图片不旋转的时候可以直接拖动，图片如果旋转过了，坐标系就会变掉，再次拖动的话，怎么判断坐标系是在原点还是已经变过了的呢？
cvsMove: function (e) {

if (e.touches.length > 1) {//二指缩放
console.log("双指缩放")
var xMove2 = Math.abs(e.touches[1].x - e.touches[0].x);
var yMove2 = Math.abs(e.touches[1].y - e.touches[0].y);
         var distance2 = Math.sqrt(xMove2 * xMove2 + yMove2 * yMove2);//开根号
         console.log(distance2);
        //  this.data.distanceList.shift()
        //  this.data.distanceList.push(distance)
        //  if (this.data.distanceList[0] == 0) { return }
        //  var distanceDiff = this.data.distanceList[1] - this.data.distanceList[0]//两次touch之间, distance的变化. >0,放大图片.<0 缩小图片
        //  var baseScale = 1 + 0.005 * distanceDiff
         var baseScale = this.data.distance1 / distance2 ;
         console.log("缩放率"+baseScale);
         const ctx = wx.createCanvasContext('myCanvas');
         ctx.scale(baseScale, baseScale);
         ctx.drawImage(this.data.tempFilePaths, this.data.lastX, this.data.lastY, 200 , 300);
        
         ctx.restore();
} else if (e.touches.length == 1){
  var touchs = e.touches[0];
  console.log('canvas被拖动了....')
  var x = touchs.x;
  var y = touchs.y;
  var moveX = x - this.data.currentX;
  var moveY = y - this.data.currentY;
  this.setData({
    newX : this.data.lastX + moveX,
    newY : this.data.lastY + moveY
  })
  const ctx = wx.createCanvasContext('myCanvas');
  ctx.save();
  ctx.setFillStyle('white');
  ctx.drawImage(this.data.tempFilePaths, this.data.newX, this.data.newY, 200, 300)
  ctx.draw();
  ctx.restore();
}

},