![logo](https://raw.githubusercontent.com/boostorg/gil/develop/doc/_static/gil.png)

# Contributing to Boost.GIL

Boost.GIL is a member of [Boost](https://www.boost.org) libraries.

If you wish to contribute a new feature or a bug fix,
please follow the workflow explained in this document.

## Table of Content

* [Prerequisites](#prerequisites)
* [Getting started with Git workflow](#getting-started-with-git-workflow)
  * [1. Clone Boost super-project](#1-clone-boost-super-project)
  * [2. Checkout Boost.GIL development branch](#2-checkout-boostgil-development-branch)
  * [3. Fork Boost.GIL repository on GitHub](#4-fork-boostgil-repository-on-github)
  * [4. Submit a pull request](#5-submit-a-pull-request)
  * [5. Update your pull request](#6-update-your-pull-request)
* [Development](#development)
  * [Using Boost.Build](#using-boostbuild)
  * [Using CMake](#using-cmake)
  * [Using Faber](#using-faber)

## Prerequisites

* Experience with `git` command line basics.
* Familiarity with build toolset and development environment of your choice.
* Although this document tries to present all commands with necessary options,
  it may be a good idea to skim through the
  [Boost Getting Started](https://www.boost.org/more/getting_started/index.html)
  chapters, especially if you are going to use
  [Boost.Build](https://boostorg.github.io/build/) for the first time.

## Getting started with Git workflow

First, you need learn some minimal basics of the
[modular Boost](https://svn.boost.org/trac/boost/wiki/ModularBoost)
super-project workflow.

The following steps are based on the official Boost
[Getting Started](https://github.com/boostorg/boost/wiki/Getting-Started).

**NOTE:** For brevity, commands below use notation for POSIX-like operating
systems and you may need to tweak them for Windows systems.

### 1. Clone Boost super-project

The preparation involves the following steps:

1. Download the Boost super-project and switch the local repository to
   `develop` branch.
2. Run `bootstrap` to build `b2` driver program for Boost.Build engine.

    ```shell
    git clone --recursive --jobs 8 https://github.com/boostorg/boost.git
    cd boost
    git checkout develop
    ./bootstrap.sh
    ```

**TIP:** [Modular Boost Library Maintenance](https://svn.boost.org/trac10/wiki/StartModMaint)
guide, for more realistic test environment, recommends to develop and test
individual Boost library against other Boost libraries as defined by
the Boost super-project `master` branch:

```shell
cd boost
git checkout master
git pull
git submodule update
```

3. Optionally, create full content of `/boost` virtual directory with all
Boost headers linked from the individual modular Boost libraries.
If you skip this step, executing `b2` to run tests will automatically
create the directory with all headers required by Boost.GIL and tests.

    ```shell
    ./b2 headers
    ```

**TIP:** For more convenient path-less invocation, you can copy the `b2`
program to a location in your `PATH`.

**TIP:** If something goes wrong, you end up with incomplete or accidentally
modified files in your clone of the super-project repository, or you simply
wish to start fresh, then you can clean and reset the whole repository and
its modules:

```shell
git clean -xfd
git submodule foreach --recursive git clean -xfd
git reset --hard
git submodule foreach --recursive git reset --hard
git submodule update --init --recursive --jobs 8
```

### 2. Checkout Boost.GIL development branch

Regardless if you decide to develop again `master` (recommended) or `develop`
branch of the Boost super-project, you should always base your work
(ie. topic branches) on Boost.GIL `develop` branch.

1. Go to the Boost.GIL library submodule.
2. Checkout the `develop` branch.

    ```shell
    cd libs/gil
    git checkout develop
    git branch -vv
    git pull origin develop
    ```

### 3. Fork Boost.GIL repository on GitHub

Follow [Forking Projects](https://guides.github.com/activities/forking/) guide
to get personal copy of [boostorg/gil](https://github.com/boostorg/gil)
repository from where you will be able to submit new contributions as
[pull requests](https://help.github.com/articles/about-pull-requests/).

Add your fork as git remote to the Boost.GIL submodule:

```shell
cd libs/gil
git remote add username https://github.com/username/gil.git
```

### 4. Submit a pull request

All Boost.GIL contributions should be developed inside a topic branch created by
branching off the `develop` branch of [boostorg/gil](https://github.com/boostorg/gil).

**NOTE:** The branching workflow model
[Boost recommends](https://svn.boost.org/trac10/wiki/StartModWorkflow)
is called Git Flow.

For example:

```shell
cd libs/gil
git checkout develop
git checkout -b feature/foo
```

Now, you are set to to develop a new feature for Boost.GIL,
then [git add](https://git-scm.com/docs/git-add) and
[git commit](https://git-scm.com/docs/git-commit) your changes.

Once it's finished, you can submit it as pull request for review:

```shell
cd libs/gil
git checkout feature/foo
git push username feature/foo
```

Finally, sign in to your GitHub account and
[create a pull request](https://help.github.com/articles/creating-a-pull-request/).

Your pull request will be automatically built and tests will run on Travis CI
and AppVeyor (see [README](README.md) for builds status). Please, keep an eye
on those CI builds and correct any problems detected in your contribution
by updating your pull request.

### 5. Update your pull request

In simplest (and recommended) case , your the pull request you submitted earlier
has *a single commit*, so you can simply update the existing commit with any
modifications required to fix failing CI builds or requested by reviewers.

First, it is a good idea to synchronize your topic branch with the latest
changes in the upstream `develop` branch:

```shell
cd libs/gil
git checkout develop
git pull origin develop
git checkout feature/foo
git rebase develop
```

Next, make your edits.

Finally, `git commit --amend` the *single-commit* in your topic branch and
update the pull request:

```shell
cd libs/gil
git checkout feature/foo
git add -A
git commit --amend
git push --force username feature/foo
```

**WARNING:** Ensure your pull request has a single commit, otherwise the
force push can corrupt your pull request.

If you wish to update pull request adding a new commit, then create new
commit and issue regular push:

```shell
git commit -m "Fix variable name"
git push username feature/foo
```

## Development

Boost.GIL is a [header-only library](https://en.wikipedia.org/wiki/Header-only)
which does not require sources compilation. Only test runners and example
programs have to be compiled.

By default, Boost.GIL uses Boost.Build to build all the executables.

We also provide configuration for two alternative build systems:

* [CMake](https://cmake.org)
* [Faber](http://stefan.seefeld.name/faber/)

**NOTE:** The CMake and Faber are optional and the corresponding build
configurations for Boost.GIL do not offer equivalents for all Boost.Build features. Most important difference to recognise is that Boost.Build will
automatically build any other Boost libraries required by Boost.GIL as dependencies.

### Using Boost.Build

The [b2 invocation](https://boostorg.github.io/build/manual/develop/index.html#bbv2.overview.invocation)
explains available options like `toolset`, `variant` and others.

Simply, just execute `b2` to run all tests built using default
`variant=debug` and default `toolset` determined for your
development environment.

**TIP:** Pass `b2` option `-d 2` to output complete action text and commands,
as they are executed. It is useful to inspect compilation flags.

If no target or directory is specified, everything in the current directory
is built. For example, all Boost.GIL tests can be built and run using:

```shell
cd libs/gil
../../b2
```

Run core tests only specifying location of directory with tests:

```shell
cd libs/gil
../../b2 test
```

Run all tests for selected extension (from Boost root directory, as alternative):

```shell
./b2 libs/gil/io/test
./b2 libs/gil/numeric/test
./b2 libs/gil/toolbox/test
```

Run I/O extension tests bundled in target called `simple`:

```shell
./b2 libs/gil/io/test//simple
```

_TODO: Explain I/O dependencies (libjpeg, etc.)_

### Using CMake

Maintainer: [@mloskot](https://github.com/mloskot)

**NOTE:** CMake configuration does not build any dependencies required by
Boost.GIL like Boost.Test and Boost.Filesystem libraries or any
third-party image format libraries used by the I/O extension.

The provided CMake configuration allows a couple of ways to develop Boost.GIL:

1. Using Boost installed from binary packages in default system-wide location.
2. Using Boost installed from sources in arbitrary location (CMake may need
   `-DBOOST_ROOT=/path/to/boost/root`, see
   [FindBoost](https://cmake.org/cmake/help/latest/module/FindBoost.html)
   documentation for details).
3. Using [cloned Boost super-project](#cloned-boost-super-project), inside modular
   `libs/gil`. This mode requires prior deployment of `boost` virtual directory
   with headers and stage build of required libraries, for example:
    ```shell
    ./b2 headers
    ./b2 --with-test --with-filesystem variant=debug stage
    ./b2 --with-test --with-filesystem variant=release stage
    ```

Using the installed Boost enables a lightweight mode for the library development,
inside a stand-alone clone Boost.GIL repository and without any need to clone the
whole Boost super-project.

Here is an example of such lightweight workflow in Linux environment (Debian-based):

* Install required Boost libraries

    ```shell
    sudo apt-get update
    sudo apt-get install libboost-dev libboost-test-dev libboost-filesystem-dev
    ```

* Optionally, install libraries required by the I/O extension

    ```
    sudo apt-get update
    sudo apt install libtiff-dev libpng-dev libjpeg-dev
    ```

* Clone Boost.GIL repository

    ```shell
    $ git clone https://github.com/boostorg/gil.git
    $ cd gil
    ```

* Configure build with CMake

    ```shell
    $ mkdir _build
    $ cd _build/
    $ cmake ..
    -- The CXX compiler identification is GNU 7.3.0
    -- Check for working CXX compiler: /usr/bin/c++
    -- Check for working CXX compiler: /usr/bin/c++ -- works
    -- Detecting CXX compiler ABI info
    -- Detecting CXX compiler ABI info - done
    -- Detecting CXX compile features
    -- Detecting CXX compile features - done
    -- Boost version: 1.65.1
    -- Found the following Boost libraries:
    --   unit_test_framework
    --   filesystem
    --   system
    -- Boost_INCLUDE_DIRS=/usr/include
    -- Boost_LIBRARY_DIRS=/usr/lib/x86_64-linux-gnu
    -- Found JPEG: /usr/lib/x86_64-linux-gnu/libjpeg.so
    -- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11")
    -- Found PNG: /usr/lib/x86_64-linux-gnu/libpng.so (found version "1.6.34")
    -- Found TIFF: /usr/lib/x86_64-linux-gnu/libtiff.so (found version "4.0.9")
    -- Configuring Boost.GIL core tests
    -- Configuring Boost.GIL IO tests
    -- Configuring Boost.GIL Numeric tests
    -- Configuring Boost.GIL Toolbox tests
    -- Configuring done
    -- Generating done
    -- Build files have been written to: /home/mloskot/gil/_build
    ```

* List available CMake targets

    ```shell
    $ cmake --build . --target help
    ```

* Build selected target with CMake

    ```shell
    cmake --build . --target gil_test_pixel
    ```

* List available CTest targets

    ```
    $ ctest --show-only | grep Test
    ```
* Run selected test with CTest

    ```
    ctest -R gil.tests.core.pixel
    ```

### Using Faber

Maintainer: [@stefanseefeld](https://github.com/stefanseefeld)

_TODO_