Chapter 26 — Game Architecture and States

Level: intermediate Estimated time: 8 hrs Prerequisites: chapters 20 to 25 (game loop, Canvas, sprites, physics, collisions, camera) and chapters 8 to 11 of PART 1A (OOP, inheritance, abstract classes, enums) What you will be able to do by the end: organize a complete game into separate entities, states, services, and files, instead of a single unreadable main.dart.

26.0 — Chapter objectives

By the end of this chapter, you will be able to:

• explain why a 2000-line file always ends up blocking a project;
• separate a game's data, logic, and rendering;
• define precisely what an entity is;
• write an abstract Entity class and subclass it cleanly;
• split the work between update(double dt) and render(Canvas canvas);
• manage a list of entities and its update loop;
• diagnose and fix the concurrent modification bug;
• set up add and remove queues;
• control the render order with a priority field;
• build an Entity → Character → Player / Enemy hierarchy and see its limits;
• replace a deep inheritance chain with composition;
• explain the principle of an ECS (entity, component, system);
• compare ECS and classic OOP in a decision table;
• describe Flame's model, a component tree;
• define a game state and write the GameState enum;
• draw the state machine of a complete game;
• implement menu, game, pause, game over, and victory;
• apply the State pattern: one class per screen;
• stack states to display a pause screen on top of the game;
• decouple the keyboard from actions with an input manager;
• offer key remapping;
• make objects communicate without coupling them through an event bus;
• centralize score, lives, and progress in a data service;
• recognize the dangers of the Singleton and practice simple dependency injection;
• organize the files of a game project;
• decide what to test in a game and write those tests;
• assemble the complete mini-engine of PART 2A;
• explain precisely what Flame will bring in chapter 27.