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Easing.js
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146 lines (121 loc) · 2.91 KB
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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*
* @providesModule Easing
* @flow
*/
'use strict';
var _bezier = require('bezier');
/**
* This class implements common easing functions. The math is pretty obscure,
* but this cool website has nice visual illustrations of what they represent:
* http://xaedes.de/dev/transitions/
*/
class Easing {
static step0(n) {
return n > 0 ? 1 : 0;
}
static step1(n) {
return n >= 1 ? 1 : 0;
}
static linear(t) {
return t;
}
static ease(t: number): number {
return ease(t);
}
static quad(t) {
return t * t;
}
static cubic(t) {
return t * t * t;
}
static poly(n) {
return (t) => Math.pow(t, n);
}
static sin(t) {
return 1 - Math.cos(t * Math.PI / 2);
}
static circle(t) {
return 1 - Math.sqrt(1 - t * t);
}
static exp(t) {
return Math.pow(2, 10 * (t - 1));
}
/**
* A simple elastic interaction, similar to a spring. Default bounciness
* is 1, which overshoots a little bit once. 0 bounciness doesn't overshoot
* at all, and bounciness of N > 1 will overshoot about N times.
*
* Wolfram Plots:
*
* http://tiny.cc/elastic_b_1 (default bounciness = 1)
* http://tiny.cc/elastic_b_3 (bounciness = 3)
*/
static elastic(bounciness: number = 1): (t: number) => number {
var p = bounciness * Math.PI;
return (t) => 1 - Math.pow(Math.cos(t * Math.PI / 2), 3) * Math.cos(t * p);
}
static back(s: number): (t: number) => number {
if (s === undefined) {
s = 1.70158;
}
return (t) => t * t * ((s + 1) * t - s);
}
static bounce(t: number): number {
if (t < 1 / 2.75) {
return 7.5625 * t * t;
}
if (t < 2 / 2.75) {
t -= 1.5 / 2.75;
return 7.5625 * t * t + 0.75;
}
if (t < 2.5 / 2.75) {
t -= 2.25 / 2.75;
return 7.5625 * t * t + 0.9375;
}
t -= 2.625 / 2.75;
return 7.5625 * t * t + 0.984375;
}
static bezier(
x1: number,
y1: number,
x2: number,
y2: number
): (t: number) => number {
return _bezier(x1, y1, x2, y2);
}
static in(
easing: (t: number) => number,
): (t: number) => number {
return easing;
}
/**
* Runs an easing function backwards.
*/
static out(
easing: (t: number) => number,
): (t: number) => number {
return (t) => 1 - easing(1 - t);
}
/**
* Makes any easing function symmetrical.
*/
static inOut(
easing: (t: number) => number,
): (t: number) => number {
return (t) => {
if (t < 0.5) {
return easing(t * 2) / 2;
}
return 1 - easing((1 - t) * 2) / 2;
};
}
}
var ease = Easing.bezier(0.42, 0, 1, 1);
module.exports = Easing;