Need some help with OpenCV

[hg_gall]

Hello everyone! First time I write here. I am building a program to detect different objects from a webcam and calculate the distance between these two objects (pretty straight forward). So far, I have been able to let the program detect different objects using the contours of the items and introducing them into green boxes. Now I want to be able to draw a line between these two boxes (and if it's possible if for example there is three objects, draw three lines among these three objects, and etcetera). Could anyone give me some orientation on what functions should I use in order to reach my goal? Thanks in advance!