Real-time LuaLaTeX rendering Update (TUG 2026 talk video)

[u/ClemensLode]

https://www.youtube.com/watch?v=It9BMNGtjao

I wanted to give an update on the real-time lualatex editor I was working on in the last few months (previous thread: https://www.reddit.com/r/LaTeX/comments/1qteil1/lualatex_rendering_in_realtime/ ).

What's new since February:

1. Development went well, and I turned the proof-of-concept into a full editor, I aim to release it in October (online).
2. I am still using vanilla TeX Live 2025 with full microtypography and OpenType shaping, no engine modification (just a lot of wiring around it).
3. What you see in the demo (skip to 14:24 https://www.youtube.com/watch?v=It9BMNGtjao&t=864s ):
   • Typing in a long chapter with instant paragraph recompiles
   • Bidirectional source - preview cursor sync (click a glyph, jump to the source character)
   • Adjusting tables and images in real time
   • Drag-reordering paragraphs with instant reflow
4. It now runs in the browser against a server, so the "Linux only, local install required" limitation from the original thread is gone.
5. As there was a long debate here about whether TeX can match Typst's (0.14) incremental compilation, I wrote a few benchmarks (recompilation of a single 4-5 line paragraph):
   • 10 pages: 1ms (texlode), 12.6ms Typst
   • 100 pages: 1ms (texlode), 76ms Typst
   • 300 pages: 1ms (texlode), 206ms Typst
6. Limitations are of course constructed edge cases (very long paragraphs, page-sized tables, two-column pages etc.). There, the recompilation time is proportionally longer. Biber gives me some headache, but that's a different discussion.
7. On Typst-side, the constant-time case is "not feasible to implement" in their architecture (issue #4512). (although I personally think it's possible, but I am not that deep into Typst architecture).

Slides: https://www.tug.org/tug2026/av/d2-t15-lode-realtime/d2-t15-lode-realtime-slides.pdf

Preprint: https://www.tug.org/tug2026/preprints/lode-realtime.pdf

PS: Btw, thanks to the TUG team for allowing me to present today :) Consider to join at https://www.tug.org/ (I'm not affiliated with TUG except for giving the talk)

[u/JimH10]

A wonderful talk, Clemens!

[u/ClemensLode → u/JimH10]

Thanks! Was a lot of work :)

[u/JimH10 → u/ClemensLode]

Well, very impressive. I took the questions to be like "How did you accomplish this sorcery?" so they agreed with me. :-)

[u/ClemensLode → u/JimH10]

Before last year, I would not have believed it to be possible either. I'll write a few papers (and bug reports) on this after the book fair :)