fillPoly, polylines, and drawContours are designed to do the same task: draw set of polygons in image. They have minor differences but it is still unclear why there 3 functions instead of one. There no documentation that compare them, so I don't even know whether each one has its own implementation or they share some code.

Kirill Kornyakov:
Suggestion is to get rid of two of them and to stay with only one.