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Daniel Schürmann edited this page Feb 15, 2022 · 108 revisions
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Google Summer of Code Advice

Thank you for your interest in working on Mixxx with Google Summer of Code! GSoC can be a fun and rewarding way to put your coding skills to use by contributing to free software. GSoC students gain valuable experience not only in programming, but also collaborating with an international community to make awesome software used by thousands of people around the world. We welcome you into our community and hope that you find working on Mixxx as fun as we do!

Mixxx is relatively small project, so students' work often makes a large impact. During and after your Summer of Code project you will have the opportunity to put your work in the hands of real DJs and hear how they've used it. Past students have had a lot of fun working on Mixxx and learned a lot at the same time. If you want challenging problems, freedom to develop your ideas, interesting people and an all-round brilliant summer, then apply to work on Mixxx.

This page has some general advice for students thinking about applying for Summer of Code with Mixxx. If you wish to apply for the program then you will need to visit the official Google Summer of Code website.

Getting Involved

We consider more than the words in your application when deciding which students to accept. We look for signs that you will become an active participant in our community and that you are someone we would want to work with over several months. Although it is not a requirement, we hope you continue to stay involved after GSOC ends. The best way to show us you will become a part of our community is to get involved before beginning your application. Here are some ways to get started:

  • Play with Mixxx and explore what it can do. Read the Mixxx manual to get a better understanding of Mixxx's capabilities and what people use it for.
  • Introduce yourself early on our Zulip chat. If you have not introduced yourself until a few days before the application deadline, we will not accept your application. Start a new topic in the #gsoc stream. Do not hesitate to ask questions, or ask for a helping hand to get started. Please make sure you have read this page carefully before. If the first question you ask is clearly answered on this page, you will likely not be accepted, because it strongly suggests that you lack the ability to work independently.
  • Participate in Zulip discussions that are not directly related to your GSOC project.
  • Test and review pull requests. Post comments on GitHub pull requests suggesting ways to improve the code more.
  • Look through the start#Developer Documentation and make a small code contribution to fix a bug or enhance an existing feature.
  • Help users with technical questions about Mixxx on the forum.
  • Report bugs on our bug tracker.

We expect that you make an effort to answer your own questions like reading the source or exploring this wiki before asking us. We are happy to give you guidance and assist you when you get stuck, but we will not do work for you. If your questions show us that you have not explored the code nor even practiced using Mixxx, you will likely not be accepted.

What Project Should I Work On?

GSOC lasts several months, so it is important that you choose a project that you are personally passionate about that you will be excited to work on for an extended period. We cannot tell you what want you want to work on, but we have some suggestions for project ideas. The best project for you is one that you would continue to use years later even if GSOC didn't exist. Before thinking too much about what project you want to work on, we suggest spending time using Mixxx and #Getting Involved in the community. This will help you understand what Mixxx currently does well and what areas could be improved. In general, your project proposal can be inspired by any of the following:

  • A project from our GSoC 2022 Ideas Page
  • A project you come up with! Make sure to contact us on Zulip before submitting to get feedback if this is your plan. Spend more than a few days using Mixxx and participating in the community before suggesting your own ideas. This will help you develop an understanding of what Mixxx's current weaknesses are that could use improvement.
  • You can use our Wishlist Bugs page for inspiration for your project.

What Would Working On Mixxx Be Like?

The Mixxx development environment is cooperative and relatively informal. Our community is small but unusually diverse with contributors from a variety of backgrounds and all over the world. Working on Mixxx you would have an opportunity to interact with a unique mixture of programmers, artists and DJs. Mixxx as a piece of software also offers some unique challenges, we are both cross-platform and (soft) real-time and support a huge range of MIDI and audio hardware devices. Students with Mixxx will have an opportunity to learn advanced skills like low-latency programming and cross-platform application deployment which will look great on your resumé.

Am I Experienced Enough?

This is a common question asked by prospective students, the answer is generally: "Yes". You do need some prior experience with C++, even if it was only for a small school project, but you do not need experience with the specific libraries or algorithms Mixxx uses.

Students who have experience using DJ hardware are at a big advantage in terms of proposing projects that will have a meaningful impact on users. You don't need to own DJ hardware for a successful GSOC project, but it is helpful and makes Mixxx more fun to use.

We value general software design and development experience above specific knowledge of a library or API. We have found in the past that an interested and motivated student who is willing to learn is more valuable than anything else. For example, if you've never used Qt before but have done lots of Java and Gtk+ UI development, please let us know that in your application.

Of course if you do have direct experience with the tools we use, you should definitely tell us about that too. The main external tools we rely on are Qt and Git.

Our expectations from students

  • Be self-motivated and stick to the schedule you write in your proposal
  • Try to answer your own questions before asking for help
  • Ask for help when you are not sure about the best way forward
  • Write a weekly report on your progress on the wiki page for your project.
  • Commit early, commit often, and push to GitHub so that we can see it
  • Actively work on your project plan and communicate with us during the community bonding period
  • Communicate every working day with your mentor. Just say "hello" if you like. We primarily use Zulip and comments on GitHub pull requests to communicate.
  • If there are good reasons for not communicating please announce them early. If you know there will be times that you are not able to work on your project as much during the summer, please let us know in your application.
  • If you don't communicate with us regularly, we will fail you.

Midterm and Final evaluations

  • Set a realistic goal for mid-term. If you fail to meet your own goal we are more likely to fail you in the evaluations.
  • Have some code merged into the master Git branch at the end of the summer to pass the final evaluation. This does not necessarily mean that your whole project must be 100% complete by the end of GSOC.
  • The later is a hard requirement so make sure that your time plan includes it.

How Do I Write A Great Application?

Firstly, think about your choice of project carefully. You're going to be doing it for a couple of months, so it's important that you choose something you're going to enjoy. Once you've made your mind up:

  1. Make sure you've thought about the project and understand what it entails
  2. Don't be afraid to come up with original solutions to the problem
  3. Set up an IDE to start exploring the area of the code you will be working on and understanding how the classes work together. Read the Developer Guide for an introduction to the organization of the Mixxx code. Feel free to ask us on Zulip if you need help figuring out where to start looking in the code.
  4. Figure out what parts of the code need to be changed and come up with a general idea of what those changes will be.
  5. Write a draft application early so we can help you with feedback before the final application deadline. We recommend submitting a draft application at least one week before the final application deadline. If you wait until the last few days to submit your first draft, it will be hard for you to respond to feedback in time.
  6. Don't be afraid to give us lots of detail about how you would approach the project
  7. UI mockups are very much encouraged where appropriate
  8. Consider how much time you need for each part of the project
  9. Include links to C++ code you have written before
  10. If you have prior experience DJing, mention it in your application

Overall, your application should make us believe that you are capable of completing the project and delivering the functionality to our users. If you aren't sure about anything, get in touch with us, we're happy to advise you.

Application evaluation criteria

Here are some criteria that we consider when reviewing applications. We suggest that you think about these when writing your application.

  • Has the student interacted with the Mixxx community before submitting their application?
  • Does the student understand the purpose of their project? Do they understand what impact their project will have on users?
  • Has the student demonstrated that they have the ability to work with Mixxx's code? The best way to do this is by submitting pull requests and getting them merged. It can also be okay if a student works on a bug but is unable to solve it before the application deadline if they demonstrate competence working with the Mixxx code. Students must have submitted a pull request to Mixxx or provide links to code they have written before in their application (ideally both).
  • Has the student demonstrated that they can work independently and solve problems on their own without asking for help every step of the way?
  • Does the student understand the design and technical details of what will be required to implement their proposal? What classes would need to be modified and how? Do new classes need to be added? How would the classes interact? We are not looking for you to have every detail figured out; you won't know that until you actually write the code. But we want to see that you understand the code you'll be working with and have a general plan of how to change it. It is more important that you show us you have the skill to work with the code and plan ahead than have the details 100% correct.
  • Is the proposed timeline realistic considering any other obligations the student may have during GSOC?
  • Do we think that the student will continue contributing to Mixxx after GSOC? The best outcome we can get from GSOC is not just a cool new feature at the end of the summer; we want someone who will become part of the community and continue to contribute cool features years after GSOC ends. The best way to show us this is to get involved early, participate in discussions on Zulip that aren't directly related to your GSOC project, and test and review pull requests.

Splitting up your project into smaller pieces

We require our students to merge some of their code into our master branch before the end of the summer. The best way to achieve this is to divide your project into small self contained subprojects and plan to merge at least one of them around midterm.

A good example for this is 'Improve our track managment':

 - handle property changes for a selection of tracks
 - add a custom editor for cue points
 - add an editor for the BPM-grid
 - build an editor to comment time slices of a track

Another approach is to analyze what the absolute minimal requirements are and then adding features on top of that. eg 'implement cover art in Mixxx':

 - handle reading/storing covers in the database and application
 - Show the cover next to the track name in a deck
 - display the covers in the library view
 - add picture flow

During your summer you'll encounter bugs in Mixxx or find code that can be refactored to help you implement your ideas. You can also immediately fix them in the master branch and help us all out. This has several advantages. All your pull request will only concentrate on specific features and are much better to review. And you'll also get direct feedback from other developers and users during the summer.

Having good time estimates

To get a feeling for the code and get some experience with our code you can go and tackle some of our easy bugs. Look at the code that you want to change, check if it follows our coding guidelines. Do some research on the API's you want to use, plan what classes you will add and how their public API will look. Write down your algorithms in pseudo code. The better your research is and the better you plan ahead the easier it will be to judge how long a given task will take. For your time estimates you should also consider that you can do less stuff during exams and try to be a bit conservative. If you have never done anything like GSoC before you will tend to underestimate the time to complete a task. I know that giving these estimates is not easy and that also professionals have problems with it. Having a good plan, knowing its weak and strong points are can help a lot.


Stéphane Lepin has kindly published his successful 2017 application.

We look forward to your application! :) - The Mixxx Development Team