@hemicycle/core

Core layout engine for rendering parliament-style hemicycle seat charts.

@hemicycle/core computes the geometry for concentric arc seating arrangements — the kind used to visualize parliaments, assemblies, and any fan-shaped seat layout. Given a seat count and a few sizing parameters, it returns precise coordinates and indices for every seat, ready to render in SVG, Canvas, or any visualization library.

Features

• Flexible seat distribution — automatically distributes seats across rows proportional to arc length, or accepts a custom seatsPerRow array
• Aisles support — insert radial (angular) aisles and/or arc (concentric) aisles to create realistic chamber layouts
• Mirroring — horizontally flip the layout for alternative orientations
• Radial & row ordering — choose between row-major or radial-major seat indexing to match your data
• Data mapping — attach arbitrary data objects to seats by index or by (rowIndex, seatIndex) coordinate
• TypeScript-first — fully typed with ESM and CJS dual output
• Zero runtime dependencies on rendering libraries — outputs plain coordinate objects

Installation

npm install @hemicycle/core

Requires Node.js ≥ 18.

Quick Start

import { Hemicycle } from "@hemicycle/core";

// 1. Create an engine with your layout config
const hemicycle = new Hemicycle({
  rows: 7,
  totalSeats: 577, // e.g. French Assemblée nationale
  innerRadius: 40,
  outerRadius: 95,
  totalAngle: 180,
});

// 2. Get the computed seat positions
const layout = hemicycle.getSeatsLayout();

// Each seat contains coordinates and indices
// layout[0] → { idx, radialIdx, rowIndex, seatIndex, x, y, innerR, outerR, angle1Rad, angle2Rad }

Support

• Issues: GitHub Issues
• Source: github.com/GabrielVidal1/hemicycle

Maintainer

Gabriel Vidal — gvidalayrinhac@gmail.com

License

MIT