Rendering System

The RenderSystem is how the entities in the ECS World (Logic) are rendered.

We use SpriteKit to render the entities, but the system itself has no SpriteKit dependency — it delegates all engine-specific work to a RenderingBackend. The SpriteKit implementation of that backend is SpriteKitRenderingAdapter.

Components Required:

For an entity to be rendered, it needs to have both a TransformComponent (position, scale, rotation) and a SpriteComponent (texture name, tint color).

The Synchronization Loop:

Every frame, RenderSystem.update() performs a sync:

1. Query all entities with both TransformComponent and SpriteComponent.
2. Create or update each entity's node via backend.syncNode(...).
3. Remove nodes for entities that are no longer renderable via backend.removeNode(...).

RenderingBackend Protocol:

RenderSystem depends on a protocol, not a concrete SpriteKit type. This means that we can swap out the rendering engine without changing the RenderSystem.

protocol RenderingBackend: AnyObject {
    func syncNode(for entity: Entity, transform: TransformComponent,
                  sprite: SpriteComponent, velocity: VelocityComponent?)
    func removeNode(for entity: Entity)
}

• SpriteKitRenderingAdapter: is the concrete SpriteKit implementation of RenderingBackend. It:
  • Keeps a private nodeRegistry: [Entity: SKSpriteNode] mapping each entity to its visual node.
  • Adds new nodes to worldLayer (not the scene root), so the SpriteKitCameraAdapter can shift the entire world layer to implement camera movement.
  • Handles flip direction based on VelocityComponent, tint color, and zPosition.

SpriteComponent

SpriteComponent drives all visual configuration for an entity. It supports two rendering modes:

Texture mode — set textureName to an asset catalog name. The texture size drives the node size.

SpriteComponent(textureName: "knight")

Colour mode — leave textureName empty and provide a renderSize. Renders as a solid-colour rectangle. Used for map geometry (walls, floors).

// Use the built-in presets for map geometry:
SpriteComponent.wall(size: SIMD2<Float>(600, 16))
SpriteComponent.floor(size: SIMD2<Float>(600, 400))

Z-Ordering

SpriteComponent has a zPosition: CGFloat field that maps directly to SpriteKit's zPosition. The established draw order is:

Layer	zPosition	Examples
Floor	0	Floor fill
Walls / obstacles	1	Perimeter walls, rocks
Characters	2	Player, enemies (default for texture sprites)

The presets SpriteComponent.wall(size:) and SpriteComponent.floor(size:) set zPosition automatically. The default SpriteComponent(textureName:) init defaults to zPosition: 1 — override when needed.