Function ShowExampleAppFullscreen

src/imgui/imgui_demo.cpp:9749–9778

Demonstrate creating a window covering the entire screen/viewport

// Demonstrate creating a window covering the entire screen/viewport
static void ShowExampleAppFullscreen(bool* p_open)
{
    static bool use_work_area = true;
    static ImGuiWindowFlags flags = ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoSavedSettings;

    // We demonstrate using the full viewport area or the work area (without menu-bars, task-bars etc.)
    // Based on your use case you may want one or the other.
    const ImGuiViewport* viewport = ImGui::GetMainViewport();
    ImGui::SetNextWindowPos(use_work_area ? viewport->WorkPos : viewport->Pos);
    ImGui::SetNextWindowSize(use_work_area ? viewport->WorkSize : viewport->Size);

    if (ImGui::Begin("Example: Fullscreen window", p_open, flags))
    {
        ImGui::Checkbox("Use work area instead of main area", &use_work_area);
        ImGui::SameLine();
        HelpMarker("Main Area = entire viewport,\nWork Area = entire viewport minus sections used by the main menu bars, task bars etc.\n\nEnable the main-menu bar in Examples menu to see the difference.");

        ImGui::CheckboxFlags("ImGuiWindowFlags_NoBackground", &flags, ImGuiWindowFlags_NoBackground);
        ImGui::CheckboxFlags("ImGuiWindowFlags_NoDecoration", &flags, ImGuiWindowFlags_NoDecoration);
        ImGui::Indent();
        ImGui::CheckboxFlags("ImGuiWindowFlags_NoTitleBar", &flags, ImGuiWindowFlags_NoTitleBar);
        ImGui::CheckboxFlags("ImGuiWindowFlags_NoCollapse", &flags, ImGuiWindowFlags_NoCollapse);
        ImGui::CheckboxFlags("ImGuiWindowFlags_NoScrollbar", &flags, ImGuiWindowFlags_NoScrollbar);
        ImGui::Unindent();

        if (p_open && ImGui::Button("Close this window"))
            *p_open = false;
    }
    ImGui::End();
}

//-----------------------------------------------------------------------------
// [SECTION] Example App: Manipulating Window Titles / ShowExampleAppWindowTitles()