Implement image comparison for visual tests

[SableRaf]

Implement a visual snapshot testing system, inspired by the one used in p5.js.

Note

This has been added to our GSoC 2025 project list.

Goals

• Develop a visual snapshot testing framework for Processing.
• Automate image comparisons using pixel matching (e.g., image-comparison).
• Integrate the testing system into GitHub workflows.
• Port existing p5.js snapshot tests and develop new ones for Processing’s Java environment.

Motivation

This will benefit both the Processing community and its future contributors by providing a reliable way to catch visual regressions, making it easier for contributors to propose changes with confidence.

References

Read more about the p5.js approach in the documentation and this contributor blog post.

[Rishab87]

Hi I would like to work on this issue, can you please assign this to me?

[SableRaf]

Hi @Rishab87,

This issue is a rather large undertaking and not ready to be assigned. However, we've added it to our GSoC 2025 project list. You're very welcome to apply!

For questions about Processing's participation in GSoC, check out this post on the Processing forum. You can also ask any question you have about this project in that thread.

[Rishab87]

Thanks for telling @SableRaf, I already made a basic implementation of it, I'll check out this project, I was already planning to apply for GSoC this year with p5

[LakshitSharma1]

Hi @SableRaf
I’m really interested in this project and plan to apply for GSoC 2025. I’ve read the p5.js documentation and blog post on snapshot testing, and I’d love to contribute to implementing a similar system for Processing.
I have experience with Java, JavaScript, and GitHub Actions, and I’d like to get more familiar with image comparison tools like image-comparison.
To get started, are there any existing test cases or Processing rendering examples that we should focus on first? Or should I look at the existing p5.js tests and try to adapt them?
Looking forward to your insights!

[SableRaf]

Hi @LakshitSharma1 and thanks for your question.

As Kit mentioned on the forum:

In the timeline, right now is the time to explore and (soon) to develop proposals. After proposals are submitted, some will be accepted, and then work can begin. So for now, please feel free to try things out and explore (and keep asking questions!), but not work on the projects directly.

For further questions, please check our GSoC 2025 FAQ or ask directly on this thread on the Processing forum.

[LakshitSharma1]

Hi @SableRaf,

Thanks for your earlier response! Now that we're further along in the GSoC timeline, I’m finalizing my proposal for this project. I’ve been exploring how snapshot testing works in p5.js and considering how it can be adapted for Processing.

I had a couple of follow-up questions:

1. Are there any specific technical constraints in Processing’s rendering system that might make snapshot testing more challenging compared to p5.js?
2. Would it be helpful to prototype a small proof of concept to demonstrate feasibility, or should I focus entirely on the proposal at this stage?
   Looking forward to your thoughts!

[SableRaf]

Hi @LakshitSharma1 for general GSoC questions please use the forum thread. If you have time sensitive questions you can use our feedback request form