003-systems

System Requirements

• Each system is a pure function that processes traits and updates ECS data.
• Use world.query(...) to get relevant entities and keep queries minimal.
• Include delta time when doing any time-based logic.
• Avoid side effects beyond ECS data changes (no DOM or React state modifications).

System Examples

// Standard system pattern
export function movementSystem(world: World) {
  const time = world.get(Time)
  if (!time) return
  world.query(Transform, Velocity).updateEach(([t, v]) => {
    t.position.addScaledVector(v.vector, time.delta)
  })
}

Advanced Usage

• Partial Queries: Use .select(...) to fetch only the needed traits for performance.
• Conditional Scheduling: Run certain systems only in specific game states (e.g. paused, menu, or combat).
• Relationships: Use relation() if the system involves parent-child or entity-to-entity logic, rather than raw references.

Performance Tips

• Reuse math objects like Vector3 or Matrix4 rather than creating new ones every frame.
• Remove or recycle entities that are no longer needed (e.g. off-screen, zero-health).
• Prefer SoA for large numeric arrays to improve cache performance.
• Consider running heavy systems at reduced frequencies instead of every frame.

Do Not

• Do not directly manipulate React components or the DOM from a system.
• Do not skip delta time in time-based updates.
• Do not implement camera or purely visual updates in systems; leave those to React or specialized visual hooks.