Drawing a Graph

[Lolzen]

I'd like to draw a Graph, but i have no clue how to accomplish this.
To be more specific, i'd like to make something like the DPSgraph in recount.

I do have the data gathered in combat, also the time spent in combat, however when i google search i get various results like libraries for handling it, or different forms of graphs, etc.

The closest i've come is to think it may have to do with some kind of x and y axis, a periodic update functon and something to draw a line. And here comes my misery, i really don't know how to accomplish this with the API given and when i look at the code from Recount or CombatGraph i don't really get it either.

So if anyone could give me a simple example in that direction that would be enough to get me going, thanks in advance!