canvas_代码007

1. fillRe c t() 简单填充模式的使用因为canvas是html5的官方标签，不需要额外引入

    <!-- 
        id: 表示元素的唯一性
        width: 画布的宽度
        height：画布的高度
     --&gt;
    <canvas id="c1" width="600" height="400"
    ></canvas>
    <script>
        //1.找到画布
        var c11 = document.getElementById("c1");
        // 2. 获取画笔，上下文对象
        var ctx =  c11.getContext("2d");
        ctx.fillStyle="#FF0000";
        //3. 绘制图形
        //3.1 绘制矩形fillRect（位置x，位置y，宽度，高度）
        ctx.fillRect(100,200,300,300);
    </script>

2.ctx.strok eRe ct()绘制路径

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 
        id: 表示元素的唯一性
        width: 画布的宽度
        height：画布的高度
     -->
    <canvas id="c1" width="600" height="400"
    ></canvas>
    <script>
        //1.找到画布
        var c11 = document.getElementById("c1");
        // 2. 获取画笔，上下文对象
        var ctx =  c11.getContext("2d");
        //3. 绘制图形
        //3.2 路径绘制矩形
        ctx.strokeRect(100,100,200,100);
        
    </script>
</body>
</html>

简单综合使用

 <div>
          <el-upload
      class="upload-demo"
      ref="upload"
      action="#"
      :show-file-list="false"
      :before-upload="beforeUpload"
      >
      <el-button slot="trigger" size="small" type="primary">选取文件</el-button>
      <el-button style="margin-left: 10px;" size="small" type="success" @click="submitUpload">上传到服务器</el-button>
      <div slot="tip" class="el-upload__tip">只能上传jpg/png文件，且不超过500kb</div>
    </el-upload>
    </div>
    <div>
      <canvas id="c1" width="600" height="400"></canvas>
    </div>
     <img id="img1" :src="file" style="width: 100px; height: 100px;"/> 
    <a :href="hrefdow"  download  style="display: inline-block;">下载</a>

<script>

    //当上传完毕之后触发函数
    beforeUpload(file1){
      this.uploadFile = file1;
      const freader = new FileReader();
      //获取文件并将其转换为url
      freader.readAsDataURL(file1);
      freader.onload = () => {
        this.file = freader.result;
        //当图片存储之后调用函数填写到canvas
        this.imageCavcas(file1);
       };
    },
    imageCavcas(file1){
      //1.找到画布
      var c11 = document.getElementById("c1");
        // 2. 获取画笔，上下文对象
      var ctx =  c11.getContext("2d");
      const img = new Image();
        img.src = this.file;
        img.onload = () =>{
          //图片挂在成功之后载入canvas
          ctx.drawImage(img, 0, 0, c11.width, c11.height);
          ctx.font="30px Arial";
          ctx.strokeText("这是一个水印",10,50);
          //从canvas导出
          this.hrefdow = c11.toDataURL();
         const img1 = document.getElementById("img1");
         img1.src = this.hrefdow;
        }
    },
<script/>