playable.js/src/tween/Ease.ts

A lightweight HTML5 game engine.

export class Ease {

	public static linear(t: number, b: number, c: number, d: number): number {
		return c * t / d + b;
	}

	public static easeInQuad(t: number, b: number, c: number, d: number): number {
		return c * (t /= d) * t + b;
	}

	public static easeOutQuad(t: number, b: number, c: number, d: number): number {
		return -c * (t /= d) * (t - 2) + b;
	}

	public static easeInOutQuad(t: number, b: number, c: number, d: number): number {
		if ((t /= d / 2) < 1) return c / 2 * t * t + b;
		return -c / 2 * ((--t) * (t - 2) - 1) + b;
	}

	public static easeInCubic(t: number, b: number, c: number, d: number): number {
		return c * (t /= d) * t * t + b;
	}

	public static easeOutCubic(t: number, b: number, c: number, d: number): number {
		return c * ((t = t / d - 1) * t * t + 1) + b;
	}

	public static easeInOutCubic(t: number, b: number, c: number, d: number): number {
		if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
		return c / 2 * ((t -= 2) * t * t + 2) + b;
	}

	public static easeInQuart(t: number, b: number, c: number, d: number): number {
		return c * (t /= d) * t * t * t + b;
	}

	public static easeOutQuart(t: number, b: number, c: number, d: number): number {
		return -c * ((t = t / d - 1) * t * t * t - 1) + b;
	}

	public static easeInOutQuart(t: number, b: number, c: number, d: number): number {
		if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;
		return -c / 2 * ((t -= 2) * t * t * t - 2) + b;
	}

	public static easeInQuint(t: number, b: number, c: number, d: number): number {
		return c * (t /= d) * t * t * t * t + b;
	}

	public static easeOutQuint(t: number, b: number, c: number, d: number): number {
		return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
	}

	public static easeInOutQuint(t: number, b: number, c: number, d: number): number {
		if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;
		return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
	}

	public static easeInSine(t: number, b: number, c: number, d: number): number {
		return (t === d) ? b + c : -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
	}

	public static easeOutSine(t: number, b: number, c: number, d: number): number {
		return c * Math.sin(t / d * (Math.PI / 2)) + b;
	}

	public static easeInOutSine(t: number, b: number, c: number, d: number): number {
		return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
	}

	public static easeInExpo(t: number, b: number, c: number, d: number): number {
		return (t === 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;
	}

	public static easeOutExpo(t: number, b: number, c: number, d: number): number {
		return (t === d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;
	}

	public static easeInOutExpo(t: number, b: number, c: number, d: number): number {
		if (t === 0) return b;
		if (t === d) return b + c;
		if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
		return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
	}

	public static easeInCirc(t: number, b: number, c: number, d: number): number {
		return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
	}

	public static easeOutCirc(t: number, b: number, c: number, d: number): number {
		return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
	}

	public static easeInOutCirc(t: number, b: number, c: number, d: number): number {
		if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
		return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
	}

	public static easeInElastic(t: number, b: number, c: number, d: number): number {
		let s = 1.70158;
		let p = 0;
		let a = c;
		if (t === 0) return b;
		if ((t /= d) === 1) return b + c;
		if (!p) p = d * 0.3;
		if (a < Math.abs(c)) {
			a = c;
			s = p / 4;
		} else {
			s = p / (2 * Math.PI) * Math.asin(c / a);
		}
		return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
	}

	public static easeOutElastic(t: number, b: number, c: number, d: number): number {
		let s = 1.70158;
		let p = 0;
		let a = c;
		if (t === 0) return b;
		if ((t /= d) === 1) return b + c;
		if (!p) p = d * 0.3;
		if (a < Math.abs(c)) {
			a = c;
			s = p / 4;
		} else {
			s = p / (2 * Math.PI) * Math.asin(c / a);
		}
		return a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b;
	}

	public static easeInOutElastic(t: number, b: number, c: number, d: number): number {
		let s = 1.70158;
		let p = 0;
		let a = c;
		if (t === 0) return b;
		if ((t /= d / 2) === 2) return b + c;
		if (!p) p = d * (0.3 * 1.5);
		if (a < Math.abs(c)) {
			a = c;
			s = p / 4;
		} else {
			s = p / (2 * Math.PI) * Math.asin(c / a);
		}
		if (t < 1) return -0.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
		return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * 0.5 + c + b;
	}

	public static easeInBack(t: number, b: number, c: number, d: number, s: number = 1.70158): number {
		return (t === d) ? b + c : c * (t /= d) * t * ((s + 1) * t - s) + b;
	}

	public static easeOutBack(t: number, b: number, c: number, d: number, s: number = 1.70158): number {
		return (t === 0) ? b : c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
	}

	public static easeInOutBack(t: number, b: number, c: number, d: number, s: number = 1.70158): number {
		if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;
		return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;
	}

	public static easeInBounce(t: number, b: number, c: number, d: number): number {
		return c - Ease.easeOutBounce(d - t, 0, c, d) + b;
	}

	public static easeOutBounce(t: number, b: number, c: number, d: number): number {
		if ((t /= d) < (1 / 2.75)) {
			return c * (7.5625 * t * t) + b;
		} else if (t < (2 / 2.75)) {
			return c * (7.5625 * (t -= (1.5 / 2.75)) * t + 0.75) + b;
		} else if (t < (2.5 / 2.75)) {
			return c * (7.5625 * (t -= (2.25 / 2.75)) * t + 0.9375) + b;
		} else {
			return c * (7.5625 * (t -= (2.625 / 2.75)) * t + 0.984375) + b;
		}
	}

	public static easeInOutBounce(t: number, b: number, c: number, d: number): number {
		if (t < d / 2) return Ease.easeInBounce(t * 2, 0, c, d) * 0.5 + b;
		return Ease.easeOutBounce(t * 2 - d, 0, c, d) * 0.5 + c * 0.5 + b;
	}

}