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Contributing to librsvg

Thank you for looking in this file! There are different ways of contributing to librsvg, and we appreciate all of them.

There is a code of conduct for contributors to librsvg; please see the file code-of-conduct.md.

Source repository

Librsvg's main source repository is at gitlab.gnome.org. You can view the web interface here:

https://gitlab.gnome.org/GNOME/librsvg

Development happens in the master branch. There are also branches for stable releases.

Alternatively, you can use the mirror at Github:

https://github.com/GNOME/librsvg

Note that we don't do bug tracking in the Github mirror; see the next section.

If you need to publish a branch, feel free to do it at any publically-accessible Git hosting service, although gitlab.gnome.org makes things easier for the maintainers of librsvg.

To work on the source code, you may find the "Hacking on librsvg" section helpful.

Reporting bugs

Please report bugs at https://gitlab.gnome.org/GNOME/librsvg/issues

If you want to report a rendering bug, or a missing SVG feature, please provide an example SVG file as an attachment to your bug report. It really helps if you can minimize the SVG to only the elements required to reproduce the bug or see the missing feature, but it is not absolutely required. Please be careful of publishing SVG images that you don't want other people to see, or images whose copyright does not allow redistribution; the bug tracker is a public resource and attachments are visible to everyone.

You can also browse the existing bugs.

Obtaining debug logs

Librsvg can be asked to output debug logs. Set the RSVG_LOG environment variable, and then librsvg will print some information to stdout:

$ RSVG_LOG=1 some-program-that-uses-librsvg
... debug output goes here ...

As of librsvg 2.43.5, there are no options you can set in the RSVG_LOG variable; the library just checks whether that environment variable is present or not.

Feature requests

Librsvg aims to be a small and relatively simple SVG rendering library. Currently we do not plan to support scripting, animation, or interactive features like mouse events on SVG elements.

However, we do aim go provide good support for SVG's graphical features. Please see the "reporting bugs" section for information about our bug tracking system; feature requests should be directed there.

It is especially helpful if you file bug for a feature request along with a sample SVG file.

Hacking on librsvg

The library's internals are being documented at https://gnome.pages.gitlab.gnome.org/librsvg/doc/rsvg_internals/index.html

Working on the source

Librsvg uses an autotools setup, which is described in detail in this blog post.

If you need to add a new source file, you need to do it in the toplevel Makefile.am. Note that this is for both C and Rust sources, since make(1) needs to know when a Rust file changed so it can call cargo as appropriate.

It is perfectly fine to ask the maintainer if you have questions about the Autotools setup; it's a tricky bit of machinery, and we are glad to help.

Please read the file ARCHITECTURE.md; this describes the overall flow of the source code, so hopefully it will be easier for you to navigate.

Taking advantage of Continuous Integration

If you fork librsvg in gitlab.gnome.org and push commits to your forked version, the Continuous Integration machinery (CI) will run automatically.

A little glossary:

  • Continuous Integration (CI) - A tireless robot that builds librsvg on every push, and runs various kinds of tests.

  • Pipeline - A set of jobs that may happen on every push. Every pipeline has stages of things that get run. You can view recent pipelines and examine their status.

  • Stages - Each stage runs some kind of test on librsvg, and depends on the previous stages succeeding. We have a Test stage that just builds librsvg as quickly as possible and runs its test suite. If that succeeds, then it will go to a Lint stage which runs rustfmt to ensure that the coding style remains consistent. Finally, there is a Cross_distro stage that tries to build/test librsvg on various operating systems and configurations.

  • Jobs - You can think of a job as "something that runs in a specific container image, and emits a success/failure result". For example, the Test stage runs a job in a fast Fedora container. The Lint stage runs rustfmt in a Rust-specific container that always contains a recent version of rustfmt. Distro-specific jobs run on container images for each distro we support.

The default CI pipeline for people's branches is set up to build your branch and to run the test suite and lints. If any tests fail, the pipeline will fail and you can then examine the job's build artifacts. If the lint stage fails, you will have to reindent your code.

Automating the code formatting: You may want to enable a client-side git hook to run rustfmt before you can commit something; otherwise the Lint stage of CI pipelines will fail:

  1. cd librsvg

  2. mv .git/hooks/pre-commit.sample .git/hooks/pre-commit

  3. Edit .git/hooks/pre-commit and put in one of the following commands:

  • If you want code reformatted automatically, no questions asked: cargo fmt Note: if this actually reformats your code while committing, you'll have to re-stage the new changes and git commit --amend. Be careful if you had unstaged changes that got reformatted!

  • If you want to examine errors if rustfmt doesn't like your indentation, but don't want it to make changes on its own:
    cargo fmt --all -- --check

Installing rustfmt As of 2018/Sep, our continuous integration pipeline assumes the version of rustfmt that is distributed through the nightly channel of rustup. You can install it with

rustup component add rustfmt-preview --toolchain=nightly

Test suite

Please make sure that the test suite passes with the changes in your branch. The easiest way to run all the tests is to go to librsvg's toplevel directory and run make check. This will run both the small unit tests and the black box tests in the librsvg/tests directory.

If you need to add new tests (you should, for new features, or for things that we weren't testing!), or for additional information on how the test suite works, please see the file tests/README.md.

In addition, the CI machinery will run librsvg's test suite automatically when you push some commits. You can tweak what happens during CI for your branch in the .gitlab-ci.yml file — for example, if you want to enable distro-specific tests to test things on a system that you don't have.

Testing changes

The most direct way to test a change is to have an example SVG file that exercises the code you want to test. Then you can rebuild librsvg, and run this:

cd /src/librsvg
libtool --mode=execute ./rsvg-convert -o foo.png foo.svg

Then you can view the resulting foo.png image. Alternatively, you can use ./rsvg-view-3 for a quick-and-dirty SVG viewer.

Please update the test suite with a suitable example file once you have things working (or before even writing code, if you like test-driven development), so we can avoid regressions later. The test suite is documented in tests/README.md.

Creating a merge request

You may create a forked version of librsvg in GNOME's Gitlab instance, or any other publically-accesible Git hosting service. You can register an account there, or log in with your account from other OAuth services.

Note that the maintainers of librsvg only get notified about merge requests (or pull requests) if your fork is in gitlab.gnome.org.

For technical reasons, the maintainers of librsvg do not get automatically notified if you submit a pull request through the GNOME mirror in Github. Please contact the maintainer directly if you have a pull request there or a branch that you would like to contribute.

Formatting commit messages

If a commit fixes a bug, please format its commit message like this:

(#123): Don't crash when foo is bar

Explanation for why the crash happened, or anything that is not
obvious from looking at the diff.

https://gitlab.gnome.org/GNOME/librsvg/issues/123

Note the (#123) in the first line. This is the line that shows up in single-line git logs, and having the bug number there makes it easier to write the release notes later — one does not have to read all the commit messages to find the ids of fixed bugs.

Also, please paste the complete URL to the bug report somewhere in the commit message, so that it's easier to visit when reading the commit logs.

Generally, commit messages should summarize what you did, and why. Think of someone doing git blame in the future when trying to figure out how some code works: they will want to see why a certain line of source code is there. The commit where that line was introduced should explain it.

Testing performance-related changes

You can use the rsvg-bench tool to benchmark librsvg. It lets you run a benchmarking program on an already-installed librsvg library. For example, you can ask rsvg-bench to render one or more SVGs hundreds of times in a row, so you can take accurate timings or run a sampling profiler and get enough samples.

Why is rsvg-bench not integrated in librsvg's sources? Because rsvg-bench depends on the rsvg-rs Rust bindings, and these are shipped outside of librsvg. This requires you to first install librsvg, and then compile rsvg-bench. We aim to make this easier in the future. Of course all help is appreciated!

Included benchmarks

The rsvg_internals/benches directory has a couple of benchmarks for functions related to SVG filter effects. You can run them with cargo bench.

These benchmarks use the Criterion crate, which supports some interesting options to generate plots and such. You can see the Criterion command line options.