I now have a semi-functional GUI system that uses the ECS style to build gui elements rather than inheritance.

ecs_gui.cpp

@@ -0,0 +1,65 @@
+#include "ecs_gui.hpp"
+#include "constants.hpp"
+
+GUECS::GUECS() {
+  $font = make_shared<sf::Font>(FONT_FILE_NAME);
+}
+
+void GUECS::position(int x, int y, int width, int height) {
+  $parser.position(x, y, width, height);
+}
+
+void GUECS::layout(std::string grid) {
+  $grid = grid;
+  $parser.parse($grid);
+}
+
+DinkyECS::Entity GUECS::entity(std::string name) {
+  auto entity = $world.entity();
+  $world.set<CellName>(entity, {name});
+  return entity;
+}
+
+void GUECS::init() {
+  $world.query<lel::Cell, Rectangle>([](const auto &, auto& cell, auto& rect) {
+    rect.init(cell);
+  });
+
+  $world.query<lel::Cell, Textual>([this](const auto &, auto& cell, auto& text) {
+    text.init(cell, $font);
+  });
+}
+
+void GUECS::render(sf::RenderWindow& window) {
+  $world.query<lel::Cell, Meter>([&](const auto &ent, const auto& cell, const auto &meter) {
+      if($world.has<Rectangle>(ent)) {
+        float level = meter.percent * float(cell.w);
+        auto& target = $world.get<Rectangle>(ent);
+        // ZED: this 6 is a border width, make it a thing
+        target.shape->setSize({std::max(level, 0.0f), float(cell.h - 6)});
+      }
+  });
+
+  $world.query<Rectangle>([&](const auto &, const auto& rect) {
+      window.draw(*rect.shape);
+  });
+
+  $world.query<Textual>([&](const auto &, const auto& text) {
+      window.draw(*text.text);
+  });
+}
+
+void GUECS::mouse(sf::RenderWindow &window) {
+  if(sf::Mouse::isButtonPressed(sf::Mouse::Button::Left)) {
+    sf::Vector2f pos = window.mapPixelToCoords(sf::Mouse::getPosition(window));
+    $world.query<lel::Cell, Clickable>([&](const auto &ent, auto& cell, auto &clicked) {
+      if((pos.x >= cell.x && pos.x <= cell.x + cell.w) &&
+          (pos.y >= cell.y && pos.y <= cell.y + cell.h))
+      {
+        auto& cn = $world.get<CellName>(ent);
+        fmt::println("clicked on entity {} with name {} and event {}",
+            ent, cn.name, clicked.event);
+      }
+    });
+  }
+}