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This repository contains the files and executable code used to build, the official documentation for

Dependencies and installation

To build this project, you need to have the following software installed:

  • Java (1.8+)
  • Python (2.7+, untested with Python 3)

(Both java and python should be in your path.)

You'll need to install the various Python library requirements as well. These requirements are provided in this repository in the standard pip-formatted requirements.txt. The easiest way to do this is to create and activate a Python virtual environment and then install the requirements with pip like so:

pip install -r requirements.txt

(Tip: For most platforms, it's easier to install lxml if you upgrade pip first. With your virtual environment activated, type pip install -U pip and then install the packages with the command above.)

Finally, you'll need the standalone JAR file. You can build from source to obtain this file, or download the pre-built JAR for your platform using the appropriate link below:

Unarchive the file you downloaded and copy the two files with a .jar extension into your processing-py-site directory.


The script takes the various files in this repository, processes them and generates a static HTML site. (You can think of as being a kind of bespoke static site generator, akin to, e.g., Jekyll.) Running the following command will build the entire site:

python build --all --images

(See below for further discussion of the command line options available in The best way to understand how the site is generated is to study's source code, but here's the basic overview.

  • The Reference/api_en directory contains a number of XML files. These files are used to generate the "Reference" section of the documentation, including the images, which are automatically generated from the <code> blocks in the XML files. (The order of sections in the Reference index is hard-coded in
  • The Tutorials directory has a number of subdirectories, each containing a tutorial that appears on in the "Tutorials" section. The tutorials themselves are written in plain HTML. The Tutorials index page is generated using the tutorials.xml file to determine the order, and using the tutorial.xml file in each subdirectory to determine metadata.
  • The content directory contains static files used in the site layout, such as stylesheets and images. The contents of this directory are simply copied verbatim to the generated site.
  • The templates directory contains a number of HTML templates, written in the Jinja templating language. These are mostly used to produce the various index pages for the reference and tutorials. The XML source code for each reference item is rendered by the reference_item_template.jinja template; there's a (fairly) straightforward correspondence between the name of the XML tag and the variable used to reference the tag in the template.
  • The jython directory contains a single script,, which is used to generate images from the example code in the reference items. (This program is executed automatically by the build process; there's no reason for you to run it yourself.)

On successful completion of, the static site ends up in the generated directory.

Building the documentation

As noted above, the script builds the site from the source files in the repository. Run python --help for full details on its command line options. Here's an overview:

To build all content:

python build --all --images

To build the site without performing the image generation process:

python build

To build only a.xml, b.xml and c.xml files from the reference (remove --images to skip the image generation process):

python build --images --files a.xml b.xml c.xml

To test the site in a local server:

python test


Here are a few common and/or possible scenarios you might run into...

Error: Could not find or load main class org.python.util.jython

You're missing the Jython code necessary to execute the image generation script. Ensure that you've copied (or linked) processing-py.jar from the standalone distribution into your processing-py-site directory.

NullPointerException - foo is probably dynamic-mode; fix that, please.

The image generation process only creates images for "static-mode" sketches, i.e., sketches that don't have a draw() function and therefore can't be animated or interactive. To fix this, rewrite the code example so it isn't interactive, or add <notest /><noimage /> as children of the <example> tag in the XML to suppress image generation for that item.

Could not initialize class com.jogamp.newt.NewtFactory

I've seen this error when trying to build on Linux without processing-py-natives-linux-amd64.jar in the processing-py-site directory. Ensure this file (or the file appropriate for your platform) is present and try again.

I can't run the image generation process in a headless environment

If you're running on a Linux machine without a connected display (say, an EC2 box), you'll need to install xvfb using the package manager for your operating system. Then run the build script like so:

xvfb-run python build --images

Reporting Issues

Before opening a new issue, please review existing issues.

Issues should include as many details as possible, including URLs and/or excerpts from the related material, and a description of what is missing/wrong or could be improved, and if possible how.