ZenGarden is a stand-alone library for running Pure Data patches.
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examples Python + pygame example for interfacing with ZenGarden Oct 30, 2009



ZenGarden (ZG) is a runtime for the Pure Data (Pd) audio programming language. It is implemented as an extensible audio library allowing full control over signal processing, message passing, and graph manipulation. ZenGarden does not have a GUI, but easily allows one to be built on top of it.

The library is written in C++ and exposes a pure C interface described exclusively in ZenGarden.h. Many audio objects are accelerated with vector operations on ARM (NEON) and x86 (SSE) platforms, and works especially well on Apple platforms (both OS X and iOS). ZenGarden allows externals to be built, also ones that override default object functionality. A language wrapper exists for Java.

ZenGarden is licensed under the LGPL. Among other things, this means that if you are going to use the libary in a public application you must:

  • Indicate that you are using the ZenGarden library.
  • If you extend the library (not including externals), you must make that code public.
  • You may use this library for any application, including commerical ones.


  • Most discussion takes place on the Google Groups mailing list.
  • Twitter user ZenGardenPd will post commits and other news.


  • ZenGarden makes use of an implementation of the Mersenne Twister in order to reliably produce random numbers.
  • ZenGarden uses JUnit in order to test the behaviour of objects. junit-4.8.2.jar is included in the repository in order to make it quick and easy to test the library after building it. See the JUnit repository for more details.


ZenGarden consists of four basic object types. These are the context (ZGContext), graph (ZGGraph), object (ZGObject), and message (ZGMessage). The first three have to do with how the signal graph is organised. The latter represents discrete messages which are sent into, processed by, and out of the graph.

A context represents a unique and independent instance of Pure Data. Think of it as Pure Data's console window. A context is defined by its block size, sample rate, and the number of input and output channels. Contexts are entirely independent and messages and objects cannot be exchanged between them.

A graph is a collection of objects and the connections between them. A ZGGraph is a subclass of ZGObject, and thus ZGGraphs can contain other ZGGraphs (such as abstraction or subgraphs). However, this does not mean that ZGGraphs and ZGObjects are interchangeable in the API. Specific functions are made available for each.

Messages represent any Pd message, be it a bang or a list of assorted float, symbols, or bangs. Messages are timestamped and contain at least one element, and may otherwise contain any number and any combination of primitives. ZenGarden messages do not distinguish between lists or arrays or singleton elementary types as in Pd. ZG messages are always lists of typed elementary types.

Graph Attachement

ZenGarden introduces the concept of graph attachement. Whenever any change in the signal graph takes place in Pd, the audio thread must wait until the reconfiguration is finished. For minor changes such as removing a connection this can be very fast and no audio underrun will occur. For larger changes, such as adding an object requiring significant initialisation, or many changes at once, such as adding a complex abstraction, audio underruns are almost guaranteed. ZenGarden solves this problem by allowing an new object or graph to be created on another thread, and then attached to a context at a convenient time. As the graph has already been instantiated, the attachement process is a relatively quick one and can thus be accomplished without causing any audio dropouts. Graph attachement generally involves registering global senders and receivers and ensuring that existing objects are aware of the new ones. Similarly, a graph can be unattached from a context, leaving it in memory yet inert.

How to Get Started

  • Download the ZenGarden repository at https://github.com/mhroth/ZenGarden

  • The repository contains an Xcode project if you are using a Mac, and also a make file for other platforms. It is strongly recommended to use the Xcode project to compile ZG for either iOS or OS X. Targets exist for both cases.

  • ZenGarden is dependent on libsndfile for reading and writing audio files in a platform independent way. Download it, install it.

  • Once you have built libzengarden.a, it may be included in any of your projects also with ZenGarden.h

Running the Tests

ZenGarden includes many tests meant to estabilsh the correct operation of the system. The test may be run by compiling the library via the included make file in the /src directory, and then running the runme-test.sh script from the base directory.

API Usage

ZenGarden implements a core C API and a Java wrapper. The C API is the official interface to ZenGarden. The Java wrapper is fully functional and is used by the project for testing with JUnit. Other language wrappers may be added.

A few examples showing the basic usage of the ZenGarden C API are detailed below.

  • Create a context, add a preexisting graph, and then process it.
  • Programmatically create a graph is also described.
  • Send a message with a known structure into a context.
  • Send a message with an unknown structure into a context.

Creating and Processing a Context

A basic example is shown below, describing how to set up a context and graph, and then process the audio blocks. The C API as described in ZenGarden.h is used, though wrappers may exist for other languages as well.

// include the ZenGarden API definition
#include "ZenGarden.h"

// A ZenGarden context (see below) communicates via a single callback funtion as show here.
// A number of ZGCallbackFunction types are available with the most common being print commands.
void *callbackFunction(ZGCallbackFunction function, void *userData, void *ptr) {
  switch (function) {
    case ZG_PRINT_STD: {
      // A standard print command.
      printf("%s\n", (const char *) ptr);
    case ZG_PRINT_ERR: {
      // A error print command.
      printf("ERROR: %s\n", (const char *) ptr);
    default: break;
  return NULL;

int main(int argc, char * const argv[]) {

  // The number of samples to be processed per block. This can be any positive integer,
  // though a power of two is strongly suggested. Typical values range between 64 and 1024.
  const int blockSize = 64;

  // The number of input channels. This can be any non-negative integer. Typical values are 0 (no input),
  // 1 (mono input), or 2 (stereo input).
  const int numInputChannels = 2;

  // The number of output channels. This can be any non-negative integer. Typical values are 0 (no output),
  // 1 (mono output), or 2 (stereo output).
  const int numOutputChannels = 2;

  // The sample rate. Any positive sample rate is supported. Typical values are i.e. 8000.0f, 22050.0f, or 44100.0f.
  const float sampleRate = 22050.0f;

  // Create a new context.
  ZGContext *context = zg_context_new(numInputChannels, numOutputChannels, blockSize, sampleRate, callbackFunction, NULL);

  // Create a new graph from the given file. The returned graph will be fully functional but it will not be attached
  // to the context. Only attached graphs are processed by the context. Unattached graphs created in a context do not
  // exist from the perspective of the context and add no overhead, but can be quickly added (and removed) as needed.
  // Graphs are not created in the audio thread and will not cause audio underruns.
  PdGraph *graph = zg_context_new_graph_from_file(context, "/path/to/", "file.pd");
  if (graph == NULL) {
    // if the returned graph is NULL then something has gone wrong.
    // If a callback function was provided to the context, then an error message will likely be reported there.
    return 1;

  // Attach the graph to its context. Attaching a graph pauses audio playback, but it is typically a fast operation
  // and is unlikely to cause an underrun.

  // dummy input and output audio buffers. Note their size.
  float finputBuffers[blockSize * numInputChannels];
  float foutputBuffers[blockSize * numOutputChannels];

  // the audio loop
  while (1) {
    // Process the context. Messages are executed and audio buffers are consumed and produced.

    // if input and output audio buffers are presented as non-interleaved floating point (32-bit) samples
    // (ZenGarden's native format), they can be processed as shown here.
    zg_context_process(context, finputBuffers, foutputBuffers);

    // if input and output audio buffers are presented as interleaved signed integer (16-bit) samples,
    // they can be processed as shown here. ZenGarden automatically takes care of the translation to and
    // from the native non-interleaved format.
    // zg_context_process_s(context, sinputBuffers, soutputBuffer);

  // Free memory. Memory can be freed in many ways.

  // The easiest is to delete the context. This not deletes the context and everything attached to it.

  // On the other hand, individual graphs can be deleted when they are no longer needed.
  // If an attached graph is deleted, it is automatically removed from the context first.
  // zg_graph_delete(graph);
  // zg_context_delete(context); // ultimately also the context must be deleted.

  return 0;

Creating a Graph Programmatically

It is also possible to manipulate graphs programmatically. For example instead of creating a graph via zg_context_new_graph_from_file(),

// create a new empty graph in a context
PdGraph *graph = zg_context_new_empty_graph(context);

// create a new [osc~ 440] object in the graph
ZGObject *objOsc = zg_graph_add_new_object(graph, "osc~ 440", 0.0f, 0.0f);

// create a new [dac~] object in the graph
ZGObject *objDac = zg_graph_add_new_object(graph, "dac~", 0.0f, 0.0f);

// conntect output 0 (the left output) of the [osc~] object to inlet 0 (the left inlet) of the [dac~] object
zg_graph_add_connection(graph, objOsc, 0, objDac, 0);

// conntect output 0 of the [osc~] object to inlet 1 (the right inlet) of the [dac~] object
zg_graph_add_connection(graph, objOsc, 0, objDac, 1);

// attach the graph to the context and prepare it for processing

Sending a Message with a Known Structure

It is possible to send messages into a context or even directly to objects. If the message has a known structure, use:

zg_context_send_messageV(context, "receverName", 0.0, "fff", 0.0f, 0.0f, 0.0f);

A message with three floats each set to 0.0f will be sent at time 0 (i.e., immediately) to receivers named "receiverName".

Sending a Message with an Unknown Structure

On the other hand if the structure of the message is not known beforehand then it can be created programmatically.

// Create a message with timestamp 0.0 and three elements.
ZGMessage *message = zg_message_new(0.0, 3);

zg_message_set_float(message, 0, 0.0f);     // set the first element to 0.0f
zg_message_set_symbol(message, 1, "hello"); // set the second element to the symbol "hello"
zg_message_set_bang(message, 2);            // set the third element to a bang

// send the message at the given time to all receivers named "receiverName".
zg_context_send_message(context, "receiverName", message);

// The message is copied by context and can be freed after it is sent.

On Externals

Making an External

Current externals can only be made using ZenGarden's native C++ API. There are two basic types of objects, each with their own base type. There are objects which only process messages, the MessageObject, and those objects which process messages and audio, the DspObject.

A MessageObject External

Here is an example of a simple message object, [+], made available as an external. First MessageAdd.h is defined.

#include "MessageObject.h"

extern "C" {
  // This is a factory function which will be used to register the external
  MessageObject *newMessageAddObject(PdMessage *initMessage, PdGraph *graph);

/** [+], [+ float] */
class MessageAdd : public MessageObject {

    MessageAdd(PdMessage *initMessage, PdGraph *graph);

    // This function is not required, but it may be helpful for debugging. It returns the name by which this
    // object is known, in this case "+".
    static const char *getObjectLabel() { return "+"; }

    // This function must be overridden in order to implement the object functionality
    void processMessage(int inletIndex, PdMessage *message);

    float constant;

MessageAdd.cpp is then defined as below.

#include "MessageAdd.h"

MessageObject *newMessageAddObject(PdMessage *initMessage, PdGraph *graph) {
  return new MessageAdd(initMessage, graph);

// The MessageAdd object as two inlets and one outlet. It exists in the given graph.
MessageAdd::MessageAdd(PdMessage *initMessage, PdGraph *graph) : MessageObject(2, 1, graph) {
  // If the object is initialised with a number, then store it. Otherwise default to zero.
  constant = initMessage->isFloat(0) ? initMessage->getFloat(0) : 0.0f;

MessageAdd::~MessageAdd() {
  // nothing to do

void MessageAdd::processMessage(int inletIndex, PdMessage *message) {
  switch (inletIndex) {
    case 0: {
      if (message->isFloat(0)) {
        // When a message arrives at the left inlet (inlet 0) with a number as the first element...

        // ZenGarden messages are typically created on the stack as this is faster an easier than creating them
        // on the heap. A macro is provided for convenience, taking as an argument the number of elements. In
        // this case, the [+] object only outputs messages with one element, namely the numberical result of its
        // operation.
        PdMessage *outgoingMessage = PD_MESSAGE_ON_STACK(1);

        // The outgoing message is configured with the time at which it is sent (the same time as the incoming
        // message, and the result.
        outgoingMessage->initWithTimestampAndFloat(message->getTimestamp(), message->getFloat(0) + constant);

        // The mesasge is then sent from outlet 0 (the left-most and only outlet).
        sendMessage(0, outgoingMessage);
    case 1: {
      if (message->isFloat(0)) {
        // When a message arrived at the right inlet (inlet 1) with a number as the first element...

        // Store the number.
        constant = message->getFloat(0);
    default: break;

A DspObject External

Here, a basic [+~] object is described. The DspObject class is extended in DspAdd.h, and the processDspWithIndex function is overridden in addition to processMessage seen in the previous example. Receiving messages and evaluating which parts of the audio buffer must be evalutated when is taken care of by the DspObject superclass. The implementation is responsible for actually filling in the buffer. Note that the discription here differs from the implementation used in ZenGarden. The one shown here does work and is the simplest way to create an external which processes audio. The internal implementation is optimised for speed and also contains additional functionality.

#include "DspObject.h"

/** [+~], [+~ float] */
class DspAdd : public DspObject {

    DspAdd(PdMessage *initMessage, PdGraph *graph);

    static const char *getObjectLabel() { return "+~"; }

    void processMessage(int inletIndex, PdMessage *message);

    // This function is responsible for filling the output buffers between the bounds given by the array indicies.
    void processDspWithIndex(int fromIndex, int toIndex);

    float constant;


#include "DspAdd.h"
#include "PdGraph.h"

DspAdd::DspAdd(PdMessage *initMessage, PdGraph *graph) : DspObject(2, 2, 0, 1, graph) {
  // initialise the constant which is added to the inlet buffer. If none is given, use zero.
  constant = initMessage->isFloat(0) ? initMessage->getFloat(0) : 0.0f;

DspAdd::~DspAdd() {
  // nothing to do

void DspAdd::processMessage(int inletIndex, PdMessage *message) {
  if (inletIndex == 1) {
    if (message->isFloat(0)) {
      // If a message is received on the right inlet and it contains a float in the first position,
      // set the constant paramter.
      constant = message->getFloat(0);

void DspAdd::processDspWithIndex(int fromIndex, int toIndex) {
  // fill the outlet buffer by adding the constant to the inlet buffer
  for (int i = fromIndex; i < toIndex; i++) {
    dspBufferAtOutlet[0][i] = dspBufferAtInlet[0][i] + constant;

Registering an External

Externals can be easily registered with individual contexts. Remember that contexts are independent and thus an external registered with one will not be visible to any others. Externals consist firstly of an indentifying string, and secondly of a factory function taking an initialisation message and the graph in which the object exists. The indentifying string, or object label, may also refer to a preexisting or default object (such as "+") in which case the functionality will be overridden. The factory function is a C function (or static C++ function). The same function can be registered many times with different labels in order to indicate that an object is known by many names. An example of this is the [bang] object which is known alternatively as "bang", "bng", and "b".

#include "ZenGarden.h"

extern ZGObject *newMessageAddObject(ZGMessage *initMessage, ZGGraph *graph);

int main(int argc, char * const argv[]) {
  // you know what to do here
  ZGContext *context = ...;

  // register an external named "+"
  zg_context_register_external_object(context, "+", newMessageAddObject);

  // also register it with the label "plus"
  zg_context_register_external_object(context, "plus", newMessageAddObject);

  // forget it, unregister the "plus" label
  zg_context_unregister_external_object(context, "plus");

A Final Note: Why ZenGarden? - by mhroth

Many people have asked me why the ZenGarden library came into existance, and why work continues on it today, especially in light of the successful libpd project. Here is my answer, offering personal opinions, some ranting, and hopefully constructive critisism. So don't take it all too seriously, ok? First, a few (obvious?) points that make me excited.

  • Pd is a great language to write audio code in.
  • A general purpose audio language that is free and open to all has a great deal of potential as a standard for many audio applications.
  • An audio library that is easy to work with can be installed on many platforms, including desktop, mobile, and web. Write once run anywhere audio? ;)
    • Let's be honest, you know that writing audio code according to the proposed Web Audio API is going to be a massive pain.

I spend a lot of time working with the Pd audio engine at RjDj and I have rarely seen such an antiquated, obfuscated, unmaintainable, and undocumented mess as Pd (the other example that I can think of is Vorbis, but that's another story). If a student or employee of mine ever wrote such code, I would fire them immediately. I have been working with Pd (the engine, not the language) for some years and I know it quite well by now. I have the highest respect for Miller that Pd works as well as it does; it is truly a technical tour-de-force. There are plenty of clever tricks and architectural innovations to learn from. But I found it incredibly difficult to find and modify functional parts of the program, for instance if you don't know where to look finding the code for something as simple as [*~] is not obvious, let alone anything more complex such as Pd's audio object ordering algorithm. The reason that libpd (i.e., Pd in the form of a traditional signal processing library) only appeared in 2010 is because everyone else who had tried before (at least since 2008), even people otherwise intimately familiar with the project, had failed (including myself). I am aware of at least two previous libpd-style implementations used in Spore (EAPd [1] [2]) and early RjDj, but neither of those were public. The Pd community owes much more than a debt of gratitude to Peter Brinkmann. But ultimately no piece of software should be so difficult to modify or extend.

And so I began to work on ZenGarden. It is intended to be a completely new runtime for the Pure Data audio programming language using modern software languages and design principles. It is written in object-oriented C++, uses the C++ STL, has plenty of comments, takes direct advantage of modern processors via vector operations, and also unit tests. It should also be easy to compile and run on all major operating systems and hardware architectures. Furthermore it is completely independent of any GUI. (Naturally all of these things could be improved, but that's the goal anyway :)