Gallery with wave transition effect

<!--DOCTYPE html-->
<html lang="en" >
<head>
  <meta charset="UTF-8">
  <title> Gallery with wave transition effect.</title>
  <link href="https://fonts.googleapis.com/css?family=Yanone+Kaffeesatz" rel="stylesheet">
  <style>
  
  *, *:before, *:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.demo {
  display: flex;
  width: 100vw;
  height: 100vh;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  background: linear-gradient(60deg, #5B5893, #2c2a49);
}
.demo__gallery {
  width: 688px;
  height: 460px;
  padding: 2px;
  flex-shrink: 0;
  background: #eee;
  perspective: 700px;
  border-radius: 5px;
}
.demo__placeholder {
  width: 110px;
  height: 110px;
  margin: 2px;
  float: left;
  background-color: lightslategrey;
  border-radius: 5px;
}
.demo__part {
  position: relative;
  float: left;
  width: 110px;
  height: 110px;
  margin: 2px;
  transform: rotateY(180deg);
  transform-style: preserve-3d;
  transition: all 0.3s ease-in-out;
}
.demo__part:hover .demo__part-front {
  box-shadow: 0 0 10px black;
  transform: scale(0.96);
}
.demo__part:hover .demo__part-front:after {
  opacity: 0;
}
.demo__part-front, .demo__part-back {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
  -webkit-backface-visibility: hidden;
          backface-visibility: hidden;
  border-radius: 5px;
  cursor: pointer;
}
.demo__part-front {
  background-color: lightslategrey;
  background-size: cover;
  background-position: center;
  transform: rotateX(0deg);
  transition: all 0.2s ease;
}
.demo__part-front:after {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: black;
  content: "";
  opacity: 0.5;
  transition: all 0.2s ease;
}
.demo__part-back {
  transform: rotateY(180deg) rotateX(0deg);
}
.demo__part-back-inner {
  width: 680px;
  height: 452px;
  background-image: url(http://kirillkiyutin.com/img/nyc/nyc1.jpg);
  background-size: cover;
  background-position: center;
  -webkit-backface-visibility: hidden;
          backface-visibility: hidden;
}
.demo__help {
  margin-bottom: 7px;
  font-size: 30px;
  font-family: "Yanone Kaffeesatz", sans-serif;
  color: white;
}
.demo__help a {
  color: white;
}
.demo__help a:hover {
  color: #E39999;
}

.demo__part-1-1 .demo__part-back-inner {
  transform: translate(0px, 0px);
}

.demo__part-1-2 .demo__part-back-inner {
  transform: translate(-114px, 0px);
}

.demo__part-1-3 .demo__part-back-inner {
  transform: translate(-228px, 0px);
}

.demo__part-1-4 .demo__part-back-inner {
  transform: translate(-342px, 0px);
}

.demo__part-1-5 .demo__part-back-inner {
  transform: translate(-456px, 0px);
}

.demo__part-1-6 .demo__part-back-inner {
  transform: translate(-570px, 0px);
}

.demo__part-2-1 .demo__part-back-inner {
  transform: translate(0px, -114px);
}

.demo__part-2-2 .demo__part-back-inner {
  transform: translate(-114px, -114px);
}

.demo__part-2-3 .demo__part-back-inner {
  transform: translate(-228px, -114px);
}

.demo__part-2-4 .demo__part-back-inner {
  transform: translate(-342px, -114px);
}

.demo__part-2-5 .demo__part-back-inner {
  transform: translate(-456px, -114px);
}

.demo__part-2-6 .demo__part-back-inner {
  transform: translate(-570px, -114px);
}

.demo__part-3-1 .demo__part-back-inner {
  transform: translate(0px, -228px);
}

.demo__part-3-2 .demo__part-back-inner {
  transform: translate(-114px, -228px);
}

.demo__part-3-3 .demo__part-back-inner {
  transform: translate(-228px, -228px);
}

.demo__part-3-4 .demo__part-back-inner {
  transform: translate(-342px, -228px);
}

.demo__part-3-5 .demo__part-back-inner {
  transform: translate(-456px, -228px);
}

.demo__part-3-6 .demo__part-back-inner {
  transform: translate(-570px, -228px);
}

.demo__part-4-1 .demo__part-back-inner {
  transform: translate(0px, -342px);
}

.demo__part-4-2 .demo__part-back-inner {
  transform: translate(-114px, -342px);
}

.demo__part-4-3 .demo__part-back-inner {
  transform: translate(-228px, -342px);
}

.demo__part-4-4 .demo__part-back-inner {
  transform: translate(-342px, -342px);
}

.demo__part-4-5 .demo__part-back-inner {
  transform: translate(-456px, -342px);
}

.demo__part-4-6 .demo__part-back-inner {
  transform: translate(-570px, -342px);
}

.show-front {
  transform: none;
}
  
  </style>

</head>
<body>
<!-- partial:index.partial.html -->
<div class="demo">
  <div class="demo__help">
    Choose a photo
  </div>
  <div class="demo__gallery">
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
    <div class="demo__placeholder"></div>
  </div>  
</div>
<!-- partial -->
  <script src='https://code.jquery.com/jquery-2.2.4.min.js'></script>
  
  <script>
  "use strict";
$(document).ready(function() {

  var rows = 4; //change this also in css
  var cols = 6; //change this also in css
  var staggerTime = 150;

  var urls = [
    "https://kiyutink.github.io/nyc/nyc1.jpg",
    "https://kiyutink.github.io/nyc/nyc2.jpg",
    "https://kiyutink.github.io/nyc/nyc3.jpg",
    "https://kiyutink.github.io/nyc/nyc4.jpg",
    "https://kiyutink.github.io/nyc/nyc5.jpg",
    "https://kiyutink.github.io/london/london1.jpg",
    "https://kiyutink.github.io/london/london2.jpg",
    "https://kiyutink.github.io/london/london3.jpg",
    "https://kiyutink.github.io/madrid/madrid1.jpg",
    "https://kiyutink.github.io/madrid/madrid2.jpg",
    "https://kiyutink.github.io/madrid/madrid3.jpg",
    "https://kiyutink.github.io/beijing/beijing1.jpg",
    "https://kiyutink.github.io/beijing/beijing2.jpg",
    "https://kiyutink.github.io/beijing/beijing3.jpg",
    "https://kiyutink.github.io/moscow/moscow1.jpg",
    "https://kiyutink.github.io/moscow/moscow2.jpg",
    "https://kiyutink.github.io/moscow/moscow3.jpg",
    "https://kiyutink.github.io/sidney/sidney1.jpg",
    "https://kiyutink.github.io/sidney/sidney2.jpg",
    "https://kiyutink.github.io/sidney/sidney3.jpg",
    "https://kiyutink.github.io/tokyo/tokyo1.jpg",
    "https://kiyutink.github.io/tokyo/tokyo2.jpg",
    "https://kiyutink.github.io/tokyo/tokyo3.jpg",
    "https://kiyutink.github.io/la/la3.jpg"
  ];

  var $gallery = $(".demo__gallery");
  var $help = $(".demo__help");
  var partsArray = [];
  var reqAnimFr = (function() {
    return window.requestAnimationFrame || function(cb) {
      setTimeout(cb, 1000 / 60);
    }
  })();

  
  $gallery.html('');
  for (let row = 1; row <= rows; row++) {
    partsArray[row - 1] = [];
    for (let col = 1; col <= cols; col++) {
      $gallery.append(`<div class="show-front demo__part demo__part-${row}-${col}" row="${row}" col="${col}"><div class="demo__part-back"><div class="demo__part-back-inner"></div></div><div class="demo__part-front"></div></div>`);
      partsArray[row - 1][col - 1] = new Part();
    }
  }
  
  var $parts = $(".demo__part");
  var $image = $(".demo__part-back-inner");
  var help = true;

  for (let i = 0; i < $parts.length; i++) {
    $parts.find(".demo__part-front").eq(i).css("background-image", `url(${urls[i]})`);
  }

  $gallery.on("click", ".demo__part-front", function() {

    $image.css("background-image", $(this).css("background-image"));
    if (help) {
      $help.html("Click any of the tiles to get back");
      help = false;
    }

    let row = +$(this).closest(".demo__part").attr("row");
    let col = +$(this).closest(".demo__part").attr("col");
    waveChange(row, col);
  });

  $gallery.on("click", ".demo__part-back", function() {
    if (!isShowingBack()) return;

    $help.html(`Check out my other <a target="blank" href="https://codepen.io/kiyutink/">pens</a> and follow me on <a target="_blank" href="https://twitter.com/kiyutin_k">twitter</a>`);

    setTimeout(function() {
      for (let row = 1; row <= rows; row++) {
        for (let col = 1; col <= cols; col++) {
          partsArray[row - 1][col - 1].showing = "front";
        }
      }
    }, staggerTime + $parts.length * staggerTime / 10);
    
    
    showFront(0, $parts.length);
    
  });
  
  function showFront(i, maxI) {
    if (i >= maxI) return;
    $parts.eq(i).addClass("show-front");
    
    reqAnimFr(function() {
      showFront(i + 1);
    });
  }

  function isShowingBack() {
    return partsArray[0][0].showing == "back" && partsArray[0][cols - 1].showing == "back" && partsArray[rows - 1][0].showing == "back" && partsArray[rows - 1][cols - 1].showing == "back";
  }

  function Part() {
    this.showing = "front";
  }

  function waveChange(rowN, colN) {
    if (rowN > rows || colN > cols || rowN <= 0 || colN <= 0) return;
    if (partsArray[rowN - 1][colN - 1].showing == "back") return;
    $(".demo__part-" + rowN + "-" + colN).removeClass("show-front");
    partsArray[rowN - 1][colN - 1].showing = "back";
    setTimeout(function() {
      waveChange(rowN + 1, colN);
      waveChange(rowN - 1, colN);
      waveChange(rowN, colN + 1);
      waveChange(rowN, colN - 1);
    }, staggerTime);
  }
});
  
  </script>

</body>
</html>
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