Easing

Named easing curves for palette fades, audio fades, and demo animation. Evaluate a curve with applyEasing, or interpolate number / Vector2i / Color32 / Rect2i values with interpolate.

Curve math matches RetroBlit by Martin Cietwierkowski (Ease class, Robert Penner's easing equations).

import { applyEasing, interpolate, Color32, Vector2i } from 'blit386';

const t = applyEasing(0.5, 'ease-in-out'); // 0..1 progress → eased value

const pos = interpolate('bounce-out', new Vector2i(0, -40), new Vector2i(0, 80), 0.7);
const tint = interpolate('cubic-out', Color32.white, Color32.green, 0.4);

Curves

EasingFunction is a string union. 'ease-in', 'ease-out', and 'ease-in-out' are the quadratic family (kept for existing palette and audio call sites).

Every curve returns 0 at t = 0 and 1 at t = 1. Values of t outside [0, 1] are not clamped. Back and elastic curves may overshoot outside [0, 1] for intermediate t.

applyEasing

import { applyEasing } from 'blit386';

const eased = applyEasing(0.5, 'cubic-in'); // 0.125

interpolate

Applies the curve to t, then interpolates from start to end.

• number - floating-point blend
• Vector2i / Rect2i - each component rounded to the nearest integer
• Color32 - each channel rounded and clamped to [0, 255]

import { interpolate, Rect2i } from 'blit386';

const bounds = interpolate('sine-in-out', new Rect2i(0, 0, 16, 16), new Rect2i(40, 20, 64, 48), 0.5);

API history

See also

Last updated on October 18, 2026