One browser API for emulated computers

Two paths to the GPU

The VMware driver (WineD3D or Mesa in the guest, slower), and API forwarding: a replacement d3d9.dll and opengl32.dll hand each call to the host, which reads vertex and texture data straight from guest memory. Direct3D 8 runs through d3d8to9.

What it needs

WebGL2 in a worker (OffscreenCanvas), SharedArrayBuffer, and a GPU. Without WebGL2 the tab says so and does not start.

Where it stops

The emulated CPU is the limit: about 250 to 280 MIPS, roughly a 300 to 500 MHz Pentium. Cube and volume textures, user clip planes, vertex blending and GLSL are not implemented, and a window overlapping the 3D window is drawn over.

import { Machine, loadProfile } from "webulator";

const m = await Machine.create({
  profile: await loadProfile("sheepshaver-g3bw-macos904.json"),
  snapshot: { url: "finder.webusnap" },   // skip the boot
  display: canvas,
});

m.input.pointer.moveTo(20, 8);    // guest pixels, lands exactly
m.input.pointer.button(0, true);
await m.input.type("Hello");

await m.pause();                   // the guest clock stops too
const state = await m.saveState();   // CPU, RAM, devices, disk writes
const writes = await m.disks.get("hd0").exportOverlay();

Equal capabilities, nothing optional

A capability enters the contract only once every core implements it and passes its tests. Hardware differences such as screen sizes and mouse buttons are reported as properties.

Snapshots restore to the same pixel

A saved state restores into a fresh worker, and its first frame matches the saved frame exactly.

A virtual clock

The guest sees no time pass while it is paused or stored, so a restored machine behaves like one that never stopped.

Disk fetches never stall the guest

Disk images load lazily over the network. While a chunk is on its way the guest keeps running, so the cursor keeps moving, as on a real machine with a busy disk.