setup

.gitignore

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+.vscode
+build
+imgui.ini

.gitmodules

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+[submodule "imgui"]
+	path = imgui
+	url = https://github.com/ocornut/imgui.git
+	branch = docking

imgui

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+Subproject commit 44aa9a4b3a6f27d09a4eb5770d095cbd376dfc4b

include/main.hpp

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+#ifndef MAIN_HPP
+#define MAIN_HPP
+
+// ImGui
+#include "imgui.h"
+#include "imgui_impl_sdl3.h"
+#include "imgui_impl_opengl3.h"
+
+// SDL3 and OpenGL
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_opengl.h>
+
+// C++ Standard Library
+#include <iostream>
+#include <string>
+#include <vector>
+
+// Structs
+
+
+
+// Variables
+int window_width = 1920;
+int window_height = 1080;
+
+float main_scale;
+SDL_WindowFlags window_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIDDEN | SDL_WINDOW_HIGH_PIXEL_DENSITY;
+SDL_Window* window;
+
+bool running;
+SDL_Event event;
+
+Uint32 last_time;
+Uint32 current_time;
+float frame_time;
+float fps;
+float frame_time_graph[100] = {0.0f};
+
+// Functions
+int main(int argc, char* argv[]);
+int initialize();
+void cleanup();
+
+#endif

makefile

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+# Directories
+INCLUDE_DIR = include
+SRC_DIR = src
+BUILD_DIR = build
+
+# ImGui directory (only set if ImGui is used)
+IMGUI_DIR = imgui
+
+# Compiler
+CXX = g++
+
+# Libs
+LIBS = -lGL `pkg-config --libs sdl3`
+
+# Compiler and linker settings
+CXXFLAGS = `pkg-config --cflags sdl3` -std=c++17 -I $(INCLUDE_DIR)
+
+# If ImGui directory is set, include its source files
+ifdef IMGUI_DIR
+CXXFLAGS += -I $(IMGUI_DIR) -I $(IMGUI_DIR)/backends
+endif
+
+# Source and object files
+SRC = $(wildcard $(SRC_DIR)/*.cpp)
+
+# If ImGui is used, add its source files to the source list
+ifdef IMGUI_DIR
+SRC += $(IMGUI_DIR)/imgui.cpp $(IMGUI_DIR)/imgui_demo.cpp $(IMGUI_DIR)/imgui_draw.cpp $(IMGUI_DIR)/imgui_tables.cpp $(IMGUI_DIR)/imgui_widgets.cpp
+SRC += $(IMGUI_DIR)/backends/imgui_impl_sdl3.cpp $(IMGUI_DIR)/backends/imgui_impl_opengl3.cpp
+endif
+
+# Target executable
+UNAME := $(shell uname -s)
+BUILD_DIR := $(BUILD_DIR)/$(UNAME)
+OBJ_DIR := $(BUILD_DIR)/objs
+BIN = $(BUILD_DIR)/main
+
+# Object files corresponding to the source files (now in obj directory)
+OBJS = $(addprefix $(OBJ_DIR)/, $(addsuffix .o, $(basename $(notdir $(SRC)))))
+
+# development target with debugging
+dev: CXXFLAGS += -g -Wall -Wformat
+dev: all
+
+# Release target
+release: CXXFLAGS += -O3
+release: all
+
+# Create directories for build output
+dirs:
+	@mkdir -p $(BUILD_DIR)
+	@mkdir -p $(OBJ_DIR)
+
+# Pattern rule for source files in src directory
+$(OBJ_DIR)/%.o: $(SRC_DIR)/%.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+# Pattern rule for ImGui source files
+ifdef IMGUI_DIR
+$(OBJ_DIR)/%.o: $(IMGUI_DIR)/%.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+$(OBJ_DIR)/%.o: $(IMGUI_DIR)/backends/%.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+endif
+
+all: dirs $(BIN)
+	@echo Build complete
+
+$(BIN): $(OBJS)
+	$(CXX) -o $@ $^ $(CXXFLAGS) $(LIBS)
+
+clean:
+	rm -rf $(BUILD_DIR)

src/main.cpp

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+#include "main.hpp"
+
+
+// Init
+int initialize() {
+    // Initialize SDL
+    if (!SDL_Init(SDL_INIT_VIDEO)) {
+        std::cerr << "SDL could not initialize! SDL_Error: " << SDL_GetError() << std::endl;
+        return 1; // Initialization failed
+    }
+
+    // Create a window with OpenGL context
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
+    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
+
+    main_scale = SDL_GetDisplayContentScale(SDL_GetPrimaryDisplay());
+    window = SDL_CreateWindow("Untitled", (int)(window_width * main_scale), (int)(window_height * main_scale), window_flags);
+    if (!window) {
+        std::cerr << "Window could not be created! SDL_Error: " << SDL_GetError() << std::endl;
+        SDL_Quit();
+        return 1; // Window creation failed
+    }
+    
+    // Initialize OpenGL context
+    SDL_GLContext gl_context = SDL_GL_CreateContext(window);
+    if (!gl_context) {
+        std::cerr << "OpenGL context could not be created! SDL_Error: " << SDL_GetError() << std::endl;
+        SDL_DestroyWindow(window);
+        SDL_Quit();
+        return 1; // OpenGL context creation failed
+    }
+
+    SDL_GL_MakeCurrent(window, gl_context);
+    SDL_GL_SetSwapInterval(1); // Enable VSync
+    SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
+    SDL_ShowWindow(window);
+
+    // Initialize ImGui
+    IMGUI_CHECKVERSION();
+    ImGui::CreateContext();
+    ImGuiIO& io = ImGui::GetIO(); (void)io;
+    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls
+
+    // Setup Dear ImGui style
+    ImGui::StyleColorsDark();
+
+    // Setup scale
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.ScaleAllSizes(main_scale);
+    style.FontScaleDpi = main_scale;
+
+    // Setup Platform/Renderer bindings
+    if (!ImGui_ImplSDL3_InitForOpenGL(window, gl_context)) {
+        std::cerr << "ImGui_ImplSDL3_InitForOpenGL failed!" << std::endl;
+        SDL_GL_DestroyContext(gl_context);
+        SDL_DestroyWindow(window);
+        SDL_Quit();
+        return 1; // Initialization failed
+    }
+
+    if (!ImGui_ImplOpenGL3_Init("#version 330")) {
+        std::cerr << "ImGui_ImplOpenGL3_Init failed!" << std::endl;
+        ImGui_ImplSDL3_Shutdown();
+        SDL_GL_DestroyContext(gl_context);
+        SDL_DestroyWindow(window);
+        SDL_Quit();
+        return 1; // Initialization failed
+    }
+
+    return 0; // Initialization successful
+}
+
+
+// Cleanup
+void cleanup() {
+    // Shutdown ImGui
+    ImGui_ImplOpenGL3_Shutdown();
+    ImGui_ImplSDL3_Shutdown();
+    ImGui::DestroyContext();
+
+    // Destroy OpenGL context
+    SDL_GLContext gl_context = SDL_GL_GetCurrentContext();
+    if (gl_context) {
+        SDL_GL_MakeCurrent(NULL, NULL);
+        SDL_GL_DestroyContext(gl_context);
+    }
+
+    // Destroy window
+    if (window) {
+        SDL_DestroyWindow(window);
+        window = nullptr;
+    }
+
+    // Quit SDL
+    SDL_Quit();
+    std::cout << "Cleanup successful." << std::endl;
+}
+
+
+// Main
+int main(int argc, char* argv[]) {
+    // Initialize
+    if (initialize() != 0) {
+        std::cerr << "Initialization failed." << std::endl;
+        return -1; // Initialization failed
+    }
+
+    // Main loop
+    running = true;
+    last_time = SDL_GetTicks();
+    while (running) {
+
+        // Handle events
+        while (SDL_PollEvent(&event)) {
+            ImGui_ImplSDL3_ProcessEvent(&event);
+            if (event.type == SDL_EVENT_QUIT) {
+                running = false; // Exit loop on quit event
+            }
+        }
+
+        // Start the ImGui frame
+        ImGui_ImplOpenGL3_NewFrame();
+        ImGui_ImplSDL3_NewFrame();
+        ImGui::NewFrame();
+
+        // Show a simple ImGui window
+        ImGui::Begin("Hello, World!");
+        ImGui::Text("This is a simple ImGui window.");
+        if (ImGui::Button("Close")) {
+            running = false; // Close button clicked
+        }
+        ImGui::End();
+
+        // Display FPS in the ImGui window
+        ImGui::Begin("FPS Counter");
+        ImGui::Text("Current FPS: %.2f", fps);
+        // Frame time graph
+        ImGui::PlotLines("##FrameTime", frame_time_graph, 100, 0, "Frame Time (ms)", 0.0f, 0.1f, ImVec2(200, 80));
+        ImGui::Text("Current Time: %u ms", current_time);
+
+        ImGui::End();
+
+        // Render
+        ImGui::Render();
+        glViewport(0, 0, (int)(window_width * main_scale), (int)(window_height * main_scale));
+        glClearColor(0.45f, 0.55f, 0.60f, 1.00f);
+        glClear(GL_COLOR_BUFFER_BIT);
+        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+        SDL_GL_SwapWindow(window);
+
+        // Calculate FPS
+        current_time = SDL_GetTicks();
+        frame_time = (current_time - last_time) / 1000.0f; // Convert milliseconds to seconds
+        fps = 1.0f / frame_time;
+        last_time = current_time;
+
+        // Update frame time graph
+        for (int i = 99; i > 0; --i) {
+            frame_time_graph[i] = frame_time_graph[i - 1]; // Shift old values
+        }
+        frame_time_graph[0] = frame_time; // Add new frame time
+    }
+
+    // Cleanup
+    cleanup();
+}