The Entity

The Entity

The game object for our game attempt is nothing else than an Entity class.

The class

Simple POJO, the Entity class will sustain some important attributes for geometry, physics, and rendering values.

In terms of geometry, position and size are the basic ones.

For the physic computation part, we will get velocity and a bounding box to manage collision. And on the rendering purpose, we get foreground and background colors, a rendering priority and a type of Entity.

@startuml
!theme plain
class Entity {
  -index:long
  +id:long
  +name:String
  +active:boolean
  --
  +x:double
  +y:double
  +w:int
  +h:int
  --
  +dx:double
  +dy:double
  +friction:double
  +elasticity:double
  +box:Rectangle2D
  --
  +type:EntityType
  +fc:Color
  +bg:Color
  +priority:int
}
@enduml

figure 3.1 - the Entity class overview

We still have some method in: the Entity#updateBox() will take care to align bounding box with current position and size.

public static class Entity {
    //...
    double x, y;
    int w, h;
    //...
    Rectangle2D box = new Rectangle2D.Double();

    //...
    public void updateBox() {
        box.setFrame(x, y, w, h);
    }
    //...
}

The Usage

To be able to add a simple Entity to the scene, you need to create a new instance <1> of Entity and add it to the entities list <2>:

public class KarmaPlatform extends JPanel implements KeyListener {
    //...
    private final Map<String, Entity> entities = new ConcurrentHashMap<>();

    //...
    public void createScene() {
        // <1>
        Entity p = new Entity("player")
                .setPosition(160, 100)
                .setSize(16, 16)
                .setFriction(0.995)
                .setElasticity(0.45)
                .setBorderColor(new Color(0.0f, 0.0f, 0.6f, 1.0f))
                .setBackgroundColor(Color.BLUE)
                .setPriority(1)
                .addAttribute("speedStep", 0.15);
        // <2>
        addEntity(p);
    }

    //...
    private void addEntity(Entity e) {
        entities.put(e.name, e);
    }
    //...
}