add on_screen_change project script event & fix UIDocument::rebuildIndices & move menu background to project script

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();
 }