VCV Prototype

Scripting language host for VCV Rack containing:

• 6 inputs
• 6 outputs
• 6 knobs
• 6 lights (RGB LEDs)
• 6 switches with RGB LEDs

Supported scripting languages:

• JavaScript (ES2020) (.js)
• Lua (.lua)
• Vult (.vult)
• Pure Data (.pd)
• Add your own below

Discussion thread

Scripting API

This is the reference API for the JavaScript script engine, along with default property values. Other script engines may vary in their syntax (e.g. block.inputs[i][j] vs block.getInput(i, j) vs input(i, j)), but the functionality should be similar.

/** Display message on LED display.
*/
display(message)

/** Skip this many sample frames before running process().
For CV generators and processors, 256 is reasonable.
For sequencers, 32 is reasonable since process() will be called every 0.7ms with
a 44100kHz sample rate, which will capture 1ms-long triggers.
For audio generators and processors, 1 is recommended, but use `bufferSize` below.
If this is too slow for your purposes, consider writing a C++ plugin, since
native VCV Rack plugins have 10-100x better performance.
*/
config.frameDivider // 32

/** Instead of calling process() every sample frame, hold this many input/output
voltages in a buffer and call process() when it is full.
This decreases CPU usage, since processing buffers is faster than processing one
frame at a time.
The total latency of your script in seconds is
`config.frameDivider * config.bufferSize * block.sampleTime`.
*/
config.bufferSize // 1

/** Called when the next block is ready to be processed.
*/
function process(block) {
	/** Engine sample rate in Hz. Read-only.
	*/
	block.sampleRate

	/** Engine sample timestep in seconds. Equal to `1 / sampleRate`. Read-only.
	Note that the actual time between process() calls is
	`block.sampleTime * config.frameDivider`.
	*/
	block.sampleTime

	/** The actual size of the input/output buffers.
	*/
	block.bufferSize

	/** Voltage of the input port of column `i`. Read-only.
	*/
	block.inputs[i][bufferIndex] // 0.0

	/** Voltage of the output port of column `i`. Read/write.
	*/
	block.outputs[i][bufferIndex] // 0.0

	/** Value of the knob of column `i`. Between 0 and 1. Read/write.
	*/
	block.knobs[i] // 0.0

	/** Pressed state of the switch of column `i`. Read-only.
	*/
	block.switches[i] // false

	/** Brightness of the RGB LED of column `i`, between 0 and 1. Read/write.
	*/
	block.lights[i][0] // 0.0 (red)
	block.lights[i][1] // 0.0 (green)
	block.lights[i][2] // 0.0 (blue)

	/** Brightness of the switch RGB LED of column `i`. Read/write.
	*/
	block.switchLights[i][0] // 0.0 (red)
	block.switchLights[i][1] // 0.0 (green)
	block.switchLights[i][2] // 0.0 (blue)
}

The Vult API is slightly different than Prototype's scripting API. See examples/template.vult for a reference of the Vult API.

Build dependencies

Windows

pacman -S mingw-w64-x86_64-premake

Mac

brew install premake

Ubuntu 16.04+

sudo apt install premake4

Arch Linux

sudo pacman -S premake

Build

Add path to Rack-SDK

export RACK_DIR=/set/path/to/Rack-SDK/

load submodules

git submodule update --init --recursive

Make

make dep
make

Adding a script engine

• Add your scripting language library to the build system so it builds with make dep, following the Duktape example in Makefile.
• Create a MyEngine.cpp file (for example) in src/ with a ScriptEngine subclass defining the virtual methods, using src/DuktapeEngine.cpp as an example.
• Build and test the plugin.
• Add a few example scripts and tests to examples/. These will be included in the plugin package for the user.
• Add your name to the Contributors list below.
• Send a pull request. Once merged, you will be added as a repo maintainer. Be sure to “watch” this repo to be notified of bug reports and feature requests for your engine.

Contributors

• Wes Milholen: panel design
• Andrew Belt: host code, Duktape (JavaScript, not used), LuaJIT (Lua), Python (in development)
• Jerry Sievert: QuickJS (JavaScript)
• Leonardo Laguna Ruiz: Vult
• CHAIR [Clemens Wegener (libpd), Max Neupert (patches)] : libpd
• add your name here