What is the pathLength attribute in SVG? What are its practical applications?

SVG's pathLength property: Flexible control of path length

Although the pathLength property in SVG seems simple, it can achieve powerful functions, especially in animation and precise control of path point positions. This article will explore in-depth the use and usage methods of pathLength attribute.

Functions of pathLength attribute

The pathLength property allows you to customize the SVG path(<path></path> ) length. This length can be any value, usually proportional to the actual length of the path. By setting this property, you can control the coordinates of points on the path more accurately, thus achieving complex animation and drawing effects.

How to use pathLength attribute

Suppose you have an SVG path element:

<svg height="100" width="100">
  <path d="M10 10 L90 90" fill="none" pathlength="10" stroke="black"></path>
</svg>

This code sets the length of the path to 10 units. No matter what the actual geometric length of the path is, pathLength normalizes it to the specified value.

Practical application cases

The following example shows how pathLength controls points on a path:

<svg height="100" width="100">
  <path d="M10 10 L90 90" fill="none" pathlength="100" stroke="black"></path>
  <circle cx="10" cy="10" fill="red" r="2"></circle> <!-- Starting point-->
  <circle cx="50" cy="50" fill="blue" r="2"></circle> <!-- path midpoint (50/100) -->
</svg>

Here, the path length is set to 100. The red circle indicates the starting point, while the blue circle is located at 50% of the path. By modifying pathLength , you can accurately adjust the coordinates of any point on the path.

Advanced Application: Animation

pathLength plays a key role in animation. For example, you can create an animation that moves along the path:

<svg height="100" width="100">
  <path d="M10 10 L90 90" fill="none" id="myPath" pathlength="100" stroke="black"></path>
  <circle fill="red" r="2">
    <animatemotion dur="5s" repeatcount="indefinite">
      <mpath xlink:href="https://www.php.cn/link/f9915a71fed113978ef38aca492f4753"></mpath>
    </animatemotion>
  </circle>
</svg>

In this example, the red circle will move along the path, the animation period is 5 seconds, and the playback will be looped. pathLength ensures precise control of animation speed and position.

Summary: The pathLength attribute gives SVG paths extremely high flexibility, giving them wide application prospects in animation and precise drawing. Understanding and applying this attribute can significantly improve the expressiveness of SVG graphics.

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