记录一下绘图里面的一些方法

    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextAddEllipseInRect(context, CGRectZero);
    //设置透明色
    CGContextSetBlendMode(context, kCGBlendModeClear);
    CGContextDrawPath(context, kCGPathFill);
    UIImage*anewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    UIBezierPath *path;
    CGContextAddPath(context, path.CGPath);