Engine

The 2D drafting engine: AutoCAD's commands, prompts, keywords and object snaps, on a canvas or headless.

The 2D drafting engine behind MellowCAD, in TypeScript and with no framework. It works the way AutoCAD does — the same commands and aliases, the same prompts and keywords, object snaps, Ortho, Polar, grips, undo — so someone who drafts in AutoCAD every day can draw with it from muscle memory.

Give it a <canvas> and it draws, takes the mouse and the keyboard, and runs commands. Give it nothing and it runs headless, in Node, on a server or in a test.

npm install @mellowcad/engine

It is ESM only and ships its TypeScript declarations.

Quick start

A canvas with a size, and a line under it for the prompt:

<canvas  id="drawing"  style="display: block; width: 100%; height: 480px"></canvas><output id="prompt"></output>

import { CadEngine, createMemoryDrawingStore } from "@mellowcad/engine"
const canvas = document.querySelector<HTMLCanvasElement>("#drawing")!const prompt = document.querySelector<HTMLOutputElement>("#prompt")!
const engine = new CadEngine(canvas, { store: createMemoryDrawingStore() })
engine.subscribe(() => {  const { commandLine, dynamicInput } = engine.getState()  const typed =    dynamicInput?.fields.find((field) => field.active)?.value ??    commandLine.buffer  prompt.textContent = `${commandLine.prompt} ${typed}`})
engine.runCommand("LINE")

Click on the canvas, type 100, press Enter, click again, press Escape: that is AutoCAD's LINE. Type C and Enter at the Command prompt for a circle, U to undo it. The engine does the rest:

it sizes the canvas's pixels to its CSS box and the screen's pixel ratio, and follows it when the box changes;
it takes the pointer, the wheel and the keys once the canvas is clicked or focused;
it redraws when something changes, and tells the page through subscribe.

Call engine.dispose() when the canvas goes away.

What the engine does, and what it leaves to you

The engine draws the drawing area: the objects, and what AutoCAD draws over them — the crosshair, snap markers, tracking paths, grips, the selection and the tooltips at the cursor.

Everything around it is yours: the command line, toolbars, the status bar, palettes, dialogs and menus. The engine's state says what each one shows, in the user's language, and its methods do what each control does. You can build that chrome yourself, or take it ready-made:

@mellowcad/react: the canvas as a React component, the state as React state, and the wiring of the fields AutoCAD users type into;
@mellowcad/editor: the whole editor, as on mellowcad.com/draw.

Guides

Guide	What it covers
How the engine works	Commands, the drawing, undo, the state, the scene, and how they fit
Building a host	The canvas, focus and keys, the command line, dynamic input and the chrome
Drawings and files	Autosave, the drawing file, open and save, the clipboard, previews, SVG
Without a browser	`CadDriver`: scripts, tests and rendering on a server
Languages	Spanish and Arabic, rewording a few words, a language of your own
API reference	Every export, with its signature and its documentation

What each command does, with its prompts and options, is in the user's command reference.

Entry points

Import	What
`@mellowcad/engine`	The engine; English is built in
`@mellowcad/engine/locales/<tag>`	One language each: `en`, `es`, `ar`, `pt-BR` (exported as `ptBR`, in progress)

No other path is public. The package has no import-time side effects and ships one module per source file, so a bundler keeps only what a page uses, and a language costs nothing until it is imported.

Versioning

The engine follows semantic versioning. What it promises is what the API reference lists — every export, its signature and every type it reaches — and the shape of a language's catalog (EngineLocale). While the version is 0.x, a breaking change bumps the minor version (0.1 → 0.2), so npm's default range (^0.1.2) never takes one. Each release is in the changelog.

License

MIT (LICENSE): the code, not the MellowCAD name or logo.

AutoCAD is a registered trademark of Autodesk, Inc. MellowCAD is an independent project, not affiliated with or endorsed by Autodesk; AutoCAD is named only to describe what it is compatible with.