Pretty collisions

Collision offsets are four variables to set in a sprite. By default, they are set to 0. Some times, it is useful to chance their values, like in our case.

This picture shows how offsets are disposed in a sprite. You can change their value with the following methods of the sprites object: setLeftCollisionOffset(int): to change the value of the left collision offset. setRightCollisionOffset(int): to change the value of the right collision offset. setTopCollisionOffset(int): to change the value of the top collision offset. setBottomCollisionOffset(int): to change the value of the bottom collision offset.

In our example, we only need to change the left and the right offsets, as show in the following picture:

6 pixels for the left collision offset 8 pixels for the right collision offset

This is done in the class DisplayRobotFinal.java.
But, we have to change something else. In the DummyRobot object, when we change the position of the new sprite, we need to consider collision offsets. In DummyRobotFinal.java, needed changes are done in changeDirection(RobotSprite, RobotSprite) method:

...
  /**
   * Changes direction of the robot
   */
  protected void changeDirection(RobotSprite fromSprite, RobotSprite toSprite) {
    PlayField parent = getParent();
    Sprite finalWrapper = getFinalWrapper();
    Point p = getPosition();
    toSprite.setCurrentPictureNumber(fromSprite.getCurrentPictureNumber());
    parent.removeSprite(finalWrapper);
    setActionSprite(toSprite);
    setPosition(p.x + (fromSprite.getLeftCollisionOffset() -
		       toSprite.getLeftCollisionOffset()) ,
		p.y);
    toSprite.fly(fromSprite.isFlying());
    parent.addSprite(finalWrapper);
  }
...

Finally, we assemble all of these elements to obtain this applet:

But, with only one type of tiles, it's a little bit boring. In the next chapter, we will see how to add new type of tiles.