automatically center entity when spawning

core.mod/src/entities/ItemStackEntity.cc

@@ -9,9 +9,8 @@ ItemStackEntity::ItemStackEntity(
 	static std::uniform_real_distribution vx(-2.3f, 2.3f);
 	static std::uniform_real_distribution vy(-2.3f, -1.2f);
 
-	item_ = &ctx.world.getItem(item);
 	body_.pos = pos;
-	body_.pos.y += 0.5 - body_.size.y / 2;
+	item_ = &ctx.world.getItem(item);
 	physics_.vel += Swan::Vec2{ vx(ctx.world.random_), vy(ctx.world.random_) };
 }
 

core.mod/src/entities/PlayerEntity.h

@@ -9,6 +9,7 @@ public:
 	PlayerEntity(const Swan::Context &ctx, const PackObject &obj);
 
 	Inventory &get(InventoryTrait::Tag) override { return inventory_; }
+	Body &get(BodyTrait::Tag) override { return body_; }
 
 	void draw(const Swan::Context &ctx, Swan::Win &win) override;
 	void update(const Swan::Context &ctx, float dt) override;

core.mod/src/main.cc

@@ -70,7 +70,7 @@ public:
 	void onTileBreak(const Swan::Context &ctx, Swan::TilePos pos, Swan::Tile &tile) {
 		if (tile.dropped_item_) {
 			ctx.plane.spawnEntity<ItemStackEntity>(
-				ctx, pos, *tile.dropped_item_);
+				ctx, (Swan::Vec2)pos + Swan::Vec2{0.5, 0.5}, *tile.dropped_item_);
 		}
 	}
 

libswan/include/swan/Collection.h

@@ -3,6 +3,7 @@
 #include <vector>
 #include <string>
 #include <typeindex>
+#include <type_traits>
 
 #include "common.h"
 #include "log.h"
@@ -131,6 +132,11 @@ inline EntityRef EntityCollection::spawn(Args&&... args) {
 	ent->index_ = idx;
 	ent->generation_ = generation;
 
+	if constexpr (std::is_base_of_v<BodyTrait, Ent>) {
+		BodyTrait::Body &body = ent->get(BodyTrait::Tag{});
+		body.pos -= body.size / 2;
+	}
+
 	return { this, idx, generation };
 }