Question

I’m building a small video game. I’m trying to do good oop/design.

I have a map object and a camera object. These are both created in the ‘world’ object.

There is a problem though. In the map I render and update everything. For performance reasons I only want to update/render what is only on the player’s screen.

The camera object has this information – but the map object can’t get to it.

There is a couple ways I could get this information, but wanted to get an option on how to do it.

Answer 1

The OO principle that is probably most pertinent here is the Single Responsibility Principle.

Consider these statements of responsibility:

• The Map object is responsible for holding the layout of the world
• The Camera object is responsible for maintaining a viewpoint that is used to observe the world

Given that, having the Map be responsible for rendering what’s on-screen is clearly outside its jurisdiction.

You should probably have a WorldRenderer, which should take in both a Map and a Camera in order to render a screen.
While we’re on the subject of good design, you might also want to make the WorldRenderer immutable in nature – it will take in a Map and Camera upon construction, and from that point on, those references can’t be changed, e.g.:

public class WorldRenderer {
    private final Map map;
    private final Camera camera;
    private final List<LightSource> lightSources;

    public WorldRenderer(Map map, Camera camera, List<LightSource> sources) {
        this.map = map;
        this.camera = camera;
        this.lightSources = sources;
    }

    public void render() {
        Viewport viewport = camera.getViewport();
        Map submap = map.getVisibleMapFor(viewport);
        Scene litScene = applyLighting(submap); // using lightSources
        renderScene(litScene);
    }

    private void renderScene(Scene scene) {
        ...
    }
}

… you might have noticed that the example provides some light sources as well. Again, that’s using SRP to decouple the rendering process from its component elements.