Killer Game Programming in Java

Finding the Surface Height

KeyBehavior interacts with HeightFinder by calling requestMoveHeight(), which stores a (x, y, z) coordinate in the global theMove Vector3d object:

    // globals
    private Vector3d theMove;  // current move request from KeyBehavior
    private boolean calcRequested;


    synchronized public void requestMoveHeight(Vector3d mv)
    { theMove.set(mv.x, mv.y, mv.z);
              // will overwrite any pending request in theMove
      calcRequested = true;
    }

The (x, z) values in theMove are used for the picking calculation. The calcRequested Boolean signals a pending request.

If the user presses the move keys rapidly, KeyBehavior will call requestMoveHeight() frequently, causing theMove to be updated frequently. When HeightFinder processes the next request, it will find only the most recent one in theMove, saving itself unnecessary work. This illustrates the decoupling of key processing from height calculation, so the users can move as fast (or as slow) as they like.

requestMoveHeight() returns immediately; KeyBehavior doesn't wait for an answer, or it might be waiting for one or two seconds. Instead, KeyBehavior uses the current y-height for its move. HeightFinder's run() method constantly loops, reads the current move request from theMove(), and then calls getLandHeight(). At the end of getLandHeight(), the new height is passed back to KeyBehavior:

    public void run()
    { Vector3d vec;
      while(true) {
        if (calcRequested) {
          vec = getMove(); // get the requested move getLandHeight(vec.x, vec.z); // pick ...