Documentation guidelines

OpenColorIO is documented using reStructuredText, processed by Sphinx.

The documentation primarily lives in the docs/ folder, within the main OpenColorIO repository.

The rST source for the C++ API documentation is extracted from comments in the public header files in include/

Installation of requirements

Scripts are available, for each platform, to install the documentation requirements.

The script in the share/ci/scripts/<Platform> directory will install the Python-related requirements for building the documentation (Sphinx, six, testresources, recommonmark, sphinx-press-theme, sphinx-tabs, and breathe) and Doxygen.

Use GitBash (provided with Git for Windows) to execute the script on Windows.

Python 3 is required to build the documentation. If you have multiple Python installs you’ll need to make sure pip and CMake find the correct version. You can manually inform CMake of which to use by adding this option to the below cmake command, which configures the documentation build:

-DPython_ROOT=<Path to Python 3 root directory>

For the Python packages, ensure their locations are in your PYTHONPATH environment variable prior to configuring the build.

Building the docs

The build is just like a regular build from source, but specify the -D OCIO_BUILD_DOCS=ON argument to CMake.

Then run the make docs target. The default HTML output will be created in build_dir/docs/build-html/

Note that CMake must be run before each invocation of make to copy the edited rST files.

Initial run:

$ mkdir build && cd build

Then after each change you wish to preview:

$ cmake -D OCIO_BUILD_DOCS=ON .. && make docs

Updating the Python docs

If a contributor makes changes to any part of OCIO which affects the Python API docs (so, public headers, Python bindings, any documentation process code, etc.) they should do a local build with the new CMake option -DOCIO_BUILD_FROZEN_DOCS=ON, and add the modified rST files under docs/api/python/frozen to their PR.

Note: If you run the scripts on Linux, the freezing process should work well. On other platforms, the process may sometimes make spurious deltas to rST files unrelated to your changes. Please don’t add these files to your PR.

The OCIO module has a switch that detects when docs are being built on GH Actions (CI env var == true) it will backup the frozen folder to a sibling backup folder on Sphinx init, and following Sphinx build completion will do a file-by-file comparison of the new frozen and the backup folders. If there are differences, the CI job may fail with an error explaining where the differences were found and with instructions on how to fix them.

The also has a switch that detects when it is being run on RTD, and in that case will itself run Doxygen to generate the XML needed by breathe prior to building the docs, and will also facilitate a CMake configure_file-like process (via Python) to handle substitutions in headers and docs source files that CMake would usually handle, but can’t in this case. One potential plus to all of this is that if someone wants to just build OCIO docs, they can technically do so by running sphinx-build in the docs directory, and nothing more. Right now that only works when the READTHEDOCS env var == True, but it could be easily exposed another way if needed.

These features required several custom Sphinx extensions tuned for our project which are located under share/docs.

Building the docs – Excluding the API docs

If you don’t need to build the API documentation, there is a quick and dirty way to do a docs build. This approach does not need to compile the C++ code but is not ideal since it modifies files in the source directory rather than the build directory:

export READTHEDOCS=True cd docs (in the source directory) mkdir _build sphinx-build -b html . _build <your web browser name> _build/index.html


  • Try to keep the writing style consistent with surrounding docs.

  • Fix all warnings output by the Sphinx build process. An example of such an warning is:

    checking consistency... [...]/build/docs/userguide/writing_configs.rst:: WARNING: document isn't included in any toctree
  • Use the following hierarchy of header decorations:

    Level 1 heading
    Level 2 heading
    Level 3 heading
    Level 4 heading
  • To add a new page, create a new .rst file in the appropriate location. In that directory’s index.rst, add the new file to the toctree directive.

    The new file should contain a top-level heading (decorated with ===== underline), and an appropriate label for referencing from other pages. For example, a new file docs/userguide/baking_luts.rst might start like this:

    .. _userguide-bakingluts:
    Baking LUT's
    In order to bake a LUT, ...


The vuepress theme that we’ve migrated to has some quirks to its design. For example, it only allows two nested table of contents (TOC). So things have to be organized in a slightly different way than other sphinx projects.

The root-level toc_redirect.rst points to where to find the different section TOCs. The name and contents of each sections TOC is defined in that sub-directory’s _index.rst file.

In this TOC the :caption: directive determines what the name of the section will be in the sidebar, and in the header of the website. The H1 header determines the name of the page in the right/left arrows navigation bar. In a lot of cases this ends up doubling up the name on the page, but this seems unavoidable at the present time. If additional explanatory text is put in the _index.rst files then it shouldn’t be as problematic.

The site will show all H1 headers in the side panel by default, these then expand when selected to show all H2 headers.

Due to the limited TOC and sidebar depth, we shouldn’t be afraid of looong pages with many H2 headings to break down the page into logical quadrants.

Emacs rST mode

Emacs’ includes a mode for editing rST files. It is documented on the docutils site

One of the features it includes is readjusting the hierarchy of heading decorations (the underlines for different heading levels). To configure this to use OCIO’s convention, put the following in your .emacs.d/init.el:

(setq rst-preferred-decorations
      '((?= simple 0)
        (?* simple 0)
        (?+ simple 0)
        (?- simple 0)))