ashlar-motion

Headless motion maths for ashlar apps: where a value is at time t, and when it stops.

• Spring: closed-form damped springs set by (duration, bounce) (SwiftUI-compatible), exact in all three damping regimes, with a settle_time that is never early. Constructors clamp; nothing panics on NaN or infinite input.
• Curve: a spring, a cubic-bezier tween (Easing), momentum decay, or an instant jump.
• Animated<T>: a value you own. Retargeting mid-flight starts from the current position and velocity, so motion never jumps; a settled value is exactly its target. Works for f32, [f32; 2], Edges (rectangles by edge), and colours (premultiplied OKLab).
• Class and MotionPrefs: settle thresholds per kind of value and the reduced-motion policy (spatial values jump, opacity and colour fade briefly, gestures are untouched; effects never overshoot).
• tokens: named enter/exit spring pairs (SNAP, SETTLE, REFLOW…), exits a little shorter.
• color: linear Rgba, OKLab/OKLCH with gamut mapping, premultiplied mixing, sRGB bytes, WCAG contrast.
• gesture: a velocity tracker, fling projection and rubber-band resistance.

use ashlar_motion::{Animated, Class, MotionPrefs, tokens};

let mut x = Animated::new(0.0_f32, Class::Spatial);
x.animate_to(120.0, tokens::SNAP.enter.into(), now, &MotionPrefs::DEFAULT);
let shown = x.sample(now); // draw this; ask for another frame while !x.is_settled(now)

No dependencies, no allocation, no UI; builds for wasm32-unknown-unknown. The egui integration lives in ashlar-ui.

Part of ashlar, a lightweight application framework for Rust powered by egui. Licensed under the BSD 3-Clause License.