HTML5 canvas drawImage方法实现读取图片数据截图拼接图片。

博客展示了代码并给出了相应结果，但未提供更多详细信息。

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代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    *{margin:0 auto;}
    .box{border: 1px solid #ccc;width:1205px;height:400px;margin:0 auto;}
    .box canvas {display:inline-block;width: 600px;height:300px;background:#ccc;}
  </style>
</head>
<body>
  <div class="prev" style="height:300px;width:300px;">
  </div>
  <div style="display:none">
    <img src="./img1.png" />
    <img src="./img2.png" />
  </div>
  <div class="box">
    <canvas id="canvas"></canvas>
    <canvas id="canvas1"></canvas>
    <div>
      <input type="file" id="file1"/>
      <input type="file" id="file2"/>
      <button id="copyBtn">复制图片</button>
    </div>
  </div>
</body>
<script>
  let canvas = document.querySelector('#canvas').getContext("2d");
  let canvas1 = document.querySelector('#canvas1').getContext("2d");
  let img = document.querySelectorAll('img')[0];
  let img1 = document.querySelectorAll('img')[1];
  document.querySelector('#file1').onchange = function (event) {
    // img.src = './img1.png';
    let file = event.target.files[0];
    let reader = new FileReader(); 
    //转base64
    reader.onload = function(e) {
      // img.src = e.target.result;
    }
    img.width = '100px';
    img.height = '100px';
    reader.readAsDataURL(file);
    canvas.drawImage(img, 0, 0, 100, 100, 10, 10, 100, 100);
    var imgData = canvas.getImageData(10,10,100,100);
    console.log(imgData);
  };
  document.querySelector('#file2').onchange = function (event) {
    // img.src = './img1.png';
    let file = event.target.files[0];
    let reader = new FileReader(); 
    //转base64
    reader.onload = function(e) {
      // img.src = e.target.result;
    }
    reader.readAsDataURL(file);
    canvas.drawImage(img1, 0, 0, 100, 100, 200, 10, 100, 100); // 画布上的大小比实际大小大2倍，画布上显示像素为200px * 200px
    var imgData = canvas.getImageData(10,10,100,100);
    console.log(imgData);
    
  };
  document.querySelector('#copyBtn').onclick = function () {
    var dataURL = document.querySelector('#canvas').toDataURL("image/png");
    console.log(dataURL);
    let img = new Image();
    img.src = dataURL;
    document.querySelector('.prev').appendChild(img);
    canvas1.drawImage(img, 0, 0);
  };
</script>
</html>

结果：