typed-ecstasy

# What is an ECS?

You might want to read this detailed GameDev.net Article (opens new window) about Entity Component Systems, but just in case the above link is broken or you want a shorter explanation, I'll summarize it:

# Inheritance

Some games, especially older ones, would create entities by using inheritance and store both data and logic in classes:

  • Entity
    • Character
      • Player
      • Enemy
    • Item

But this way, you might end up duplicating code and possibly having very large classes containing all the logic.

# Composition Over Inheritance

With an ECS, instead of creating classes, which contain both data and logic for a specific entity type, you separate the data and the logic:

  • An entity is only an id and a list of components
  • A component contains only data
  • A system contains the logic to process entities with certain components

# Component Examples

  • PositionComponent (x, y)
  • HealthComponent (value)
  • SpriteComponent (image, animations, ...)

# System Examples

  • PhysicsSystem - Applies velocity to positions and checks for collision
  • RenderSystem - Draws sprites
  • DamageSystem - Adjusts the health level in case of a damage event.

# Benefits

  • Write logic that can be reused on multiple entity types and doesn't have to know how the other game logic behaves.
  • Use a data-driven approach or persist your game-state.
  • Prevent conflicts while multiple people work on the same entity type, but on different logic.
  • Creating new entity types might be as easy as composing different components.
  • Trying new logic is a matter of enabling new systems and possibly disabling others.

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