如何使用 offset-path CSS 属性从其原点位置偏移 SVG 路径

Question

I have a bunch of SVG paths that are text letters. On scroll I want to animate them along offset-path starting from their original position. So I give 0x and 0y starting position to offset-path property and then give randomized Line to offset-path along which I want to animate SVG letters, like so:

path.setAttribute("style", "offset-path: path('M" + 0 +" " + 0 + " L " + generateRandomAnimationPathLine() + " " + generateRandomAnimationPathLine() + "')"); 

But once I give all SVG paths offset-path with random L attributes they are already all over the screen with offset-distance set to 0% . Why is that? Shouldn't they stay in their origin if offset-distance is set to 0? Why L in offset-path: path() moves SVG from their origin even though M are set to 0?

You can inspect each SVG letter and check off offset-distance to see that they are already out of origin point. How can I animate SVG paths starting from their original position? I'm trying to achieve an effect where as you scroll it slowly destructs the "Hello, World" and when you scroll back up it goes back to original form.

Image to explain what I'm trying to achieve. When SVG is on screen, set offset-path to random Lines/L along which I want to animate SVG letters from their original position by changing offset-distance from 0% to 100% relative to the scroll, like so:

path.style.offsetDistance = element.intersectionRatio * 100 + "%";

Live example: https://codepen.io/Limpuls/pen/KKzZWEm

Code:

 <section class="row first">
                <div class="col-lg-12">
                    <div class="svg">
                        <svg viewBox="-145 -90 500 500" fill="none" xmlns="http://www.w3.org/2000/svg">
                            <path d="M26 2V30H19.52V18.52H6.80001V30H0.320007V2H6.80001V13.04H19.52V2H26Z" fill="black"/>
                            <path d="M53.2647 19.32C53.2647 19.4 53.2247 19.96 53.1447 21H36.8647C37.158 22.3333 37.8514 23.3867 38.9447 24.16C40.038 24.9333 41.398 25.32 43.0247 25.32C44.1447 25.32 45.1314 25.16 45.9847 24.84C46.8647 24.4933 47.678 23.96 48.4247 23.24L51.7447 26.84C49.718 29.16 46.758 30.32 42.8647 30.32C40.438 30.32 38.2914 29.8533 36.4247 28.92C34.558 27.96 33.118 26.64 32.1047 24.96C31.0914 23.28 30.5847 21.3733 30.5847 19.24C30.5847 17.1333 31.078 15.24 32.0647 13.56C33.078 11.8533 34.4514 10.5333 36.1847 9.6C37.9447 8.64 39.9047 8.16 42.0647 8.16C44.1714 8.16 46.078 8.61333 47.7847 9.52C49.4914 10.4267 50.8247 11.7333 51.7847 13.44C52.7714 15.12 53.2647 17.08 53.2647 19.32ZM42.1047 12.88C40.6914 12.88 39.5047 13.28 38.5447 14.08C37.5847 14.88 36.998 15.9733 36.7847 17.36H47.3847C47.1714 16 46.5847 14.92 45.6247 14.12C44.6647 13.2933 43.4914 12.88 42.1047 12.88Z" fill="black"/>
                            <path d="M57.4191 0.319998H63.6591V30H57.4191V0.319998Z" fill="black"/>
                            <path d="M69.4503 0.319998H75.6903V30H69.4503V0.319998Z" fill="black"/>
                            <path d="M91.7216 30.32C89.4549 30.32 87.4149 29.8533 85.6016 28.92C83.8149 27.96 82.4149 26.64 81.4016 24.96C80.3882 23.28 79.8816 21.3733 79.8816 19.24C79.8816 17.1067 80.3882 15.2 81.4016 13.52C82.4149 11.84 83.8149 10.5333 85.6016 9.6C87.4149 8.64 89.4549 8.16 91.7216 8.16C93.9882 8.16 96.0149 8.64 97.8016 9.6C99.5882 10.5333 100.988 11.84 102.002 13.52C103.015 15.2 103.522 17.1067 103.522 19.24C103.522 21.3733 103.015 23.28 102.002 24.96C100.988 26.64 99.5882 27.96 97.8016 28.92C96.0149 29.8533 93.9882 30.32 91.7216 30.32ZM91.7216 25.2C93.3216 25.2 94.6282 24.6667 95.6416 23.6C96.6816 22.5067 97.2016 21.0533 97.2016 19.24C97.2016 17.4267 96.6816 15.9867 95.6416 14.92C94.6282 13.8267 93.3216 13.28 91.7216 13.28C90.1216 13.28 88.8016 13.8267 87.7616 14.92C86.7216 15.9867 86.2016 17.4267 86.2016 19.24C86.2016 21.0533 86.7216 22.5067 87.7616 23.6C88.8016 24.6667 90.1216 25.2 91.7216 25.2Z" fill="black"/>
                            <path d="M109.819 22.56C110.939 22.56 111.859 22.92 112.579 23.64C113.299 24.3333 113.659 25.2533 113.659 26.4C113.659 26.9333 113.592 27.4667 113.459 28C113.326 28.5333 113.032 29.3333 112.579 30.4L110.299 36.16H106.339L108.099 29.8C107.432 29.5333 106.899 29.1067 106.499 28.52C106.126 27.9067 105.939 27.2 105.939 26.4C105.939 25.2533 106.299 24.3333 107.019 23.64C107.766 22.92 108.699 22.56 109.819 22.56Z" fill="black"/>
                            <path d="M171.976 2L162.816 30H155.856L149.696 11.04L143.336 30H136.416L127.216 2H133.936L140.256 21.68L146.856 2H152.856L159.256 21.84L165.776 2H171.976Z" fill="black"/>
                            <path d="M183.792 30.32C181.525 30.32 179.485 29.8533 177.672 28.92C175.885 27.96 174.485 26.64 173.472 24.96C172.459 23.28 171.952 21.3733 171.952 19.24C171.952 17.1067 172.459 15.2 173.472 13.52C174.485 11.84 175.885 10.5333 177.672 9.6C179.485 8.64 181.525 8.16 183.792 8.16C186.059 8.16 188.085 8.64 189.872 9.6C191.659 10.5333 193.059 11.84 194.072 13.52C195.085 15.2 195.592 17.1067 195.592 19.24C195.592 21.3733 195.085 23.28 194.072 24.96C193.059 26.64 191.659 27.96 189.872 28.92C188.085 29.8533 186.059 30.32 183.792 30.32ZM183.792 25.2C185.392 25.2 186.699 24.6667 187.712 23.6C188.752 22.5067 189.272 21.0533 189.272 19.24C189.272 17.4267 188.752 15.9867 187.712 14.92C186.699 13.8267 185.392 13.28 183.792 13.28C182.192 13.28 180.872 13.8267 179.832 14.92C178.792 15.9867 178.272 17.4267 178.272 19.24C178.272 21.0533 178.792 22.5067 179.832 23.6C180.872 24.6667 182.192 25.2 183.792 25.2Z" fill="black"/>
                            <path d="M205.723 11.32C206.469 10.28 207.469 9.49333 208.723 8.96C210.003 8.42667 211.469 8.16 213.123 8.16V13.92C212.429 13.8667 211.963 13.84 211.723 13.84C209.936 13.84 208.536 14.3467 207.523 15.36C206.509 16.3467 206.003 17.84 206.003 19.84V30H199.763V8.48H205.723V11.32Z" fill="black"/>
                            <path d="M216.833 0.319998H223.073V30H216.833V0.319998Z" fill="black"/>
                            <path d="M250.784 0.319998V30H244.824V27.52C243.278 29.3867 241.038 30.32 238.104 30.32C236.078 30.32 234.238 29.8667 232.584 28.96C230.958 28.0533 229.678 26.76 228.744 25.08C227.811 23.4 227.344 21.4533 227.344 19.24C227.344 17.0267 227.811 15.08 228.744 13.4C229.678 11.72 230.958 10.4267 232.584 9.52C234.238 8.61333 236.078 8.16 238.104 8.16C240.851 8.16 242.998 9.02667 244.544 10.76V0.319998H250.784ZM239.184 25.2C240.758 25.2 242.064 24.6667 243.104 23.6C244.144 22.5067 244.664 21.0533 244.664 19.24C244.664 17.4267 244.144 15.9867 243.104 14.92C242.064 13.8267 240.758 13.28 239.184 13.28C237.584 13.28 236.264 13.8267 235.224 14.92C234.184 15.9867 233.664 17.4267 233.664 19.24C233.664 21.0533 234.184 22.5067 235.224 23.6C236.264 24.6667 237.584 25.2 239.184 25.2Z" fill="black"/>
                            </svg>                       
                    </div>           
                </div>
    </section>

JS:

let thresholdArray = []
for (let i = 10; i < 100; i += 1){    
    thresholdArray.push(i / 100);    
}

let options = {
  root: null,
  rootMargin: "20px",
  threshold: thresholdArray
};

let pathGenerated = false;
let callback = (entries, observer) => {
    entries.forEach(element => {
        element.target.querySelectorAll("path").forEach(path => {
        if (element.isIntersecting) {
            if (!pathGenerated) {           
              path.setAttribute("style", "offset-path: path('M" + 0 +" " + 0 + " L " + generateRandomAnimationPathLine() + " " + generateRandomAnimationPathLine() + "')"); 
            }
            path.style.offsetDistance = element.intersectionRatio * 100 + "%";          
        } else {           
            pathGenerated = false;
            path.style.removeProperty("offset-path");            
        }
        
    });
    }); 
    pathGenerated = true;  
}

let generateRandomAnimationPathLine = (element) => {
    return Math.floor(Math.random() * Math.floor(100));
}

let observer = new IntersectionObserver(callback, options);

document.querySelectorAll('section').forEach(section => {
    console.log(section)
    observer.observe(section);
});

Answer 1

I have to say I find the usage of offset-path for the goal you want to achieve suboptimal. Support for several properties of the Motion path CSS module is incomplete, and as we have found out, the relation of rotation to the path is counter-intuitive. SVG itself has a mechanism for shifting and rotating individual letters in a text that can do this without any compatibility issues. This assumes you can use a <text> element instead of letters converted to paths.

<text> and <tspan> elements accept a number of attributes that take a list of space-separated numbers as argument. The nth number is applied to the nth letter inside the element:

• dx and dy shift each letter away from the position it would be rendered at. The shifting is accumulative. In other words: after the first letter is shifted according to the first values, the second letter is rendered next to the shifted first letter, and is shifted away from that position according to the second values.
• rotate rotates each letter, but is not accumulative: each number represents the rotation away from its original orientation.

The following example is a bit reduced from your pen, setting the "distance" with a slider instead of using an Observer. The maximum distances and rotations are stored in a global object. On each slider change, the list of values in the dx , dy and rotate attributes is recomputed to a fraction of the maximum distance and angle. Because of the accumulative nature of the distance values, the shift is "reset" for each letter by subtracting the shift of the previous letter.

 const offsets = []; for (let i = 0; i < 11; i++) { offsets.push({ x: Math.random() * 60 - 30, y: Math.random() * 60 - 30, a: Math.random() * 360 - 180 }); } const text = document.querySelector('.mesg'); document.querySelector('#distance').addEventListener('change', (ev) => { const dist = parseFloat(ev.target.value); const attrs = offsets.reduce((attr, o, i) => { attr.dx.push((i ? ox - offsets[i-1].x : ox) * dist); attr.dy.push((i ? oy - offsets[i-1].y : oy) * dist); attr.rotate.push(oa * dist); return attr; }, {dx: [], dy: [], rotate: []}); for (let [key, value] of Object.entries(attrs)) { text.setAttribute(key, value.join(" ")); } })

 text { font-size: 20px; font-family: sans-serif; }

 <div><input id="distance" type="range" min="0" max="1" step="0.05" value="0"></input></div> <svg viewBox="0 0 200 100" width="100%" height="150"> <text x="10" y="60" class="mesg">Hello World</text> </svg>

Answer 2

There are two misunderstandings. The first one concerns the way offset-path works. If you have a path defined along which to move a letter, this is done using a moving coordinate system:

• The origin of the coordinate system is moved to the point on the path indicated by offset-distance .
• If nothing else is set for the property offset-rotate , the coordinate system is rotated automatically such that the x-axis points along the tangent to the path at the current used point.
• Then, the letter is drawn in the moved and rotated coordinate system.

Contrary to what your grafic above implies, the letters are not moved away from their original position with an increasing distance, each of them always has a distance from the origin of its unmoved coordinate system, which is rotated and moved along the offset path. (Since each path has a separate offset path, this means a separate coordinate system for each letter.)

In a sense, for your straight lines, the rotation is applied before there is even a small distance, and that is why the letters end up all over the place.

As soon as you set

path {
  offset-rotate: 0deg;
}

the rotation of the coordinate system is suppressed, and at offset-distance: 0 the letters are displayed at their original place. For greater distances, they still move in different directions, but unrotated.

If you want to give the letters an increasing rotation dependent on the distance, you would have to compute that in the script. But remember, the center of rotation is not the moved letter position, but the origin of the original coordinate system! That has the consequence that a linear function that rotates the letter increasingly with declining intersection, combined with an increasing distance, will produce a movement along a spiral . (Think of the combination of distance and rotation as polar coordinates.)

The second misunderstanding lies in the value of intersectionRatio the IntersectionObserver gives back. An intersection of 0% means the object is outside the reference, 100% means is is inside . Therefore, if you want to positiion the letters "orderly" as long as the section is visible, you have to compute the offset distance as inverse to the intersection:

let callback = (entries, observer) => {
    entries.forEach(element => {
      element.target.querySelectorAll("path").forEach(path => {
        if (element.isIntersecting) {
          if (!pathGenerated) {           
            const x1 = 0;        
            const y1 = 0;        
            const x2 = generateRandomAnimationPathLine();        
            const y2 = generateRandomAnimationPathLine();
            path.style.offsetPath = `path('M ${x1} ${y1} L ${x2} ${y2}')`;
          }
          path.style.offsetDistance = (1 - element.intersectionRatio) * 100 + "%";
        } else {           
          pathGenerated = false;
          path.style.removeProperty("offset-path");            
        }
      });
    }); 
    pathGenerated = true;  
}