Detailed explanation of the example of using css to achieve the picture magnifying glass effect (picture)

This article explains how to use css to achieve PictureMagnifying glass effect ? The following is a detailed explanation of the CSS example of the picture magnifying glass effect.

The effect is as shown in the figure (in the example, I secretly linked a picture of Tmall, I hope it’s okay-.-):

The implementation process is simple, but we still start the analysis from css. The process is as follows (the picture is a square as an example):

css:

/* 图片容器 */
    .imgBox{
      width: 200px; /* 各位大老爷们看着办 */
      height: 200px; /* 各位大老爷们看着办 */
      position: relative; /* 必需 */
    }
 
    /* 图片标签 */
    .mainImg{
      width: 100%; /* 各位大老爷们看着办，尽量100%好看些[斜眼笑] */
      height: 100%; /* 各位大老爷们看着办，尽量100%好看些[斜眼笑] */
    }
 
    /* 遮罩层-既放大区域 */
    .glass{
      position: absolute; /* 必需 */
      width: 50px; /* 遮罩层宽度 此处是放大4倍，所以为200/4=50 */
      height: 50px; /* 遮罩层高度 此处是放大4倍，所以为200/4=50  */
      top: -9999px; /* 绝对位置，先放远些 */
      left: -9999px; /* 绝对位置，先放远些 */
      cursor: move; /* 鼠标样式，好看些 */
      background: rgba(0,0,180,0.5); /* 遮罩层样式，好看些 */
    }
 
    /* 大图所在的容器 */
    .imgMax{
      position: absolute;  /* 必需 */
      overflow: hidden; /* 必需，盖掉超出的大图[斜眼笑] */
      left: 210px; /* 必需，此处为距原图左边10像素 */
      top: 0; /* 必需，此处为距上边0像素 */
      width: 200px; /* 放大图片容器的宽度 此处此处是放大4倍，为200，保持和原图容器一般大，若此处为400，则是放大2*4倍，那么相应的放大图片应该是200*4*2=1600 */
      height: 200px; /* 放大图片容器的高度 此处此处是放大4倍，为200，保持和原图容器一般大，若此处为400，则是放大2*4倍，那么相应的放大图片应该是200*4*2=1600 */
      display: none; /* 先隐藏 */
    }
    .maxImg{
      position: absolute; /* 必需 */
      width: 800px; /* 此处是放大4倍，所以为200*4=800  受放大图片所在的容器影响，规则如上 */
      height: 800px; /* 此处是放大4倍，所以为200*4=800  受放大图片所在的容器影响，规则如上 */
    }

What you need to pay attention to in the above css are several positions and scaling ratios. Pay attention to the adjustments.

After writing the style, let’s take a look at the layout:

html：

<!-- 图片容器 -->
    <pclass>
      <!-- 需要放大的图片-原始图 -->
      <img  class="J_mainImg mainImg lazy" src="/static/imghwm/default1.png" data-src="http://img.alicdn.com/bao/uploaded/i7/TB1Xpe_NXXXXXXRXFXXGTq09XXX_035318.jpg_430x430q90.jpg" alt="Detailed explanation of the example of using css to achieve the picture magnifying glass effect (picture)" >
      <!-- 遮罩-既放大的区域 -->
      <pclass>
      <!-- 大图的容器 -->
      <pclass>
        <!-- 大图 -->
        <img  class="J_maxImg maxImg lazy" src="/static/imghwm/default1.png" data-src="https://img.php.cn/upload/article/000/000/164/92904c7f39f2e60a002ba228e687b2e8-1.png?x-oss-process=image/resize,p_40" alt="Detailed explanation of the example of using css to achieve the picture magnifying glass effect (picture)" >
      
    </pclass></pclass></pclass>

Next is the main js code, with comments as always:

js:

(function(){
    /* 放大镜函数
    ** @imgContainer  需要实现放大镜效果的图片容器  此处是 class 为 J_imgBox 的 p
    */
    function imgZoom(imgContainer){
 
      // 取大图url，不知道淘宝图片规则如何，反正看了详情页的大图和小图url对比，随便写了个替换
      var imgUrl = imgContainer.querySelector('.J_mainImg').src.replace(/.(jpg|jpeg|png|gif)(_)(d+)(x)(d+)(q90)?/g,'');
 
      // 取大图标签的节点
      var maxImg = imgContainer.querySelector('.J_maxImg');
 
      // 给该节点的src属性赋值为大图的url
      maxImg.src = imgUrl;
 
      // 取大图所在的容器
      var maxImgContainer = imgContainer.querySelector('.J_imgMax');
 
      // 取遮罩块
      var glassBlock = imgContainer.querySelector('.J_glass');
 
      // 取消放大镜效果
      var hideMaxImg = function(){
        glassBlock.style.top = '-9999px';
        glassBlock.style.left = '-9999px';
        maxImgContainer.style.display = 'none';
      }
 
      // 鼠标移出图片区域，取消放大镜效果
      imgContainer.onmouseout = function(event){
        event.stopPropagation();
        hideMaxImg();
      };
 
      // 鼠标在图片区域内移动事件
      imgContainer.onmousemove = function(event) {
        event.stopPropagation();
 
        // 取图片容器的大小及其相对于视口的位置，需要实时取，所以放在move事件里
        var clientRect = event.currentTarget.getBoundingClientRect();
 
        // 获取距鼠标距的上和左的坐标
        var leftX = event.clientX - clientRect.left;
        var leftY = event.clientY - clientRect.top;
 
        // 动态设置遮罩块的left和top位置  这里需要减去遮罩层的一半，因为鼠标位于遮罩块中心点
        var pointerLeft = leftX - 25;
        var pointerTop = leftY - 25;
 
        // 如果鼠标坐标移动超出原始图片区域边缘 则取消放大镜效果  因为这里存在快速移动鼠标到大图区域时，鼠标仍处在外层的图片区域内，并不会触发mouseout事件(虽然中间隔了小小的间距，但是快速移动仍能产生这个bug,如代码下面的图所示)
        if((pointerLeft+25) > clientRect.width || pointerLeft  clientRect.height || pointerTop ){
          hideMaxImg();
          return !1;
        };
 
        // 遮罩块在最左边的时候，鼠标仍在图片区域内，可在遮罩块左边缘至中心线区域内移动，且这时遮罩块为距左0像素
        if(pointerLeft ){
          pointerLeft = 0;
        };
 
        // 同上 右边限制
        if(pointerLeft > clientRect.width - 50){
          pointerLeft = clientRect.width - 50;
        };
 
        // 同上 顶部限制
        if(pointerTop ){
          pointerTop = 0;
        };
 
        // 同上 底部限制
        if(pointerTop > clientRect.height - 50){
          pointerTop = clientRect.height - 50;
        };
 
        // 设置遮罩块的位置
        glassBlock.style.left = pointerLeft;
        glassBlock.style.top = pointerTop;
 
        // 取遮罩快距离左边的位置和图片区域的宽高比，用于计算大图偏移距离，展示遮罩块所对应的图片区域
        var percentLeft = pointerLeft/clientRect.width;
        var percentHeight = pointerTop/clientRect.height;
 
        // 设置大图偏移距离 因为其父元素存在 overflow:hidden 所以只会展示对应区块
        maxImg.style.left = -(percentLeft*maxImg.clientWidth)+'px';
        maxImg.style.top = -(percentHeight*maxImg.clientHeight)+'px';
      };
    }
 
    var elem = document.querySelectorAll('.J_imgBox');
 
    elem.forEach(function(item,idx){
      imgZoom(item)
    })
  })()

bug fixing picture:

After reading this, do you feel that it is not too simple? Next, let’s take a look at the more practical knowledge points that can be extracted from the above code in daily development:

Element .getBoundingClientRect()

Element.getBoundingClientRect() method returns the size of the element and its position relative to the viewport

Example:

<bodystyle>
      <pid>
      <script>
        (function(){
          var elem = document.getElementById(&#39;testp&#39;);
          document.body.addEventListener(&#39;click&#39;,function(){
              console.log(elem.getBoundingClientRect())
          },false)
        })()
      </script>
    </pid></bodystyle>

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