xo-imgui: ex4 refactor [wip]

xo-imgui/example/ex4/imgui_ex4.cpp

@@ -1,11 +1,46 @@
 /* imgui_ex4.cpp */
 
 #include "xo/imgui/VulkanApp.hpp"
+#include <backends/imgui_impl_sdl2.h>
+#include <backends/imgui_impl_vulkan.h>
 #include <iostream>
 
+namespace {
+    ImDrawData *
+    imgui_draw_frame(ImGuiContext * imgui_cx)
+    {
+        // Start the Dear ImGui frame
+        ImGui_ImplVulkan_NewFrame();
+        ImGui_ImplSDL2_NewFrame();
+        ImGui::NewFrame();
+
+        // Create a simple ImGui window
+        ImGui::Begin("Hello, Vulkan + SDL2!");
+        ImGui::Text("This is a minimal ImGui + Vulkan + SDL2 example!");
+        static float f = 0.0f;
+        static int counter = 0;
+        ImGui::SliderFloat("float", &f, 0.0f, 1.0f);
+        if (ImGui::Button("Button"))
+            ++counter;
+        ImGui::SameLine();
+        ImGui::Text("counter = %d", counter);
+        ImGui::Text("Application average %.3f ms/frame (%.1f FPS)",
+                    1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
+        ImGui::End();
+
+        // Rendering
+        ImGui::Render();
+        ImDrawData* draw_data = ImGui::GetDrawData();
+
+        return draw_data;
+    }
+}
+
 int main() {
     VulkanApp app;
 
+    app.assign_imgui_draw_frame(imgui_draw_frame);
+
     try {
         app.run();
     } catch (const std::exception& e) {