easingsFunctions.ts

type EasingFunction = (progress: number) => number;

interface EasingDictionary {
	[easing: string]: EasingFunction;
}

const pow = Math.pow;
const sqrt = Math.sqrt;
const sin = Math.sin;
const cos = Math.cos;
const PI = Math.PI;
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: EasingFunction = function (x) {
	const n1 = 7.5625;
	const d1 = 2.75;

	if (x < 1 / d1) {
		return n1 * x * x;
	} else if (x < 2 / d1) {
		return n1 * (x -= 1.5 / d1) * x + 0.75;
	} else if (x < 2.5 / d1) {
		return n1 * (x -= 2.25 / d1) * x + 0.9375;
	} else {
		return n1 * (x -= 2.625 / d1) * x + 0.984375;
	}
};

const easingsFunctions: EasingDictionary = {
	linear: (x) => x,
	easeInQuad: function (x) {
		return x * x;
	},
	easeOutQuad: function (x) {
		return 1 - (1 - x) * (1 - x);
	},
	easeInOutQuad: function (x) {
		return x < 0.5 ? 2 * x * x : 1 - pow(-2 * x + 2, 2) / 2;
	},
	easeInCubic: function (x) {
		return x * x * x;
	},
	easeOutCubic: function (x) {
		return 1 - pow(1 - x, 3);
	},
	easeInOutCubic: function (x) {
		return x < 0.5 ? 4 * x * x * x : 1 - pow(-2 * x + 2, 3) / 2;
	},
	easeInQuart: function (x) {
		return x * x * x * x;
	},
	easeOutQuart: function (x) {
		return 1 - pow(1 - x, 4);
	},
	easeInOutQuart: function (x) {
		return x < 0.5 ? 8 * x * x * x * x : 1 - pow(-2 * x + 2, 4) / 2;
	},
	easeInQuint: function (x) {
		return x * x * x * x * x;
	},
	easeOutQuint: function (x) {
		return 1 - pow(1 - x, 5);
	},
	easeInOutQuint: function (x) {
		return x < 0.5 ? 16 * x * x * x * x * x : 1 - pow(-2 * x + 2, 5) / 2;
	},
	easeInSine: function (x) {
		return 1 - cos((x * PI) / 2);
	},
	easeOutSine: function (x) {
		return sin((x * PI) / 2);
	},
	easeInOutSine: function (x) {
		return -(cos(PI * x) - 1) / 2;
	},
	easeInExpo: function (x) {
		return x === 0 ? 0 : pow(2, 10 * x - 10);
	},
	easeOutExpo: function (x) {
		return x === 1 ? 1 : 1 - pow(2, -10 * x);
	},
	easeInOutExpo: function (x) {
		return x === 0
			? 0
			: x === 1
			? 1
			: x < 0.5
			? pow(2, 20 * x - 10) / 2
			: (2 - pow(2, -20 * x + 10)) / 2;
	},
	easeInCirc: function (x) {
		return 1 - sqrt(1 - pow(x, 2));
	},
	easeOutCirc: function (x) {
		return sqrt(1 - pow(x - 1, 2));
	},
	easeInOutCirc: function (x) {
		return x < 0.5
			? (1 - sqrt(1 - pow(2 * x, 2))) / 2
			: (sqrt(1 - pow(-2 * x + 2, 2)) + 1) / 2;
	},
	easeInBack: function (x) {
		return c3 * x * x * x - c1 * x * x;
	},
	easeOutBack: function (x) {
		return 1 + c3 * pow(x - 1, 3) + c1 * pow(x - 1, 2);
	},
	easeInOutBack: function (x) {
		return 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;
	},
	easeInElastic: function (x) {
		return x === 0
			? 0
			: x === 1
			? 1
			: -pow(2, 10 * x - 10) * sin((x * 10 - 10.75) * c4);
	},
	easeOutElastic: function (x) {
		return x === 0
			? 0
			: x === 1
			? 1
			: pow(2, -10 * x) * sin((x * 10 - 0.75) * c4) + 1;
	},
	easeInOutElastic: function (x) {
		return x === 0
			? 0
			: x === 1
			? 1
			: 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;
	},
	easeInBounce: function (x) {
		return 1 - bounceOut(1 - x);
	},
	easeOutBounce: bounceOut,
	easeInOutBounce: function (x) {
		return x < 0.5
			? (1 - bounceOut(1 - 2 * x)) / 2
			: (1 + bounceOut(2 * x - 1)) / 2;
	},
};

export default easingsFunctions;