add root entity. release children with parent.

src/entity.c

@@ -29,6 +29,11 @@ struct entity_store *entity_store_alloc(void)
     store->arena = arena;
     store->entities = arena_dry_push(&arena, struct entity);
     ASSERT((u64)store->entities - (u64)store == STORE_ENTITIES_OFFSET);  /* Offset must be correct */
+
+    struct entity *root = entity_alloc_unlinked(store);
+    root->root = true;
+    store->root = root->handle;
+
     return store;
 }
 
@@ -51,7 +56,7 @@ void entity_store_copy_replace(struct entity_store *dest, struct entity_store *s
  * Allocation
  * ========================== */
 
-struct entity *entity_alloc(struct entity_store *store)
+struct entity *entity_alloc_unlinked(struct entity_store *store)
 {
     struct entity *entity = NULL;
     struct entity_handle handle = { 0 };
@@ -71,13 +76,34 @@ struct entity *entity_alloc(struct entity_store *store)
     return entity;
 }
 
+struct entity *entity_alloc_top(struct entity_store *store)
+{
+    struct entity *e = entity_alloc_unlinked(store);
+    struct entity *root = entity_from_handle(store, store->root);
+    entity_link(root, e);
+    return e;
+}
+
+struct entity *entity_alloc_child(struct entity *parent)
+{
+    struct entity_store *store = entity_get_store(parent);
+    struct entity *e = entity_alloc_unlinked(store);
+    entity_link(parent, e);
+    return e;
+}
+
 void entity_release(struct entity_store *store, struct entity *entity)
 {
-    /* FIXME: Unlink entity */
     ++entity->handle.gen;
     entity->valid = false;
     entity->next_free = store->first_free;
     store->first_free = entity->handle;
+    /* Release children */
+    if (entity->first.gen) {
+        for (struct entity *child = entity_from_handle(store, entity->first); child->valid; child = entity_from_handle(store, child->next)) {
+            entity_release(store, child);
+        }
+    }
 }
 
 /* ========================== *
@@ -86,19 +112,20 @@ void entity_release(struct entity_store *store, struct entity *entity)
 
 struct entity_store *entity_get_store(struct entity *ent)
 {
-    struct entity_store *store = entity_store_nil();
     if (ent->valid) {
         u64 first_entity_addr = (u64)(ent - ent->handle.idx);
-        store = (struct entity_store *)(first_entity_addr - STORE_ENTITIES_OFFSET);
+        struct entity_store *store = (struct entity_store *)(first_entity_addr - STORE_ENTITIES_OFFSET);
         ASSERT(store->entities == (struct entity *)first_entity_addr);
-    }
         return store;
+    } else {
+        return entity_store_nil();
+    }
 }
 
 /* Returns a valid entity or nil entity. Always safe to read result, need to check `valid` to write. */
 struct entity *entity_from_handle(struct entity_store *store, struct entity_handle handle)
 {
-    if (handle.idx < store->count) {
+    if (handle.gen != 0 && handle.idx < store->count) {
         struct entity *entity = &store->entities[handle.idx];
         if (entity->handle.gen == handle.gen) {
             return entity;
@@ -202,4 +229,32 @@ void entity_link(struct entity *parent, struct entity *child)
     }
 }
 
-/* TODO: entity_unlink() */
+void entity_unlink(struct entity *ent)
+{
+    struct entity_store *store = entity_get_store(ent);
+    ASSERT(!entity_handle_eq(ent->handle, store->root));
+
+    struct entity *parent = entity_from_handle(store, ent->parent);
+    struct entity *prev = entity_from_handle(store, ent->prev);
+    struct entity *next = entity_from_handle(store, ent->next);
+
+    /* Unlink from parent & siblings */
+    if (prev->valid) {
+        prev->next = next->handle;
+    } else {
+        parent->first = next->handle;
+    }
+    if (next->valid) {
+        next->prev = prev->handle;
+    } else {
+        parent->last = prev->handle;
+    }
+
+    /* Link children to grandparent */
+    if (ent->first.gen) {
+        struct entity_handle parent_handle = parent->handle;
+        for (struct entity *child = entity_from_handle(store, ent->first); child->valid; child = entity_from_handle(store, child->next)) {
+            child->parent = parent_handle;
+        }
+    }
+}

src/entity.h

@@ -29,6 +29,7 @@ struct entity_store {
     struct arena arena;
     u64 count;
     struct entity_handle first_free;
+    struct entity_handle root;
     struct entity *entities;
 };
 
@@ -43,6 +44,9 @@ struct entity {
     /* Special value stored in first entity in store array */
     u64 store_offset;
 
+    /* Is this the root entity */
+    b32 root;
+
     /* Tree */
     struct entity_handle parent;
     struct entity_handle next;
@@ -118,6 +122,25 @@ struct entity_prop_array {
     u64 count;
 };
 
+/* ========================== *
+ * Handle helpers
+ * ========================== */
+
+INLINE struct entity_handle entity_nil_handle(void)
+{
+    return (struct entity_handle) { 0 };
+}
+
+INLINE b32 entity_handle_is_nil(struct entity_handle h)
+{
+    return h.gen == 0;
+}
+
+INLINE b32 entity_handle_eq(struct entity_handle a, struct entity_handle b)
+{
+    return a.gen == b.gen && a.idx == b.idx;
+}
+
 /* ========================== *
  * Nil
  * ========================== */
@@ -171,7 +194,9 @@ void entity_store_release(struct entity_store *store);
 void entity_store_copy_replace(struct entity_store *dest, struct entity_store *src);
 
 /* Entity */
-struct entity *entity_alloc(struct entity_store *store);
+struct entity *entity_alloc_unlinked(struct entity_store *store);
+struct entity *entity_alloc_top(struct entity_store *store);
+struct entity *entity_alloc_child(struct entity *parent);
 void entity_release(struct entity_store *store, struct entity *entity);
 
 /* Xform */
@@ -188,5 +213,6 @@ struct entity *entity_find_first_match_all(struct entity_store *store, struct en
 
 /* Tree */
 void entity_link(struct entity *parent, struct entity *child);
+void entity_unlink(struct entity *ent);
 
 #endif

src/game.c

@@ -173,7 +173,7 @@ INTERNAL void game_update(void)
             struct v2 size = V2(1, 1);
             f32 r = 0;
 
-            struct entity *e = entity_alloc(G.world.entity_store);
+            struct entity *e = entity_alloc_top(G.world.entity_store);
             e->xform = XFORM_TRS(.t = pos, .r = r, .s = size);
 
             e->sprite = sprite_tag_from_path(STR("res/graphics/tim.ase"));
@@ -195,7 +195,7 @@ INTERNAL void game_update(void)
 
         /* Camera ent */
         {
-            struct entity *e = entity_alloc(G.world.entity_store);
+            struct entity *e = entity_alloc_top(G.world.entity_store);
             e->xform = XFORM_IDENT;
 
             entity_enable_prop(e, ENTITY_PROP_CAMERA);

src/user.c

@@ -755,6 +755,7 @@ INTERNAL void user_update(void)
 
         struct entity *ent = &entities_array.entities[entity_index];
         if (!ent->valid) continue;
+        if (ent->root) continue;
 
         b32 skip_debug_draw = !G.debug_camera && ent == active_camera;
         b32 skip_debug_draw_transform = ent == active_camera;
@@ -871,7 +872,7 @@ INTERNAL void user_update(void)
 
             /* Draw hierarchy */
             struct entity *parent = entity_from_handle(G.world.entity_store, ent->parent);
-            if (parent->valid) {
+            if (parent->valid && !parent->root) {
                 u32 color = RGBA_32_F(0.6, 0.6, 1, 0.75);
                 f32 thickness = 5;
                 f32 arrow_height = 15;