diff --git a/src/jasper/modules/world/include/jasper/world/objectcache.hpp b/src/jasper/modules/world/include/jasper/world/objectcache.hpp
index 05a1ce8..5cd73ef 100644
--- a/src/jasper/modules/world/include/jasper/world/objectcache.hpp
+++ b/src/jasper/modules/world/include/jasper/world/objectcache.hpp
@@ -18,7 +18,7 @@ class ObjectCache {
 		struct Obj {
 			ObjectId id{};
 			uint16_t palBank{};
-			size_t tileIdx{};
+			size_t tilesheetIdx{};
 		};
 	private:
 		struct ObjSet {
@@ -40,13 +40,15 @@ class ObjectCache {
 		[[nodiscard]]
 		ox::Optional<Obj> obj(uint64_t setId, ObjectId objId) const noexcept;
 		[[nodiscard]]
-		ncore::TileSheetSet const&tilesheets() const noexcept;
+		ncore::TileSheetSet const&tilesheetSet() const noexcept;
+		[[nodiscard]]
+		ox::Vector<ox::FileAddress> const&tilesheets() const noexcept;
 		[[nodiscard]]
 		ox::Vector<ox::FileAddress> const&palettes() const noexcept;
 	private:
-		void addTileSheet(ox::FileAddress path, int32_t tiles) noexcept;
+		void addTileSheetSetEntry(ox::FileAddress path, int32_t tiles) noexcept;
 };
 
 ox::Result<ObjectCache> buildObjCache(keel::Context &kctx, WorldDoc const&doc) noexcept;
 
-}
\ No newline at end of file
+}
diff --git a/src/jasper/modules/world/include/jasper/world/world.hpp b/src/jasper/modules/world/include/jasper/world/world.hpp
index 09f879d..166314e 100644
--- a/src/jasper/modules/world/include/jasper/world/world.hpp
+++ b/src/jasper/modules/world/include/jasper/world/world.hpp
@@ -6,8 +6,6 @@
 
 #include <nostalgia/core/context.hpp>
 
-#include "consts.hpp"
-#include "worldobject.hpp"
 #include "worldstatic.hpp"
 
 namespace jasper::world {
@@ -18,6 +16,7 @@ class World {
 	private:
 		ncore::Context &m_nctx;
 		WorldStatic const&m_worldStatic;
+		ox::Vector<keel::AssetRef<ncore::CompactTileSheet>, 32> m_tilesheets;
 #ifndef OX_OS_BareMetal
 		//turbine::TimeMs m_prevUpdateTime{};
 		turbine::TimeMs m_nextUpdateTime{};
diff --git a/src/jasper/modules/world/include/jasper/world/worlddoc.hpp b/src/jasper/modules/world/include/jasper/world/worlddoc.hpp
index 7e82a89..cde902e 100644
--- a/src/jasper/modules/world/include/jasper/world/worlddoc.hpp
+++ b/src/jasper/modules/world/include/jasper/world/worlddoc.hpp
@@ -6,6 +6,7 @@
 
 #include <ox/fs/fs.hpp>
 #include <ox/std/error.hpp>
+#include <ox/std/hash.hpp>
 #include <ox/std/size.hpp>
 #include <ox/std/types.hpp>
 #include <ox/std/vector.hpp>
@@ -31,11 +32,19 @@ struct DocObjRef {
 	constexpr static auto TypeVersion = 1;
 	uint64_t worldObjectSetId{};
 	ObjectId worldObjectId{};
+	bool unique{};
 };
 
+constexpr bool operator==(DocObjRef const&a, DocObjRef const&b) noexcept {
+	return a.worldObjectSetId == b.worldObjectSetId
+	    && a.worldObjectId == b.worldObjectId
+	    && a.unique == b.unique;
+}
+
 OX_MODEL_BEGIN(DocObjRef)
 	OX_MODEL_FIELD_RENAME(worldObjectSetId, world_object_set_id)
 	OX_MODEL_FIELD_RENAME(worldObjectId, world_object_id)
+	OX_MODEL_FIELD(unique)
 OX_MODEL_END()
 
 struct TileDoc {
@@ -82,25 +91,29 @@ struct WorldDoc {
 	constexpr static auto TypeVersion = 1;
 	ox::Vector<ObjectSetEntry> objSets; // paths
 	uint64_t objSetIdIdx{};
-	int columns{};
-	int rows{};
+	int32_t columns{};
+	int32_t rows{};
 	TileMap tiles;
 };
 
 [[nodiscard]]
-constexpr ox::Result<ox::String> objectSetPath(WorldDoc const&wd, uint64_t setId) noexcept {
-	auto const obj = ox::find_if(wd.objSets.begin(), wd.objSets.end(), [setId](ObjectSetEntry const&e) {
-		return e.id == setId;
-	});
+constexpr ox::Result<ox::String> objectSetPath(
+		WorldDoc const&wd, uint64_t setId) noexcept {
+	auto const obj = ox::find_if(wd.objSets.begin(), wd.objSets.end(),
+		[setId](ObjectSetEntry const&e) {
+			return e.id == setId;
+		});
 	OX_RETURN_ERROR(ox::Error(obj == wd.objSets.end(), "Obj set not found"));
 	return obj->path;
 }
 
 [[nodiscard]]
-constexpr ox::Result<uint64_t> objectSetId(WorldDoc const&wd, ox::StringView setPath) noexcept {
-	auto const obj = ox::find_if(wd.objSets.begin(), wd.objSets.end(), [setPath](ObjectSetEntry const&e) {
-		return e.path == setPath;
-	});
+constexpr ox::Result<uint64_t> objectSetId(
+		WorldDoc const&wd, ox::StringViewCR setPath) noexcept {
+	auto const obj = ox::find_if(wd.objSets.begin(), wd.objSets.end(),
+		[setPath](ObjectSetEntry const&e) {
+			return e.path == setPath;
+		});
 	OX_RETURN_ERROR(ox::Error(obj == wd.objSets.end(), "Obj set not found"));
 	return obj->id;
 }
@@ -151,3 +164,13 @@ auto &tile(
 void resize(WorldDoc &doc, ox::Size const&sz) noexcept;
 
 }
+
+template<>
+struct std::hash<jasper::world::DocObjRef> {
+	[[nodiscard]]
+	constexpr size_t operator()(jasper::world::DocObjRef const&v) const noexcept {
+		return static_cast<uint32_t>(v.worldObjectSetId) 
+		     | (static_cast<uint32_t>(v.worldObjectId) << 15)
+		     | (static_cast<uint32_t>(v.unique) << 31);
+	}
+};
diff --git a/src/jasper/modules/world/include/jasper/world/worldstatic.hpp b/src/jasper/modules/world/include/jasper/world/worldstatic.hpp
index e983c70..87e69d7 100644
--- a/src/jasper/modules/world/include/jasper/world/worldstatic.hpp
+++ b/src/jasper/modules/world/include/jasper/world/worldstatic.hpp
@@ -10,31 +10,28 @@
 #include <ox/std/types.hpp>
 #include <ox/std/vector.hpp>
 
-#include <nostalgia/core/tilesheet.hpp>
-
 #include <jasper/world/objectcache.hpp>
 
 #include "worlddoc.hpp"
-#include "worldobject.hpp"
 
 namespace jasper::world {
 
 namespace ncore = nostalgia::core;
 
-constexpr void setTopEdge(uint8_t &layerAttachments, unsigned val) noexcept {
-	const auto val8 = static_cast<uint8_t>(val);
+constexpr void setTopEdge(uint8_t &layerAttachments, unsigned const val) noexcept {
+	auto const val8 = static_cast<uint8_t>(val);
 	layerAttachments = (layerAttachments & 0b11111100) | val8;
 }
-constexpr void setBottomEdge(uint8_t &layerAttachments, unsigned val) noexcept {
-	const auto val8 = static_cast<uint8_t>(val);
+constexpr void setBottomEdge(uint8_t &layerAttachments, unsigned const val) noexcept {
+	auto const val8 = static_cast<uint8_t>(val);
 	layerAttachments = (layerAttachments & 0b11110011) | static_cast<uint8_t>(val8 << 2);
 }
-constexpr void setLeftEdge(uint8_t &layerAttachments, unsigned val) noexcept {
-	const auto val8 = static_cast<uint8_t>(val);
+constexpr void setLeftEdge(uint8_t &layerAttachments, unsigned const val) noexcept {
+	auto const val8 = static_cast<uint8_t>(val);
 	layerAttachments = (layerAttachments & 0b11001111) | static_cast<uint8_t>(val8 << 4);
 }
-constexpr void setRightEdge(uint8_t &layerAttachments, unsigned val) noexcept {
-	const auto val8 = static_cast<uint8_t>(val);
+constexpr void setRightEdge(uint8_t &layerAttachments, unsigned const val) noexcept {
+	auto const val8 = static_cast<uint8_t>(val);
 	layerAttachments = (layerAttachments & 0b00111111) | static_cast<uint8_t>(val8 << 6);
 }
 
@@ -57,25 +54,23 @@ constexpr unsigned rightEdge(uint8_t layerAttachments) noexcept {
 
 
 struct TileStatic {
-	constexpr static auto TypeName = "net.drinkingtea.jasper.world.TileStatic";
-	constexpr static auto TypeVersion = 1;
-	uint16_t tileIdx{};
-	uint8_t palBank{};
+	static constexpr auto TypeName = "net.drinkingtea.jasper.world.TileStatic";
+	static constexpr auto TypeVersion = 1;
+	uint8_t objIdxRefSet{};
 	uint8_t tileType{};
 	uint8_t layerAttachments{};
 };
 
 OX_MODEL_BEGIN(TileStatic)
-	OX_MODEL_FIELD(tileIdx)
-	OX_MODEL_FIELD(palBank)
+	OX_MODEL_FIELD(objIdxRefSet)
 	OX_MODEL_FIELD(tileType)
 	OX_MODEL_FIELD(layerAttachments)
 OX_MODEL_END()
 
 
 struct BgLayer {
-	constexpr static auto TypeName = "net.drinkingtea.jasper.world.BgLayer";
-	constexpr static auto TypeVersion = 1;
+	static constexpr auto TypeName = "net.drinkingtea.jasper.world.BgLayer";
+	static constexpr auto TypeVersion = 1;
 	uint8_t cbb{};
 	ox::Vector<TileStatic> tiles;
 };
@@ -86,11 +81,47 @@ OX_MODEL_BEGIN(BgLayer)
 OX_MODEL_END()
 
 
+struct ObjTileRefSet {
+	static constexpr auto TypeName = "net.drinkingtea.jasper.world.ObjTileRefSet";
+	static constexpr auto TypeVersion = 1;
+	uint16_t palBank{};
+	uint16_t tilesheetIdx{};
+	uint16_t cbbIdx{};
+	uint8_t cbb{};
+	// which tilesheet to use
+	uint8_t tilesheetId{};
+	uint8_t tileCnt{};
+	// each successive frame will use tileIdx[i] + tileCnt * frameNo for the tileIdx
+	uint8_t frames{};
+};
+
+OX_MODEL_BEGIN(ObjTileRefSet)
+	OX_MODEL_FIELD(palBank)
+	OX_MODEL_FIELD(tilesheetIdx)
+	OX_MODEL_FIELD(cbbIdx)
+	OX_MODEL_FIELD(cbb)
+	OX_MODEL_FIELD(tilesheetId)
+	OX_MODEL_FIELD(tileCnt)
+	OX_MODEL_FIELD(frames)
+OX_MODEL_END()
+
+[[nodiscard]]
+constexpr bool operator==(ObjTileRefSet const&a, ObjTileRefSet const&b) noexcept {
+	return
+		a.tilesheetId == b.tilesheetId &&
+		a.tileCnt == b.tileCnt &&
+		a.frames == b.frames &&
+		a.tilesheetIdx == b.tilesheetIdx;
+}
+
+
 struct WorldStatic {
-	constexpr static auto TypeName = "net.drinkingtea.jasper.world.WorldStatic";
-	constexpr static auto TypeVersion = 1;
-	constexpr static auto Preloadable = true;
-	ncore::TileSheetSet tilesheets;
+	static constexpr auto TypeName = "net.drinkingtea.jasper.world.WorldStatic";
+	static constexpr auto TypeVersion = 1;
+	static constexpr auto Preloadable = true;
+	ncore::TileSheetSet tilesheetSet;
+	ox::Vector<ObjTileRefSet> objTileRefSets;
+	ox::Vector<ox::FileAddress> tilesheets;
 	ox::Vector<ox::FileAddress> palettes;
 	int16_t columns{};
 	int16_t rows{};
@@ -98,6 +129,8 @@ struct WorldStatic {
 };
 
 OX_MODEL_BEGIN(WorldStatic)
+	OX_MODEL_FIELD(tilesheetSet)
+	OX_MODEL_FIELD(objTileRefSets)
 	OX_MODEL_FIELD(tilesheets)
 	OX_MODEL_FIELD(palettes)
 	OX_MODEL_FIELD(columns)
@@ -105,9 +138,22 @@ OX_MODEL_BEGIN(WorldStatic)
 	OX_MODEL_FIELD(map)
 OX_MODEL_END()
 
-void loadTile(ObjectCache const&objCache, TileStatic &dst, TileDoc const&src) noexcept;
+[[nodiscard]]
+constexpr bool valid(WorldStatic const&ws) noexcept {
+	auto const tileCnt = static_cast<size_t>(ws.columns * ws.rows);
+	return ox::all_of(ws.map.begin(), ws.map.end(), [tileCnt](BgLayer const&v) {
+		return v.tiles.size() == tileCnt;
+	});
+}
 
-ox::Result<WorldStatic> loadWorldStatic(ObjectCache const&objCache, WorldDoc const&doc) noexcept;
+void loadTile(TileStatic &dst, TileDoc const&src) noexcept;
+
+ox::Result<WorldStatic> loadWorldStatic(keel::Context &kctx, ObjectCache const&objCache, WorldDoc const&doc) noexcept;
+
+[[nodiscard]]
+constexpr size_t layers(WorldStatic const&ws) noexcept {
+	return ws.map.size();
+}
 
 [[nodiscard]]
 auto &tile(
@@ -124,7 +170,4 @@ auto &cbb(ox::CommonRefWith<WorldStatic> auto&ws, size_t lyr) noexcept {
 	return ws.map[lyr].cbb;
 }
 
-[[nodiscard]]
-bool isValid(WorldStatic const&ws) noexcept;
-
 }
diff --git a/src/jasper/modules/world/src/keel/typeconv.cpp b/src/jasper/modules/world/src/keel/typeconv.cpp
index fc7016d..d084db3 100644
--- a/src/jasper/modules/world/src/keel/typeconv.cpp
+++ b/src/jasper/modules/world/src/keel/typeconv.cpp
@@ -16,7 +16,7 @@ ox::Error WorldDocToWorldStaticConverter::convert(
 		WorldDoc &src,
 		WorldStatic &dst) const noexcept {
 	OX_REQUIRE(oc, buildObjCache(kctx, src));
-	return loadWorldStatic(oc, src).moveTo(dst);
+	return loadWorldStatic(kctx, oc, src).moveTo(dst);
 }
 
 }
diff --git a/src/jasper/modules/world/src/objectcache.cpp b/src/jasper/modules/world/src/objectcache.cpp
index 9651242..4d9279f 100644
--- a/src/jasper/modules/world/src/objectcache.cpp
+++ b/src/jasper/modules/world/src/objectcache.cpp
@@ -20,25 +20,28 @@ void ObjectCache::clear() noexcept {
 
 ox::Error ObjectCache::indexSet(
 		keel::Context &kctx,
-		uint64_t setId,
+		uint64_t const setId,
 		WorldObjectSet const&objSet) noexcept {
 	auto &set = m_objSets.emplace_back(ObjSet{
 		.setId = setId,
 		.objects = {},
 	});
 	OX_REQUIRE(ts, readObj<ncore::TileSheet>(kctx, objSet.tilesheet));
+	auto tsId = ox::find(m_tilesheets.begin(), m_tilesheets.end(), objSet.tilesheet);
+	if (tsId == m_tilesheets.end()) {
+		m_tilesheets.emplace_back(objSet.tilesheet);
+	}
 	for (auto const&obj : objSet.objects) {
 		set.objects.emplace_back(Obj{
 			.id = obj.id,
 			.palBank = static_cast<uint16_t>(obj.palBank + m_palBank),
-			.tileIdx = getTileIdx(*ts, obj.subsheetId) + m_tileIdx,
+			.tilesheetIdx = getTileIdx(*ts, obj.subsheetId).or_value(0) + m_tileIdx,
 		});
 	}
 	auto const tileCnt = getTileCnt(*ts);
 	m_tileIdx += tileCnt;
-	m_tilesheets.emplace_back(objSet.tilesheet);
 	m_tilesheetSet.bpp = 4;
-	addTileSheet(objSet.tilesheet, static_cast<int32_t>(tileCnt));
+	addTileSheetSetEntry(objSet.tilesheet, static_cast<int32_t>(tileCnt));
 	for (auto const&pal : objSet.palettes) {
 		m_palettes.emplace_back(pal);
 		OX_REQUIRE(p, readObj<ncore::Palette>(kctx, pal));
@@ -61,15 +64,19 @@ ox::Optional<ObjectCache::Obj> ObjectCache::obj(uint64_t setId, ObjectId objId)
 	return {};
 }
 
-ncore::TileSheetSet const&ObjectCache::tilesheets() const noexcept {
+ncore::TileSheetSet const&ObjectCache::tilesheetSet() const noexcept {
 	return m_tilesheetSet;
 }
 
+ox::Vector<ox::FileAddress> const&ObjectCache::tilesheets() const noexcept {
+	return m_tilesheets;
+}
+
 ox::Vector<ox::FileAddress> const&ObjectCache::palettes() const noexcept {
 	return m_palettes;
 }
 
-void ObjectCache::addTileSheet(ox::FileAddress path, int32_t tiles) noexcept {
+void ObjectCache::addTileSheetSetEntry(ox::FileAddress path, int32_t tiles) noexcept {
 	ncore::TileSheetSetEntry entry;
 	entry.tilesheet = std::move(path);
 	entry.sections.push_back({
diff --git a/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.cpp b/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.cpp
index d9db3a0..6b69f70 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.cpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.cpp
@@ -8,27 +8,21 @@
 namespace jasper::world {
 
 EditWorldSizeCommand::EditWorldSizeCommand(
-		ObjectCache const&objCache,
 		WorldDoc &doc,
-		WorldStatic &worldStatic,
 		ox::Size const&size):
-		m_objCache(objCache),
 		m_doc(doc),
-		m_worldStatic(worldStatic),
 		m_oldSize(m_doc.columns, m_doc.rows),
 		m_newSize(size) {}
 
 ox::Error EditWorldSizeCommand::redo() noexcept {
 	m_oldMap = m_doc.tiles;
 	resize(m_doc, m_newSize);
-	OX_RETURN_ERROR(loadWorldStatic(m_objCache, m_doc).moveTo(m_worldStatic));
 	return {};
 }
 
 ox::Error EditWorldSizeCommand::undo() noexcept {
 	resize(m_doc, m_oldSize);
 	m_doc.tiles = std::move(m_oldMap);
-	OX_RETURN_ERROR(loadWorldStatic(m_objCache, m_doc).moveTo(m_worldStatic));
 	return {};
 }
 
diff --git a/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.hpp b/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.hpp
index 757b083..ca82ca2 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.hpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/commands/editsize.hpp
@@ -14,18 +14,14 @@ namespace jasper::world {
 
 class EditWorldSizeCommand: public studio::UndoCommand {
 	private:
-		ObjectCache const&m_objCache;
 		WorldDoc &m_doc;
-		WorldStatic &m_worldStatic;
 		size_t m_insertIdx{};
 		ox::Size const m_oldSize;
 		WorldDoc::TileMap m_oldMap;
 		ox::Size m_newSize;
 	public:
 		EditWorldSizeCommand(
-				ObjectCache const&objCache,
 				WorldDoc &doc,
-				WorldStatic &worldStatic,
 				ox::Size const&size);
 		ox::Error redo() noexcept override;
 		ox::Error undo() noexcept override;
diff --git a/src/jasper/modules/world/src/studio/worldeditor/commands/modifytiles.cpp b/src/jasper/modules/world/src/studio/worldeditor/commands/modifytiles.cpp
index 91e5489..6beef5f 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/commands/modifytiles.cpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/commands/modifytiles.cpp
@@ -47,7 +47,7 @@ void ModifyTilesCommand::swap() noexcept {
 		auto &activeTile = tile(m_worldStatic, mod.layer, mod.tileAddr.x, mod.tileAddr.y);
 		std::swap(docTile.obj.worldObjectId, mod.objId);
 		std::swap(docTile.obj.worldObjectSetId, mod.setId);
-		loadTile(m_objCache, activeTile, docTile);
+		loadTile(activeTile, docTile);
 	}
 }
 
diff --git a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
index a125cc6..a459309 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
@@ -77,12 +77,12 @@ constexpr ox::Point fbPtToTileAddr(
 	};
 }
 
-WorldEditorImGui::WorldEditorImGui(studio::StudioContext &sctx, ox::StringView path):
-		Editor(path),
+WorldEditorImGui::WorldEditorImGui(studio::StudioContext &sctx, ox::StringParam path):
+		Editor(std::move(path)),
 		m_sctx(sctx),
-		m_doc(makeValid(*readObj<WorldDoc>(keelCtx(m_sctx), path).unwrapThrow())),
+		m_doc(makeValid(*readObj<WorldDoc>(keelCtx(m_sctx), itemPath()).unwrapThrow())),
 		m_objCache(buildObjCache(keelCtx(m_sctx), m_doc).unwrapThrow()),
-		m_worldStatic(loadWorldStatic(m_objCache, m_doc)),
+		m_worldStatic(loadWorldStatic(keelCtx(m_sctx), m_objCache, m_doc)),
 		m_view(m_sctx, m_worldStatic) {
 	OX_THROW_ERROR(loadObjectSets());
 	m_objSetPicker.filePicked.connect(this, &WorldEditorImGui::addObjSet);
@@ -249,7 +249,7 @@ void WorldEditorImGui::drawPropEditor() noexcept {
 			if (ig::PopupControlsOkCancel(popupSz.x, m_sizeEditor.show) == ig::PopupResponse::OK) {
 				if (changed) {
 					std::ignore = pushCommand<EditWorldSizeCommand>(
-							m_objCache, m_doc, m_worldStatic, ox::Size{m_sizeEditor.columns, m_sizeEditor.rows});
+							m_doc, ox::Size{m_sizeEditor.columns, m_sizeEditor.rows});
 				}
 			}
 			ImGui::EndPopup();
@@ -389,7 +389,7 @@ ox::Error WorldEditorImGui::handleDrop(float fbPaneScale) noexcept {
 				m_objCache,
 				std::move(mods));
 	}
-	OX_RETURN_ERROR(loadWorldStatic(m_objCache, m_doc).moveTo(m_worldStatic));
+	OX_RETURN_ERROR(loadWorldStatic(keelCtx(m_sctx), m_objCache, m_doc).moveTo(m_worldStatic));
 	return {};
 }
 
@@ -416,7 +416,7 @@ ox::Error WorldEditorImGui::handleDepUpdate(ox::StringView, ox::UUID const&uuid)
 	                     || ox::any_of(m_dependencies.pairs().begin(), m_dependencies.pairs().end(), depMatches);
 	if (depUpdated) {
 		OX_RETURN_ERROR(buildObjCache(kctx, m_doc).moveTo(m_objCache));
-		OX_RETURN_ERROR(loadWorldStatic(m_objCache, m_doc).moveTo(m_worldStatic));
+		OX_RETURN_ERROR(loadWorldStatic(keelCtx(m_sctx), m_objCache, m_doc).moveTo(m_worldStatic));
 		OX_RETURN_ERROR(loadObjectSets());
 	}
 	return {};
@@ -437,8 +437,11 @@ ox::Error WorldEditorImGui::loadObjectSets() noexcept {
 	return {};
 }
 
-ox::Error WorldEditorImGui::undoStackChanged(studio::UndoCommand const*) {
+ox::Error WorldEditorImGui::undoStackChanged(studio::UndoCommand const*cmd) {
 	OX_RETURN_ERROR(m_view.setupWorld());
+	if (dynamic_cast<EditWorldSizeCommand const*>(cmd)) {
+        OX_RETURN_ERROR(loadWorldStatic(keelCtx(m_sctx), m_objCache, m_doc).moveTo(m_worldStatic));
+	}
 	return {};
 }
 
diff --git a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
index 20cd8d3..1e70a41 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
@@ -8,8 +8,7 @@
 
 #include <studio/studio.hpp>
 
-#include <turbine/context.hpp>
-
+#include <jasper/world/consts.hpp>
 #include <jasper/world/objectcache.hpp>
 
 #include "worldeditorview.hpp"
@@ -23,8 +22,7 @@ class WorldEditorImGui: public studio::Editor {
 		ox::Optional<studio::Selection> m_selection;
 		uint8_t m_activeLayer{};
 		studio::StudioContext &m_sctx;
-		studio::ig::FilePicker m_objSetPicker{
-			m_sctx, ox::String("Choose Object Set"), ox::String(FileExt_jwob)};
+		studio::ig::FilePicker m_objSetPicker{m_sctx, "Choose Object Set", FileExt_jwob};
 		WorldDoc m_doc;
 		ObjectCache m_objCache;
 		struct ObjSetRef {
@@ -51,7 +49,7 @@ class WorldEditorImGui: public studio::Editor {
 		} m_sizeEditor;
 
 	public:
-		WorldEditorImGui(studio::StudioContext &ctx, ox::StringView path);
+		WorldEditorImGui(studio::StudioContext &ctx, ox::StringParam path);
 
 		void draw(studio::StudioContext&) noexcept final;
 
diff --git a/src/jasper/modules/world/src/studio/worldobjectseteditor/worldobjectseteditor-imgui.cpp b/src/jasper/modules/world/src/studio/worldobjectseteditor/worldobjectseteditor-imgui.cpp
index b85af1d..c4a5e2e 100644
--- a/src/jasper/modules/world/src/studio/worldobjectseteditor/worldobjectseteditor-imgui.cpp
+++ b/src/jasper/modules/world/src/studio/worldobjectseteditor/worldobjectseteditor-imgui.cpp
@@ -140,7 +140,7 @@ void WorldObjectSetEditorImGui::loadObj() noexcept {
 		w = m_subsheet->columns;
 		h = m_subsheet->rows;
 	}
-	auto const idx = getTileIdx(*m_tileSheet, obj.subsheetId);
+	auto const idx = getTileIdx(*m_tileSheet, obj.subsheetId).or_value(0);
 	oxLogError(m_colView.setup(
 			m_doc.tilesheet,
 			m_doc.palettes[obj.palBank],
diff --git a/src/jasper/modules/world/src/world.cpp b/src/jasper/modules/world/src/world.cpp
index e750929..c8ff88d 100644
--- a/src/jasper/modules/world/src/world.cpp
+++ b/src/jasper/modules/world/src/world.cpp
@@ -15,6 +15,13 @@ World::World(ncore::Context &nctx, WorldStatic const&worldStatic) noexcept:
 	m_worldStatic(worldStatic) {}
 
 ox::Error World::setupDisplay() noexcept {
+	auto &kctx = keelCtx(m_nctx);
+	if (m_tilesheets.empty()) {
+		for (auto const&tsAddr : m_worldStatic.tilesheets) {
+			OX_REQUIRE_M(ts, keel::readObj<ncore::CompactTileSheet>(kctx, tsAddr));
+			m_tilesheets.emplace_back(std::move(ts));
+		}
+	}
 	if (m_worldStatic.palettes.empty()) {
 		return ox::Error(1, "World has no palettes");
 	}
@@ -23,7 +30,16 @@ ox::Error World::setupDisplay() noexcept {
 		OX_RETURN_ERROR(ncore::loadBgPalette(m_nctx, i, *pal));
 		++i;
 	}
-	OX_RETURN_ERROR(ncore::loadBgTileSheet(m_nctx, 0, m_worldStatic.tilesheets));
+	OX_RETURN_ERROR(ncore::loadBgTileSheet(m_nctx, 0, m_worldStatic.tilesheetSet));
+	for (auto const&rs : m_worldStatic.objTileRefSets) {
+		OX_RETURN_ERROR(ncore::loadBgTileSheet(
+			m_nctx,
+			rs.cbb,
+			*m_tilesheets[rs.tilesheetId],
+			rs.cbbIdx,
+			rs.tilesheetIdx,
+			rs.tileCnt));
+	}
 	ncore::setBgStatus(m_nctx, 0); // disable all backgrounds
 	for (auto layerNo = 0u; auto const&layer : m_worldStatic.map) {
 		setupLayer(layerNo, layer.cbb);
@@ -33,8 +49,8 @@ ox::Error World::setupDisplay() noexcept {
 }
 
 void World::setupLayer(
-		uint_t lyr,
-		uint_t cbb) const noexcept {
+		uint_t const lyr,
+		uint_t const cbb) const noexcept {
 	ncore::clearBg(m_nctx, lyr);
 	ncore::setBgStatus(m_nctx, lyr, true);
 	ncore::setBgCbb(m_nctx, lyr, cbb);
@@ -45,21 +61,22 @@ void World::setupLayer(
 			auto &t = tile(m_worldStatic, lyr, x, y);
 			auto const tx = x * 2;
 			auto const ty = y * 2;
+			auto const &obj = m_worldStatic.objTileRefSets[t.objIdxRefSet];;
 			ncore::setBgTile(m_nctx, lyr, tx + 0, ty + 0, {
-				.tileIdx = static_cast<uint_t>(t.tileIdx + 0),
-				.palBank = t.palBank,
+				.tileIdx = static_cast<uint_t>(obj.cbbIdx + 0),
+				.palBank = obj.palBank,
 			});
 			ncore::setBgTile(m_nctx, lyr, tx + 1, ty + 0, {
-				.tileIdx = static_cast<uint_t>(t.tileIdx + 1),
-				.palBank = t.palBank,
+				.tileIdx = static_cast<uint_t>(obj.cbbIdx + 1),
+				.palBank = obj.palBank,
 			});
 			ncore::setBgTile(m_nctx, lyr, tx + 0, ty + 1, {
-				.tileIdx = static_cast<uint_t>(t.tileIdx + 2),
-				.palBank = t.palBank,
+				.tileIdx = static_cast<uint_t>(obj.cbbIdx + 2),
+				.palBank = obj.palBank,
 			});
 			ncore::setBgTile(m_nctx, lyr, tx + 1, ty + 1, {
-				.tileIdx = static_cast<uint_t>(t.tileIdx + 3),
-				.palBank = t.palBank,
+				.tileIdx = static_cast<uint_t>(obj.cbbIdx + 3),
+				.palBank = obj.palBank,
 			});
 		}
 	}
diff --git a/src/jasper/modules/world/src/worldstatic.cpp b/src/jasper/modules/world/src/worldstatic.cpp
index 13ce27a..6e486dd 100644
--- a/src/jasper/modules/world/src/worldstatic.cpp
+++ b/src/jasper/modules/world/src/worldstatic.cpp
@@ -2,17 +2,18 @@
  * Copyright 2023 - 2024 Gary Talent (gary@drinkingtea.net). All rights reserved.
  */
 
+#include <keel/media.hpp>
+
 #include <nostalgia/core/gfx.hpp>
 
+#include <jasper/world/worldobject.hpp>
 #include <jasper/world/worldstatic.hpp>
 
 namespace jasper::world {
 
-void loadTile(ObjectCache const&objCache, TileStatic &dst, TileDoc const&src) noexcept {
-	auto const obj = objCache.obj(src.obj.worldObjectSetId, src.obj.worldObjectId).or_value({});
-	dst.palBank = src.palBank;
-	dst.tileIdx = static_cast<uint16_t>(obj.tileIdx);
-	dst.palBank = static_cast<uint8_t>(obj.palBank);
+void loadTile(
+		TileStatic &dst,
+		TileDoc const&src) noexcept {
 	dst.tileType = src.type;
 	setTopEdge(dst.layerAttachments, src.topLayerAttachment);
 	setBottomEdge(dst.layerAttachments, src.bottomLayerAttachment);
@@ -20,41 +21,110 @@ void loadTile(ObjectCache const&objCache, TileStatic &dst, TileDoc const&src) no
 	setRightEdge(dst.layerAttachments, src.rightLayerAttachment);
 }
 
-ox::Result<WorldStatic> loadWorldStatic(ObjectCache const&objCache, WorldDoc const&doc) noexcept {
-	auto const tileCnt =
-		static_cast<size_t>(doc.columns) * static_cast<size_t>(doc.rows);
-	WorldStatic out {
-		.tilesheets = {},
-		.palettes = {},
-		.columns = static_cast<int16_t>(doc.columns),
-		.rows = static_cast<int16_t>(doc.rows),
-		.map = {
-			{.tiles = ox::Vector<TileStatic>(tileCnt),},
-			{.tiles = ox::Vector<TileStatic>(tileCnt),},
-			{.tiles = ox::Vector<TileStatic>(tileCnt),},
-		},
-	};
-	// resources
-	out.tilesheets = objCache.tilesheets();
-	out.palettes = objCache.palettes();
-	// tiles
-	for (auto lyr = 0u; lyr < 3; ++lyr) {
-		for (auto x = 0u; x < static_cast<size_t>(out.columns); ++x) {
-			for (auto y = 0u; y < static_cast<size_t>(out.rows); ++y) {
-				auto &dst = tile(out, lyr, x, y);
-				auto &src = tile(doc, lyr, x, y);;
-				loadTile(objCache, dst, src);
-			}
+/**
+ * Returns the index in rsrcs for the given docObjRef.
+ */
+static ox::Result<uint8_t> setupTileResrc(
+		ox::SmallMap<DocObjRef, uint8_t> &cache,
+		keel::Context &kctx,
+        ox::Vector<ox::FileAddress> const&tilesheets,
+        ox::SmallMap<uint64_t, WorldObjectSet> const&objSets,
+		ox::Vector<ObjTileRefSet> &rsrcs,
+		uint16_t &cbbIt,
+		DocObjRef const&docObjRef) noexcept {
+	if (!docObjRef.unique) {
+		auto const [out, err] = cache.at(docObjRef);
+		if (!err) {
+			return *out;
 		}
 	}
+	OX_REQUIRE(objSet, objSets.at(docObjRef.worldObjectSetId));
+	auto const obj = ox::find_if(
+		objSet->objects.begin(), objSet->objects.end(),
+		[&docObjRef](WorldObject const&o) {
+			return o.id == docObjRef.worldObjectId;
+		});
+	if (obj == objSet->objects.end()) {
+		return ox::Error{obj == objSet->objects.end(), "could not find WorldObject in WorldObjectSet"};
+	}
+	OX_REQUIRE(ts, keel::readObj<ncore::TileSheet>(kctx, objSet->tilesheet));
+	OX_REQUIRE(tsIdx, ox::findIdx(
+		tilesheets.begin(), tilesheets.end(), objSet->tilesheet).to<uint8_t>());
+	auto const subsheetOffset = ncore::getTileIdx(*ts, obj->subsheetId);
+	if (!subsheetOffset) {
+		return ox::Error{1, "invalid subsheet idx"};
+	}
+	auto const subsheet = ncore::getSubsheet(*ts, obj->subsheetId);
+	if (!subsheet) {
+		return ox::Error{1, "could not find subsheet"};
+	}
+	auto const out = static_cast<uint8_t>(rsrcs.size());
+	auto const&refSet = rsrcs.emplace_back(ObjTileRefSet{
+		.palBank = obj->palBank,
+		.tilesheetIdx = static_cast<uint16_t>(*subsheetOffset),
+		.cbbIdx = cbbIt,
+		.tilesheetId = tsIdx,
+		.tileCnt = static_cast<uint8_t>(subsheet->size()),
+	});
+	cbbIt += refSet.tileCnt;
+	if (!docObjRef.unique) {
+		cache[docObjRef] = out;
+	}
 	return out;
 }
 
-bool isValid(WorldStatic const&ws) noexcept {
-	auto const tileCnt = static_cast<size_t>(ws.columns * ws.rows);
-	return ox::all_of(ws.map.begin(), ws.map.end(), [tileCnt](auto &v) {
-		return v.tiles.size() == tileCnt;
-	});
+ox::Result<WorldStatic> loadWorldStatic(
+		keel::Context &kctx,
+		ObjectCache const&objCache,
+		WorldDoc const&doc) noexcept {
+	auto const tilesPerLayer =
+		static_cast<size_t>(doc.columns) * static_cast<size_t>(doc.rows);
+	ox::SmallMap<uint64_t, WorldObjectSet> objSets;
+	for (auto const&setRef : doc.objSets) {
+		auto [set, err] =
+			keel::readObj<WorldObjectSet>(kctx, setRef.path);
+		if (!err) {
+			objSets[setRef.id] = *set;
+		}
+	}
+	ox::Result<WorldStatic> result = WorldStatic{
+        .tilesheetSet = objCache.tilesheetSet(),
+        .objTileRefSets = {},
+        .tilesheets = objCache.tilesheets(),
+        .palettes = objCache.palettes(),
+        .columns = static_cast<int16_t>(doc.columns),
+        .rows = static_cast<int16_t>(doc.rows),
+        .map = {
+            {.tiles = ox::Vector<TileStatic>{tilesPerLayer},},
+            {.tiles = ox::Vector<TileStatic>{tilesPerLayer},},
+            {.tiles = ox::Vector<TileStatic>{tilesPerLayer},},
+        },
+	};
+	auto &out = result.value;
+    ox::SmallMap<DocObjRef, uint8_t> refSetCache;
+	uint16_t cbbIt = 4;
+	// tiles
+	for (auto lyr = 0u; lyr < layers(out); ++lyr) {
+		for (auto x = 0u; x < static_cast<size_t>(out.columns); ++x) {
+			for (auto y = 0u; y < static_cast<size_t>(out.rows); ++y) {
+				auto &dst = tile(out, lyr, x, y);
+				auto &src = tile(doc, lyr, x, y);;
+				loadTile(dst, src);
+				auto const refSetIdx = setupTileResrc(
+						refSetCache,
+						kctx,
+						out.tilesheets,
+						objSets,
+						out.objTileRefSets,
+						cbbIt,
+						src.obj);
+				if (refSetIdx.ok()) {
+					dst.objIdxRefSet = refSetIdx.value;
+				}
+			}
+		}
+	}
+	return result;
 }
 
 }