canvas高阶应用之clip查看全图

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前言

往期文章

本文将讲解 canvas-clip 方法的高级用法,比如 游戏或相册中,有权限查看完整图片或关卡时,点击展示全图

效果图

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说明

  1. 设置图片 blur
  2. 在图片上盖住一个canvas,它加载正常清晰的图片
  3. 通过clip(),开始设置裁剪区域为一个小圆,点击“展示全图”时,慢慢调整裁剪区域的大小,直到展示完整图片

代码

  • html
<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width,initial=1.0,user-scalable=no">
  <title>查看全图</title>
  <link rel="stylesheet" href="index.css">
</head>

<body>
  <div class="blur-box">
    <img class="blur-img"
      src="https://gimg2.baidu.com/image_search/src=http%3A%2F%2F07.imgmini.eastday.com%2Fmobile%2F20180717%2F20180717221449_f908566137c38a753a8e55cf0d44a372_7.jpeg&refer=http%3A%2F%2F07.imgmini.eastday.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=jpeg?sec=1640181264&t=feffa7375872c64946a936481abf913b">
    <canvas id="canvas">不支持canvas</canvas>
    <div class="button" id="show-button">SHOW</div>
  </div>
  <script>
    const _w = document.body.clientWidth;
    const _h = document.body.clientHeight;

    const showButton = document.getElementById('show-button');

    const canvas = document.getElementById('canvas');
    const ctx = canvas.getContext('2d');
    canvas.width = _w;
    canvas.height = _h;

    const radius = 50;
    let clipRegion;
    let timer = null;

    let image = new Image();
    image.src = 'https://gimg2.baidu.com/image_search/src=http%3A%2F%2F07.imgmini.eastday.com%2Fmobile%2F20180717%2F20180717221449_f908566137c38a753a8e55cf0d44a372_7.jpeg&refer=http%3A%2F%2F07.imgmini.eastday.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=jpeg?sec=1640181264&t=feffa7375872c64946a936481abf913b';
    image.onload = () => {
      // 随机生成裁剪区位置
      clipRegion = { x: Math.random() * (_w - 2 * radius) + radius, y: Math.random() * (_h - 2 * radius) + radius, r: radius };
      draw(image, clipRegion);
    };

    function draw(image, clipRegion) {
      ctx.clearRect(0, 0, _w, _h);
      ctx.save();
      setClipingRegion(clipRegion);
      ctx.drawImage(image, 0, 0, _w, _h);
      ctx.restore();
    }

    function setClipingRegion(clipRegion) {
      ctx.beginPath();
      ctx.arc(clipRegion.x, clipRegion.y, clipRegion.r, 0, Math.PI * 2);
      ctx.clip();
    }


    showButton.addEventListener('click', () => {
      // 隐藏按钮
      showButton.style.display = 'none';

      timer = setInterval(
        function () {
          clipRegion.r += 20;
          draw(image, clipRegion);
          if (clipRegion.r >= 2 * Math.max(_w, _h)) {
            clearInterval(timer);
            timer = null;
          }
        }, 30);
    }, false);

  </script>
</body>

</html>
  • css
* {
  padding: 0;
  margin: 0;
}

html,
body {
  height: 100%;
  overflow: hidden;
}

.blur-box {
  width: 100%;
  height: 100%;
  position: relative;
}
.blur-img,
#canvas {
  display: block;
  position: absolute;
  left: 0;
  right: 0;
}
.blur-img {
  width: 100%;
  height: 100%;
  /*滤镜模糊*/
  filter: blur(20px);
  z-index: 0;
}
#canvas {
  z-index: 1;
}
.button {
  display: block;
  position: absolute;
  z-index: 2;
  width: 100px;
  height: 30px;
  color: #fff;
  text-decoration: none;
  text-align: center;
  line-height: 30px;
  border-radius: 5px;
}
#show-button {
  left: 0;
  right: 0;
  bottom: 50px;
  background: #085;
  margin: 0 auto;
  cursor: pointer;
}
#show-button:hover {
  background: #074;
}