imgui-docking/examples/sdl_opengl2_example/main.cpp

// ImGui - standalone example application for SDL2 + OpenGL
// If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
// (SDL is a cross-platform general purpose library for handling windows, inputs, OpenGL/Vulkan graphics context creation, etc.)

// **DO NOT USE THIS CODE IF YOUR CODE/ENGINE IS USING MODERN OPENGL (SHADERS, VBO, VAO, etc.)**
// **Prefer using the code in the sdl_opengl3_example/ folder**
// See imgui_impl_sdl.cpp for details.

#include "imgui.h"
#include "imgui_impl_sdl_gl2.h"
#include <stdio.h>
#include <SDL.h>
#include <SDL_opengl.h>

int main(int, char**)
{
    // Setup SDL
    if (SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER) != 0)
    {
        printf("Error: %s\n", SDL_GetError());
        return -1;
    }

    // Setup window
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
    SDL_DisplayMode current;
    SDL_GetCurrentDisplayMode(0, &current);
    SDL_Window *window = SDL_CreateWindow("ImGui SDL2+OpenGL example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
    SDL_GLContext glcontext = SDL_GL_CreateContext(window);
    SDL_GL_SetSwapInterval(1); // Enable vsync

    // Setup ImGui binding
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO(); (void)io;
    //io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;  // Enable Keyboard Controls
    ImGui_ImplSdlGL2_Init(window);

    // Setup style
    ImGui::StyleColorsDark();
    //ImGui::StyleColorsClassic();

    // Load Fonts
    // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them. 
    // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple. 
    // - If the file cannot be loaded, the function will return NULL. Please handle those errors in your application (e.g. use an assertion, or display an error and quit).
    // - The fonts will be rasterized at a given size (w/ oversampling) and stored into a texture when calling ImFontAtlas::Build()/GetTexDataAsXXXX(), which ImGui_ImplXXXX_NewFrame below will call.
    // - Read 'misc/fonts/README.txt' for more instructions and details.
    // - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
    //io.Fonts->AddFontDefault();
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf", 15.0f);
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf", 16.0f);
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/ProggyTiny.ttf", 10.0f);
    //ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf", 18.0f, NULL, io.Fonts->GetGlyphRangesJapanese());
    //IM_ASSERT(font != NULL);

    bool show_demo_window = true;
    bool show_another_window = false;
    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    // Main loop
    bool done = false;
    while (!done)
    {
        // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
        // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
        // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
        // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
        SDL_Event event;
        while (SDL_PollEvent(&event))
        {
            ImGui_ImplSdlGL2_ProcessEvent(&event);
            if (event.type == SDL_QUIT)
                done = true;
        }
        ImGui_ImplSdlGL2_NewFrame(window);

        // 1. Show a simple window.
        // Tip: if we don't call ImGui::Begin()/ImGui::End() the widgets automatically appears in a window called "Debug".
        {
            static float f = 0.0f;
            static int counter = 0;
            ImGui::Text("Hello, world!");                           // Display some text (you can use a format string too)
            ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f    
            ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color

            ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our windows open/close state
            ImGui::Checkbox("Another Window", &show_another_window);

            if (ImGui::Button("Button"))                            // Buttons return true when clicked (NB: most widgets return true when edited/activated)
                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);
        }

        // 2. Show another simple window. In most cases you will use an explicit Begin/End pair to name your windows.
        if (show_another_window)
        {
            ImGui::Begin("Another Window", &show_another_window);
            ImGui::Text("Hello from another window!");
            if (ImGui::Button("Close Me"))
                show_another_window = false;
            ImGui::End();
        }

        // 3. Show the ImGui demo window. Most of the sample code is in ImGui::ShowDemoWindow(). Read its code to learn more about Dear ImGui!
        if (show_demo_window)
        {
            ImGui::SetNextWindowPos(ImVec2(650, 20), ImGuiCond_FirstUseEver); // Normally user code doesn't need/want to call this because positions are saved in .ini file anyway. Here we just want to make the demo initial state a bit more friendly!
            ImGui::ShowDemoWindow(&show_demo_window);
        }

        // Rendering
        glViewport(0, 0, (int)ImGui::GetIO().DisplaySize.x, (int)ImGui::GetIO().DisplaySize.y);
        glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
        glClear(GL_COLOR_BUFFER_BIT);
        //glUseProgram(0); // You may want this if using this code in an OpenGL 3+ context where shaders may be bound
        ImGui::Render();
        ImGui_ImplSdlGL2_RenderDrawData(ImGui::GetDrawData());
        SDL_GL_SwapWindow(window);
    }

    // Cleanup
    ImGui_ImplSdlGL2_Shutdown();
    ImGui::DestroyContext();

    SDL_GL_DeleteContext(glcontext);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}