canvas指定区域生成图片（canvas实现图片镜像翻转的2种方式）

  var img = new Image(); //这个就是 img标签的dom对象
  img.src = './sy.png';
  img.onload = function () {
    //图片加载完成后，执行此方法
    ctx.drawImage(img, posx, posy, 210, 80);
  };

play.addEventListener('click', function () {
     ctx.clearRect(0, 0, canvas.width, canvas.height);//清除画布
     //位移来做镜像翻转
     ctx.translate(210+ posx * 2, 0);
     ctx.scale(-1, 1); //左右镜像翻转
     
     //ctx.translate(0, 160 + posy * 2);
     //ctx.scale(1, -1); //上下镜像翻转
     ctx.drawImage(img, 0, 0, 210, 80);
  });

//竖向像素反转
    function imageDataVRevert(sourceData, newData) {
      for (var i = 0, h = sourceData.height; i < h; i++) {
        for (var j = 0, w = sourceData.width; j < w; j++) {
          newData.data[i * w * 4 + j * 4 + 0] =
            sourceData.data[(h - i) * w * 4 + j * 4 + 0];
          newData.data[i * w * 4 + j * 4 + 1] =
            sourceData.data[(h - i) * w * 4 + j * 4 + 1];
          newData.data[i * w * 4 + j * 4 + 2] =
            sourceData.data[(h - i) * w * 4 + j * 4 + 2];
          newData.data[i * w * 4 + j * 4 + 3] =
            sourceData.data[(h - i) * w * 4 + j * 4 + 3];
        }
      }
      return newData;
    }

    //横向像素反转
    function imageDataHRevert(sourceData, newData) {
      for (var i = 0, h = sourceData.height; i < h; i++) {
        for (j = 0, w = sourceData.width; j < w; j++) {
          newData.data[i * w * 4 + j * 4 + 0] =
            sourceData.data[i * w * 4 + (w - j) * 4 + 0];
          newData.data[i * w * 4 + j * 4 + 1] =
            sourceData.data[i * w * 4 + (w - j) * 4 + 1];
          newData.data[i * w * 4 + j * 4 + 2] =
            sourceData.data[i * w * 4 + (w - j) * 4 + 2];
          newData.data[i * w * 4 + j * 4 + 3] =
            sourceData.data[i * w * 4 + (w - j) * 4 + 3];
        }
      }
      return newData;
    }
``

var img = new Image(); //这个就是 img标签的dom对象
  img.src = './sy.png';
  img.onload = function () {
    //图片加载完成后，执行此方法
    ctx.drawImage(img, 0, 0, 210, 80);
  };
  
    //像素点操作
    var imgData = ctx.getImageData(0, 0, 210, 80);
    var newImgData = ctx.getImageData(0, 0, 210, 80);

    // var newImgData = ctx.getImageData(0, 0, w, h);
    ctx.putImageData(imageDataVRevert(newImgData, imgData), 0, 0);  //上下翻转
    // ctx.putImageData(imageDataHRevert(newImgData, imgData), 0, 0);//左右翻转~~~~