Progress bar along the borders of a rectangle

Progress bar along the borders of a rectangle

CSS：

CSS可以使用多个线性渐变作为
背景并将其适当放置，从而达到此效果。方法如下：

linear-gradient为元素的每个边框创建4个稀薄的背景。边框的粗细决定了background-size。也就是说，如果边框厚度为5px，则产生顶部和底部边框的线性渐变将为100% 5px（100％宽度5px高度），而产生左右边框的线性渐变将为5px 100%（3px宽度100％高度）。最初background-position设置时，所有边框都不可见。在动画期间，我们将每个背景渐变设置为正确的位置。这将产生具有动画边框的效果。我在下面的代码段中使用了CSS关键帧，因此它会自动从头到尾进行动画处理（也就是说，仅在绘制完整边框后才停止动画处理），但是如果您希望对其进行更多控制（并说将其停在中间，例如进度条），则可以使用JS并background-position根据进度百分比进行修改。

.progress {  height: 300px;  width: 500px;  background: linear-gradient(to right, black 99.99%, transparent), linear-gradient(to bottom, black 99.99%, transparent), linear-gradient(to right, black 99.99%, transparent), linear-gradient(to bottom, black 99.99%, transparent);  background-size: 100% 5px, 5px 100%, 100% 5px, 5px 100%;  background-repeat: no-repeat;  animation: progress 4s linear forwards;  background-position: -500px 0px, 495px -300px, 500px 295px, 0px 300px;}@keyframes progress {  0% {    background-position: -500px 0px, 495px -300px, 500px 295px, 0px 300px;  }  25% {    background-position: 0px 0px, 495px -300px, 500px 295px, 0px 300px;  }  50% {    background-position: 0px 0px, 495px 0px, 500px 295px, 0px 300px;  }  75% {    background-position: 0px 0px, 495px 0px, 0px 295px, 0px 300px;  }  100% {    background-position: 0px 0px, 495px 0px, 0px 295px, 0px 0px;  }}<!-- prefix free library is only to avoid browser prefixes --><script src="https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js"></script><div ></div>

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没有自动动画的CSS版本：

这是代码段的CSS版本，该代码版本接受输入百分比值并根据该值设置边框。在文本框中输入0到100之间的值，然后单击Enter。

window.onload = function() {  var progress = document.querySelector('.progress'),    totalLength = (progress.offsetWidth * 2) + (progress.offsetHeight * 2);  var btn = document.querySelector('#enter'),    progressVal = document.querySelector('#progress');  btn.addEventListener('click', function() {    input = (progressVal.value > 100) ? 100 : progressVal.value;    borderLen = (input / 100) * totalLength;    console.log(borderLen);    if (borderLen <= progress.offsetWidth) {      backgroundPos = 'background-position: ' + (-500 + borderLen) + 'px 0px, 495px -300px, 500px 295px, 0px 300px';      progress.setAttribute('style', backgroundPos);    } else if (borderLen <= (progress.offsetWidth + progress.offsetHeight)) {      backgroundPos = 'background-position: 0px 0px, 495px ' + (-300 + (borderLen - progress.offsetWidth)) + 'px, 500px 295px, 0px 300px';      progress.setAttribute('style', backgroundPos);    } else if (borderLen <= (progress.offsetWidth * 2 + progress.offsetHeight)) {      backgroundPos = 'background-position: 0px 0px, 495px 0px, ' + (500 - (borderLen - progress.offsetWidth - progress.offsetHeight)) + 'px 295px, 0px 300px';      progress.setAttribute('style', backgroundPos);    } else {      backgroundPos = 'background-position: 0px 0px, 495px 0px, 0px 295px, 0px ' + (300 - (borderLen - (progress.offsetWidth * 2) - progress.offsetHeight)) + 'px';      progress.setAttribute('style', backgroundPos);    }  });};.progress {  height: 300px;  width: 500px;  margin-top: 20px;  background: linear-gradient(to right, black 99.99%, transparent), linear-gradient(to bottom, black 99.99%, transparent), linear-gradient(to right, black 99.99%, transparent), linear-gradient(to bottom, black 99.99%, transparent);  background-size: 100% 5px, 5px 100%, 100% 5px, 5px 100%;  background-repeat: no-repeat;  background-position: -500px 0px, 495px -300px, 500px 295px, 0px 300px;}<!-- prefix free library is only to avoid browser prefixes --><script src="https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js"></script><input id='progress' type='text' /><button id='enter'>Set Progress</button><div ></div>

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使用SVG：

使用SVG时，方法如下：

创建一个path元素，使其形成框的边界，并使用getTotalLength()方法获得其长度。设置stroke-dasharray和的stroke-dashoffset属性，以path使路径最初不可见。通过stroke-dashoffset根据进度百分比修改，我们可以产生类似于进度条的效果。再次，我使用动画从头到尾自动触发移动，但是如果您想要类似效果的进度条，则可以删除动画并仅基于进度百分比设置偏移量。

window.onload = function() {  var progress = document.querySelector('.progress path');  var borderLen = progress.getTotalLength() + 5,    offset = borderLen;  progress.style.strokeDashoffset = borderLen;  progress.style.strokeDasharray = borderLen + ',' + borderLen;  anim = window.requestAnimationframe(progressBar);  function progressBar() {    offset -= 1;    progress.style.strokeDashoffset = offset;    anim = window.requestAnimationframe(progressBar);    if (offset < 0)      window.cancelAnimationframe(anim);  }};.progress {  height: 300px;  width: 500px;}.progress svg {  height: 100%;  width: 100%;}path {  stroke: black;  stroke-width: 5;  fill: none;}<div >  <svg viewBox='0 0 510 310' preserveAspectRatio='none'>    <path d='M5,5 505,5 505,305 5,305 5,2.5' />    <!-- end is start point - stroke width/2 -->  </svg></div>

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没有自动动画的SVG版本：

这是该片段的SVG版本，该版本接受输入百分比值并根据该值设置边框。在文本框中输入0到100之间的值，然后单击Enter。

window.onload = function() {  var progress = document.querySelector('.progress path');  var borderLen = progress.getTotalLength() + 5,    offset;  progress.style.strokeDashoffset = borderLen;  progress.style.strokeDasharray = borderLen + ',' + borderLen;  var btn = document.querySelector('#enter'),      progressVal = document.querySelector('#progress');    btn.addEventListener('click', function(){        input = (progressVal.value > 100) ? 100 : progressVal.value;        offsetToSet = (input/100) * borderLen;        console.log(borderLen - offsetToSet);        progress.style.strokeDashoffset = borderLen - offsetToSet;    });};.progress {  height: 300px;  width: 500px;}.progress svg {  height: 100%;  width: 100%;}path {  stroke: black;  stroke-width: 5;  fill: none;}<input id='progress' type='text'/><button id='enter'>Set Progress</button><div >  <svg viewBox='0 0 510 310' preserveAspectRatio='none'>    <path d='M5,5 505,5 505,305 5,305 5,2.5' />    <!-- end is start point - stroke width/2 -->  </svg></div>