Moving image on scroll through svg path

Question

I want to move object through svg path on scroll=) I was trying to add parts of path on scroll into path, but it still doesn't work. Help!!!=) https://jsfiddle.net/YuriiBielozertsev/Ltx9ed0L/

<?xml version="1.0"?>
<svg viewBox="0 0 120 120" xmlns="http://www.w3.org/2000/svg" version="1.1" xmlns:xlink="http://www.w3.org/1999/xlink">
    <!-- Draw the outline of the motion path in grey, along with 2 small circles at key points -->
    <path d="M10,110 A120,120 -45 0,1 110 10 A120,120 -45 0,1 10,110" stroke="green" stroke-width="2" fill="none" id="theMotionPath"/>
        <circle cx="10" cy="110" r="3" fill="#000"/>
        <circle cx="110" cy="10" r="3" fill="#000"/>

        <!-- Red circle which will be moved along the motion path. -->
        <circle cx="0" cy="" r="5" fill="red">

        <!-- Define the motion path animation -->
        <animateMotion dur="6s" repeatCount="indefinite">
            <mpath xlink:href="#theMotionPath"/>
        </animateMotion>
    </circle>
</svg>

Answer 1

Something like this?

How this works:

1. When we get a scroll event we:
2. Calculate how far down the page we are
3. Convert this percentage to a position on the path using the <path> element functions getTotalLength() and getPointAtLength().
4. Reposition the dot so that it appears at this point.

function positionTheDot() {

  // What percentage down the page are we? 
  var scrollPercentage = (document.documentElement.scrollTop + document.body.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);

  // Get path length
  var path = document.getElementById("theMotionPath");
  var pathLen = path.getTotalLength();
  
  // Get the position of a point at <scrollPercentage> along the path.
  var pt = path.getPointAtLength(scrollPercentage * pathLen);
  
  // Position the red dot at this point
  var dot = document.getElementById("dot");
  dot.setAttribute("transform", "translate("+ pt.x + "," + pt.y + ")");
  
};

// Update dot position when we get a scroll event.
window.addEventListener("scroll", positionTheDot);

// Set the initial position of the dot.
positionTheDot();

.verylong {
  height: 2000px;
}

svg {
  position: fixed;
  width: 200px;
  height: 200px;
}

<svg viewBox="0 0 120 120" xmlns="http://www.w3.org/2000/svg" version="1.1" xmlns:xlink="http://www.w3.org/1999/xlink">
    <!-- Draw the outline of the motion path in grey, along with 2 small circles at key points -->
    <path d="M10,110 A120,120 -45 0,1 110 10 A120,120 -45 0,1 10,110" stroke="green" stroke-width="2" fill="none" id="theMotionPath"/>
    <circle cx="10" cy="110" r="3" fill="#000"/>
    <circle cx="110" cy="10" r="3" fill="#000"/>

    <!-- Red circle which will be moved along the motion path. -->
    <circle cx="0" cy="0" r="5" fill="red" id="dot"/>
</svg>

<div class="verylong">
</div>