Implement image comparison for visual tests

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

[!NOTE]
This has been added to our pr05 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.

首先阅读所引用的 p5.js 视觉测试文档并检查图像比较项目，然后检查 Processing 现有的 GitHub 工作流和当前的快照测试。完成的标准是：Processing 已有视觉快照框架，像素比较和工作流集成已实现自动化，并且相关的 p5.js 测试已完成移植，或已添加新的 Java 测试。