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CSS Base

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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

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HTML

            
              <h1>Synching Animation Clocks with the Web Animation API</h1>
<p>This demo was made for <a href="http://www.smashingmagazine.com/?p=210830">my post on Smashing Magazine about where web animation is headed.</a> It uses a <a href="https://github.com/web-animations/web-animations-js">polyfill</a> to enable the Web Animation API. (Psst: Check out the JavaScript and CSS to see how it's done.) To learn more about the Web Animation API, <a href="http://rachelnabors.com/waapi/">check out my WAAPI resource page!</a></p>
<div id="CSSCats">
  <h2>Cats animated with <br />CSS Animations</h2>
  <p>Currently, it is impossible to synch two separate animations with CSS animations. Try adding new cats animated with CSS below. Notice that they do not run in synch with each other.</p>
  <div class="cat withCSS"></div>
  <button onclick="animateNewCatWithCSS()">Add a Cat</button>
</div>

<div id="WAAPICats">
  <h2>Cats animated with the <br />Web Animation API</h2>
  <p>But with the Web Animation API, you're able to set the <code>startTime</code> value across animations to properly synch them. When you add cats with the Web Animation API, they run lockstep!</p>
  <div class="cat" id="withWAAPI"></div>
  <button onclick="animateNewCatWithWAAPI()">Add a Cat</button>
</div>
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CSS

            
              /* All cats have the same dimensions and the same sprite for a background image. */
.cat {
  background: url(http://stash.rachelnabors.com/24ways2012/cat_sprite.png) -800px 0 no-repeat; 
  height: 200px; width: 400px;
}

/* The cats animated with CSS have their running animations set with CSS */
.cat.withCSS {
  animation: run-cycle;
  animation-duration: .75s;
  animation-timing-function: steps(13,end);
  animation-iteration-count: infinite;
}

/* The keyframes for the run cycle.
   This moves the background image sprite around. */
@keyframes run-cycle {  
  0% {background-position: -800px 0; }
  100% {background-position: -800px -2591px; } 
}

/* More information on this spriting technique in my 24 Ways article: 
http://24ways.org/2012/flashless-animation/ 
*/

/* It's all presentational from here on. 
   Nothing to see here! */
#CSSCats, #WAAPICats {
  display: inline-block;
  text-align: center;
  vertical-align: top;
  width: 400px;
}

@media only screen and (min-width: 850px) {

  #CSSCats, #WAAPICats {
    margin: 3em 1em;
  }
}

#CSSCats p, #WAAPICats p {
  text-align: left;  
}

body { 
  background: #e5e6e9;
  color: #071933;
  font-family: 'Lato', sans-serif;
  font-size: 1em; 
  line-height: 1.5em;
  margin: 1em 1em;
  text-align: center;
  width: 100%;
}

@media only screen and (min-width: 850px) { 
  body {
    margin: 4em auto;
    width: 80%;
  }
}
h1 {
  font-family: 'Aleo', sans-serif;
  font-weight: 200;
  font-size: 2em;
  line-height: 1.25em;
}

h2 {
  font-family: 'Aleo', sans-serif;
  font-weight: 400;
  font-size: 1.5em;
  line-height: 1.25em;  
}

p {
  margin: .5em 0;
}

button {
  background: #2d0d3c;
  border: 0;
  color: #f7e6ff;
  cursor: pointer;
  font-size: .9em;
  padding: .7em 2em;
}

@media only screen and (min-width: 850px) { 
  button {
    padding: 1em 3em;
    font-size: 1em;
  }
}

code { font-family: monospace;}

a:link { color: #1954c0; } a:visited {color: #702096; }
a:hover, a:active, a:focus {
  color: #646d97;
}
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JS

            
              // Here we set up a keyframes object containing values set in an '@keyframes' CSS rule
var keyframes = [
  {backgroundPosition: "-800px 0"},
  {backgroundPosition: "-800px -2591px"}
];
// and a timing object, which contains values we'd normally put in the 'animation' CSS rule
var timing = {
  duration: 750,
  iterations: Infinity,
  easing: "steps(13, end)"
};

/* with the WAAPI's animate function, we apply both keyframes and timing objects to .cat#withWAAPI 
(Have a look in your DOM inspector!)*/
var catRunning = document.getElementById ("withWAAPI").animate(keyframes, timing);

/* A function that makes new cats! 
Goodie! This will be useful below. */
function addCat(){
  var newCat = document.createElement("div");
  newCat.classList.add("cat");
  return newCat;
}

/* This is the function that adds a cat to the CSS column */
function animateNewCatWithCSS() {
  // make a new cat
  var newCat = addCat();
  // Add the CSS class that kicks off the CSS animation
  newCat.classList.add("withCSS");
  CSSCats.appendChild(newCat);
}

/* This is the function that adds a cat to the WAAPI column */
function animateNewCatWithWAAPI() {
  // make a new cat
  var newCat = addCat();
  // animate said cat with the WAAPI's "animate" function
  var newAnimationPlayer = newCat.animate(keyframes, timing);
  // set that player object's start time to be the same as the original .cat#withWAAPI
  newAnimationPlayer.startTime = catRunning.startTime;
  WAAPICats.appendChild(newCat);
}
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