First cut of pulling out the relevant parts of my original game to make a little framework.

src/gui/status_ui.cpp

@@ -0,0 +1,132 @@
+#include "gui/status_ui.hpp"
+#include "game/components.hpp"
+#include <guecs/ui.hpp>
+#include "algos/rand.hpp"
+#include <fmt/xchar.h>
+#include "gui/guecstra.hpp"
+#include "game/systems.hpp"
+#include "game/inventory.hpp"
+#include "game/level.hpp"
+
+namespace gui {
+  using namespace guecs;
+  using std::any, std::any_cast, std::string, std::make_any;
+
+  StatusUI::StatusUI(size_t x, size_t y, size_t width, size_t height)
+  {
+    $gui.position(x, y, width, height);
+    $gui.layout(
+        "[=slot1]"
+        "[=slot2]"
+        "[=hand_r]"
+        "[=pocket_l]");
+  }
+
+  void StatusUI::init() {
+    $gui.set<Background>($gui.MAIN, {$gui.$parser, });
+
+    for(auto& [name, cell] : $gui.cells()) {
+      auto gui_id = $gui.entity(name);
+
+      $gui.set<Rectangle>(gui_id, {});
+
+      $gui.set<Text>(gui_id, {guecs::to_wstring(name)});
+      $gui.set<Clickable>(gui_id, {
+          guecs::make_action(gui_id, game::Event::INV_SELECT, {gui_id})
+      });
+      $gui.set<DropTarget>(gui_id, {
+          .commit=[&, gui_id](DinkyECS::Entity world_target) -> bool {
+          return place_slot(gui_id, world_target);
+        }
+      });
+    }
+
+    $gui.init();
+    update();
+  }
+
+  bool StatusUI::mouse(float x, float y, guecs::Modifiers mods) {
+    return $gui.mouse(x, y, mods);
+  }
+
+  void StatusUI::update() {
+    auto world = GameDB::current_world();
+    auto player = world->get_the<components::Player>();
+    auto& inventory = world->get<inventory::Model>(player.entity);
+
+    for(const auto& [slot, cell] : $gui.cells()) {
+
+      if(inventory.has(slot)) {
+        auto gui_id = $gui.entity(slot);
+        auto world_entity = inventory.get(slot);
+
+        auto& sprite = world->get<components::Sprite>(world_entity);
+        $gui.set_init<guecs::Icon>(gui_id, {sprite.name});
+        guecs::GrabSource grabber{ world_entity,
+          [&, gui_id]() { return remove_slot(gui_id); }};
+        grabber.setSprite($gui, gui_id);
+        $gui.set<guecs::GrabSource>(gui_id, grabber);
+      } else {
+        auto gui_id = $gui.entity(slot);
+
+        if($gui.has<guecs::GrabSource>(gui_id)) {
+          $gui.remove<guecs::GrabSource>(gui_id);
+          $gui.remove<guecs::Icon>(gui_id);
+        }
+      }
+    }
+  }
+
+  void StatusUI::render(sf::RenderWindow &window) {
+    $gui.render(window);
+    // $gui.debug_layout(window);
+  }
+
+  void StatusUI::update_level() {
+    init();
+  }
+
+  bool StatusUI::place_slot(guecs::Entity gui_id, DinkyECS::Entity world_entity) {
+    auto& level = GameDB::current_level();
+    auto& slot_name = $gui.name_for(gui_id);
+    auto& inventory = level.world->get<inventory::Model>(level.player);
+
+    if(inventory.add(slot_name, world_entity)) {
+      level.world->make_constant(world_entity);
+      update();
+      return true;
+    }  else {
+      dbc::log("there's something there already");
+      return false;
+    }
+  }
+
+  void StatusUI::drop_item(DinkyECS::Entity item_id) {
+    System::drop_item(item_id);
+    update();
+  }
+
+  // NOTE: do I need this or how does it relate to drop_item?
+  void StatusUI::remove_slot(guecs::Entity slot_id) {
+    auto player = GameDB::the_player();
+    auto& slot_name = $gui.name_for(slot_id);
+    System::remove_from_container(player, slot_name);
+    update();
+  }
+
+  void StatusUI::swap(guecs::Entity gui_a, guecs::Entity gui_b) {
+    if(gui_a != gui_b) {
+      auto player = GameDB::the_player();
+      auto& a_name = $gui.name_for(gui_a);
+      auto& b_name = $gui.name_for(gui_b);
+      System::inventory_swap(player, a_name, b_name);
+    }
+
+    update();
+  }
+
+  bool StatusUI::occupied(guecs::Entity slot) {
+    auto player = GameDB::the_player();
+    return System::inventory_occupied(player, $gui.name_for(slot));
+  }
+}