code: private void drawOuterBorder(Point[] points, Canvas canvas) {
          Path border = getOuterBorder(points);
          Paint paint = new Paint();
          paint.setAntiAlias(true);
          // 再画边框
          paint.setColor(_outer_border_color);
          paint.setStyle(Paint.Style.STROKE);
          paint.setStrokeWidth(_outer_border_width);
          canvas.drawPath(border, paint);
      }
docs: 画外边框