vue下canvas裁剪图片

            oMark2[‘canvas1‘] = ‘canvasImg2‘;  // 展示结果canvas id
            oMark2[‘canvas2‘] = ‘dymCurrImg2‘; //画布原始图片canvas id
            oMark2[‘ImgUrl‘] = carImgUrl;
            oMark2[‘offsetLeft‘] = location[0];
            oMark2[‘offsetTop‘] = location[2];
            oMark2[‘offsetWidth‘] = location[1] - location[0];
            oMark2[‘offsetHeight‘] = location[3] - location[2];        

     TailoringImg(oMark) {
        // 设置三个canvas 分别为 canvas1 ，canvas2，canvas3
        //   每个canvas的作用 canvas1原始图片画布（页面中隐藏）；
        //   canvas2原图和裁剪结果之间转换；
        //   canvas3裁剪之后的结果展示（页面中展示）；
        let res2 = oMark[‘ImgUrl‘];
        let that = this;
        return new Promise(function (resolve, reject) {
          //图片剪切处理
          var canvas1 = document.getElementById(oMark[‘canvas2‘]);
          var canvas3 = document.getElementById(oMark[‘canvas1‘]);
          canvas1.height = 1080;
          canvas1.width = 1920;

          canvas3.height = 198;
          canvas3.width = 400;
          var cxt1 = canvas1.getContext("2d"); // getContext() 方法返回一个用于在画布上绘图的环境
          var img = new Image();
          img.crossOrigin = ‘‘;
          img.src = res2;
          var canvas2 = document.createElement("canvas"); // 创建虚拟画布环境
          var cxt2 = canvas2.getContext("2d");

          img.onload = function () {
            // 计算图片缩放比例
            var Rwidth = canvas1.width / img.width;
            var Rheight = canvas1.height / img.height;

            cxt1.drawImage(img, 0, 0, canvas1.width, canvas1.height); // --第一步-- 原图绘制在画布上  drawImage方法在画布上绘制图像、画布或视频。也能够绘制图像的某些部分，以及/或者增加或减少图像的尺寸。
　　　　　　　　// 计算缩放好后的尺寸
            var srcX = oMark.offsetLeft * Rwidth;
            var srcY = oMark.offsetTop * Rheight;
            var sWidth = oMark.offsetWidth * Rwidth;
            var sHeight = oMark.offsetHeight * Rheight;
            var dataImg = cxt1.getImageData(srcX, srcY, sWidth, sHeight); //  --第二步-- getImageData() 复制原图画布上指定矩形的像素数据

            canvas2.width = sWidth;
            canvas2.height = sHeight;
            cxt2.putImageData(dataImg, 0, 0, 0, 0, canvas2.width, canvas2.height);  //  --第三步-- 通过 putImageData() 将原图图像数据放到canvas2画布中
            var img2 = canvas2.toDataURL("image/png"); //  --第四步--  toDataURL()将canvas2画布保存为图像

            var cxt3 = canvas3.getContext("2d"); // getContext() 方法返回一个用于在画布上绘图的环境
            var img3 = new Image();  // 创建图像对象
            img3.crossOrigin = ‘‘;  //  图像跨域设置
            img3.src = img2;        // 设置图像地址
            img3.onload = function () {  // onload内可以获取图像信息
              cxt3.drawImage(img3, 0, 0, canvas3.width, canvas3.height) //  --第五步--  将canvas2画布生成的图像放在canvas3画布中

            };
            resolve();
          }
        })
      },