railway-drawio

name	railway-drawio
description	Generate top-down schematic railway track diagrams as draw.io (.drawio) XML files. LEGO/BRIO-style snap-together pieces using turtle graphics — straight, bend, wide bend, turnout, merger. Use when the user asks to create railway track diagrams, causal flow topology diagrams with track metaphors, or draw.io files with railway-style layouts.

Railway Track — draw.io Generation

Generate top-down schematic railway track diagrams as .drawio XML files with LEGO/BRIO-style building pieces that snap together via turtle graphics.

See README.md in this folder for full component specifications, dimensions, and derived constants.

Engine Location

.cursor/skills/railway-drawio/_railway-engine.js

Building Pieces

Piece	API	Length	Description
Straight	t.straight()	200px	Standard straight track
Half Straight	t.halfStraight()	100px	Half-length straight
Bend	t.bendRight() / t.bendLeft()	45° arc, R=283	Standard curve (dx=200, grid-aligned)
Wide Bend	t.wideBendRight() / t.wideBendLeft()	45° arc, R=449	Outer oval curve
Turnout	t.turnoutLeft(fn) / t.turnoutRight(fn)	400px	S-curve switch — both exits parallel, 166px offset
Merger	t.mergerLeft() / t.mergerRight()	400px	Reverse S-curve — branch merges into main
Label	t.label(text)	—	Text label at current position

Key Geometry

• L = 200px — straight piece length
• R = 283px — bend radius (L/sin 45°), makes bend dx = L
• GAP = 166px — track-to-track offset from turnout S-curve
• R_WIDE = 449px — wide bend radius (R + GAP), for outer ovals
• 4 bends = 180° half-circle; 4 wide bends = wider half-circle matching GAP

Turtle Graphics

Each piece's exit defines the next piece's entry. No manual coordinate math.

const r = require('./_railway-engine');
r.reset();
const t = r.track(x, y, heading);  // heading in radians (0 = right)
t.straight().bendRight().straight();
r.writeXml('output.drawio');

Turnout branches receive a new TrackBuilder in the callback:

t.turnoutLeft(branch => {
  branch.straight().wideBendRight().wideBendRight()
    .straight().wideBendRight().wideBendRight().straight();
});

Examples

• example-race.js — double-oval race track with inner/outer ovals connected by a turnout and merger
• example-race.drawio — generated output (open in draw.io)

Usage Pattern

1. Create a generator script in this folder (or require the engine from elsewhere)
2. Call r.reset(), build tracks with r.track(), call r.writeXml(path)
3. Open the .drawio file in draw.io to view