<div class="ba-slider">
  <img src="http://kdkl.bplaced.net/Portrait/NACHER_2-NEU.jpg" alt="after">       
  <div class="resize">
    <img src="http://kdkl.bplaced.net/Portrait/VORHER_2.jpg" alt="before">
  </div>
  <span class="handle"></span>
</div>

@import "lesshat";
@import "https://fonts.googleapis.com/css?family=Roboto:100, 500";

html,
body {
  background-color: black;
  height: auto;
  overflow-x: hidden;
}

.ba-slider {
  position: relative;
  overflow: hidden;
  height: auto;
}

.ba-slider img {
  width: 100%;
  display: block;
}

.resize {
  position: absolute;
  top: 0;
  left: 0;
  width: 50%;
  overflow: hidden;
}

.handle {
  /* Thin line seperator */
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: 1px;
  margin-left: -2px;
  border: 1px;
  background: white;
  cursor: ew-resize;
}

.handle:after {
  /* Big orange knob  */
  position: absolute;
  top: 50%;
  width: 50px;
  height: 50px;
  margin: -50px/2 0 0 -54px/2;
  background: black;
  border: 2px solid white;

  content: "<>";
  color: white;
  font-family: sans-serif;
  font-weight: 100;
  font-size: 30px;
  text-align: center;
  line-height: 45px;

  border-radius: 100%;
  transition: all 0.3s ease;
}

.draggable:after {
  width: 40px;
  height: 40px;
  margin: -22px 0 0 -22px;
  line-height: 40px;
  font-size: 20px;
}

// Call & init
$(document).ready(function(){
  $('.ba-slider').each(function(){
    var cur = $(this);
    // Adjust the slider
    var width = cur.width()+'px';
    cur.find('.resize img').css('width', width);
    // Bind dragging events
    drags(cur.find('.handle'), cur.find('.resize'), cur);
  });
});

// Update sliders on resize. 
// Because we all do this: i.imgur.com/YkbaV.gif
$(window).resize(function(){
  $('.ba-slider').each(function(){
    var cur = $(this);
    var width = cur.width()+'px';
    cur.find('.resize img').css('width', width);
  });
});

function drags(dragElement, resizeElement, container) {
	
  // Initialize the dragging event on mousedown.
  dragElement.on('mousedown touchstart', function(e) {
    
    dragElement.addClass('draggable');
    resizeElement.addClass('resizable');
    
    // Check if it's a mouse or touch event and pass along the correct value
    var startX = (e.pageX) ? e.pageX : e.originalEvent.touches[0].pageX;
    
    // Get the initial position
    var dragWidth = dragElement.outerWidth(),
        posX = dragElement.offset().left + dragWidth - startX,
        containerOffset = container.offset().left,
        containerWidth = container.outerWidth();
 
    // Set limits
    minLeft = containerOffset + 10;
    maxLeft = containerOffset + containerWidth - dragWidth - 10;
    
    // Calculate the dragging distance on mousemove.
    dragElement.parents().on("mousemove touchmove", function(e) {
    	
      // Check if it's a mouse or touch event and pass along the correct value
      var moveX = (e.pageX) ? e.pageX : e.originalEvent.touches[0].pageX;
      
      leftValue = moveX + posX - dragWidth;
      
      // Prevent going off limits
      if ( leftValue < minLeft) {
        leftValue = minLeft;
      } else if (leftValue > maxLeft) {
        leftValue = maxLeft;
      }
      
      // Translate the handle's left value to masked divs width.
      widthValue = (leftValue + dragWidth/2 - containerOffset)*100/containerWidth+'%';
			
      // Set the new values for the slider and the handle. 
      // Bind mouseup events to stop dragging.
      $('.draggable').css('left', widthValue).on('mouseup touchend touchcancel', function () {
        $(this).removeClass('draggable');
        resizeElement.removeClass('resizable');
      });
      $('.resizable').css('width', widthValue);
    }).on('mouseup touchend touchcancel', function(){
      dragElement.removeClass('draggable');
      resizeElement.removeClass('resizable');
    });
    e.preventDefault();
  }).on('mouseup touchend touchcancel', function(e){
    dragElement.removeClass('draggable');
    resizeElement.removeClass('resizable');
  });
}