Killer Game Programming in Java

Worm Obstacles

The Obstacles object maintains an array of Rectangle objects called boxes. Each object contains the top-left hand coordinate of a box and the length of its square sides.

The public methods in the Obstacles class are synchronized since the event thread of the game could add a box to the obstacles list (via a call to add()) while the animation thread is examining or drawing the list.

add() is defined as

    synchronized public void add(int x, int y)
    {
      boxes.add( new Rectangle(x,y, BOX_LENGTH, BOX_LENGTH));
      wcTop.setBoxNumber( boxes.size() );   // report new no. of boxes
    }

The method updates the boxes text field at the top-level of the game by calling setBoxNumber().

WormPanel delegates the task of drawing the obstacles to the Obstacles object, by calling draw():

    synchronized public void draw(Graphics g)
    // draw a series of blue boxes
    {
      Rectangle box;
      g.setColor(Color.blue);
      for(int i=0; i < boxes.size(); i++) {
        box = (Rectangle) boxes.get(i);
        g.fillRect( box.x, box.y, box.width, box.height);
      }
    }  // end of draw()

Worm communicates with Obstacles to determine if its new head (a Point object, p) intersects with any of the boxes:

    synchronized public boolean hits(Point p, int size)
    {
      Rectangle r = new Rectangle(p.x, p.y, size, size);
      Rectangle box;
      for(int i=0; i < boxes.size(); i++) {
        box = (Rectangle) boxes.get(i);
        if (box.intersects(r))
          return true;
      }
      return false;
    }  // end of hits()