OpenCV Homography, Transform a point, what is this code doing?

Question

I\'m working with a homography calculated by OpenCV. I currently use this homography to transform points using the function below. This function performs the task I require

Answer 1

OpenCV Python implementation following @Ben answer

p = np.array((x,y,1)).reshape((3,1))
temp_p = M.dot(p)
sum = np.sum(temp_p ,1)
px = int(round(sum[0]/sum[2]))
py = int(round(sum[1]/sum[2]))