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Entity Component System
- 1. Entity Component System Lunch& Learn 2015-01-21
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- 3. ECS is apattern that makes a distinction between entities, components and systems.
- 4. An entity isa discrete object representing an actor in a simulated space. Realize first that we are simulating a universe - the game’s universe. All the visible, tangible ‘things’ in the universe can be represented as entities. Entity
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- 6. Can you thinkof some more examples?
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- 9. A component describesa singular behavior ascribed to an entity. The name of a component should ideally communicate what behavior the entity will exhibit, even to someone who isn’t familiar with the implementation. Component
- 10. Component Behavior Transform Transformsthe entities position, rotation and scale (from the origin). Health Attributes a health value, which can be increased or decreased by receiving ‘heal’ or ‘damage’ messages. At zero, it fires the message ‘died’. Collider Entity can collide with others. The implementation will depend on the physics system, but this could be an abstract base component. DamageOnCollision Will send a ‘damage’ message with a data-defined value to any entities it collides with. Requires its entity to have a Collider component. ParticleEmitter The entity will emit particles, the nature of which depends on data-defined values.
- 11. Systems iterate overlists of components to perform low level functions such as rendering graphics, performing physics calculations, or pathfinding. Not every component needs to be managed by a system. Components should use systems to offload computationally difficult or shared workloads. System
- 12. If a systemis totally unrelated to gameplay it might actually be a service.
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- 14. Why are weusing ECS?
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- 17. Classical Inheritance EntityComponent Pros ● Sub-classing can feel intuitive ● Lots of existing research ● Shorter, less complex code ● Promotes thinking in terms of behaviors ● Very flexible ● Emergent behavior ● Enables scripting of behavior by non-techies Cons ● Leads to highly complex code ● Less flexible ● Difficult to apply correctly, easy to mis-use ● Good components require more thinking about design
- 18. Disclaimer ECS is notthe be-all end-all solution to game programming.
- 19. How should weuse ECS?
- 20. Components ● Should begeneric and re-usable. ● Configure via parameters from data, or from a system. ● Should describe a singular behavior. ● Avoid depending on other components too much. ● Try to avoid writing very large or complex components. It’s usually a sign you could split up your code further.
- 21. Think in termsof behavior What do I want my entity to do? What is that behavior called? Can I simplify it?
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- 23. Exercise: Components ● Thinkabout the game you’re currently working on. ● As a group, brainstorm components that the game currently uses, or new ones that you could write for it. ● Write them down on post it notes. ● Try organizing them a bit, are there similarities or overlaps in functionality? ● Do the component names make it obvious what they do?
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- 25. Messages ● Should begeneric and re-usable. ● Pass useful information as parameters. ● Whenever you need to react to an event, first look if a suitable message is being sent. ● Don’t use messages if a component has a hard dependency that can only be solved by one specific kind of component, just use a reference in that case.
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- 27. Exercise: Messages ● Brainstormmessages that your components might send or receive. ● Write them down on post it notes. ● Can you show which components send which messages? ● Are all messages sent by components? ● Do the message names make it obvious what data or event they are conveying?
- 28. Always remember theSRP Single Responsibility Principle
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