Generated png is not reproducible anymore if same code is ran in a different env

[Ilyes512]

Our CI test broke after upgrading from 6.0.3 to 6.0.4. Locally we use a php container and in the CI we just run it in the CI Github runner (Ubuntu 24). I believe because it's ran in a different environment with differently compiled PHP (and GD extension) the output of imagetruecolortopalette is not consistent even if the provided arguments are the same.

Perhaps we shouldn't snapshot test the base64 output of the QR code in the first place, but at the very least I wanted to report this change in output.

The change that is causing my current problem can be found here: https://github.com/endroid/qr-code/blob/main/src/Writer/Result/PngResult.php#L24

Diff between 6.0.3 vs 6.0.4:
74b62f4#diff-5d46da5b28b5ad39f4093489d68d3a46fefaf23455e18b965d9f465de84f265b

I also tried to get the old behaviour by setting the following writer options: [PngWriter::WRITER_OPTION_NUMBER_OF_COLORS => null]. But that won't work because an isset() check on such element would still return false.

[endroid]

Hi @Ilyes512 thanks for noticing, it was indeed impossible to set the option back to null this way so I fixed that. If you find the reason why the imagetruecolortopalette method is not working on one of your environments please mention it here, maybe it helps others. Good luck!

[Ilyes512]

Just to clarify: It's not that it does not work! Both environments produce an (base64 PNG) output. When you turn that output to the actual PNG, they look exactly the same, but the output (the base64 string) it self are different. And the only difference between the versions is the call to imagetruecolortopalette.