Unfortunately the most important thing here is missing - the whole explanation, like how did we get there, what those fonts can do and so on..

OpenType specification is Turing complete, its hinting engine does math during rasterization and its GSUB (Glyph Substitution, a layout and shaping engine) does glyph stacking, QR code correction, etc to finalize the QR. The nice thing about it is if you copy and paste it, it goes to the original text.

That’s a common downside of HN: submitters often link the GitHub repository rather than the project’s explanation. The article’s had the project link added at the top (just below the GitHub link) and it has a much clearer story.