diff --git a/res/project_script.lua b/res/project_script.lua
new file mode 100644
index 00000000..5f28c300
--- /dev/null
+++ b/res/project_script.lua
@@ -0,0 +1,26 @@
+local menubg
+
+function on_screen_changed(screen)
+    if screen ~= "menu" then
+        if menubg then
+            menubg:destruct()
+            menubg = nil
+        end
+        return
+    end
+    local controller = {}
+    function controller.resize_menu_bg()
+        local w, h = unpack(gui.get_viewport())
+        if menubg then
+            menubg.region = {0, math.floor(h / 48), math.floor(w / 48), 0}
+            menubg.pos = {0, 0}
+        end
+        return w, h
+    end
+    _GUI_ROOT.root:add(
+        "<image id='menubg' src='gui/menubg' size-func='DATA.resize_menu_bg' "..
+        "z-index='-1000' interactive='true'/>", controller)
+    menubg = _GUI_ROOT.menubg
+    controller.resize_menu_bg()
+    menu.page = "main"
+end
diff --git a/src/engine/Engine.cpp b/src/engine/Engine.cpp
index 6596733f..5e5ba681 100644
--- a/src/engine/Engine.cpp
+++ b/src/engine/Engine.cpp
@@ -60,6 +60,17 @@ static std::unique_ptr<ImageData> load_icon() {
     return nullptr;
 }
 
+static std::unique_ptr<scripting::IProjectScript> load_project_script() {
+    io::path scriptFile = "project:project_script.lua";
+    if (io::exists(scriptFile)) {
+        logger.info() << "starting project script";
+        return scripting::load_project_script(scriptFile);
+    } else {
+        logger.warning() << "project script does not exists";
+    }
+    return nullptr;
+}
+
 Engine::Engine() = default;
 Engine::~Engine() = default;
 
@@ -166,12 +177,15 @@ void Engine::initialize(CoreParameters coreParameters) {
         }
     });
     scripting::initialize(this);
+
     if (!isHeadless()) {
         gui->setPageLoader(scripting::create_page_loader());
     }
     keepAlive(settings.ui.language.observe([this](auto lang) {
         langs::setup(lang, paths.resPaths.collectRoots());
     }, true));
+
+    projectScript = load_project_script();
 }
 
 void Engine::loadSettings() {
@@ -228,6 +242,7 @@ void Engine::run() {
     }
 }
 
+#include "graphics/ui/elements/Container.hpp"
 void Engine::postUpdate() {
     network->update();
     postRunnables.run();
@@ -270,6 +285,7 @@ void Engine::saveSettings() {
 }
 
 void Engine::close() {
+    projectScript.reset();
     saveSettings();
     logger.info() << "shutting down";
     if (screen) {
@@ -349,6 +365,12 @@ void Engine::setScreen(std::shared_ptr<Screen> screen) {
     audio::reset_channel(audio::get_channel_index("regular"));
     audio::reset_channel(audio::get_channel_index("ambient"));
     this->screen = std::move(screen);
+    if (this->screen) {
+        this->screen->onOpen();
+    }
+    if (projectScript && this->screen) {
+        projectScript->onScreenChange(this->screen->getName());
+    }
 }
 
 void Engine::onWorldOpen(std::unique_ptr<Level> level, int64_t localPlayer) {
diff --git a/src/engine/Engine.hpp b/src/engine/Engine.hpp
index a3427c14..d82fc4e6 100644
--- a/src/engine/Engine.hpp
+++ b/src/engine/Engine.hpp
@@ -38,6 +38,10 @@ namespace devtools {
     class Editor;
 }
 
+namespace scripting {
+    class IProjectScript;
+}
+
 class initialize_error : public std::runtime_error {
 public:
     initialize_error(const std::string& message) : std::runtime_error(message) {}
@@ -71,6 +75,7 @@ class Engine : public util::ObjectsKeeper {
     std::unique_ptr<Input> input;
     std::unique_ptr<gui::GUI> gui;
     std::unique_ptr<devtools::Editor> editor;
+    std::unique_ptr<scripting::IProjectScript> projectScript;
     PostRunnables postRunnables;
     Time time;
     OnWorldOpen levelConsumer;
@@ -178,4 +183,8 @@ public:
     const Project& getProject() {
         return *project;
     }
+
+    scripting::IProjectScript* getProjectScript() {
+        return projectScript.get();
+    }
 };
diff --git a/src/engine/Mainloop.cpp b/src/engine/Mainloop.cpp
index bdde4f53..a14c5464 100644
--- a/src/engine/Mainloop.cpp
+++ b/src/engine/Mainloop.cpp
@@ -5,10 +5,10 @@
 #include "devtools/Project.hpp"
 #include "frontend/screens/MenuScreen.hpp"
 #include "frontend/screens/LevelScreen.hpp"
-#include "interfaces/Process.hpp"
-#include "logic/scripting/scripting.hpp"
 #include "window/Window.hpp"
 #include "world/Level.hpp"
+#include "graphics/ui/GUI.hpp"
+#include "graphics/ui/elements/Container.hpp"
 
 static debug::Logger logger("mainloop");
 
@@ -31,26 +31,15 @@ void Mainloop::run() {
             ));
         }
     });
-    
-    io::path projectScript = "project:project_script.lua";
-    std::unique_ptr<Process> process;
-    if (io::exists(projectScript)) {
-        logger.info() << "starting project script";
-        process = scripting::start_coroutine(projectScript);
-    } else {
-        logger.warning() << "project script does not exists";
-    }
 
     logger.info() << "starting menu screen";
     engine.setScreen(std::make_shared<MenuScreen>(engine));
     
     logger.info() << "main loop started";
     while (!window.isShouldClose()){
-        if (process) {
-            process->update();
-        }
         time.update(window.time());
         engine.updateFrontend();
+
         if (!window.isIconified()) {
             engine.renderFrame();
         }
diff --git a/src/frontend/UiDocument.cpp b/src/frontend/UiDocument.cpp
index 7c6f8d13..3e9a3a27 100644
--- a/src/frontend/UiDocument.cpp
+++ b/src/frontend/UiDocument.cpp
@@ -14,11 +14,13 @@ UiDocument::UiDocument(
     const std::shared_ptr<gui::UINode>& root,
     scriptenv env
 ) : id(std::move(id)), script(script), root(root), env(std::move(env)) {
-    gui::UINode::getIndices(root, map);
+    rebuildIndices();
 }
 
 void UiDocument::rebuildIndices() {
+    map.clear();
     gui::UINode::getIndices(root, map);
+    map["root"] = root;
 }
 
 const UINodesMap& UiDocument::getMap() const {
diff --git a/src/frontend/screens/LevelScreen.cpp b/src/frontend/screens/LevelScreen.cpp
index ca80ed11..aa007293 100644
--- a/src/frontend/screens/LevelScreen.cpp
+++ b/src/frontend/screens/LevelScreen.cpp
@@ -97,7 +97,6 @@ LevelScreen::LevelScreen(
     animator->addAnimations(assets.getAnimations());
 
     loadDecorations();
-    initializeContent();
 }
 
 LevelScreen::~LevelScreen() {
@@ -112,6 +111,10 @@ LevelScreen::~LevelScreen() {
     engine.getPaths().setCurrentWorldFolder("");
 }
 
+void LevelScreen::onOpen() {
+    initializeContent();
+}
+
 void LevelScreen::initializeContent() {
     auto& content = controller->getLevel()->content;
     for (auto& entry : content.getPacks()) {
diff --git a/src/frontend/screens/LevelScreen.hpp b/src/frontend/screens/LevelScreen.hpp
index b4f6c93a..616258e5 100644
--- a/src/frontend/screens/LevelScreen.hpp
+++ b/src/frontend/screens/LevelScreen.hpp
@@ -53,8 +53,13 @@ public:
     );
     ~LevelScreen();
 
+    void onOpen() override;
     void update(float delta) override;
     void draw(float delta) override;
 
     void onEngineShutdown() override;
+
+    const char* getName() const override {
+        return "level";
+    }
 };
diff --git a/src/frontend/screens/MenuScreen.cpp b/src/frontend/screens/MenuScreen.cpp
index be114ed3..c1339494 100644
--- a/src/frontend/screens/MenuScreen.cpp
+++ b/src/frontend/screens/MenuScreen.cpp
@@ -13,12 +13,6 @@
 #include "engine/Engine.hpp"
 
 MenuScreen::MenuScreen(Engine& engine) : Screen(engine) {
-    engine.getContentControl().resetContent();
-    
-    auto menu = engine.getGUI().getMenu();
-    menu->reset();
-    menu->setPage("main");
-
     uicamera =
         std::make_unique<Camera>(glm::vec3(), engine.getWindow().getSize().y);
     uicamera->perspective = false;
@@ -29,33 +23,17 @@ MenuScreen::MenuScreen(Engine& engine) : Screen(engine) {
 
 MenuScreen::~MenuScreen() = default;
 
+void MenuScreen::onOpen() {
+    engine.getContentControl().resetContent();
+    
+    auto menu = engine.getGUI().getMenu();
+    menu->reset();
+}
+
 void MenuScreen::update(float delta) {
 }
 
 void MenuScreen::draw(float delta) {
-    auto assets = engine.getAssets();
-
     display::clear();
     display::setBgColor(glm::vec3(0.2f));
-
-    const auto& size = engine.getWindow().getSize();
-    uint width = size.x;
-    uint height = size.y;
-
-    uicamera->setFov(height);
-    uicamera->setAspectRatio(width / static_cast<float>(height));
-    auto uishader = assets->get<Shader>("ui");
-    uishader->use();
-    uishader->uniformMatrix("u_projview", uicamera->getProjView());
-
-    auto bg = assets->get<Texture>("gui/menubg");
-    batch->begin();
-    batch->texture(bg);
-    batch->rect(
-        0, 0, 
-        width, height, 0, 0, 0, 
-        UVRegion(0, 0, width / bg->getWidth(), height / bg->getHeight()), 
-        false, false, glm::vec4(1.0f)
-    );
-    batch->flush();
 }
diff --git a/src/frontend/screens/MenuScreen.hpp b/src/frontend/screens/MenuScreen.hpp
index f9b5dd48..a8caf0fe 100644
--- a/src/frontend/screens/MenuScreen.hpp
+++ b/src/frontend/screens/MenuScreen.hpp
@@ -13,6 +13,12 @@ public:
     MenuScreen(Engine& engine);
     ~MenuScreen();
 
+    void onOpen() override;
+
     void update(float delta) override;
     void draw(float delta) override;
+
+    const char* getName() const override {
+        return "menu";
+    }
 };
diff --git a/src/frontend/screens/Screen.hpp b/src/frontend/screens/Screen.hpp
index dde2f555..c24dc8b3 100644
--- a/src/frontend/screens/Screen.hpp
+++ b/src/frontend/screens/Screen.hpp
@@ -13,7 +13,9 @@ protected:
 public:
     Screen(Engine& engine);
     virtual ~Screen();
+    virtual void onOpen() = 0;
     virtual void update(float delta) = 0;
     virtual void draw(float delta) = 0;
     virtual void onEngineShutdown() {};
+    virtual const char* getName() const = 0;
 };
diff --git a/src/graphics/ui/GUI.cpp b/src/graphics/ui/GUI.cpp
index ceb2f4a0..79e9fd63 100644
--- a/src/graphics/ui/GUI.cpp
+++ b/src/graphics/ui/GUI.cpp
@@ -56,6 +56,13 @@ GUI::GUI(Engine& engine)
     store("tooltip", tooltip);
     store("tooltip.label", UINode::find(tooltip, "tooltip.label"));
     container->add(tooltip);
+
+    rootDocument = std::make_unique<UiDocument>(
+        "core:root",
+        uidocscript {},
+        std::dynamic_pointer_cast<gui::UINode>(container),
+        nullptr
+    );
 }
 
 GUI::~GUI() = default;
@@ -74,15 +81,8 @@ std::shared_ptr<Menu> GUI::getMenu() {
 }
 
 void GUI::onAssetsLoad(Assets* assets) {
-    assets->store(
-        std::make_unique<UiDocument>(
-            "core:root",
-            uidocscript {},
-            std::dynamic_pointer_cast<gui::UINode>(container),
-            nullptr
-        ),
-        "core:root"
-    );
+    rootDocument->rebuildIndices();
+    assets->store(rootDocument, "core:root");
 }
 
 void GUI::resetTooltip() {
diff --git a/src/graphics/ui/GUI.hpp b/src/graphics/ui/GUI.hpp
index 92e58db5..f2255fb5 100644
--- a/src/graphics/ui/GUI.hpp
+++ b/src/graphics/ui/GUI.hpp
@@ -22,6 +22,8 @@ namespace devtools {
     class Editor;
 }
 
+class UiDocument;
+
 /*
  Some info about padding and margin.
     Padding is element inner space, margin is outer
@@ -70,6 +72,7 @@ namespace gui {
         std::shared_ptr<UINode> pressed;
         std::shared_ptr<UINode> focus;
         std::shared_ptr<UINode> tooltip;
+        std::shared_ptr<UiDocument> rootDocument;
         std::unordered_map<std::string, std::shared_ptr<UINode>> storage;
 
         std::unique_ptr<Camera> uicamera;
diff --git a/src/logic/scripting/lua/libs/libgui.cpp b/src/logic/scripting/lua/libs/libgui.cpp
index 66a8f648..2f37bcb2 100644
--- a/src/logic/scripting/lua/libs/libgui.cpp
+++ b/src/logic/scripting/lua/libs/libgui.cpp
@@ -79,9 +79,12 @@ static int l_textbox_paste(lua::State* L) {
 
 static int l_container_add(lua::State* L) {
     auto docnode = get_document_node(L);
+    if (docnode.document == nullptr) {
+        throw std::runtime_error("target document not found");
+    }
     auto node = dynamic_cast<Container*>(docnode.node.get());
     if (node == nullptr) {
-        return 0;
+        throw std::runtime_error("target container not found");
     }
     auto xmlsrc = lua::require_string(L, 2);
     try {
@@ -99,7 +102,7 @@ static int l_container_add(lua::State* L) {
         UINode::getIndices(subnode, docnode.document->getMapWriteable());
         node->add(std::move(subnode));
     } catch (const std::exception& err) {
-        throw std::runtime_error(err.what());
+        throw std::runtime_error("container:add(...): " + std::string(err.what()));
     }
     return 0;
 }
diff --git a/src/logic/scripting/lua/lua_engine.cpp b/src/logic/scripting/lua/lua_engine.cpp
index 891b89c7..be37e7bb 100644
--- a/src/logic/scripting/lua/lua_engine.cpp
+++ b/src/logic/scripting/lua/lua_engine.cpp
@@ -58,12 +58,8 @@ static void create_libs(State* L, StateType stateType) {
     openlib(L, "vec4", vec4lib);
     openlib(L, "yaml", yamllib);
 
-    if (stateType == StateType::SCRIPT) {
-        openlib(L, "app", applib);
-    } else if (stateType == StateType::BASE) {
-        openlib(L, "__vc_app", applib);
-    }
     if (stateType == StateType::BASE || stateType == StateType::SCRIPT) {
+        openlib(L, "__vc_app", applib);
         openlib(L, "assets", assetslib);
         openlib(L, "audio", audiolib);
         openlib(L, "console", consolelib);
diff --git a/src/logic/scripting/scripting.cpp b/src/logic/scripting/scripting.cpp
index 39168843..04db321e 100644
--- a/src/logic/scripting/scripting.cpp
+++ b/src/logic/scripting/scripting.cpp
@@ -116,11 +116,42 @@ public:
     }
 };
 
-std::unique_ptr<Process> scripting::start_coroutine(
+class LuaProjectScript : public IProjectScript {
+public:
+    LuaProjectScript(lua::State* L, scriptenv env) : L(L), env(std::move(env)) {}
+
+    void onScreenChange(const std::string& name) override {
+        if (!lua::pushenv(L, *env)) {
+            return;
+        }
+        if (!lua::getfield(L, "on_screen_changed")) {
+            lua::pop(L);
+            return;
+        }
+        lua::pushlstring(L, name);
+        lua::call_nothrow(L, 1, 0);
+        lua::pop(L);
+    }
+private:
+    lua::State* L;
+    scriptenv env;
+};
+
+std::unique_ptr<IProjectScript> scripting::load_project_script(
     const io::path& script
 ) {
     auto L = lua::get_main_state();
-    if (lua::getglobal(L, "__vc_start_coroutine")) {
+    auto source = io::read_string(script);
+    auto env = create_environment(nullptr);
+    lua::loadbuffer(L, *env, source, script.name());
+    lua::call(L, 0);
+    return std::make_unique<LuaProjectScript>(L, std::move(env));
+}
+
+std::unique_ptr<Process> scripting::start_coroutine(const io::path& script) {
+    auto L = lua::get_main_state();
+    auto method = "__vc_start_coroutine";
+    if (lua::getglobal(L, method)) {
         auto source = io::read_string(script);
         lua::loadbuffer(L, 0, source, script.name());
         if (lua::call(L, 1)) {
diff --git a/src/logic/scripting/scripting.hpp b/src/logic/scripting/scripting.hpp
index bae5aac6..b6f8733d 100644
--- a/src/logic/scripting/scripting.hpp
+++ b/src/logic/scripting/scripting.hpp
@@ -65,9 +65,16 @@ namespace scripting {
 
     void process_post_runnables();
 
-    std::unique_ptr<Process> start_coroutine(
-        const io::path& script
-    );
+    class IProjectScript {
+    public:
+        virtual ~IProjectScript() {}
+
+        virtual void onScreenChange(const std::string& name) = 0;
+    };
+
+    std::unique_ptr<IProjectScript> load_project_script(const io::path& script);
+
+    std::unique_ptr<Process> start_coroutine(const io::path& script);
 
     void on_world_load(LevelController* controller);
     void on_world_tick(int tps);