# Pretext — Fast Accurate Text Measurement and Layout Engine

> A high-performance TypeScript library for precise text measurement, shaping, and layout with sub-pixel accuracy across platforms.

## Install

Save as a script file and run:

# Pretext — Fast Accurate Text Measurement and Layout Engine

## Quick Use
```bash
npm install pretext
```
```typescript
import { measure, layout } from 'pretext';
const result = measure('Hello world', { font: 'Inter', size: 16 });
```

## Introduction
Pretext is a TypeScript library that solves the long-standing problem of accurate text measurement and layout in web and cross-platform applications. It provides pixel-perfect font metrics, line breaking, and text shaping that work consistently across browsers, Node.js, and native runtimes.

## What Pretext Does
- Measures text dimensions with sub-pixel accuracy across all platforms
- Performs correct Unicode-aware line breaking and word wrapping
- Handles complex text shaping including ligatures and kerning
- Provides a layout engine for multi-line text with alignment and truncation
- Works in browsers, Node.js, and WebAssembly environments

## Architecture Overview
Pretext uses a hybrid approach combining compiled font parsing with a platform-independent shaping engine. Font metrics are extracted at load time and cached for fast repeated measurements. The layout algorithm processes text in a streaming fashion, calculating break opportunities and glyph positions in a single pass for optimal performance.

## Self-Hosting & Configuration
- Install via npm, yarn, or pnpm as a dependency
- Import measurement and layout functions directly
- Provide font data as ArrayBuffer for precise metrics
- Configure default text properties like language and direction
- Tree-shakeable exports keep bundle size minimal

## Key Features
- Sub-pixel accurate text measurement consistent across platforms
- Full Unicode support including emoji, CJK, and bidirectional text
- Streaming layout algorithm handles large text blocks efficiently
- Zero native dependencies with optional WASM acceleration
- Comprehensive TypeScript types for all APIs

## Comparison with Similar Tools
- **Canvas measureText** — browser-only and imprecise; Pretext is cross-platform and exact
- **opentype.js** — focuses on font parsing; Pretext adds full layout and line breaking
- **Skia/CanvasKit** — heavy WASM binary; Pretext is lightweight and tree-shakeable
- **Yoga** — flexbox layout engine; Pretext focuses specifically on text measurement

## FAQ
**Q: Why not use the browser's native text measurement?**
A: Browser APIs produce inconsistent results across engines and lack features like line-break prediction needed for custom renderers.

**Q: Does it support variable fonts?**
A: Yes, Pretext reads OpenType variation axes and applies them during measurement.

**Q: What is the bundle size?**
A: The core measurement module is under 20 KB gzipped without WASM acceleration.

**Q: Can I use it in a canvas renderer?**
A: Yes, Pretext is designed to work with any rendering backend including HTML Canvas, WebGL, and SVG.

## Sources
- https://github.com/chenglou/pretext

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Source: https://tokrepo.com/en/workflows/asset-15d59a07
Author: Script Depot