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++){  
            contourFinder.blobs[i].draw(360,20);  
            getX = contourFinder.blobs.at(i).centroid.x;  
            getY = contourFinder.blobs.at(i).centroid.y;  
        }  
    }  
  

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?