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HTML 

              
                <h1>GSAP 3 getRelativePosition() Demo</h1><div id="outer">
  <div id="middle">
    <div id="inner"></div>
  </div>
</div>
<div id="dot-container">
  <div id="dot"></div>
</div>

<link href='//fonts.googleapis.com/css?family=Signika+Negative:300,400' rel='stylesheet' type='text/css'>
!

CSS 

              
                body {
  background-color: black;
  color: white;
  font-family: "Signika Negative", Arial, sans-serif;
  font-weight: 300;
  padding: 5px 15px;
}
#dot {
  position: absolute;
  top: 0;
  left: 0;
  width: 16px;
  height: 16px;
  background-color: red;
  border-radius: 50%;
}
#dot-container {
  position: absolute;
  top: 0;
  left: 0;
  width: 100px;
  height: 50px;
  border: 2px solid green;

}
#outer {
  width: 500px;
  height: 350px;
  background-color: #444;
}
#middle {
  width: 300px;
  height: 200px;
  background-color: #656565;
}
#inner {
  width: 100px;
  height: 60px;
  background-color: #ccc;
}
!

JS 

              
                // The red dot goes to the center of the light rectangle even though it's nested inside multiple elements with various transforms applied!

// First, let's add some wacky transforms to every element (nested!)
var tl = gsap.timeline({defaults: {duration:1, delay:0.5, ease: "power1.inOut"}})
  .to("#outer", {xPercent: 50, yPercent: 20, rotation: -20, y: -80})
  .to("#middle", {x: 100, y: 50, scale: 0.7, rotation: 60})
  .to("#inner", {x: 140, y: 100, transformOrigin: "50% 50%", rotation: 40})
  .to("#dot-container", {x:50, y:80, scale:0.5, rotation:-25})
  .call(function() {
    // RED DOT MOVEMENT:
    var inner = document.querySelector("#inner"),
        dot = document.querySelector("#dot"),
        delta = getRelativePosition(dot, inner, [0.5, 0.5], [0.5, 0.5]);
    gsap.to(dot, {
      x: "+=" + delta.x,
      y: "+=" + delta.y,
      duration: 2,
      delay: 1,
      repeat: -1,
      yoyo: true,
      repeatDelay:1,
      ease: "power2.inOut"
    });
  });




// feed two elements to this method and it'll return the gap between them as a point {x, y} according to the coordinate system of the fromElement's parent. By default, it will align their centers, but you can define a different origin for each, like [0, 0] would be the top left corner, [0.5, 0.5] would be the center, [1, 1] would be the bottom right, etc. 
function getRelativePosition(fromElement, toElement, fromOrigin, toOrigin) {
	let matrix = MotionPathPlugin.getGlobalMatrix,
		originToPoint = (element, origin) => {
			let o = origin || [0.5, 0.5],
				svg = element.ownerSVGElement && element.getBBox(),
				w = svg ? svg.width : element.offsetWidth || 0,
				h = svg ? svg.height : element.offsetHeight || 0;
			return {x: o[0] * w, y: o[1] * h};
		},
		parentMatrix = matrix(fromElement.parentNode, true),
		fromPoint = parentMatrix.apply(matrix(fromElement).apply(originToPoint(fromElement, fromOrigin))),
		toPoint = parentMatrix.apply(matrix(toElement).apply(originToPoint(toElement, toOrigin)));
	return {x: toPoint.x - fromPoint.x, y: toPoint.y - fromPoint.y};
}
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999px

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