commit dc2a692c7df6b2ebd6f2bb316c42d6c7841411d0
Author: samstalhandske <samstalhandske@hotmail.com>
Date:   Fri Nov 21 03:41:29 2025 +0100

    Initial commit.

diff --git a/ecs.odin b/ecs.odin
new file mode 100644
index 0000000..67e5f70
--- /dev/null
+++ b/ecs.odin
@@ -0,0 +1,176 @@
+package ecs
+
+import "core:container/queue"
+import "core:log"
+
+Entity :: struct {
+    id: Entity_ID,
+    generation: Entity_Generation,
+}
+
+Entity_ID :: distinct u32
+Entity_Generation :: distinct u32
+
+Invalid_Entity :: Entity { id = 0, generation = 0 }
+@(private="file") Start_Entity_ID :: 1
+
+entity_valid :: proc(entity: Entity) -> bool {
+    return entity != Invalid_Entity
+}
+
+entity_old :: proc(world: ^World, entity: Entity) -> bool {
+    if !entity_valid(entity) {
+        return false;
+    }
+
+    current_gen := world.entity_generations[entity.id - Start_Entity_ID]
+    return entity.generation < current_gen
+}
+
+Component_Storage :: struct {
+    data:  []typeid,
+    alive: []bool,
+}
+Component_Registry :: map[typeid]Component_Storage
+
+World :: struct {
+    name: string,
+    component_registry: Component_Registry,
+
+    entity_id_queue: queue.Queue(Entity_ID),
+    entity_generations: []Entity_Generation
+}
+
+create_world :: proc(name: string, max_entities: u32, components_to_register: []typeid) -> (^World, bool) {
+    world := new(World)
+    
+    registry, err := make(Component_Registry, max_entities)
+    if err != .None {
+        free(world)
+        return nil, false
+    }
+    
+    world.component_registry = registry
+
+    for c in components_to_register {
+        // log.infof("Registered component '%v'.", c)
+    
+        if c in world.component_registry {
+            // log.warnf("Component '%v' already registered.", c)
+            continue
+        }
+        
+        world.component_registry[c] = Component_Storage {
+            data  = make([]typeid, max_entities),
+            alive = make([]bool,   max_entities)
+        }
+    }
+
+    { // Set up the world's queue of available entity-ids.
+        assert(u64(max_entities) <= u64(max(int)))
+        queue.init(&world.entity_id_queue, capacity = int(max_entities))
+        for i in 0..<max_entities {
+            queue.push_back(&world.entity_id_queue, Entity_ID(Start_Entity_ID + i))
+        }
+    }
+
+    { // Set up the world's array of entity-generations.
+        world.entity_generations = make([]Entity_Generation, max_entities)
+    }
+
+    return world, true
+}
+
+destroy_world :: proc(world: ^World) {
+    assert(world != nil)
+
+    for c, e in &world.component_registry {
+        delete(e.data)
+        delete(e.alive)
+        
+        delete_key(&world.component_registry, c)
+    }
+
+    clear(&world.component_registry)
+    delete(world.component_registry)
+
+    queue.destroy(&world.entity_id_queue)
+
+    delete(world.entity_generations)
+
+    free(world)
+}
+
+create_entity :: proc(world: ^World) -> (Entity, bool) {
+    // Try to get a free entity.
+    id, ok := queue.pop_front_safe(&world.entity_id_queue)
+    if !ok {
+        return Invalid_Entity, false
+    }
+
+    // Grow a generation.
+    gen := &world.entity_generations[id]
+    gen^ += 1;
+
+    return Entity {
+        id = id,
+        generation = gen^,
+    }, true
+}
+
+add_component :: proc(entity: Entity, world: ^World, component: $T) -> (^T, bool) {
+    if !entity_valid(entity) {
+        log.warnf("Failed to add component %v - entity is invalid.", typeid_of(T), entity)
+        return nil, false
+    }
+
+    _, has_component := get_component(T, entity, world)
+    if has_component {
+        log.warnf("Failed to add component %v - entity already has this component on it.", typeid_of(T), entity)
+        return nil, false
+    }
+
+    if entity_old(world, entity) {
+        log.warnf("Failed to add component %v - entity %v is old.", typeid_of(T), entity)
+        return nil, false
+    }
+
+    component_storage := &world.component_registry[T]
+    comp := transmute(^T)(&component_storage.data[entity.id - Start_Entity_ID])
+    comp^ = component
+
+    component_storage.alive[entity.id - Start_Entity_ID] = true
+    
+    return comp, true
+}
+
+get_component :: proc($T: typeid, entity: Entity, world: ^World) -> (^T, bool) {
+    if !entity_valid(entity) {
+        log.warnf("Failed to get component %v - entity is invalid.", typeid_of(T), entity)
+        return nil, false
+    }
+
+    if entity_old(world, entity) {
+        log.warnf("Failed to get component %v - entity %v is old.", typeid_of(T), entity)
+        return nil, false
+    }
+
+    component_storage := &world.component_registry[T]
+    if !component_storage.alive[entity.id - Start_Entity_ID] {
+        return nil, false
+    }
+    
+    comp := transmute(^T)(&component_storage.data[entity.id - Start_Entity_ID])
+    return comp, true
+}
+
+remove_component :: proc($T: typeid, entity: Entity, world: ^World) -> (bool) {
+    if comp, ok := get_component(T, entity, world); ok {
+        component_storage := &world.component_registry[T]
+        comp^ = {}
+        component_storage.alive[entity.id - Start_Entity_ID] = false
+        return true
+    }
+
+    return false
+}
\ No newline at end of file
diff --git a/ecs_test.odin b/ecs_test.odin
new file mode 100644
index 0000000..3dc8435
--- /dev/null
+++ b/ecs_test.odin
@@ -0,0 +1,82 @@
+package ecs
+
+import "core:container/queue"
+import "core:testing"
+
+@(test) create_world_test :: proc(t: ^testing.T) {
+    A :: struct { v: [3]u32 }
+    B :: struct { v: [3]u32 }
+    C :: struct { v: [3]u32 }
+    
+    w, ok := create_world(
+        name = "World",
+        max_entities = 16,
+        components_to_register = { A, B, C, }
+    )
+    assert(ok)
+    defer destroy_world(w)
+}
+
+@(test) check_entity_id_queue_test :: proc(t: ^testing.T) {
+    A :: struct { v: [3]u32 }
+    B :: struct { v: [3]u32 }
+    C :: struct { v: [3]u32 }
+    
+    MAX_ENTITIES :: 16
+    w, ok := create_world(
+        name = "World",
+        max_entities = MAX_ENTITIES,
+        components_to_register = { A, B, C, }
+    )
+    assert(ok)
+    defer destroy_world(w)
+
+    assert(queue.len(w.entity_id_queue) == MAX_ENTITIES)
+}
+
+@(test) create_entities_test :: proc(t: ^testing.T) {
+    A :: struct { v: [3]u32 }
+    B :: struct { v: [3]u32 }
+    C :: struct { v: [3]u32 }
+    
+    w, ok := create_world(
+        name = "World",
+        max_entities = 1,
+        components_to_register = { A, B, C, }
+    )
+    assert(ok)
+    defer destroy_world(w)
+    
+    // This entity should be OK.
+    e1, created_1 := create_entity(w)
+    assert(created_1)
+    assert(e1 != Invalid_Entity)
+
+    // This entity should NOT be OK (because 'max_entities' is 1).
+    e2, created_2 := create_entity(w)
+    assert(!created_2)
+    assert(e2 == Invalid_Entity)
+}
+
+@(test) add_component_test :: proc(t: ^testing.T) {
+    A :: struct { v: [3]u32 }
+    B :: struct { v: [3]u32 }
+    C :: struct { v: [3]u32 }
+    
+    w, ok := create_world(
+        name = "World",
+        max_entities = 1,
+        components_to_register = { A, B, C, }
+    )
+    assert(ok)
+    defer destroy_world(w)
+    
+    e, created := create_entity(w)
+    assert(created)
+    assert(e != Invalid_Entity)
+
+    added_component, component_added := add_component(e, w, A { v = { 1, 2, 3 } })
+    assert(component_added)
+    assert(added_component != nil)
+    assert(added_component.v == { 1, 2, 3})
+}
\ No newline at end of file