• Functional programming approach with Cats Effect and FS2
• Event-driven keyboard handling with exclusive device access
• Support for custom key mappings and actions
• Native executable for efficient performance
• Secure alternative to proprietary manufacturer software

How It Works

The application:

1. Opens a specified input device path (e.g., /dev/input/event11)
2. Uses EVIOCGRAB ioctl to grab the device exclusively, preventing other programs from receiving input events
3. Processes input events in a streaming fashion using FS2
4. Performs custom actions based on key presses (e.g. volume control)

Getting Started

Prerequisites

• Linux system with access to input devices
• Scala Native 0.5.x
• Root privileges or udev rules for accessing input devices
• Scala installed https://www.scala-lang.org/download/

Building

# Compile the project
scala compile

# Create a native executable
scala --power package

# Clean build artifacts
scala clean

Running

# Run the application (requires proper permissions to access input devices)
scala run main.scala

# Or run the pre-built native executable
./org.polyvariant.macropad4s.App

# Run with a specific input device path
./org.polyvariant.macropad4s.App /dev/input/event0

Example Usage

By default, the application listens to events on /dev/input/event11 and handles:

• Key 1: Decreases volume
• Key 3: Increases volume

You can modify these mappings in main.scala to suit your needs.

Device Detection

To find your specific input device, you can use:

# Find your device by vendor and product ID
VENDOR="514c"; PRODUCT="8851"; for ev in /dev/input/event*; do udevadm info -q property -n "$ev" | grep -q "ID_VENDOR_ID=${VENDOR}" && udevadm info -q property -n "$ev" | grep -q "ID_MODEL_ID=${PRODUCT}" && echo "$ev"; done

Architecture

The application is built with:

• Scala Native - For low-level system access using ioctl calls
• Cats Effect - For functional effects and resource management
• FS2 - For streaming input processing
• Scala CLI - For dependency management and build