Contributing to Open3D

The Open3D project was started by Qianyi Zhou and Jaesik Park. The project is developed and maintained by a community effort. To contribute to the project, you need to

  • Know how to use Open3D;
  • Know basic development rules such as coding style, issues, and pull requests;
  • Be willing to follow the guidelines in this page.

Issues and pull requests

The master branch is used only for stable development versions of Open3D. Any code change is made through four steps using the issues and pull requests system.

  1. An issue is opened for a feature request or a bug fix.
  2. A contributor starts a new branch or forks the repository, makes changes, and submits a pull request.
  3. Code change is reviewed and discussed in the pull request. Modifications are made to address the issues raised in the discussion.
  4. One of the admins merges the pull request to the master branch.

Tip

Code review is known to be the best practice to maintain the usability and consistency of a large project. Though it takes some time at the beginning, it saves a lot of time in the long run. For new contributors, it can be viewed as a training procedure, in which an experienced contributor, as a reviewer, walks the new contributor through everything he needs to know.

Note

There is an exception for this rule. Small changes can be made directly to the master branch, such as fixing typos, formatting documents, and fixing an obvious bug.

Maintain sanity of the project

Most importantly, do not break the build. Before submitting a pull request, make sure the project builds without any error or warning under the following toolchains:

  • Windows, Visual Studio 2015 update 3+, CMake 3.0+
  • OS X, Clang included in the latest Xcode, CMake 3.0+
  • Ubuntu 16.04, native gcc (4.8+ or 5.x), CMake 3.0+

For C++ code, it is recommended to use C++11 features. However, do not use C++14 or C++17 features since some of them are not properly supported by mainstream compilers.

For Python code, make sure it runs on both Python 2.7 and Python 3.x.

Note

The easiest way to start coding as a new contributor is to take an existing code snippet as reference and write some code similar to it.

Coding style

Consistent coding style is an important factor of code readability. Some principles:

  1. Code itself is a document. Name functions and variables in a way they are self explanatory.
  2. Be consistent with existing code and documents. Be consistent with C++ conventions.
  3. Use common sense.

We generally follow the Google C++ Style Guide, with a few modifications:

  • Use 4 spaces for indent. Use two indents for a forced line break (usually due to the 80 character length limit).
  • Use #pragma once for header guard.
  • All Open3D classes and functions are nested in namespace open3d.
  • Avoid using naked pointers. Use std::shared_ptr and std::unique_ptr instead.
  • C++11 features are recommended.

Another good reading for modern C++ coding style is C++ Core Guidelines

Automated style Checker

Open3D’s CI checks for code formatting based on the style specified in the .clang-format file. Please build the check-style and apply-style CMake target before submitting a pull request, or use your editor’s clang-format integration to format the source code automatically.

Different clang-format versions may produce slightly different formatting results. For standardization, clang-format version 5.0 shall be used.

Installing clang-format-5.0

By default, the make system tries to detect either clang-format-5.0 or clang-format from PATH.

Ubuntu

# Ubuntu 14.04
sudo apt update
sudo apt install wget software-properties-common -y
sudo wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
sudo apt-add-repository "deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-5.0 main"
sudo apt update
sudo apt install clang-format-5.0 -y
clang-format-5.0 --version

# Ubuntu 16.04
sudo apt update
sudo apt install clang-format-5.0
clang-format-5.0 --version

# Ubuntu 18.04
sudo apt update
sudo apt install clang-format-5.0
clang-format-5.0 --version

macOS

curl https://raw.githubusercontent.com/IntelVCL/Open3D-3rdparty/master/clang-format/clang-format%405.rb -o $(brew --repo)/Library/Taps/homebrew/homebrew-core/Formula/clang-format@5.rb
brew install clang-format@5
clang-format --version

# (Optional) If another clang-format version was previously installed, we can keep
# both versions and switch the default to version 5
brew unlink clang-format
brew link clang-format@5

# (Optional) If you'd like to uninstall
brew uninstall clang-format@5

Alternatively, download the clang-5.0 macOS package from LLVM Download Page, unzip and add the directory containing clang-format to PATH.

Windows

Download clang-5.0 Windows package from LLVM Download Page. During installation, select the option which allows adding clang toolchains to PATH. After installation, open a CMD terminal and try

clang-format --version

Checking and applying format

Before starting, check your clang-format version by

# In most cases
clang-format --version

# Or, when installed as clang-format-5.0, e.g. on Ubuntu
clang-format-5.0 --version

and make sure that version 5.0 is installed.

Ubuntu & macOS

After CMake config, to check style, run

make check-style

After CMake config, to apply proper style, run

make apply-style

Windows

After CMake config, to check style, run

cmake --build . --target check-style

After CMake config, to apply the proper style, run

cmake --build . --target apply-style