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                <h2>Custom Animation Demo</h2>
<p>You can manipulate the animation of the box with the function. I think it's most interesting when you add the function together multiple times.</p>
F(X) = <table class="equation">
    <td class="numerator">(End Unit - Start Unit)</td>
    <td>(End Time)<sup>Acceleration Modifier</sup> - (Start Time)<sup>Acceleration Modifier</sup></td>
</table>X +<table class="equation">
    <td class="numerator">[(Start Unit) * (End Time)<sup>Acceleration Modifier</sup>] - [(End Unit) * (Start Time)<sup>Acceleration Modifier</sup>]</td>
    <td>(End Time)<sup>Acceleration Modifier</sup> - (Start Time)<sup>Acceleration Modifier</sup></td>
<p>For a constant rate set the acceleration modifier equal to 1.</p>
<table class="input">
    <th>Start Unit</th>
    <th><input class='start-unit' type='number' value="0"/></th>
    <th>End Unit</th>
    <th><input class='end-unit' type='number' value="200"/></th>
    <th>Start time <sub>(in seconds)</sub></th>
    <th><input class='start-time' type='number' value="0"/></th> 
     <th>End time <sub>(in seconds)</sub></th>
    <th><input class='end-time' type='number' value="1"/></th> 
    <th>Acceleration Modifier</th>
    <th><input class='accel-mod' type='number' value="1"/></th>
    <th>FPS <sub>(must be <= 100)</sub></th>
    <th><input class='fps' type='number' value="60"/>
      <option class="unit">px</option>
      <option class="unit">rem</option>
      <option class="unit">vh</option>
      <option class="unit">vw</option>
    <th><button onclick="start()">Animate</button></th>
<div class="box"></div>


                .numerator {
  border-bottom: 1px solid black;
.equation {
  display: inline-block;
  vertical-align: middle;
.equation td {
  text-align: center;
.input {
  margin-top: 1.5rem;
.box {
 position: relative;
 height: 6rem;
 width: 6rem;
 background-color: red;
.error {
  color: red;


                var secondsPerFrame;
var unit = "px";

var start = function () {
    //Remove previous errors
    //Grab input
    var startUnit, endUnit, startTime, endTime, accelMod;
    startUnit = Number($('.start-unit').val());
    endUnit = Number($('.end-unit').val());
    startTime = Number($('.start-time').val());
    endTime = Number($('.end-time').val());
    accelMod = Number($('.accel-mod').val());
    secondsPerFrame = Math.pow($('.fps').val(), -1);
    unit = $('.unit:selected').val();
    //Check constraints
	if (meetsConstraints(startUnit, endUnit, startTime, endTime, accelMod)){
	    $('button').attr('disabled', 'disabled');
		animate(startUnit, endUnit, startTime, endTime, accelMod)

var meetsConstraints = function (startUnit, endUnit, startTime, endTime, accelMod) {
    var isUndefined = (startUnit === "" || endUnit === "" || startTime === "" || endTime === "" || accelMod === "");
    var isNonNumber = (isNaN(secondsPerFrame) || isNaN(startUnit) || isNaN(endUnit) || isNaN(startTime) || isNaN(endTime) || isNaN(accelMod));
    var variableConstraints = (startUnit < 0 || startTime < 0 || startTime > endTime || startUnit > endUnit || startTime == endTime || secondsPerFrame > endTime || secondsPerFrame < 0.01);
    if (isUndefined || isNonNumber || variableConstraints) {
        error("Your input does not meet the constraints");
        return false;
    return true;

var animate = function (a, b, c, d, n) {
    //Starts at 1 to ensure that x doesnt equal zero when n < 1 (constraint)
    var secondTracker = 1;
    c += 1;
    d += 1;
    //Start loop
    animation = setInterval(function () {
        secondTracker += secondsPerFrame;
        //When we hit the end time... stop
        if (secondTracker >= d) {
        //When we hit the start time... start
        if (secondTracker >= c) {
            $('.box').css("left", animationFunction(a, b, c, d, n, secondTracker) + unit);
    }, secondsPerFrame * 1000);

    a = Starting Unit
    b = Ending Unit
    c = Animation Start (in seconds)
    d = Animation End (in seconds)
    n = Rate at which the element moves
    x is the current time in the animation 
var animationFunction = function (a, b, c, d, n, x) {
    var x = Math.pow(x, n);
    var m = (b - a) / (Math.pow(d, n) - Math.pow(c, n));
    var k = (a * Math.pow(d, n) - b * Math.pow(c, n)) / (Math.pow(d, n) - Math.pow(c, n));
    return m * x + k

var stopAnimation = function () {

var error = function (msg) {
    $('body').append("<p class='error'>" + msg + "</p>")