Adding a player controlled entity

The player will control Hanny by using the arrow keys. Again we will use a DynamicSpriteEntity.

Create a class for Hanny in the same package as SwordFish. Make sure Hanny is placed in the top left corner of the scene.

You might notice that the image of Hanny contains two Hannies. This approach is a standard way to animate a figure in a game. The image itself contains multiple sprites, and the game engine is responsible for showing only one of those sprites, or cycling through them to create the impression of movement.

Yaeger supports this through its DynamicSpriteEntity, by explicitly stating the number of rows and columns of sprites an image contains. In case of Hanny, we have one row, that contains two columns. By default, a DynamicSpriteEntity assumes the image contains only one sprite, but by calling the correct constructor, we can change this.

With this in mind, the constructor of Hanny should look like:

public Hanny(Coordinate2D location){
    super("sprites/hanny.png", location, new Size(20,40), 1, 2);
}

Now use the setupEntities() from the GameLevel to add Hanny. Place her in the top left corner of the screen.

Animate Hanny

To animate Hanny, we are going to let her listen to user input through the keyboard. As with the MouseButtonPressedListener, we are going to add an interface. In its event handler, we are going to call setMotion(), so we can change the direction based on the key being pressed. When no buttons are pressed, we use setSpeed(0) to make sure Hanny keeps her location.

Let Hanny implement the interface KeyListener and implement the event handler in the following way:

@Override
public void onPressedKeysChange(Set<KeyCode> pressedKeys){
    if(pressedKeys.contains(KeyCode.LEFT)){
        setMotion(3,270d);
    } else if(pressedKeys.contains(KeyCode.RIGHT)){
        setMotion(3,90d);
    } else if(pressedKeys.contains(KeyCode.UP)){
        setMotion(3,180d);
    } else if(pressedKeys.contains(KeyCode.DOWN)){
        setMotion(3,0d);
    } else if(pressedKeys.isEmpty()){
        setSpeed(0);
    }
}

Notice how the event handler receives a Set<KeyCode>. This Set will contain all the keys that are currently being pressed. Depending on which keys are in this Set, we set the motion of Hanny.

Change the frame index depending on the direction of the Hanny

We must still change the frame index depending on the direction of Hanny. To select either the left facing or right facing part (sprite) of Hanny's bitmap and prevent that she swims backwars, but always looks in the direction she is swimming.

For this, a DynamicSpriteEntity provides the method setCurrentFrameIndex(int).

Set the correct frame index. Make sure only the left and right buttons change the direction in which Hanny seems to be swimming.

Make sure Hanny doesn't leave the scene

To ensure that Hanny remains on the screen, we can use the interface SceneBorderTouchingWatcher, which provides an event handler that gets called whenever the entity touches the border of the scene. By implementing this interface, the entity needs to implement the method void notifyBoundaryTouching(SceneBorder), which receives which of the four borders was touched. We can use this the set either the x or y-coordinate of Hanny to ensure she remains within the screen. Besides that, we also set her speed to 0.

@Override
public void notifyBoundaryTouching(SceneBorder border){
    setSpeed(0);

    switch(border){
        case TOP:
            setAnchorLocationY(1);
            break;
        case BOTTOM:
            setAnchorLocationY(getSceneHeight() - getHeight() - 1);
            break;
        case LEFT:
            setAnchorLocationX(1);
            break;
        case RIGHT:
            setAnchorLocationX(getSceneWidth() - getWidth() - 1);
        default:
            break;
        }
}

Note that when Hanny is initially being placed on the scene, we should make sure she doesn't touch the scene border, because that will lead to strange unwanted behaviour.

Implement the interface SceneBorderTouchingWatcher and use the event handler to ensure that Hanny doesn't leave the screen.

Make Hanny experience gravity and friction

Yaeger supports a simple approach to enable gravity and friction, which can be enabled by implementing the Newtonian interface. With this interface the entity will continually experience gravitational pull and friction whenever it moves. To learn more about this interface, have a look at the API .

Add the interface Newtonian to Hanny and add the following two lines to Hanny's constructor:

setGravityConstant(0.005);
setFrictionConstant(0.04);

They will ensure very low gravity and high friction, which would be the case when swimming in the ocean.

Last thing to do, is to make sure Hanny does not stop swimming when none of the arrow buttons are pressed. To do this remove the following line from the event handler from the KeyListener interface:

else if(pressedKeys.isEmpty()){
    setSpeed(0);
}

Change the event handler from the KeyListener interface to ensure the speed is no longer set to 0.