ZigMachine

A Fantasy Console (or Fantasy Computer, not sure) written in Zig and running in the browser as a Web Assembly binary. The ZigMachine is dedicated to provide a fun sandbox to learn how to code oldskool effects as no advanced features are provided, only the basics of the 80s computers and video game consoles.

This project is inspired by WAB and CODEF by my friend NoNameNo who... already more than 10 years ago... provided a way to code oldskool effects in the browser without Flash but only HTML5 and javascript. Time to go one step further. 0% Flash, 0% HTML, 0% Javascript, only Zig!

Screenshots and live version below!

Live version

Live website with the latest build: ZigMachine (Click on the + and - buttons to change channels!)

The machine is sealed

The big idea, and the thing that makes this more than a demo loop: the hardware is a separate binary from the software running on it.

The browser loads four wasm modules that share ONE WebAssembly.Memory:

module	thread	what it is
machine-video.wasm	main	the sealed video hardware — shifter, borders, blitter
machine-audio.wasm	worklet	the sealed sound hardware — YM2149 + 4 sample channels
demo.wasm	main	your code: the cart currently in the slot
demo-audio.wasm	worklet	your players, driving the sound chips

They talk through a memory-mapped register ABI (machine/sdk/), exactly like poking hardware registers on a real machine. The app cannot reach inside the hardware, and the hardware cannot see the app — so the machine can be handed to someone else and still behave.

A fifth module, rom.wasm, is the system software (GEM — a desktop, windows, dialogs and a file manager), which carts call through a flat handle-based ABI rather than linking it.

The host JavaScript is deliberately dumb: it is glass and a speaker. It blits the framebuffer, forwards input, and plays the file a scene asks for. Everything else happens in wasm.

Specs

The specs will keep evolving, but they try to match what I would have loved to get in the 80-90s:

Memory / CPU

• 7 MB of shared linear memory (112 pages of 64 KB), of which a cart gets a 2 MB window for its code, data and stack — and the build fails if it overruns.
• CPU frequency is whatever your browser's WebAssembly can do. So, pretty (too...) fast.
• Assets can be ZX0-packed and depacked into free cart RAM at run time (~38% of raw across the whole shelf).

Graphics

• 1 physical RGBA framebuffer, 400x280 with borders, 320x200 visible.
• 4 logical indexed framebuffers (each pixel an entry in a 256-colour RGBA palette), composited as stacked layers — palette entry alpha 0 is transparent.
• 1 palette of 256 colours (RGBA, 8 bits per component) per logical framebuffer.
• Per-scanline (HBL) and per-frame (VBL) callbacks, per-plane and global — this is how you do copper bars.
• Overscan the honest way: there is no "fullscreen" flag. You open a border by flickering the resolution register from an HBL handler at exactly the right column, as on real hardware. Miss the column and you get garbage on that line.
• Blitter, hardware scrolling, and a copper helper for per-line palette tables.

Sound

• YM2149 PSG + 4 Paula-style sample channels, both sealed hardware.
• Players (the open half): ProTracker MOD, YM register dumps, raw PCM streaming off a disk, and SNDH — which runs the tune's own 68000 replay code on an emulated Motorola 68000 (Musashi), trapping its PSG writes to the sealed chip. The chip music is genuinely being played by the original driver.
• A scene just asks for a tune by name; the machine reclaims the sound chip when a program ends.

OS

• ZigOS, the open library layer: planes, palettes, HBL handlers, blitting, text.
• GEM in rom.wasm: a TOS-1.00-style desktop with windows, icons, dialogs, drag and drop, rename, and DESKTOP.INF.
• Programs live on floppies (.zmd) with a FAT and a bootable sector; GEM can launch one off the disk, and an app can quit back to the desktop.

Demo framework

Reusable oldskool effects: scrolltexts (with X/Y offset tables), 2D/3D starfields, 3D transforms, triangle/line/pixel drawing, sprites, bobs, fades, tile engines, parallax, and a clipped signed-coordinate blitter.

Any language, not just Zig

The seal is a wasm ABI, not a Zig API, so a cart can be written in anything that compiles to wasm. apps/c/ and apps/rust/ hold working carts — including a full cracktro port in C that opens the borders with the same resolution-flicker trick, driven entirely by register pokes and an exported HBL callback from C.

apps/zig/scenes/    the Zig scenes (one cart each)
apps/c/scenes/      C carts        apps/rust/   Rust carts
machine/            the sealed hardware + its SDK headers
rom/                system software (GEM)
libs/{zig,c,rust}/  reusable libraries (ZigOS lives in libs/zig)
docs/               the web root, the built wasm, and the API docs

The channels

34 screens ship as cartridges, most of them ports of Atari ST cracktros and demo screens from WAB's CODEF remakes. The + / − buttons on the monitor step through them like TV channels, with an analogue-noise transition; the boot menu lists them all.

Credit belongs to the originals. Each scene's source header names the demo, its coders, graphicians and musicians, and the author of the CODEF remake it was read from. CODEF itself is MIT-licensed. The music is from the SNDH archive. If you are one of the original authors and would rather your work were not here, please open an issue.

Docs

• docs/HW_API.md — the sealed hardware ABI
• docs/ZIGOS_API.md — the open library
• docs/HARDWARE_SPEC.md — design and status
• docs/FLOPPY_DISK.md — the disk format
• decisions.md — architecture decision records

Build

Prerequisites

• Zig 0.16.0
• Python 3 for the asset tools and the dev server
• Node (optional) for the headless test harnesses

The only target is wasm32-freestanding-musl.

./build.sh

That builds every module and cart, then runs the gate: RAM-window checks, the native tests, a repack of every floppy, and headless harnesses that drive the real machine end to end. Use it instead of a bare zig build — the failures it catches are the silent ones, like a cart overrunning its window and corrupting the video region instead of trapping.

Run

./serve.sh          # serves docs/ with no-store caching

Then open http://localhost:3333. Hard-reload (Ctrl+Shift+R) after a rebuild.

To boot straight into one cart: http://localhost:3333/?demo=demo-dbug.wasm

Screenshots

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