Question

我取得的成就：

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.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() {
  // What % down is it?
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
  // Length to offset the dashes
  var draw = length * scrollpercent;

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;

  //get point at length
  endPoint = myline.getPointAtLength(draw);
  circle.setAttribute("cx", endPoint.x);
  circle.setAttribute("cy", endPoint.y);

}

body {
  height: 2000px;
  background: #f1f1f1;
}

#circle {
  fill: red;
}

#mySVG {
  position: absolute;
  top: 15%;
  width: 100%;
  height: 1000px;
  
}

.st1 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: grey;
  stroke-width: 4;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}
.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <path  class="st1" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <circle id="circle" cx="10" cy="10" r="10"/>
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

我想要的是无论SVG <path>是哪种大小或形状增长线应该在屏幕中间。

我尝试更改myline.style.strokeDashoffset = length //+newvalue - draw;的值，但所做的一切只是破坏一致性。有没有人可以帮助我解决这个问题。

任何帮助都是高度赞赏的。

Answer 1

（更新/新答案）

我认为这正是您想要的...

更新（根据需要添加缓动）：

通过向#body添加transition: stroke-dashoffset ease-in-out 0.2s;使#body的长度平滑增加

在#head上添加transition: cx ease-in-out 0.2s, cy ease-in-out 0.2s;不能使#head的移动变得平滑，因为那样会使它跳跃而不是沿着路径移动。

如果您希望#head沿轨道平滑移动，则必须通过用js手动实现缓动来完成，这是很多工作。所以跳过了那部分。

let roadmapSvg = document.getElementById("roadmap-svg");
let track = document.getElementById("track");
let body = document.getElementById("body");
let head = document.getElementById("head");

let totalLength = track.getTotalLength();
let trackPoints = [];
let getTrackBounds = () => track.getBoundingClientRect();
let scaleFactor;

body.style.strokeDasharray = totalLength;
body.style.strokeDashoffset = totalLength;

function setScaleFactor(){
  scaleFactor = roadmapSvg.getBoundingClientRect().width / roadmapSvg.viewBox.baseVal.width;
}   
setScaleFactor();

function setTrackPoints(){
  let divisions = 1000;
  let unitLength = totalLength / divisions;
  trackPoints = [];
  for(let i=0; i < divisions; i++){
    let length = unitLength * i;
    let {x,y} = track.getPointAtLength(length);
    trackPoints.push({x: x*scaleFactor, y: y*scaleFactor, length});
  }
}
setTrackPoints();


function draw(){
  let currentLength = getCurrentLength();
  body.style.strokeDashoffset = totalLength - currentLength;
  headPos = track.getPointAtLength(currentLength);
  head.setAttribute("cx", headPos.x);
  head.setAttribute("cy", headPos.y);
}

function getCurrentLength(){
  let centreY = window.innerHeight / 2;
  let trackBounds = getTrackBounds();
  let currentY = centreY - trackBounds.y;
  if(currentY < 0) return 0;
  
  // if currentY is greater that track height, that means the user has scrolled pass the track (and the whole svg) in such case the animation should be completed i.e. the head should be at the final position i.e. at totalLength 
  if(currentY > trackBounds.height) return totalLength;
  
  for(let point of trackPoints){
    if(point.y >= currentY){
      return point.length;
    }
  }
  
  // (For safety) Sometimes none of the conditions match bcoz of low precision... Such situation only occurs a point very close to total length... Thus...
  return totalLength;
}

document.addEventListener("scroll", draw);

window.addEventListener("resize", () => {
  setScaleFactor();
  setTrackPoints();
  draw();
});

body {
  background: #f1f1f1;
  margin: 0;
  padding: 0 20%;
  font-family: sans-serif;
}

#roadmap-svg{
  display: block;
  max-width: 600px;
  margin: 20px auto;
  overflow: visible;
}

#roadmap-svg #head{
  fill: red;
}

#roadmap-svg #track{
  fill: none;
  stroke-dashoffset: 3px;
  stroke: grey;
  stroke-width: 4;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}
#roadmap-svg #body{
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
  transition: stroke-dashoffset ease-in-out 0.2s;
}

.center-line{
  position: fixed;
  left: 0;
  right: 0;
  top: 50%;
  border-top: 1px solid red;
  background-color: rgba(255,255,255,0.9);
}

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<svg id="roadmap-svg" viewBox="0 0 760 300">
  <path  id="track" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" />
  <path id="body" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" />
  <circle id="head" cx="10" cy="10" r="10"/>
</svg>
<div class="center-line">Center Line</div>
<div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Sapiente officia saepe facilis? Cupiditate rem vel, quaerat ratione ipsam magnam fugiat praesentium incidunt! Eveniet cum officia impedit obcaecati id animi rerum?
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Answer 2

我尝试了几种方法来移动点

在盒子里
直到结束都不会滑动
对原始内容的更改最少。

我进行了以下更改（以下工作示例）：

我输入2000的百分比除法器（等于2000px，包含身体高度）
我将顶部的滚动量乘以18（无论顶部或底部的行为方式如何，适当的值都是一个折衷方案）
然后最后我检查了百分比值是否不大于一个（它从另一端开始吃掉了“蠕虫”）。

就是这样！也许不是最幻想的，但是可以。

这里的问题是svg线从上到下不是线性的，因此无法选择与直接元素相关的值，或者至少我找不到。因此，我最终得到了简单的解决方案并使用了参数。

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.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() {
  // What % down is it?
  var scrollpercent = (document.documentElement.scrollTop * 18) / 2000;
  if (scrollpercent > 1) scrollpercent = 1;
  var draw = length * scrollpercent;

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;

  //get point at length
  endPoint = myline.getPointAtLength(draw);
  circle.setAttribute("cx", endPoint.x);
  circle.setAttribute("cy", endPoint.y);
}

body {
  height: 2000px;
  background: #f1f1f1;
}

#circle {
  fill: red;
}

#mySVG {
  position: absolute;
  top: 15%;
  width: 100%;
  height: 1000px;
  
}

.st1 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: grey;
  stroke-width: 4;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}
.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <path  class="st1" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <circle id="circle" cx="10" cy="10" r="10"/>
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

Answer 3

根据注释以及对CSS和SVG代码的少量修改，我能够将行移到页面的中心，请检查以下工作示例：

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.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() {
  // What % down is it?
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
  // Length to offset the dashes
  var draw = length * scrollpercent;

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;

  //get point at length
  endPoint = myline.getPointAtLength(draw);
  circle.setAttribute("cx", endPoint.x);
  circle.setAttribute("cy", endPoint.y);
}

body {
  margin: 0;
  height: 1000px;
  background: #f1f1f1;
}
#circle {
  fill: red;
}
#mySVG {
  top: 15%;
  position: absolute;
  width: 100%;
}
.st1 {
  fill: none;
  stroke-dashoffset: 1;
  stroke: grey;
  stroke-width: .5;
  stroke-miterlimit: 1;
  stroke-dasharray: 2;
}
.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 1;
  stroke-miterlimit: 1;
  stroke-dasharray: 2;
}
.grid {
  position: fixed;
  width: 1px;
  height: 100%;
  background: blue;
  left: 50%;
  top: 0;
}

<div class="grid"></div>
<svg id="mySVG" viewBox="0 0 200 72" preserveAspectRatio="xMidYMin slice">
  <path class="st1" stroke-dasharray="10,9" d="m 0,5 0,4 c 0,3 2,6 5,6 l 108,0 c 4,0 7,4 7,8 0,4 -3,7 -7,7 l -25,0 c -3,0 -6,3 -6,6 0,3 3,6 6,6 l 35,0 c 4,0 7,4 7,8 0,4 -3,7 -7,7 l -18,0 c -3,0 -5,3 -5,6 l 0,4" />
</svg>

<svg id="mySVG" viewBox="0 0 200 72" preserveAspectRatio="xMidYMin slice">
  <circle id="circle" cx="0" cy="3" r="2" />
  <path id="myline" class="st0" stroke-dasharray="10,9" d="m 0,5 0,4 c 0,3 2,6 5,6 l 108,0 c 4,0 7,4 7,8 0,4 -3,7 -7,7 l -25,0 c -3,0 -6,3 -6,6 0,3 3,6 6,6 l 35,0 c 4,0 7,4 7,8 0,4 -3,7 -7,7 l -18,0 c -3,0 -5,3 -5,6 l 0,4" />
</svg>

Answer 4

我会选择其他方法。我了解您想在路径上找到最靠近屏幕中间的点。让我们做到这一点：

找到屏幕中间的坐标，并将其转换为路径的坐标系。 SVG API为此具有两个功能：.getScreenCTM()和SVGPoint.matrixTransform()。
在路径上找到最靠近这些坐标的点（及其在路径上的距离）。要做一些数学和搜索算法。 Mike Bostock拥有shown这样的算法，并在这里使用。请注意，他的功能需要一些调整（precision参数）。
使用这些数据绘制圆和点偏移。

最好通过引入throttle for the scroll events（第二个变体）然后设置CSS transitions来避免可见的跳动来完善这一点。

圆定位的过渡仅适用于CSS transform属性。（我的解决方案不必在过渡时沿路径移动圆。可以实现这一点，但远远超出了此答案的范围。）

var mySVG = document.getElementById("mySVG");
// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var pathLength = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = pathLength;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.style.strokeDashoffset = pathLength;

// throttled scroll event listener
function throttle(ms, callback) {
    var timer, lastCall=0;

    return function() {
        var now = new Date().getTime(),
            diff = now - lastCall;
        if (diff >= ms) {
            lastCall = now;
            callback();
        }
    };
}

window.addEventListener("scroll", throttle(100, myFunction));

// one initial execution
myFunction();

function myFunction() {
  var center = mySVG.createSVGPoint();
  // middle of browser viewport
  center.x = window.innerWidth / 2;
  center.y = window.innerHeight / 2;
  // transform to path coordinate system
  var matrix = myline.getScreenCTM().inverse();
  center = center.matrixTransform(matrix);

  //find nearest length on path
  var draw = getNearestLength(center);

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = -draw - pathLength;

  //get point at length
  endPoint = myline.getPointAtLength(draw);
  circle.style.transform = "translate(" + endPoint.x + "px, " + endPoint.y + "px)";
}

function getNearestLength(point) {
  var precision = 8,
      best,
      bestLength,
      bestDistance = Infinity;
  // linear scan for coarse approximation
  for (var scan, scanLength = 0, scanDistance; scanLength <= pathLength; scanLength += precision) {
    if ((scanDistance = distance2(scan = myline.getPointAtLength(scanLength))) < bestDistance) {
      best = scan, bestLength = scanLength, bestDistance = scanDistance;
    }
  }
  // binary search for precise estimate
  precision /= 2;
  while (precision > 0.5) {
    var before,
        after,
        beforeLength,
        afterLength,
        beforeDistance,
        afterDistance;
    if ((beforeLength = bestLength - precision) >= 0 && (beforeDistance = distance2(before = myline.getPointAtLength(beforeLength))) < bestDistance) {
      best = before, bestLength = beforeLength, bestDistance = beforeDistance;
    } else if ((afterLength = bestLength + precision) <= pathLength && (afterDistance = distance2(after = myline.getPointAtLength(afterLength))) < bestDistance) {
      best = after, bestLength = afterLength, bestDistance = afterDistance;
    } else {
      precision /= 2;
    }
  }
  return bestLength;

  function distance2(p) {
    var dx = p.x - point.x,
        dy = p.y - point.y;
    return dx * dx + dy * dy;
  }
}

body {
  height: 2000px;
  background: #f1f1f1;
}

#circle {
  fill: red;
}

#mySVG {
  position: absolute;
  top: 15%;
  width: 100%;
  height: 1000px;
  
}

.st1 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: grey;
  stroke-width: 4;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}
.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
  transition: stroke-dashoffset 0.2s;
}

#circle {
   transform: translate(10px, 10px);
   transition: transform 0.2s;
   }

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <path  class="st1" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <circle id="circle" cx="0" cy="0" r="10"/>
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

SVG`<path>`JavaScript动画无法正常工作

4 个答案: