Project content and report anchors

Viewports and anchors solve different integration problems. A viewport projects content; an anchor reports geometry.

Project a larger child

use urushi::{
    Available, Projection, ProjectionBoundary, TextStyle, View, Viewport,
    resolve,
};

let view = View::viewport(
    Viewport::horizontal(Projection::new(2, ProjectionBoundary::Preserve)),
    View::text("abcdef", TextStyle::new()),
);
let resolved = resolve(&view, Available::size(3, 1))?;

assert_eq!(resolved.size().width(), 3);

Three-cell viewport at column 2

cde

Preserve uses the requested signed origin exactly, including blank space past an edge. Clamp moves it so the child fills the viewport when possible. Choose horizontal, vertical, or both-axis projection. Every projected axis requires a finite allocation.

The application owns scroll state and changes the projection origin.

At an origin near the right edge, the boundary policy is the only difference:

let preserve = Viewport::horizontal(Projection::new(5, ProjectionBoundary::Preserve));
let clamp = Viewport::horizontal(Projection::new(5, ProjectionBoundary::Clamp));

Three-cell projection of abcdef

Preserve: |f··|  (· is a blank cell beyond the child)
Clamp:    |def|

Report a resolved region

use urushi::{Available, BlockStyle, Length, View, resolve};

let chart = View::anchor_block(
    "chart",
    BlockStyle::new().width(Length::Cells(20)).height(Length::Cells(8)),
    View::empty(),
);
let resolved = resolve(&chart, Available::NONE)?;
let region = resolved.anchor("chart").expect("chart anchor");

assert_eq!((region.width(), region.height()), (20, 8));

Resolved anchor

key=chart  x=0  y=0  width=20  height=8  visible=20×8

anchor_block behaves exactly like a block and reports its content rectangle. titled_anchor_block adds a border title. anchor reports only a zero-size origin, which is useful for cursor placement.

Anchors do not add focus, widget, or rendering semantics. The caller interprets the opaque key and hands the rectangle to the foreign renderer.