OpenGL 渲染器与 ImGui 和 SDL2

我正在尝试使用所有 3 个库或其他什么，但我对示例代码感到非常困惑，我无法完全遵循文档。这是代码，下面解释了我的困惑：

#include <iostream>
#include <string> 

#include <SDL2/SDL.h>

#include <GL/glew.h>

#include <imgui/imgui.h>
#include <imgui/imgui_stdlib.h>
#include <imgui/imgui_impl_sdl.h>
#include <imgui/imgui_impl_opengl3.h>




// Main code
int main(int argc, char* argv[])
{
    if (SDL_Init(SDL_INIT_VIDEO) != 0)
    {
        std::cout << SDL_GetError() << std::endl;
        return -1;
    }

    // GL 3.0 + GLSL 130
    const char* glsl_version = "#version 130";
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

    // Create window with graphics context
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
    SDL_WindowFlags window_flags = (SDL_WindowFlags)(SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI);
    SDL_Window* window = SDL_CreateWindow("Dear ImGui SDL2+OpenGL3 example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, window_flags);
    SDL_GLContext gl_context = SDL_GL_CreateContext(window);
    SDL_GL_MakeCurrent(window, gl_context);
    SDL_GL_SetSwapInterval(0); // Disable vsync

    
    if (glewInit() != GLEW_OK) {
        std::cout << "Error initializing glew\n";
    }

    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls
    //io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;      // Enable Gamepad Controls

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

    // Setup Platform/Renderer backends
    ImGui_ImplSDL2_InitForOpenGL(window, gl_context);
    ImGui_ImplOpenGL3_Init(glsl_version);



    ImFont* font = io.Fonts->AddFontFromFileTTF("C:\\Windows\\Fonts\\Arial.ttf", 30.0f);

    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    // Main loop
    bool running = false;
    SDL_Event event;

    while (!running)
    {

        while (SDL_PollEvent(&event))
        {
            ImGui_ImplSDL2_ProcessEvent(&event);
            if (event.type == SDL_QUIT)
                running = true;
            if (event.type == SDL_WINDOWEVENT && event.window.event == SDL_WINDOWEVENT_CLOSE && event.window.windowID == SDL_GetWindowID(window))
                running = true;
        }

        // Start the Dear ImGui frame
        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplSDL2_NewFrame(window);
        ImGui::NewFrame();


        {
                
            static std::string buf = "";

            ImGui::PushFont(font);

            ImGui::Begin("Window");


            ImGui::InputText("Hello", &buf);
            //std::cout << io.Fonts->Fonts.size() << std::endl;


            ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);


            ImGui::End();

            ImGui::PopFont();

        }



        // Rendering
        
        glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
        glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui::Render();
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
        SDL_GL_SwapWindow(window);

    }

    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplSDL2_Shutdown();
    ImGui::DestroyContext();

    SDL_GL_DeleteContext(gl_context);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}

SDL_RendererglClear（GL_COLOR_BUFFER_BIT）调用的;（SDL_RenderFillRect（）

ImGui::Render();
ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
SDL_GL_SwapWindow(window);

ImGui：：RenderImGui_ImplOpenGL3_RenderDrawData（ImGui：：GetDrawData（））;SDL_GL_SwapWindowglClear（）。ImGui：：EndFrame（）ImGui：：NewFrameImGui_ImplOpenGL3_NewFrame（） 相同;ImGui_ImplSDL2_NewFrame（窗口）;