Dear ImGui docking bug

main.cpp

#include <imgui.h>
#include <imgui_impl_sdl.h>
#include <imgui_impl_opengl2.h>

#include <SDL.h>
#include <SDL_opengl.h>

#include <string>

class Application
{
protected:
  SDL_Window*       _window;
  SDL_GLContext     _glContext;

public:
  Application() = default;

  bool init(std::string const& title, int width, int height)
  {
    // Setup SDL
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
    {
      return false;
    }

    // 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);
    _window = SDL_CreateWindow(title.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI);

    if (_window == NULL)
    {
      return false;
    }

    _glContext = SDL_GL_CreateContext(_window);

    if (_glContext == NULL)
    {
      SDL_DestroyWindow(_window);
      return false;
    }

    SDL_GL_MakeCurrent(_window, _glContext);
    SDL_GL_SetSwapInterval(1);

    // Setup ImGui
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();
    io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;

    ImGui::StyleColorsDark();

    ImGui_ImplSDL2_InitForOpenGL(_window, _glContext);
    ImGui_ImplOpenGL2_Init();

    return true;
  }

  void destroy()
  {
    ImGui_ImplOpenGL2_Shutdown();
    ImGui_ImplSDL2_Shutdown();
    ImGui::DestroyContext();

    SDL_GL_DeleteContext(_glContext);
    SDL_DestroyWindow(_window);
    SDL_Quit();
  }

  void run()
  {
    bool done = false;

    do
    {
      SDL_Event event;

      while (SDL_PollEvent(&event))
      {
        if (!ImGui_ImplSDL2_ProcessEvent(&event))
        {
          switch (event.type)
          {
          case SDL_QUIT:
            done = true;
            break;

          case SDL_CONTROLLERDEVICEADDED:
          case SDL_CONTROLLERDEVICEREMOVED:
          case SDL_CONTROLLERBUTTONUP:
          case SDL_CONTROLLERBUTTONDOWN:
          case SDL_CONTROLLERAXISMOTION:
            break;
          }
        }
      }

      ImGui_ImplOpenGL2_NewFrame();
      ImGui_ImplSDL2_NewFrame(_window);
      ImGui::NewFrame();

      draw();

      ImGui::Render();

      glViewport(0, 0, (int)ImGui::GetIO().DisplaySize.x, (int)ImGui::GetIO().DisplaySize.y);
      glClearColor(0.05f, 0.05f, 0.05f, 0);
      glClear(GL_COLOR_BUFFER_BIT);

      ImGui_ImplOpenGL2_RenderDrawData(ImGui::GetDrawData());

      SDL_GL_SwapWindow(_window);
      SDL_Delay(1);
    }
    while (!done);
  }

  void draw()
  {
    const float oldWindowRounding = ImGui::GetStyle().WindowRounding;
    ImGui::GetStyle().WindowRounding = 0;
    const ImVec2 oldWindowPadding = ImGui::GetStyle().WindowPadding;

    // Uncomment the following line to force the bug.
    ImGui::GetStyle().WindowPadding = ImVec2(0.0f, 0.0f);

    ImGui::SetNextWindowPos(ImVec2(0.0f, 0.0f));
    ImGui::SetNextWindowSize(ImGui::GetIO().DisplaySize);
    ImGui::SetNextWindowBgAlpha(1.0f);

    const ImGuiWindowFlags flags = ImGuiWindowFlags_NoNav | ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoInputs
                                 | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_NoSavedSettings;

    ImGui::Begin("dock", nullptr, flags);
    ImGui::GetStyle().WindowRounding = oldWindowRounding;
    ImGui::GetStyle().WindowPadding = oldWindowPadding;

    ImGui::DockSpace(ImGui::GetID("dock"));

    ImGui::End();

    if (ImGui::Begin("Test 1")) {}
    ImGui::End();

    if (ImGui::Begin("Test 2")) {}
    ImGui::End();
  }
};

int main(int, char**)
{
  Application app;

  if (!app.init("Docking bug", 1024, 640))
  {
    return 1;
  }

  app.run();
  app.destroy();
  return 0;
}