GameObject and Behaviors

A GameObject can share some of their behaviors.

To be able to share such code, we need to create a new interface named Behavior, definig some of the possible interaction between GameObject and the rest of the world.

public interface Behavior {
    void input(InputHandler ih);

    void update(GameObject go, long dt);

    void renderer(GameObject go, Render r);
}

This simple interface can let add new behavior to a GameObject by adding an implementation to the object:

public class GameObject {
    private List<Behavior> behaviors = new ArrayList<>();

    public GameObject add(Behavior b) {
        assert (behaviors.contains(b));
        behaviors.add(b);
        return this;
    }
}

Then at Game engine level, we will need to process the corresponding implementation’s input, update and renderer call.

The Player Action Behavior

As a player, I must be able to interact with the Game, and move my character on screen.

This is what we are going to try and achieve by implementing the PlayerActionBehavior.

Start implementing this behavior :

public class PlayerActionBehavior implements Behavior<GameObject> {
    public PlayerActionBehavior() {
        ah = (ActionHandler) SystemManager.get(ActionHandler.class);
    }
}

We need to focus on what we want to be able to achieve as move:

• move LEFT,
• move RIGHT,
• make the character JUMP,
• RESET every velocity and acceleration parameters (only for debug purpose)

So we will capture the onInput() method to catch left and right key press:

public class PlayerActionBehavior implements Behavior<GameObject> {

    //...
    @Override
    public void onInput(GameObject go, ActionHandler ih) {
        if (ih.get(KeyEvent.VK_LEFT)) {
            go.acceleration.x = -accel;
        }
        if (ih.get(KeyEvent.VK_RIGHT)) {
            go.acceleration.x = accel;
        }
    }
    
}

but we rely on the onAction() to detect JUMP and RESET parameter.

public class PlayerActionBehavior implements Behavior<GameObject> {

    //...
    @Override
    public void onAction(GameObject go, ActionHandler.ACTIONS action) {
        accelStep = (Double) go.getAttribute("accelStep");
        jumpAccel = (Double) go.getAttribute("jumpAccel");
        jumping = (boolean) go.getAttribute("jumping");

        if (ah.getCtrl()) {
            accel = accelStep * 10;
        } else if (ah.getShift()) {
            accel = accelStep * 5;
        } else {
            accel = accelStep;
        }
        switch (action) {
            case UP:
                jumping = (boolean) go.getAttribute("jumping");
                if (!jumping) {
                    go.acceleration.y = jumpAccel * accel;
                    go.addAttribute("jumping", true);
                }
                break;
            case FIRE1:
                if (go.debug > 0) {
                    go.acceleration.x = 0;
                    go.acceleration.y = 0;
                    go.velocity.x = 0;
                    go.velocity.y = 0;
                }
                break;
            default:
                break;
        }
    }
}