JPEG XL format internals are beautiful -- control structures are self-similar and the image coding itself is used to code substructures, similar to WebP lossles

JPEG XL format internals are beautiful -- control structures are self-similar and the image coding itself is used to code substructures, similar to WebP lossless. libjxl C++ implementation is modern high-performance multi-threaded SIMD code, with layering, animation, streaming and progressive features, it can look scary. With some less emphasis on performance it could be written rather elegantly.