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我有一个在滚动时发生的简单 svg 动画。但是我怎样才能让动画在页面的下方开始呢？

现在它在我开始滚动时就开始了。

// Get the id of the <path> element and the length of <path>
var triangle = document.getElementById("triangle");
var length = triangle.getTotalLength();

// The start position of the drawing
triangle.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
triangle.style.strokeDashoffset = length;

// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);

function myFunction() {
var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);

  var draw = length * scrollpercent;
  
  // Reverse the drawing (when scrolling upwards)
  triangle.style.strokeDashoffset = length - draw;
}
<h2>Scroll down this window to draw a triangle.</h2>
<p>Scroll back up to reverse the drawing.</p>

<svg id="mySVG">
  <path fill="none" stroke="red" stroke-width="3" id="triangle" d="M150 0 L75 200 L225 200 Z" />
  Sorry, your browser does not support inline SVG.
</svg>

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1 回答 1

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确定您希望动画在滚动的哪个部分发生。然后将其映射到您的实际动画百分比。

例如，假设您希望动画在 50% 滚动到 90% 滚动范围内发生。然后您需要将范围 (0.5->0.9) 映射到 (0.0->1.0)。

  • 所以任何输入值 <= 0.5 都映射到输出值 0。
  • 并且任何输入值 >= 0.9 都映射为 1。
  • 两者之间的值在 0 和 1 之间按比例缩放。

有关此映射的代码，请参见mapRange()以下示例中的函数。

// Get the id of the <path> element and the length of <path>
var triangle = document.getElementById("triangle");
var length = triangle.getTotalLength();

// The start position of the drawing
triangle.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
triangle.style.strokeDashoffset = length;

// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);

function myFunction() {
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);

  var draw = length * mapRange(scrollpercent, 0.5, 0.9, 0, 1);
  
  // Reverse the drawing (when scrolling upwards)
  triangle.style.strokeDashoffset = length - draw;
}

// Maps n from the range (fromStart->fromEnd) to the range (toStart->toEnd).
function mapRange(n, fromStart, fromEnd, toStart, toEnd) {
  const out = toStart + (n - fromStart) * ((toEnd - toStart) / (fromEnd - fromStart));
  // Exclude any values outside to toStart->toEnd range
  return Math.min(toEnd, Math.max(toStart, out));
}
body {
  min-height: 1000px;
}

svg {
  position: fixed;
  width: 300px;
  height: 300px;
}
<h2>Scroll down this window to draw a triangle.</h2>
<p>Scroll back up to reverse the drawing.</p>

<svg id="mySVG">
  <path fill="none" stroke="red" stroke-width="3" id="triangle" d="M150 0 L75 200 L225 200 Z" />
  Sorry, your browser does not support inline SVG.
</svg>

于 2020-04-04T12:45:09.277 回答