easing function

easing.ts

type EaseFunc = (t: number) => number
interface Easing {
  [key: string]: EaseFunc
}
export const easing: Easing = {
  // no easing, no acceleration
  linear: (t) => t,

  // accelerating from zero velocity
  easeInQuad: (t) => t * t,

  // decelerating to zero velocity
  easeOutQuad: (t) => t * (2 - t),

  // acceleration until halfway, then deceleration
  easeInOutQuad: (t) => t < 0.5 ? 2 * t * t : -1 + (4 - 2 * t) * t,

  // accelerating from zero velocity
  easeInCubic: (t) => t * t * t,

  // decelerating to zero velocity
  easeOutCubic: (t) => (--t) * t * t + 1,

  // acceleration until halfway, then deceleration
  easeInOutCubic: (t) =>
    t < 0.5 ? 4 * t * t * t : (t - 1) * (2 * t - 2) * (2 * t - 2) + 1,

  // accelerating from zero velocity
  easeInQuart: (t) => t * t * t * t,

  // decelerating to zero velocity
  easeOutQuart: (t) => 1 - (--t) * t * t * t,

  // acceleration until halfway, then deceleration
  easeInOutQuart: (t) =>
    t < 0.5 ? 8 * t * t * t * t : 1 - 8 * (--t) * t * t * t,

  // accelerating from zero velocity
  easeInQuint: (t) => t * t * t * t * t,

  // decelerating to zero velocity
  easeOutQuint: (t) => 1 + (--t) * t * t * t * t,

  // acceleration until halfway, then deceleration
  easeInOutQuint: (t) =>
    t < 0.5 ? 16 * t * t * t * t * t : 1 + 16 * (--t) * t * t * t * t,
}