3 Layer Image After/Before Comparison Slider

Preview:

Description:

A fancy image comparison slider that allows you to compare the differences among 3 layered images.

How to use it:

Add 3 images together with the SVG based comparison sliders to the webpage.

<div class="wrapper">
  <div class="bottom">
    <img src="1.jpg" draggable="false"/>
  </div>
  <div class="middle">
    <img src="2.jpg" draggable="false"/>
  </div>
  <div class="scroller scroller-middle">
    <svg class="scroller__thumb" xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100"><polygon points="0 50 37 68 37 32 0 50" style="fill:#FFCCBC"/><polygon points="100 50 64 32 64 68 100 50" style="fill:#FFCCBC"/></svg>
  </div>
  <div class="top">
    <img src="3.jpg" draggable="false"/>
  </div>
  <div class="scroller scroller-top">
    <svg class="scroller__thumb" xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100"><polygon points="0 50 37 68 37 32 0 50" style="fill:#FFAB91"/><polygon points="100 50 64 32 64 68 100 50" style="fill:#FFAB91"/></svg>
  </div>
</div>

The necessary CSS styles for the image comparison view.

/* Our wrapper */

.wrapper {
  width: 690px;
  height: 600px;
  max-height: 100vh;
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate3d(-50%, -50%, 0);
  overflow: hidden;
  box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);
}

/* Our image information */

.bottom, .middle, .top {
  width: 100%;
  height: 100%;
  background-repeat: no-repeat;
  background-color: white;
  background-size: cover;
  background-position: center;
  position: absolute;
  top: 0;
  left: 0;
  pointer-events: none;
  overflow: hidden;
 &>img {
 height:100%;
}
}

.top { width: 125px; }

.scroller {
  width: 50px;
  height: 50px;
  position: absolute;
  left: 100px;
  top: 50%;
  transform: translateY(-50%);
  border-radius: 50%;
  background-color: #fff;
  opacity: 0.9;
  transition: opacity 0.12s ease-in-out;
  pointer-events: auto;
  cursor: pointer;
  box-shadow: 3.5px 0px 7px rgba(100, 100, 100, 0.2);
}

.scroller-middle { margin-top: 25px; }

.scroller-top { margin-top: -25px; }

.scroller:hover { opacity: 1; }

.scrolling {
  pointer-events: none;
  opacity: 1;
 // z-index: 1;
}

.scroller__thumb {
  width: 100%;
  height: 100%;
  border-radius: 50%;
  padding: 7px;
}

.scroller:before, .scroller:after {
  content: " ";
  display: block;
  width: 7px;
  height: 9999px;
  position: absolute;
  left: 50%;
  margin-left: -3.5px;
  z-index: 30;
  transition: 0.1s;
  box-shadow: 3.5px 0px 7px rgba(100, 100, 100, 0.2);
}

.scroller:before { top: 49px; }

.scroller:after { bottom: 49px; }

/* If you want to cahnge the colors, make sure you change the fill in the svgs to match */

.scroller-middle>.scroller__thumb { border: 5px solid #FFCCBC; }

.scroller-middle:before, .scroller-middle:after { background: #FFCCBC; }

.scroller-top>.scroller__thumb { border: 5px solid #FFAB91; }

.scroller-top:before, .scroller-top:after { background: #FFAB91; }

The core JavaScript to active the image comparison sliders.

// I hope this over-commenting helps. Let's do this!
// Let's use the 'active' variable to let us know when we're using it
let active = false;

// First we'll have to set up our event listeners
// We want to watch for clicks on our scroller
document.querySelector('.scroller-middle').addEventListener('mousedown',function(){
  active = "middle";
  // Add our scrolling class so the scroller has full opacity while active
  document.querySelector('.scroller-middle').classList.add('scrolling');
});
// We also want to watch the body for changes to the state,
// like moving around and releasing the click
// so let's set up our event listeners
document.body.addEventListener('mouseup',function(){
  active = false;
  document.querySelector('.scroller-middle').classList.remove('scrolling');
});
document.body.addEventListener('mouseleave',function(){
  active = false;
  document.querySelector('.scroller-middle').classList.remove('scrolling');
});
// We'll have to do the same for our top scroller
document.querySelector('.scroller-top').addEventListener('mousedown',function(){
    active = "top";
    document.querySelector('.scroller-top').classList.add('scrolling');
});
document.body.addEventListener('mouseup',function(){
  active = false;
  document.querySelector('.scroller-top').classList.remove('scrolling');
});
document.body.addEventListener('mouseleave',function(){
  active = false;
  document.querySelector('.scroller-top').classList.remove('scrolling');
});

// Let's figure out where their mouse is at
document.body.addEventListener('mousemove',function(e){
  if (!active) return;
  // Their mouse is here...
  let x = e.pageX;
  // but we want it relative to our wrapper
  x -= document.querySelector('.wrapper').getBoundingClientRect().left;
  // Okay let's change our state
  scrollIt(x);
});

// Let's use this function
function scrollIt(x){
  // Calculate our transform
  let transform = Math.max(0,(Math.min(x,document.querySelector('.wrapper').offsetWidth)));
  // we show all our bottom image but how much of our middle and top,
  // that'll depend on what we're dragging
  // if we're dragging the middle slider
  if (active==="middle"){
    document.querySelector('.middle').style.width = transform+"px";
    document.querySelector('.scroller-middle').style.left = transform-25+"px";
    // if we're using scroller-middle, middle must always be to the right of top
    if (document.querySelector('.scroller-top').getBoundingClientRect().left>document.querySelector('.scroller-middle').getBoundingClientRect().left-5){
      document.querySelector('.top').style.width = transform-5+"px";
      document.querySelector('.scroller-top').style.left = transform-30+"px";
    }
  }
  // if we're dragging the top slider
  if (active==="top"){
    document.querySelector('.top').style.width = transform+"px";
    document.querySelector('.scroller-top').style.left = transform-25+"px";
    // if we're using scroller-top, top must always be to the left
    if (document.querySelector('.scroller-top').getBoundingClientRect().left>document.querySelector('.scroller-middle').getBoundingClientRect().left-5){
      document.querySelector('.middle').style.width = transform+5+"px";
      document.querySelector('.scroller-middle').style.left = transform-20+"px";
    }
  }
}

// Let's set our opening state based off the width, 
// we want to show a bit of both images so the user can see what's going on
active = "middle";
scrollIt(460);
active = "top";
scrollIt(230);
active = false;


// And finally let's repeat the process for touch events
// first our middle scroller...
document.querySelector('.scroller-middle').addEventListener('touchstart',function(){
    active = "middle";
    document.querySelector('.scroller-middle').classList.add('scrolling');
});
document.body.addEventListener('touchend',function(){
    active = false;
    document.querySelector('.scroller-middle').classList.remove('scrolling');
});
document.body.addEventListener('touchcancel',function(){
    active = false;
    document.querySelector('.scroller-middle').classList.remove('scrolling');
});

// then scroller top, our second scroller
document.querySelector('.scroller-top').addEventListener('touchstart',function(){
    active = "top";
    document.querySelector('.scroller-top').classList.add('scrolling');
});
document.body.addEventListener('touchend',function(){
    active = false;
    document.querySelector('.scroller-top').classList.remove('scrolling');
});
document.body.addEventListener('touchcancel',function(){
    active = false;
    document.querySelector('.scroller-top').classList.remove('scrolling');
});

document.querySelector('.wrapper').addEventListener('touchmove',function(e){
    if (!active) return;
    e.preventDefault();
    let x = e.touches[0].pageX;
    x -= document.querySelector('.wrapper').getBoundingClientRect().left;
    scrollIt(x);
});