Kurvengefahr

"Achtung, die Kurve!"

A browser-based CAM tool for pen plotters. Compose on a virtual bed - handwriting, text, vector shapes, imported SVG and DXF, traced photos, generative patterns, STL wireframes - preview the exact toolpath, and plot it: download G-code, or drive an AxiDraw or GRBL plotter live over USB. Everything runs client-side; nothing is uploaded.

Live app - installable PWA, works offline. Machine profiles cover Prusa printers with a pen attachment (or any G-code machine), AxiDraw-style EBB plotters, and GRBL machines, with presets for popular models.

Features

• Handwriting - a recurrent neural network (Graves' handwriting model) writes your text as real handwriting, not a font; consistent across words, reproducible per seed and neatness.
• Text - single-stroke engraving fonts, plus outline fonts you can fill with any hatch. Real typesetting: honest font metrics, kerning, word wrap, and justification.
• Shapes and paths - rectangles, ellipses, polygons, stars, Béziers, and freehand, with full node editing on the canvas; booleans, join, and weld turn several shapes into one editable path.
• Flood fill - click any enclosed region and every visible stroke acts as its boundary: the area becomes a regular hatch-filled path (holes included) you can edit like any other shape.
• Groups, clips, and effects - nest elements into containers, clip anything to a shape, and stack non-destructive distortions (roughen, smooth, wave, sketch, twist, bulge, taper, offset, hull) on any of it. The source stays editable throughout.
• Generative patterns - spirographs, L-system fractals, Truchet tiles, Voronoi diagrams, and flow fields, reproducible per seed.
• Logo programs - write turtle graphics in a real Logo (procedures, recursion, lists, seeded randomness) in an editor with live diagnostics and autocomplete; param declarations become inspector knobs, setpen/setpressure drive color and line weight from code, and programs save as reusable tools in the sidebar, importable and exportable. There is a tutorial and a full language reference.
• SVG and DXF import - files become native, editable paths at real-world size, colors mapped to pens; occluded fill regions are clipped away so they don't plot.
• Raster tracing - restyle a photo as strokes: outlines, centerlines, topographic levels, hatching, scanlines, a single TSP tour, flow fields, or spirals, with live preview.
• 3D models - import an STL, orbit it in an interactive preview, and it renders as a plottable wireframe of the model's feature edges: silhouettes, creases at a tunable angle, and boundaries, with hidden lines removed or kept and a perspective or orthographic camera.
• Hatch fills - a pen can't lay solid ink, so closed shapes fill with lines, rings, one-line Fermat spirals, Hilbert curves, mazes, and friends, at an adjustable density.
• Made for pens - a pen per element with color-grouped output and swap pauses, pressure as line weight (mapped to Z on spring-loaded holders), dashed strokes, travel-optimized ordering, a registration pause to line up the paper, and a scrubbable preview of the exact toolpath.
• Plot it - download G-code, send it to a PrusaLink printer with the companion Bridge extension, or plot live over Web Serial with pause/resume and a moving playhead - AxiDraw-style machines and GRBL 1.1 plotters (Z-axis or servo pen, optional homing) alike. Artwork also exports as SVG, PNG, or PDF, and prints at true physical scale for a paper proof.
• A real editor - autosaved multi-document tabs with cross-tab sync, undo/redo that survives a refresh, an elements tree, a command palette, clipboard across tabs, light/dark themes.
• Share a link - turn a document into a link that opens a read-only view of that snapshot, with an "Edit a copy" action to keep editing. The document is encrypted in your browser before upload; the key rides in the link itself and never reaches the server. Self-hosters can run their own share service or simply build without one.

The docs are the full manual: the editor, every element type, effects, plotting and export, sharing, machine profiles, the Logo tutorial and reference, plus the .kgz file format and the browser API for userscripts and headless tooling.

How it works

Every mark - handwriting, a shape, an imported path, a traced image - reduces to the same thing: a list of pen-down polylines in millimeters. That representation flows through one pipeline (place on the page, clip to the reachable area, optimize stroke order, then emit G-code or plan machine motion), so adding a new input type never touches the machinery downstream.

The app is client-only React, but all the geometry - the handwriting model, font and text layout, shape and path math, polygon booleans, SVG and DXF parsing, occlusion, image tracing, generative patterns, the Logo interpreter, clipping, and path optimization - is Rust compiled to WebAssembly (the kg_core crate). The handwriting model, image tracing, and Logo programs run in Web Workers so the UI stays responsive.

Building

npm install
npm run dev        # builds the wasm crate, then starts Vite
npm run build      # wasm + tsc + vite build

Requires the Rust wasm32-unknown-unknown target and wasm-pack. After changing crate/, rebuild with npm run build:wasm. The Rust crate has tests (cargo test), including a NumPy reference that validates the handwriting model.

Sharing is optional: set VITE_SHARE_API_URL at build time to the base URL of a share service instance to enable it; leave it unset and the app builds with no share UI at all. For local development, docker compose -f share-api/dev/compose.yml up --build runs a Garage-backed share service that npm run dev targets automatically (via .env.development).

CI runs on every push to main; publishing to GitHub Pages at kurvengefahr.org is a manual workflow run.

Contributing and license

Bug reports and feature requests are the most valued contribution; code is welcome too - see CONTRIBUTING.md. Licensed under the GNU GPL v2.0 (GPL-2.0-only).