graphing inside openCV example

I was wondering what i could do to be able to graph the centroids of the blobs and put them into a time dependent graph.

With the x axis as time in seconds and the y axis their position (either x or y coordinate of the centroid)

As of know i can obtain the coordinates of the blob as well as the current time which they are written in code.

in void Draw

        for (int i = 0; i < contourFinder.nBlobs; i++){  
            getX =;  
            getY =;  

and i can call them in void update as well

cout << getX << " , " << getY << " <> " << ofGetElapsedTimef() << "s : " << currentTime  << endl;  

But if i try making a line, note the other constants are there to just offset the lines and put them into a visible part of the screen, nothing happens. The program compiles but there is nothing shown.

ofLine(300 + (int)currentTime,640+(int)getX,301+(int)currentTime,640+(int)getX);  

any thoughts?