let-go-lab

Experiments on let-go — sixel graphics, terminal UI, wasm-in-the-browser — decoupled from any one client app.

▶ Live in your browser, no install (let-go compiled to WASM): every demo is on the lab's index page: mandelbrot · pathtrace · ptcanvas · microgpt sampler.

Quick start

just play            # native TUI (needs a sixel-capable terminal)
just serve           # build + serve in the browser; open the printed URL

Both default to the mandelbrot demo and to the lg in the symlinked checkout (./let-go) — use the let-go release pinned in config/let-go-release. See CLAUDE.md for the lg requirement, cert setup for LAN/phone serving, and how to add a demo.

To compile a complete demo to a native executable:

just native mandelbrot       # also: pathtrace, microgpt
dist/native/mandelbrot

This optional build caches the audited let-go SHA from config/let-go-native.sha. Browser CI and Pages use the release pin. See native builds for requirements, measurements, and compiler limitations.

Demos

• mandelbrot — an escape-time Mandelbrot. In the browser it draws to a <canvas> (surface/present), sized to the window; in a terminal it draws sixel graphics. Interactive zoom / pan / maxiter, tap-to-recenter (a central tap zooms, an edge tap pans), a dim-while-computing cue, live phase timing, and a sixel encoder that works from the coarse grid.

  Controls: +/- zoom · hjkl / arrows pan · ,/. maxiter · r reset · q quit · wheel to zoom. Click/tap to recenter — a central tap zooms in, an edge tap only pans (shift+click zooms out) — exact in the browser (taps map straight to the canvas), and native too where the terminal's cell size can be measured (under tmux, or a terminal that answers the xterm window-ops), with keyboard pan/zoom as the fallback. The browser page adds buttons for touch. The same program also runs in the browser as sixel in xterm.js (demos/mandelbrot-sixel, at /mandelbrot-sixel/ on Pages).

  The same .lg runs natively in any sixel-capable terminal (just play):

  

  A link or flags can set the starting view, e.g. ?x=-0.745&y=0.11&zoom=50 or just play mandelbrot --zoom 50 --x -0.745 --y 0.11 (also maxiter).

• pathtrace — a small progressive Monte Carlo path tracer that encodes its own PNG and shows it through the iTerm2 inline-image protocol, in xterm.js or natively in iTerm2. Each pass adds a sample per pixel, so the noise visibly settles. Controls: hjkl / arrows orbit · n next scene · r reset · q quit; --scene N / ?scene=N picks the starting scene. Headless runs render 32 samples/pixel and write out.png.

• ptcanvas — an allocation-free path tracer (scalars only, scene as flat arrays), ported from a JS original to test whether manual unboxing helps the let-go VM. Draws to a <canvas> in the browser (just serve ptcanvas); a non-TTY native run prints M paths/s.

• mandelbrot-aot — the mandelbrot escape kernel lowered from .lg to native Go with lg compile, driven by a Go terminal renderer: same output as the VM, about 72× faster.

Experiments

• aot — the mandelbrot kernel lowered to native Go through lg compile, against the VM and a hand-written Go port.
• microgpt — Karpathy's scalar GPT in one let-go file: train on the VM or natively, sample in the browser, and check numerical agreement with Python. Includes trained weights and reproducible timings.
• cueplay — intro-then-gapless-loop cue player on oto, with no cgo: the prototype for let-go's native audio binding (nooga/let-go#255).