Pure Data Visual Programming Environment ported to an HTML5 GUI


maintainer: Ivica Ico Bukvic ico@vt.edu

maintainer: Albert Graef aggraef@gmail.com

maintainer: Jonathan Wilkes jancsika@yahoo.com

One Paragraph Overview

Pure Data (aka Pd) is a visual programming language. That means you can use it to create software graphically by drawing diagrams instead of writing lines of code. These diagrams show how data flows through the software, displaying on the screen what text-based languages require you to piece together in your mind.

Flavors of Pure Data

There are currently three main distributions of Pure Data:

  1. Pd-L2Ork. Version used by Ivica Bukvic for his laptop orchestra. This guide is for Pd-L2Ork.
  2. Pure Data "Vanilla". Miller Puckette's personal version which he hosts on his website and maintains. It doesn't include external libraries like objects for doing graphics, video, etc.
  3. Pure Data Extended. A monolithic distribution which ships with lots of external libraries. As of August 2015 it hasn't been updated since January 2014.

Three Paragraph Overview

Pd has been designed with an emphasis on generating sound, video, 2D/3D graphics, and connecting through sensors, input devices, and MIDI as well as OSC devices.

Pd has a special emphasis on generating audio and/or video in real time, with low latency. Much of its design focuses on receiving, manipulating, and delivering high-quality audio signals. Specifically, the software addresses the problem of how to do this efficiently and reliably on general purpose operating systems like OSX, Windows, Debian, etc.-- i.e., systems designed mainly for multi-tasking.

Pd can easily work over local and remote networks. It can be used to integrate wearable technology, motor systems, lighting rigs, and other equipment. Pd is also suitable for learning basic multimedia processing and visual programming methods, as well as for realizing complex systems for large-scale projects.


Pd-L2ork has the following goals:

  1. Documentation. We like documentation. It's like code, except friendly.
  2. Be reliable. Binary releases must be usable for performances and installations. The git repo must always be in a workable state that can be compiled. Regressions must be fixed quickly.
  3. Be discoverable. Undocumented features are buggy. Missing help files are bugs. Patches for new functionality that lack documentation are spam.
  4. Be consistent. Consistent interfaces are themselves a kind of documentation. We like documentation, so it follows that we like consistent interfaces

Installation Guide


Time to build: 40 minutes to 1.5 hours Hard drive space required: roughly 2.5 GB To install using a pre-compiled binary, follow these instructions: http://l2ork.music.vt.edu/main/?page_id=56

To set up a development environment, first make sure you have the following package dependencies listed here: http://l2ork.music.vt.edu/main/?page_id=56

Then follow the steps outlined here: http://l2ork.music.vt.edu/main/?page_id=56#install-dev

OSX 64-bit using Homebrew

Time to build: 50 minutes to 1.5 hours Hard drive space required: roughly 2 GB

  1. Install Homebrew (15 minutes) (asks for password twice-- once for command line tools, once for homebrew)
  2. Install the dependencies (10 minutes): brew install wget brew install autoconf brew install automake brew install libtool brew install fftw brew install python brew install fluidsynth brew install lame brew install libvorbis brew install speex brew install gsl brew install libquicktime brew install pkg-config
  3. Clone the Purr-Data repository (10 minutes) git clone https://git.purrdata.net/jwilkes/purr-data.git
  4. Change to the directory cd purr-data/l2ork_addons
  5. Run the installer (15 minutes) ./tar_em_up.sh -X
  6. When the installer finishes, type cd ..
  7. There should now be a .dmg file in your current directory

Windows 32-bit Using msys2

Time to build: roughly 1.5 hours-- 30 minutes of this is for Gem alone Hard drive space required to build: rougly 2.5 GB

Important note: check the name of your Windows user account. If it has a space in it-- like "My Home Computer" or "2nd Laptop", then stop. You may not use this guide. (Actually you can probably just install everything in ~/.. in that case, but I haven't tested doing it like that. Sorry. Get a better OS...)

  1. Download and install msys2 (5 minutes)
    There are two installers-- one for 32-bit Windows systems (i386) and one for 64-bit Windows (x_64). Be sure you know which version of Windows you are running and download the appropriate installer.
    Note: don't run it after it installs. You'll open it manually in the next step.
  2. Download and install inno setup (5 minutes)
  3. Run MinGW-w64 Win32 Shell (less than a minute)
    msys2 adds three Start Menu items for different "flavors" of shell:
    • MinGW-w64 Win32 Shell <- click this one!
    • MinGW-w64 Win64 Shell
    • MSYS Shell
  4. Install the dependencies (5-10 minutes)
    Once the shell opens, we need to install the dependencies for building Purr Data. Issue the following command: pacman -S autoconf automake git libtool \ make mingw-w64-i686-dlfcn mingw-w64-i686-fftw \ mingw-w64-i686-fluidsynth \ mingw-w64-i686-ftgl mingw-w64-i686-fribidi \ mingw-w64-i686-ladspa-sdk mingw-w64-i686-lame \ mingw-w64-i686-libsndfile mingw-w64-i686-libvorbis \ mingw-w64-i686-lua mingw-w64-i686-toolchain \ rsync unzip wget
  5. Download the source code (3-6 minutes) Issue the following command to create a new directory "purr-data" and clone the repository to it: git clone https://git.purrdata.net/jwilkes/purr-data.git
  6. Enter the purr-data/l2ork_addons directory (less than a minute) cd purr-data/l2ork_addons
  7. Finally, build Purr-Data (45-80 minutes) ./tar_em_up.sh -Z
  8. Look in purr-data/packages/win32_inno/Output and click the setup file to start installing Purr Data to your machine.

Code of Conduct

  1. No sarcasm, please
  2. Don't appear to lack empathy
  3. You can't live here. If you're spending hours a day writing Purr Data code or-- worse-- spending hours a day writing emails about code that has yet to be written, you're doing it wrong
  4. If working on something for the first time, ask to be mentored
  5. If no one asked you to mentor them, don't teach
  6. It is better to let small things go then to risk taking time away from solving bigger problems

It is a bad idea to break this Code of Conduct even if no one complains about your behavior.

Contributor Guide

Contributing is easy:

  1. Join the development list: http://disis.music.vt.edu/cgi-bin/mailman/listinfo/l2ork-dev
  2. Tell us what you'd like to work on. Unfortunately there are lots of externals and even core features that are poorly documented. We can help make sure you aren't duplicating functionality (or that you at least know what's already been implemented).
  3. Send us your patch and we'll try it out. If it's well-documented and there aren't any bugs we'll add it to the software.
  4. If you want to do regular development and have commit access, just request it, then follow the Pd-L2Ork goals above.

Here are some of the current tasks:

  • writing small audio/visual Pd games or demos to include in the next release
    • skills needed: ability to write Pd programs
    • status: I wrote a little sprite-based game that will ship with the next version of Pd-L2Ork. In it, the character walks around in an actual Pd diagram shoots at the objects to progress, and to make realtime changes to the music. What I'd like is to include a new, smallish game with each release that has a link in the Pd console. It can be a little demo or game, just something fun that shows off what can be done using Pure Data.
  • designing/implementing regression test template

Human Interface Guidelines

General Look and Feel

Pd is a multi-window application that consists of three parts:

  1. A main window, called the "Pd Window" or "Console Window". This window displays informational and error messages for Pd programs.
  2. One or more "canvas" windows-- aka "patch" windows, used to display the diagrams that make up a Pd program.
  3. One or more dialog windows used to configure the various parts of Pd.

All should look simple and uncluttered. Although "canvas" windows cannot (yet) be traversed and edited using only the keyboard, all three parts of Pd should be designed so that they can be manipulated using only the keyboard.

Hooks for new users

It should also be possible to produce sound and interact when a new user runs program for the very first time. In every release, there should be a link at the bottom of the Console Window to a short game written in Pd that demonstrates one or more of the capabilities of the Pd environment. The game should be designed to be fun outside of its efficacy as a demonstration of Pd.


Pd ships with "DejaVu Sans Mono", which is used for the text in canvas windows. Fonts are sized to fit the hard-coded constraints in Pd Vanilla. This way box sizes will match as closely as possible across distributions and OSes.

These hard-coded sizes are maximum character widths and heights. No font fits these maximums exactly, so it's currently impossible to tell when looking at a Pd canvas whether the objects will collide on a system using a different font (or even a different font-rendering engine).

Dialogs and console button labels may use variable-width fonts. There is not yet a suggested default to use for these.

The console printout area currently uses "DejaVu Sans Mono". Errors are printed as a link so that the user can click them to highlight the corresponded canvas or object that triggered the error.


Nothing set in stone yet.

Core Pd Notes

The following is adapted from Pd Vanilla's original source notes. (Found in pd/src/CHANGELOG.txt for some reason...)

Sections 2-3 below are quite old. Someone needs to check whether they even hold true for Pd Vanilla any more.

Structure definition roadmap.

First, the containment tree of things that can be sent messages ("pure data"). (note that t_object and t_text, and t_graph and t_canvas, should be unified...)

BEFORE 0.35:

m_pd.h      t_pd                    anything with a class
                t_gobj              "graphic object"
                    t_text          text object
                    t_glist         list of graphic objects
g_canvas.c              t_canvas    Pd "document"

AFTER 0.35:

m_pd.h      t_pd                    anything with a class
                t_gobj              "graphic object"
                    t_text          patchable object, AKA t_object
g_canvas.h              t_glist     list of graphic objects, AKA t_canvas

Other structures:

g_canvas.h  t_selection -- linked list of gobjs
            t_editor -- editor state, allocated for visible glists
m_imp.h     t_methodentry -- method handler
            t_widgetbehavior -- class-dependent editing behavior for gobjs
            t_parentwidgetbehavior -- objects' behavior on parent window
            t_class -- method definitions, instance size, flags, etc.

1. Coding Style

1.0 C coding style. The source should pass most "warnings" of C compilers (-Wall on linux, for instance; see the makefile.) Some informalities are intentional, for instance the loose use of function prototypes (see below) and uncast conversions from longer to shorter numerical formats. The code doesn't respect "const" yet.

1.1. Prefixes in structure elements. The names of structure elements always have a K&R-style prefix, as in ((t_atom)x)->a_type, where the a_ prefix indicates "atom." This is intended to enhance readability (although the convention arose from a limitation of early C compilers.) Common prefixes are:

  • w_ (word)
  • a_ (atom)
  • s_ (symbol)
  • ob_ (object)
  • te_ (text object)
  • g_ (graphical object)
  • gl_ (glist, a list of graphical objects).

Also, global symbols sometimes get prefixes, as in s_float (the symbol whose string is "float"). Typedefs are prefixed by t_. Most private structures, i.e., structures whose definitions appear in a ".c" file, are prefixed by x_.

1.2. Function arguments. Many functions take as their first argument a pointer named x, which is a pointer to a structure suggested by the function prefix; e.g., canvas_dirty(x, n) where x points to a canvas (t_canvas *x).

1.3. Function Prototypes. Functions which are used in at least two different files (besides where they originate) are prototyped in the appropriate include file. Functions which are provided in one file and used in one other are prototyped right where they are used. This is just to keep the size of the ".h" files down for readability's sake.

1.4. Whacko private terminology. Some terms are lifted from other historically relevant programs, notably "ugen" (which is just a tilde object; see d_ugen.c.)

1.5. Spacing. Tabs are 8 spaces; indentation is 4 spaces. Indenting curly brackets are by themselves on their own lines, as in:

if (x)
    x = 0;

Lines should fit within 80 spaces.

2. Compatibility with Max

2.0. Max patch-level compatibility. "Import" and "Export" functions are provided which aspire to strict compatibility with 0.26 patches (ISPW version), but which don't get anywhere close to that yet. Where possible, features appearing on the Mac will someday also be provided; for instance, the connect message on the Mac offers segmented patch cords; these will devolve into straight lines in Pd. Many, many UI objects in Opcode Max will not appear in Pd, at least at first.

3. Source-level Compatibility with Max

3.0. Compatibility with Max 0.26 "externs"-- source-level compatibility. Pd objects follow the style of 0.26 objects as closely as possible, making exceptions in cases where the 0.26 model is clearly deficient. These are:

3.1. Anything involving the MacIntosh "Handle" data type is changed to use char * or void * instead.

3.2. Pd passes true single-precision floating-point arguments to methods; Max uses double. Typedefs are provided:

t_floatarg, t_intarg for arguments passed by the message system
t_float, t_int for the "word" union (in atoms, for example.)

3.3. Badly-named entities got name changes:

w_long --> w_int (in the "union word" structure)

3.4. Many library functions are renamed and have different arguments; I hope to provide an include file to alias them when compiling Max externs.

4. Function name prefixes

4.0. Function name prefixes. Many function names have prefixes which indicate what "package" they belong to. The exceptions are:

typedmess, vmess, getfn, gensym (m_class.c)
getbytes, freebytes, resizebytes (m_memory.c)
post, error, bug (s_print.c)

which are all frequently called and which don't fit into simple categories. Important packages are:

(pd-gui:)   pdgui -- everything
(pd:)       pd -- functions common to all "pd" objects
            obj -- fuctions common to all "patchable" objects ala Max
            sys -- "system" level functions
            binbuf -- functions manipulating binbufs
            class -- functions manipulating classes
            (other) -- functions common to the named Pd class

5. Source file prefixes

5.0. Source file prefixes.


s    system interface
m    message system
g    graphics stuff
d    DSP objects
x    control objects
z    other


gui    GUI front end

6. Javascript style

  1. Brackets on the same line as declaration or expression: if (a) {
  2. Single line comments only: //
  3. Use double-quotes for strings
  4. Use underscores to separate words of function names and variables

GUI Messaging Specification

Public GUI interface

Purpose: a set of functions to communicate with the gui without putting language-specific strings (like tcl) into the C code. The new interface is a step toward separating some (but not all) of the GUI logic out from the C code. Of course the GUI can still be designed to parse and evaluate incoming messages as commands. But the idiosyncracies of the GUI toolkit can be limited to either the GUI code itself or to a small set of modular wrappers around sys_vgui.

The public interface consists of the following:

gui_vmess(const char *msg, const char *format, ...);

where const char *format consists of zero or more of the following:

  • f - floating point value (t_float)
  • i - integer (int)
  • s - c string (`char* )
  • x - hexadecimal integer value, with a precision of at least six digits. (hex value is preceded by an 'x', like x123456)

For some of Pd's internals like array visualization, the message length may vary. For these special cases, the following functions allow the developer to iteratively build up a message to send to the GUI.

gui_start_vmess(const char *msg, const char *format, ...);
gui_start_array();      // start an array
gui_f(t_float float);   // floating point array element (t_float)
gui_i(int int);         // integer array element (int)
gui_s(const char *str); // c string array element
gui_end_array();        // end an array
gui_end_vmess();        // terminate the message

The above will send a well-formed message to the GUI, where the number of array elements are limited by the amount of memory available to the GUI. Because of the complexity of this approach, it may only be used when it is necessary to send a variable length message to the GUI. (Some of the current code may violate this rule, but that can be viewed as a bug which needs to get fixed.)

The array element functions gui_f, gui_i, and gui_s may only be used inside an array. Arrays may be nested, but this adds complexity and should be avoided if possible.

Private Wrapper for Nw.js Port

The public functions above should fit any sensible message format. Unfortunately, Pd's message format (FUDI) is too simplistic to handle arbitrary c-strings and arrays, so it cannot be used here. (But if it happens to improve in the future it should be trivial to make a wrapper for the public interface above.)

The current wrapper was made with the assumption that there is a Javascript Engine at the other end of the message. Messages consist of a selector, followed by whitespace, followed by a comman-delimited list of valid Javascript primitives (numbers, strings, and arrays). For the arrays, Javascript's array notation is used. This is a highly idiosyncratic, quick-and-dirty approach. But the point is that the idiosyncracy exists in a single file of the source code, and can be easily made more modular (or replaced entirely by something else) without affecting any of the rest of the C code.