Package: Pretext

Pretext is the backend-agnostic engine package. It owns preparation, segmentation, bidi handling, break analysis, and the line-fitting APIs that the rest of the repository builds on.

Install it when

you want deterministic text preparation and line layout without taking a UI framework dependency
you are building your own control, canvas, export pipeline, or layout engine
you want to pair the core engine with one or more first-party or custom backends

Package role

Pretext owns:

PretextLayout
prepared-text creation with Prepare and PrepareWithSegments
aggregate layout with Layout
materialized lines with LayoutWithLines
streamed layout with LayoutNextLine, LayoutNextLineRange, and WalkLineRanges
rich-inline preparation and streamed materialization
backend discovery and explicit backend override

What it does not own

Pretext does not draw text. Your host still owns:

painting and antialiasing
baseline placement
line-height policy
hit testing and selection
scroll/view invalidation

Package relationship

Pretext depends on Pretext.Contracts and expects a text-measurement factory to be available at runtime.

Typical pairings:

Pretext + Pretext.DirectWrite for Windows-native hosts
Pretext + Pretext.FreeType for Linux-native hosts
Pretext + Pretext.CoreText for macOS-native hosts
Pretext + Pretext.SkiaSharp for portable SkiaSharp hosts or as a fallback

Key runtime behavior

If you do not call PretextLayout.SetTextMeasurerFactory(...), the engine discovers factories from referenced Pretext*.dll assemblies, filters them by IsSupported, then picks the supported factory with the highest Priority.

That means:

host-native backends win on their matching OS
Pretext.SkiaSharp stays available as the low-priority portable fallback
custom or test backends can still be selected explicitly