Cursor (the pointer’s shape over a piece)

Authoring

use day::prelude::*;

link_row.cursor(Cursor::Pointer)
canvas.cursor(Cursor::Crosshair)
divider.cursor(Cursor::ColResize)

// Reactive: a tool palette, or a busy state. A constant, a Signal<Cursor>, or a closure.
let tool = Signal::new(Tool::Pen);
canvas.cursor(move || match tool.get() {
    Tool::Pen => Cursor::Crosshair,
    Tool::Pan => Cursor::Grab,
})

// A shape only one toolkit names, compiled only under that backend's feature.
#[cfg(feature = "appkit")]
trash.cursor(day::cursor::appkit::DISAPPEARING_ITEM)

// Anything a backend names that Day does not; ignored everywhere else.
row.cursor(Cursor::native("screenshot-cursor"))

Three rules:

• The cursor applies to the piece’s realized widget and its descendants, until a descendant sets its own. The nearest ancestor wins.
• Cursor::Default releases the piece to the platform rather than pinning an arrow, so a reactive cursor can hand back what it took.
• A shape is a pointer affordance and nothing else. A touch screen never shows one, and that is correct; an affordance that only a cursor reveals (a resize handle with no visible grip) should check capability(Cap::Cursor) before it counts on being discovered.

The vocabulary

Cursor is the CSS cursor vocabulary as an enum, plus one open variant. CSS names are the largest set any toolkit accepts as they are (GTK and the DOM take them verbatim), and every other toolkit’s set is a subset of them or maps onto them, so the enum is the contract and the table below is the only mapping written down.

Cursor::css_name() answers the keyword, and Cursor::NAMED walks the named set in order, which is what the Showcase’s Cursors page draws.

Per toolkit

The duty and its implementors are in duty-matrix.md; the capability answers in coverage-matrix.md. Both are generated and diffed in CI.

Shapes only one toolkit names

The day::cursor module carries them, one submodule per toolkit, each gated on the facade’s backend feature:

Each is a Cursor::Native value, so the named backend resolves it by its own table and any other ignores it. The gate is the point: a name only AppKit has is a compile error in a GTK build rather than a silent arrow, and the app wraps the use in the same #[cfg(feature = …)]. Cursor::native("…") is the ungated form for a name Day has no constant for.

How it reaches the widget

Decorate::cursor pushes an op that, after the inner piece is built, calls TreeOps::set_node_cursor, which forwards to Toolkit::set_cursor on the node’s handle. A reactive source also binds a closure that calls the same setter on change. The setter is idempotent and cheap on every toolkit, so there is no patch enum and no extra native node; a layout-only inner piece has no widget of its own and the op resolves the nearest realized node the way .selectable() does.

Trying it

The Showcase’s Cursors page (Controls group): every named shape as a tile to hover, one box whose shape follows a picker, a nested pair that shows the nearest ancestor winning, and the toolkit’s extras.

day launch -p macos-appkit --script dayscript/cursors.yaml

The walkthrough asserts the support row and drives the picker. The shape itself is the acceptance test, and it needs a person with a mouse: on macOS, in a browser, on the Android emulator with a mouse attached, and on the iPad simulator with pointer support enabled.