Bring in a simple SDL2 demo for completeness. It's running in a main.cpp to test SDL2 in C++.

sfmldemo/main.cpp

@@ -0,0 +1,44 @@
+#include "imgui.h"
+#include "imgui-SFML.h"
+
+#include <SFML/Graphics/CircleShape.hpp>
+#include <SFML/Graphics/RenderWindow.hpp>
+#include <SFML/System/Clock.hpp>
+#include <SFML/Window/Event.hpp>
+
+int main() {
+  sf::RenderWindow window(sf::VideoMode(1920, 1080), "ImGui + SFML = <3");
+  // window.setFramerateLimit(60);
+  window.setVerticalSyncEnabled(true);
+  ImGui::SFML::Init(window);
+
+  sf::CircleShape shape(100.f);
+  shape.setFillColor(sf::Color::Green);
+
+  sf::Clock deltaClock;
+  while (window.isOpen()) {
+    sf::Event event;
+    while (window.pollEvent(event)) {
+      ImGui::SFML::ProcessEvent(window, event);
+
+      if (event.type == sf::Event::Closed) {
+        window.close();
+      }
+    }
+
+    ImGui::SFML::Update(window, deltaClock.restart());
+
+    ImGui::ShowDemoWindow();
+
+    ImGui::Begin("Hello, world!");
+    ImGui::Button("Look at this pretty button");
+    ImGui::End();
+
+    window.clear();
+    window.draw(shape);
+    ImGui::SFML::Render(window);
+    window.display();
+  }
+
+  ImGui::SFML::Shutdown();
+}