libpng 1.8.0 late beta: default branch switch and release preparation

[ctruta]

Hi everyone,

Following up on the early beta announcement from July: libpng 1.8.0 has been progressing well, and we've now reached the late beta stage!

This is a major milestone. The default branch on GitHub has been switched from libpng16 to libpng18. This reflects our confidence in the 1.8.0 codebase, and it signals that we're approaching release readiness.

WHAT'S HAPPENING NOW:

• The libpng18 branch is stable and feature-complete, with APNG support fully integrated.
• The documentation is being reorganized and updated. The "What's new in libpng 1.8" part is coming up soon.
• We're still working on code deprecations, code cleanups, and build system refactorings and cleanups.

WHAT TO KEEP IN MIND:

• To the best of our knowledge, the correctness of libpng 1.8.0 beta and the correctness of libpng 1.6.51 beta are on par. In other words, there are no more known bugs in the upcoming libpng 1.8.0 release than there are in the upcoming 1.6.51 release.
• The 1.6.x line is effectively in maintenance mode. With the development work shifted onto 1.8.0, we will cherry-pick commits into 1.6.x as needed, but the focus will be almost exclusively on correctness and security. On the other hand, the work on 1.8.x line will be merged upward to 2.x on a regular basis.

WHAT WE NEED FROM YOU:

Testing! If you're using libpng in production (browsers, image tools, embedded systems), now is the time to test the libpng18 branch with your configurations. We especially want to hear from:

• Users with custom build configurations.
• Projects with platform-specific optimizations.
• Anyone using libpng in security-critical contexts.

Please report any issues you encounter. The more testing we get now, the smoother the final release will be.

The finish line is in sight. Stay tuned for the final 1.8.0 release!

Sincerely,
Cosmin