Simplify archetype graph to a single list of neighbors per node (#433)

CHANGELOG.md

@@ -5,6 +5,10 @@
 * Adds an example for `World.Mask`, showing how to check whether a filter "contains" an entity (#428)
 * Adds the [beecs](https://github.com/mlange-42/beecs) implementation of [BEEHAVE](https://beehave-model.net/) to the showcase (#429)
 
+### Performance
+
+* Simplifies the archetype graph to use only a single list of neighbors per node, saving a bit of memory (#433)
+
 ## [[v0.13.2]](https://github.com/mlange-42/arche/compare/v0.13.1...v0.13.2)
 
 ### Bugfixes

ecs/archetype_node.go

@@ -26,8 +26,7 @@ type nodeData struct {
 	zeroValue         []byte                // Used as source for setting storage to zero
 	archetypes        pagedSlice[archetype] // Storage for archetypes in nodes with entity relation
 	archetypeData     pagedSlice[archetypeData]
-	TransitionAdd     idMap[*archNode] // Mapping from component ID to add to the resulting archetype
-	TransitionRemove  idMap[*archNode] // Mapping from component ID to remove to the resulting archetype
+	neighbors         idMap[*archNode] // Mapping from component ID to add/remove, to the resulting archetype
 	capacityIncrement uint32           // Capacity increment
 }
 
@@ -70,8 +69,7 @@ func newArchNode(mask Mask, data *nodeData, relation ID, hasRelation bool, capac
 	data.capacityIncrement = uint32(capacityIncrement)
 	data.zeroValue = zeroValue
 	data.zeroPointer = zeroPointer
-	data.TransitionAdd = newIDMap[*archNode]()
-	data.TransitionRemove = newIDMap[*archNode]()
+	data.neighbors = newIDMap[*archNode]()
 
 	return archNode{
 		nodeData:    data,

ecs/world_internal.go

@@ -922,12 +922,12 @@ func (w *World) findOrCreateArchetype(start *archetype, add []ID, rem []ID, targ
 			relation = ID{}
 			hasRelation = false
 		}
-		if next, ok := curr.TransitionRemove.Get(id.id); ok {
+		if next, ok := curr.neighbors.Get(id.id); ok {
 			curr = next
 		} else {
 			next, _ := w.findOrCreateArchetypeSlow(mask, relation, hasRelation)
-			next.TransitionAdd.Set(id.id, curr)
-			curr.TransitionRemove.Set(id.id, next)
+			next.neighbors.Set(id.id, curr)
+			curr.neighbors.Set(id.id, next)
 			curr = next
 		}
 	}
@@ -946,12 +946,12 @@ func (w *World) findOrCreateArchetype(start *archetype, add []ID, rem []ID, targ
 			relation = id
 			hasRelation = true
 		}
-		if next, ok := curr.TransitionAdd.Get(id.id); ok {
+		if next, ok := curr.neighbors.Get(id.id); ok {
 			curr = next
 		} else {
 			next, _ := w.findOrCreateArchetypeSlow(mask, relation, hasRelation)
-			next.TransitionRemove.Set(id.id, curr)
-			curr.TransitionAdd.Set(id.id, next)
+			next.neighbors.Set(id.id, curr)
+			curr.neighbors.Set(id.id, next)
 			curr = next
 		}
 	}