I'm playing around with PyGame.

Now I'm trying to implement a QIX clone.

I have my game loop, and I can move the player (cursor) on the screen.

In QIX, the movment of the player leaves a trace (tail) on the screen, creating a polyline.

If the polyline with the screen boundaries creates a polygon, the area is filled.

How I can accomplish this behaviour ?

How store the tail in memory ?

How to detect when it build a closed shape that should be filled ?

I don't need an exact working solution, some pointers, algo names would be cool.