add memory per entity to archetype stats (#124)

CHANGELOG.md

@@ -6,6 +6,10 @@ Nothing
 
 ## [[v0.4.5]](https://github.com/mlange-42/arche/compare/v0.4.4...v0.4.5)
 
+### Features
+
+* Adds memory per entity to archetype stats (!124)
+
 ### Other
 
 * Adds benchmarks of Arche vs. Array of Structs (AoS) and Array of Pointers (AoP), for different memory per entity and number of entities (!123)

ecs/archetype.go

@@ -183,18 +183,20 @@ func (a *archetype) Stats(reg *componentRegistry) stats.ArchetypeStats {
 	}
 
 	cap := int(a.Cap())
-	memory := cap * int(entitySize)
+	memPerEntity := 0
 	for i := 0; i < len(a.components); i++ {
 		comp := &a.components[i]
-		memory += int(comp.itemSize) * cap
+		memPerEntity += int(comp.itemSize)
 	}
+	memory := cap * (int(entitySize) + memPerEntity)
 
 	return stats.ArchetypeStats{
-		Size:           int(a.Len()),
-		Capacity:       cap,
-		Components:     aCompCount,
-		ComponentIDs:   ids,
-		ComponentTypes: aTypes,
-		Memory:         memory,
+		Size:            int(a.Len()),
+		Capacity:        cap,
+		Components:      aCompCount,
+		ComponentIDs:    ids,
+		ComponentTypes:  aTypes,
+		Memory:          memory,
+		MemoryPerEntity: memPerEntity,
 	}
 }

ecs/stats/stats.go

@@ -49,6 +49,8 @@ type ArchetypeStats struct {
 	ComponentTypes []reflect.Type
 	// Total reserved memory for entities and components, in bytes
 	Memory int
+	// Memory for components per entity
+	MemoryPerEntity int
 }
 
 func (s *WorldStats) String() string {
@@ -83,7 +85,7 @@ func (s *ArchetypeStats) String() string {
 		typeNames[i] = tp.Name()
 	}
 	return fmt.Sprintf(
-		"Archetype -- Components: %2d, Entities: %6d, Capacity: %6d, Memory: %7.1f kB\n  Components: %s\n",
-		s.Components, s.Size, s.Capacity, float64(s.Memory)/1024.0, strings.Join(typeNames, ", "),
+		"Archetype -- Components: %2d, Entities: %6d, Capacity: %6d, Memory: %7.1f kB, Per entity: %4d B\n  Components: %s\n",
+		s.Components, s.Size, s.Capacity, float64(s.Memory)/1024.0, s.MemoryPerEntity, strings.Join(typeNames, ", "),
 	)
 }