Adding Collisions

This tutorial builds on previous Adding Images and Sounds. Please complete it first if you haven't done so.

Tutorial Brief

Works with

1. Add a coin entity.
2. Add a collision handler between the player and the coin.

Preparation

For our collisions to work we first need to let FXGL know about entity types. In our game, they are: player and coin. It is recommended that a type is represented by an enum. So, we create an enum EntityType:

public enum EntityType {
    PLAYER, COIN
}

Add a coin

We are going to add a brand new entity - coin. In initGame():

Entities.builder()
        .type(EntityType.COIN)
        .at(500, 200)
        .viewFromNodeWithBBox(new Circle(15, Color.YELLOW))
        .with(new CollidableComponent(true))
        .buildAndAttach(getGameWorld());

We set its type by calling .type(). Then we use viewFromNodeWithBBox() to ask FXGL to generate the entity bounding box from its view, which is a yellow circle. Finally, we attach CollidableComponent to mark the entity that it should participate in collision detection and handling.

Add a collision handler

We are going to slightly modify our player entity creation. You should now have enough knowledge to understand all following method calls.

player = Entities.builder()
        .type(EntityType.PLAYER)
        .at(300, 300)
        .viewFromTextureWithBBox("brick.png")
        .with(new CollidableComponent(true))
        .buildAndAttach(getGameWorld());

Now, both player and coin are ready to participate in collision detection. The last thing to add is the actual handler, i.e. the code that runs when player and coin collide.

@Override
protected void initPhysics() {
    getPhysicsWorld().addCollisionHandler(new CollisionHandler(EntityType.PLAYER, EntityType.COIN) {

        // order of types is the same as passed into the constructor
        @Override
        protected void onCollisionBegin(Entity player, Entity coin) {
            coin.removeFromWorld();
        }
    });
}

We attach the handler to the physics world. The handler constructor takes two entity types. We passed PLAYER first and then COIN. Therefore, in onCollisionBegin() and other overriddable callbacks the order of entities will be player and then coin. The only thing we call in this example is coin.removeFromWorld();, which removes the coin entity from the game world.

You now have the knowledge to make two entities collide with each other and listen for their collision events. Well done!

Link to the full source code of this tutorial. Enjoy!

Want some more? Follow a more complex video tutorial. Explore Core Features, or experiment with pre-made games.