pretext

Native Unicode paragraph preparation and layout for the Pretext Rust workspace.

pretext owns font discovery, shaping, bidi resolution, whitespace handling, line breaking, paragraph measurement, and reusable layout caches. It is renderer-agnostic: use it directly for measurement or pair it with pretext-egui for painting in egui.

Install

[dependencies]
pretext = "0.1.0"

Basic paragraph layout

use pretext::{
    PretextEngine, PretextParagraphOptions, PretextStyle, WhiteSpaceMode,
};

let engine = PretextEngine::builder().build();
let style = PretextStyle {
    families: vec!["Times New Roman".to_owned(), "Arial".to_owned()],
    size_px: 18.0,
    weight: 400,
    italic: false,
};
let options = PretextParagraphOptions {
    white_space: WhiteSpaceMode::Normal,
    ..Default::default()
};

let prepared = engine.prepare_paragraph("Hello, pretext.", &style, &options);
let metrics = prepared.measure(&engine, 320.0, 24.0);
let layout = prepared.layout(&engine, 320.0, 24.0);
let geometry = prepared.measure_line_geometry(&engine, 320.0);
let natural_width = prepared.measure_natural_width(&engine);

assert!(metrics.line_count >= 1);
assert_eq!(layout.line_count, metrics.line_count);
assert_eq!(geometry.line_count, layout.line_count);
assert!(natural_width >= geometry.max_line_width);

Font setup

By default, PretextEngine::builder().build() includes system fonts. For deterministic output, provide font bytes and disable system font fallback:

use pretext::PretextEngine;

let font_data = vec![std::fs::read("NotoSans-Regular.ttf")?];
let engine = PretextEngine::builder()
    .with_font_data(font_data)
    .include_system_fonts(false)
    .build();
# Ok::<(), std::io::Error>(())

Lower-level APIs

• Use root exports such as PretextEngine, PretextStyle, and PretextParagraphOptions for the stable path.
• Use pretext::rich_inline for inline-only mixed-style flow with atomic placeholders.
• Use pretext::advanced for cursor-driven line continuation, glyph runs, and custom renderers.