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Mat rotation gets wrong result

I want to rotate an image by 90 degrees. My code is like following:

void rotate90(Mat & src, Mat & dst, int direction) {
    int src_width = src.cols, src_height = src.rows;
    cout << src_width << " " << src_height << endl;
    Point center(src_width / 2.0f, src_height / 2.0f);
    double angle = 0;
    if(direction > 0)
         angle = 90.0;
   else
        angle = -90.0;

    Mat rot_mat = getRotationMatrix2D(center, angle, 1);

    warpAffine(src, dst, rot_mat, Size(src_height, src_width)); 
}


int main(int argc, const char *argv[])
 {
    Mat img = imread("/Users/chuanliu/Desktop/src4/p00.JPG");

    resize(img, img, Size(1024, 683));
    rotate90(img, img, 1);

    imwrite("/Users/chuanliu/Desktop/roatation.jpg",img);

    return 0; 
}

But the result is like following:
Before rotation:
image description

After rotation:
image description

It seems that the center of rotation has sth wrong. But I don't think I set a wrong center. Is there anyone can tell me what is wrong?