How can I animate a point moving on triangle sides?  
I can generate traingle and point but I have no idea how to define point movement.
I'm guessing that I have to use sin and cos in coordinates but I can't find a way to define triangle in this way.  
Can someone help me a bit with that?


![enter image description here][1]


  [1]: https://i.sstatic.net/NT2tR.jpg