Pretext Layout

Efficient Text Measurement & Layout

The Pretext Layout skill enables AI agents to integrate and debug high-performance multiline text measurement using the @chenglou/pretext library. It solves the common frontend performance bottleneck of "layout thrashing" by replacing slow DOM-based height probes with a fast, browser-native API approach.

What it does

This skill provides developers with a structured methodology for measuring text width and height without repeated DOM reflows. It supports high-level block height calculation for virtualization and low-level line-by-line geometry for custom Canvas or SVG rendering workflows. It handles complex edge cases including web fonts, emoji, and bidirectional text.

Supported Workflows

• Virtualization: Pre-measure list item heights for smooth scroll anchoring.
• Custom Rendering: Extract per-line ranges for manual drawing in Canvas or SVG.
• Responsive Design: Rapidly recalculate layouts during window resize events on the hot path.
• Debugging: Verify layout accuracy against real-world CSS styles and font loading states.

Why use this skill?

While a general AI can write basic JavaScript, this skill understands the specific lifecycle of the Pretext library—such as partitioning the expensive "prepare" phase from the lightweight "layout" phase. It ensures your agent correctly manages browser-only runtime constraints, font loading promises, and locale-specific white-space behaviors to prevent layout shifts and flickering.