Contributing to libjpeg-turbo
libjpeg-turbo is a stable and mature product with a worldwide reach, it is an ISO/ITU-T reference implementation of the JPEG standard, and its maintainer does not earn a salary for maintaining it. Thus, not every code contribution can or will be accepted into the libjpeg-turbo code base. In order to maximize the chances that a code contribution is acceptable, please adhere to the following guidelines:
If the code contribution is a bug fix, then please ensure that enough information is provided so that the maintainer can readily reproduce and document the bug. That information should include:
- A clear and concise description of the bug
- The steps and (if applicable) images necessary to reproduce the bug
- The compilers, operating systems, and CPUs with which the bug was observed
- The versions of libjpeg-turbo with which the bug was observed
- If the bug is a regression, the specific commit that introduced the bug (use
git bisect to determine this)
If the code contribution will implement a major new feature, then please contact the project maintainer (through a GitHub issue, direct e-mail, or the libjpeg-turbo-devel mailing list) prior to implementing the feature. In general, major new features that are potentially disruptive to the quality of libjpeg-turbo are unlikely to be accepted unless:
- The new feature is within the existing scope of libjpeg-turbo.
- The new feature has been thoroughly regression tested and benchmarked on all of the supported platforms that are potentially affected by it.
- The new feature has been documented clearly and concisely in the change log and (if applicable) the libjpeg and TurboJPEG API documentation and man pages.
- The code implementing the new feature is formatted consistently with the rest of the libjpeg-turbo code base (use checkstyle to validate this.)
- The new feature does not introduce new members into the exposed libjpeg API structures (doing so would break backward ABI compatibility.)
- The new feature does not alter existing libjpeg-turbo usage or development workflows.
- The code implementing the new feature is elegant, easily maintainable, and causes the least possible amount of disruption to the libjpeg-turbo code base.
- The new feature is based on the dev branch of the libjpeg-turbo repository.
... OR ...
- Your organization is prepared to pay for the labor necessary to ensure all of the above. Even the most well-written patches can still require a significant amount of labor to clean up, test, and integrate. (See above RE: the maintainer not earning a salary.)
Specific types of features that will not be accepted:
- Features that extend the scope of libjpeg-turbo to support image formats other than DCT-based JPEG and JFIF
- Features that extend the scope of libjpeg-turbo to support image processing algorithms that are not necessary for JPEG compression or decompression
- Extensions to the JPEG format that have not been approved by the appropriate standards bodies
- Non-trivial performance enhancements that have less than a 5% overall impact on performance
If the code contribution is a build system enhancement, then please be prepared to justify the enhancement. In general, build system enhancements are unlikely to be accepted unless:
- The enhancement is potentially beneficial to a significant number of upstream libjpeg-turbo users/developers. (If the enhancement is only beneficial to a downstream project, then it does not belong here.)
- The enhancement has been tested with the following CMake versions:
- The earliest version of CMake that libjpeg-turbo currently supports (refer to CMakeLists.txt)
- The most recent major version of CMake
- (if applicable) The earliest version of CMake with which the enhancement can be used
- The enhancement has been tested on all of the major platforms (Mac, Linux, Windows/Visual C++, Windows/MinGW) that are potentially affected by it.
- The enhancement does not introduce new build system requirements or CMake variables unless absolutely necessary.
- The enhancement does not alter existing libjpeg-turbo development workflows.
Specific types of build system enhancements that will not be accepted:
- Enhancements that allow libjpeg-turbo to be built from a subdirectory of a downstream repository. These enhancements are not maintainable in the upstream libjpeg-turbo build system. Use the CMake
ExternalProject_Add() function instead.
- Enhancements that introduce new (non-CMake-based) build systems