Romain Lepert (Aug 02 2026 at 00:15): Romain Lepert (Aug 02 2026 at 00:15):Hi everyone,
I'd like to share with you Terrocotta: a Roc native UI library.
I have been working on it for the past +1month and I think is in a good enough shape to share.
At its core terrocotta is a port of Clay to pure Roc, rendered using roc-ray. It is as faithful to the original implementation as possible and adds some niceties on top: MVU, event bindings, text style inheritance, etc.
The demo examples currently run at 300-600 fps (terrocotta: roc build --opt=speed, roc-ray: zig build -Doptimize=ReleaseFast) but there is probably quite some room for improvement since Clay advertises 10_000 fps.
I hope that it can help the UI effort to some extent. For those interested, I recommend reading the docs/architecture.md for internal explanations.
I also sometimes dump some Roc experience feedback to #24
Luke Boswell (Aug 02 2026 at 01:04):Wow, looks great!
Luke Boswell (Aug 02 2026 at 01:04):I guess I need to make a roc-ray release with an optimized host :sweat_smile:
Luke Boswell (Aug 02 2026 at 01:25):Luke Boswell said:
I guess I need to make a roc-ray release with an optimized host :sweat_smile:
Here's a fresh release https://github.com/lukewilliamboswell/roc-ray/releases/tag/0.8.2
blu (Aug 02 2026 at 01:41):Does this build to both native and web? How might you compare/contrast this with something like iced? Big fan of these "write once, run anywhere" libraries esp. Elm-inspired, and I've been looking for a good roc library for this, but roc-iced seems to be only old roc compiler and unmaintained. If it supports web/wasm, I'll give Terracotta a shot!
blu (Aug 02 2026 at 01:43):Btw the code examples you have are so much easier to understand than the original Clay ones. Elm-architecture + Multiplatform + functional/no runtime panic guarantees should be the future IMO. Good stuff!
blu (Aug 02 2026 at 01:46):@Luke Boswell I looked into this the other day and pretty sure that roc-ray doesn't yet compile to WASM/web, though raylib itself can? Which I assume means it just hasn't been implemented yet. Was wondering if that was on the roadmap or if I'm thinking about that correctly?
Luke Boswell (Aug 02 2026 at 01:48):It used to target web too, but I deleted all that when I migrated to the new compiler just to keep the scope simpler.
Luke Boswell (Aug 02 2026 at 01:49):If anyone is interested in adding that I'd love it ... but it's not something I'm working on or anything
Luke Boswell (Aug 02 2026 at 01:56):Luke Boswell said:
Luke Boswell said:
I guess I need to make a roc-ray release with an optimized host :sweat_smile:
Here's a fresh release https://github.com/lukewilliamboswell/roc-ray/releases/tag/0.8.2
Something went wrong and the host is still the debug version... I'm looking into it
Luke Boswell (Aug 02 2026 at 02:24):Ok here's a better fix ... from 40 up to 900 frames per second
https://github.com/lukewilliamboswell/roc-ray/releases/tag/0.8.3
blu (Aug 02 2026 at 02:28):If anyone is interested in adding that I'd love it ... but it's not something I'm working on or anything
I might look into this at some point. Write once, run anywhere UI story in a functional language is very compelling (and if I'm not mistaken one of the reasons Roc was created, feeling the limitations of Elm to be only web, right?). I guess this is sort of the inverse
Luke Boswell (Aug 02 2026 at 02:44):Also -- heres a PR that fixes the ARC bug and leaks in Roc these examples exposed https://github.com/roc-lang/roc/pull/10539
Thank you @Romain Lepert
Romain Lepert (Aug 02 2026 at 06:44):As always you are quick on the draw Luke. Thank you !
Romain Lepert (Aug 02 2026 at 06:50):blu said:
Does this build to both native and web? How might you compare/contrast this with something like iced? Big fan of these "write once, run anywhere" libraries esp. Elm-inspired, and I've been looking for a good roc library for this, but roc-iced seems to be only old roc compiler and unmaintained. If it supports web/wasm, I'll give Terracotta a shot!
It should be possible since the original clay has both a canvas renderer and a html/css renderer. Given the immediate mode nature only the canvas makes real sense but you lose the web accessibility, bot crawling, etc. The html/css renderer might only make sense for static websites maybe.
Anton (Aug 03 2026 at 12:49):feeling the limitations of Elm to be only web
Yes indeed, although Roc was not made with a UI focus in mind as I remember.
Richard Feldman (Aug 03 2026 at 14:37):yeah my feeling at the time was "I already have an Elm-like experience for Web UIs: Elm!" :smile:
that said, I do want something for native GUIs and I also appreciate that there's a lot of interest in having the same language on the server and on the client, including browser-based clients
Nicola 'tekNico' Larosa (Aug 05 2026 at 13:32):Terracotta
Apparently the idea is:
Terracotta + Roc -> TerROCotta
blu (Aug 05 2026 at 22:40):that said, I do want something for native GUIs and I also appreciate that there's a lot of interest in having the same language on the server and on the client, including browser-based clients
Totally fair, and thinking about this more maybe the HTML/JS/CSS trifecta vs. native UI architectures are just too conceptually different to unify cleanly. I guess I was just reading the iced philosophy and started dreaming of UItopia.
blu (Aug 05 2026 at 22:41):And in that UItopia I'd rather write in a Roc-like friendly syntax than Rust :sweat_smile:
Romain Lepert (Aug 06 2026 at 15:11):Contrary to immediate mode Terrocotta, iced.rs is retained mode. Nonetheless when targeting the web it uses WebGPU/WebGL, not HTML+DOM. That means it has the same restrictions as Terrocotta which hypothetically could do Canvas2D or WebGL or WebGPU.
Romain Lepert (Aug 06 2026 at 15:21):By restrictions I mean things like: SEO, browser translation, printing, password managers, autofill. Things of that nature
Last updated: Aug 12 2026 at 12:35 UTC