Support compression and decompression in JavaScript API

[bjorn]

Something like tiled.compress and tiled.decompress, to make it easier to support zlib, gzip or zstd compression in JS extensions.

See mapeditor/tiled-extensions#11.

[eishiya]

Bumping for interest.

I recently wrote a custom map format that lets me define "sprites" made out of multiple tiles that my game can then use similarly to regular sprites, and it stores the layer data similarly to Tiled's map JSON format. It would be nice to support the same compression options without including bulky libraries in the script. For now, I can only conveniently support "csv" (native JSON array) and uncompressed base64 encoding.

Edit: I wonder what the argument and output types should be. For use with Qt.btoa, it would have to be a string, but those not using Qt.btoa and Qt.atob might prefer ArrayBuffers, for easier use with BinaryFile.

[eishiya]

After spending some quality time with Qt's base64 encoder Qt.btoa(), I've realised it's either bugged or their approach is fundamentally broken: it works on UTF-8 strings that cannot accurately represent binary data: https://bugreports.qt.io/browse/QTBUG-71511

Because of this, I think Tiled should provide its own base64 encode/decode methods that can work with binary data (using e.g. ArrayBuffer), and Tiled's compress/decompress should probably also not use strings, to avoid encoding issues with JavaScript strings.

Edit: Apparently even the Qt devs recommend exposing one's own C++ functions for base64 encoding binary data, see the comments at the bottom here: https://codereview.qt-project.org/c/qt/qtdeclarative/+/244268

[bjorn]

After spending some quality time with Qt's base64 encoder Qt.btoa(), I've realised it's either bugged or their approach is fundamentally broken: it works on UTF-8 strings that cannot accurately represent binary data: https://bugreports.qt.io/browse/QTBUG-71511

That's rather surprising and quite unfortunate. Hopefully the new tiled.toBase64 and tiled.fromBase64 added by #3593 will work better.