Pretext

Pretext is a deterministic text preparation and line-layout engine with pluggable text-measurement backends. It prepares text once, exposes segment and break metadata, and lets you compute line counts, materialized lines, or streamed line geometry without relying on control reflow.

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What This Library Does

Prepare once, reuse often

`Prepare` and `PrepareWithSegments` precompute widths, break opportunities, and whitespace behavior so repeated layout passes stay cheap.

Batch and streaming layout

Use `Layout` for quick metrics, `LayoutWithLines` for materialized lines, or `LayoutNextLine` and `WalkLineRanges` for incremental custom layout engines.

Real text behavior

The engine handles grapheme-aware breaks, discretionary hyphens, tabs, preserved whitespace, bidi text, and locale-aware segmentation on desktop targets.

Scope

Pretext is a layout engine, not a text renderer. It answers questions such as:

  • how many lines fit in a given width
  • what text ends up on each line
  • where the next line should start for a custom flow algorithm
  • which whitespace, punctuation, and discretionary break opportunities should stay visible

You still own:

  • drawing the text in your host UI
  • choosing the line height and baseline policy
  • arranging lines into columns, cards, obstacles, or custom panels
  • invalidating or repainting your UI when layout inputs change

Documentation Map

Getting Started

Install the packages, learn the font string contract, and build the first useful `Prepare` + `Layout` flow.

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Concepts

Understand the prepared-text lifecycle, whitespace modes, break kinds, locale-aware segmentation, bidi, and line fitting.

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Guides

Integrate `Pretext` into Uno, native Windows/Linux/macOS hosts, or any SkiaSharp-based renderer, then reuse the shared sample-host patterns for shrinkwrap, editorial, and obstacle-aware layouts.

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Reference

Browse every public type and operation, the package-by-package reference pages, platform notes, and repository structure.

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Repository Layout

Path Purpose
src/Pretext The packable library project containing PretextLayout and the text preparation/layout pipeline.
src/Pretext.Contracts Shared backend contracts and first-party font-string parsing helpers.
src/Pretext.Layout Platform-neutral wrap and obstacle-layout helpers built on top of Pretext.
src/Pretext.DirectWrite Windows DirectWrite measurement backend.
src/Pretext.FreeType Linux FreeType + Fontconfig measurement backend.
src/Pretext.CoreText macOS CoreText measurement backend.
src/Pretext.SkiaSharp Portable SkiaSharp measurement backend and fallback.
src/Pretext.Uno The source for the Pretext.Uno package, with Uno-specific reusable controls and render scheduling helpers.
tests/Pretext.Uno.Tests Deterministic parity tests for whitespace handling, break behavior, bidi text, and line walking.
samples/PretextSamples.Shared Shared sample catalog, assets, and data/model layer reused by the sample hosts.
samples/PretextSamples.Uno A Uno sample host with layout demos including bubbles, masonry, editorial, and justification views.
samples/PretextSamples.MacOS A native AppKit sample host on net10.0-macos using Pretext.CoreText.

Published Packages

Package Purpose
Pretext Backend-agnostic text preparation and layout engine.
Pretext.Contracts Public backend contracts and shared font parsing.
Pretext.Layout Platform-neutral wrap and obstacle-layout helpers.
Pretext.DirectWrite Windows-native DirectWrite backend.
Pretext.FreeType Linux-native FreeType + Fontconfig backend.
Pretext.CoreText macOS-native CoreText backend.
Pretext.SkiaSharp Portable SkiaSharp backend and fallback.
Pretext.Uno Uno-specific controls layered on top of Pretext.

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