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:

1. 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)

2. If the code contribution will implement a major new feature, then please
contact the project maintainer (through a
[GitHub issue](https://github.com/libjpeg-turbo/libjpeg-turbo/issues/new),
[direct e-mail](https://libjpeg-turbo.org/About/Contact), or the
[libjpeg-turbo-devel mailing list](https://libjpeg-turbo.org/About/MailingLists))
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](https://github.com/libjpeg-turbo/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

3. 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