ease.ts

const { pow } = Math;
const { sqrt } = Math;
const { sin } = Math;
const { cos } = Math;
const { PI } = Math;
const c1 = 1.70158;
const c2 = c1 * 1.525;
const c3 = c1 + 1;
const c4 = (2 * PI) / 3;
const c5 = (2 * PI) / 4.5;

const bounceOut = (x: number) => {
  const n1 = 7.5625;
  const d1 = 2.75;
  if (x < 1 / d1) {
    return n1 * x * x;
  }
  if (x < 2 / d1) {
    return n1 * (x -= 1.5 / d1) * x + 0.75;
  }
  if (x < 2.5 / d1) {
    return n1 * (x -= 2.25 / d1) * x + 0.9375;
  }
  return n1 * (x -= 2.625 / d1) * x + 0.984375;
};

export const easeInQuad = (x: number) => x * x;

export const easeOutQuad = (x: number) => 1 - (1 - x) * (1 - x);

export const easeInOutQuad = (x: number) => (x < 0.5 ? 2 * x * x : 1 - pow(-2 * x + 2, 2) / 2);

export const easeInCubic = (x: number) => x * x * x;

export const easeOutCubic = (x: number) => 1 - pow(1 - x, 3);

export const easeInOutCubic = (x: number) => (x < 0.5 ? 4 * x * x * x : 1 - pow(-2 * x + 2, 3) / 2);

export const easeInQuart = (x: number) => x * x * x * x;

export const easeOutQuart = (x: number) => 1 - pow(1 - x, 4);

export const easeInOutQuart = (
  x: number,
) => (x < 0.5 ? 8 * x * x * x * x : 1 - pow(-2 * x + 2, 4) / 2);

export const easeInQuint = (x: number) => x * x * x * x * x;

export const easeOutQuint = (x: number) => 1 - pow(1 - x, 5);

export const easeInOutQuint = (
  x: number,
) => (x < 0.5 ? 16 * x * x * x * x * x : 1 - pow(-2 * x + 2, 5) / 2);

export const easeInSine = (x: number) => 1 - cos((x * PI) / 2);

export const easeOutSine = (x: number) => sin((x * PI) / 2);

export const easeInOutSine = (x: number) => -(cos(PI * x) - 1) / 2;

export const easeInExpo = (x: number) => (x === 0 ? 0 : pow(2, 10 * x - 10));

export const easeOutExpo = (x: number) => (x === 1 ? 1 : 1 - pow(2, -10 * x));

export const easeInOutExpo = (x: number) => {
  if (x === 0) {
    return 0;
  }
  if (x === 1) {
    return 1;
  }
  return x < 0.5 ? pow(2, 20 * x - 10) / 2 : (2 - pow(2, -20 * x + 10)) / 2;
};

export const easeInCirc = (x: number) => 1 - sqrt(1 - pow(x, 2));

export const easeOutCirc = (x: number) => sqrt(1 - pow(x - 1, 2));

export const easeInOutCirc = (
  x: number,
) => (x < 0.5 ? (1 - sqrt(1 - pow(2 * x, 2))) / 2 : (sqrt(1 - pow(-2 * x + 2, 2)) + 1) / 2);

export const easeInBack = (x: number) => c3 * x * x * x - c1 * x * x;

export const easeOutBack = (x: number) => 1 + c3 * pow(x - 1, 3) + c1 * pow(x - 1, 2);

export const easeInOutBack = (
  x: number,
) => (x < 0.5
  ? (pow(2 * x, 2) * ((c2 + 1) * 2 * x - c2)) / 2
  : (pow(2 * x - 2, 2) * ((c2 + 1) * (x * 2 - 2) + c2) + 2) / 2);

export const easeInElastic = (x: number) => {
  if (x === 0) {
    return 0;
  }
  if (x === 1) {
    return 1;
  }
  return -pow(2, 10 * x - 10) * sin((x * 10 - 10.75) * c4);
};

export const easeOutElastic = (x: number) => {
  if (x === 0) {
    return 0;
  }
  if (x === 1) {
    return 1;
  }
  return pow(2, -10 * x) * sin((x * 10 - 0.75) * c4) + 1;
};

export const easeInOutElastic = (x: number) => {
  if (x === 0) {
    return 0;
  }
  if (x === 1) {
    return 1;
  }
  return x < 0.5
    ? -(pow(2, 20 * x - 10) * sin((20 * x - 11.125) * c5)) / 2
    : (pow(2, -20 * x + 10) * sin((20 * x - 11.125) * c5)) / 2 + 1;
};

export const easeInBounce = (x: number) => 1 - bounceOut(1 - x);

export const easeInOutBounce = (
  x: number,
) => (x < 0.5 ? (1 - bounceOut(1 - 2 * x)) / 2 : (1 + bounceOut(2 * x - 1)) / 2);