Assuming you know the coordinates of all the points and obstacles (and holes?), you can follow the below steps.
Points P1(x1,y1) and P2(x2,y2). Let obstacle be O(x3,y3).
Check the distance between P1 and P2. Compare it with that of P1->O + O->P2. if both are the same, them O lies between P1 and P2 and is in LoS.
Euclidean distance between two points -> sqrt((x2-x1)^2+(y2-y1)^2))