class TrackModule
{

  private float th = 80; //brightness 0-255
  private int hh = 80; //percent 0-100

    TrackModule()
  {

  }

  float processBitmap(PImage bm)
  {
    int index;
    int hits;
    int successive_hits = bm.width * (hh / 100);

    /*  this is a sort of filter.
     we run through the pixels one horizontal line at the time
     if we find a pixel with a brightness below the threshold (th)
     we add a hit. So if 80 percent of a line is dark enought to
     trigger the filter we count that as a dark line spotted and we retun the 
     y value were it was spotted.
     */

    for(int y = 0; y < bm.height; y++)
    {
      hits = 0;
      index = y * bm.width;
      for(int x = 0; x < bm.width; x++)
      {
        color c = bm.pixels[index + x];
        if( brightness(c) < th)
        {
          hits++;
          if(hits > successive_hits)
          {
            return y;
          }
        }
      }
    }
    return 0.0;
  }
}