FerroUI Pretext Layout

Platform-neutral sizing and obstacle-aware flow for prepared text. Preparation and text measurement come from ferroui-pretext; this crate adds no renderer, native backend, thread, clock or file dependency.

APIs

API	Purpose
`PreparedTextMetrics::measure_max_line_width`	Measure genuinely unwrapped text, honoring preserved hard breaks.
`PreparedTextMetrics::collect_wrap_metrics`	Measure count, height and widest painted line without materializing strings.
`PreparedTextMetrics::find_tight_wrap_metrics`	Find the smallest integral width without increasing the original line count.
`ObstacleLayoutHelper::carve_text_line_slots`	Subtract overlapping intervals from an available horizontal line slot.
`ObstacleLayoutHelper::circle_interval_for_band`	Compute circle exclusion over an entire text band.
`ObstacleLayoutHelper::ellipse_interval_for_band`	Compute ellipse exclusion with independent radii and padding.
`ObstacleLayoutHelper::get_rect_intervals_for_band`	Select rectangle exclusions intersecting a text band.
`ObstacleLayoutHelper::pick_slot`	Select the widest slot, with an explicit tie direction.
`ColumnFlowLayout::layout_into_columns`	Flow text through ordered rectangular columns around rectangles and circles.

Coordinates and widths use the configured measurer's units. Circle x and y are its center. Band boundaries are half open: tangent obstacles do not block a row. Column flow uses one widest slot on each row; remaining text beyond the last column is not materialized.

use std::rc::Rc;
use ferroui_pretext::{DelegateTextMeasurerFactory, PrepareOptions, PretextLayout};
use ferroui_pretext_layout::{ColumnFlowLayout, RectObstacle};

# fn main() -> Result<(), Box<dyn std::error::Error>> {
// Use the native FerroUI adapter in a real application. This deterministic
// measurer keeps the example independent of installed fonts.
let engine = PretextLayout::new(Rc::new(DelegateTextMeasurerFactory::new(
    |text: &str, _: &str| text.chars().count() as f64 * 8.0,
)));
let prepared = engine.prepare_with_segments(
    "Prepare once and flow across multiple columns.",
    "16px Inter",
    PrepareOptions::default(),
)?;
let columns = [
    RectObstacle { x: 0.0, y: 0.0, width: 160.0, height: 40.0 },
    RectObstacle { x: 180.0, y: 0.0, width: 160.0, height: 40.0 },
];
let lines = ColumnFlowLayout::layout_into_columns(
    &prepared, &columns, &[], &[], 20.0, 20.0,
)?;
for line in lines {
    println!("{} at ({}, {})", line.text, line.x, line.y);
}
# Ok(())
# }

Source mapping and deliberate corrections

All four source files from Pretext.Layout are mapped one to one:

Source	Rust
`LayoutPrimitives.cs`	`layout_primitives.rs`
`PreparedTextMetrics.cs`	`prepared_text_metrics.rs`
`ObstacleLayoutHelper.cs`	`obstacle_layout_helper.rs`
`ColumnFlowLayout.cs`	`column_flow_layout.rs`

The source's IsExternalInit.cs polyfill is unnecessary in Rust. C# optional parameters are explicit Rust arguments. Plain data records have public fields and derived value equality; stateless classes retain associated functions.

This port corrects the following observed source defects:

No-fitting-slot selection returns None. The source's value-type FirstOrDefault() produced (0, 0) and consumed text in blocked rows.
Circle exclusion in column flow uses the entire row band, rather than its midpoint, so glyph rectangles do not overlap a circle near a row edge.
Maximum line width uses infinity rather than a magic 100_000 width.
Empty slot selection returns None rather than indexing an absent element.
Column flow rejects nonpositive/nonfinite line heights, invalid geometry and coordinates that cannot advance to another finite row. Tight-wrap search rejects invalid widths and bounds the search to exactly representable f64 integers. Both return LayoutError instead of looping indefinitely.
Columns with no possible slot (zero width, narrower than the minimum slot, too short, or completely covered by one rectangle) are skipped immediately, avoiding a row-by-row scan for tiny positive line heights.
Geometry helpers ignore degenerate/nonfinite blocked intervals, return no intersection for invalid shapes, and reject invalid base slots and padding.

See docs/porting/pretext.md in the repository for the complete port report. The upstream MIT notice is included in NOTICE.md.

ferroui-pretext-layout 0.4.0

FerroUI Pretext Layout

APIs

Source mapping and deliberate corrections