imgui/examples/imgui_impl_sdl.cpp

// dear imgui: Platform Binding for SDL2
// This needs to be used along with a Renderer (e.g. DirectX11, OpenGL3, Vulkan..)
// (Info: SDL2 is a cross-platform general purpose library for handling windows, inputs, graphics context creation, etc.)

// Implemented features:
//  [X] Platform: Mouse cursor shape and visibility. Disable with 'io.ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange'.
//  [X] Platform: Clipboard support.
//  [X] Platform: Keyboard arrays indexed using SDL_SCANCODE_* codes, e.g. ImGui::IsKeyPressed(SDL_SCANCODE_SPACE).
//  [X] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
// Missing features:
//  [ ] Platform: SDL2 handling of IME under Windows appears to be broken and it explicitly disable the regular Windows IME. You can restore Windows IME by compiling SDL with SDL_DISABLE_WINDOWS_IME.
//  [ ] Platform: Gamepad support (need to use SDL_GameController API to fill the io.NavInputs[] value when ImGuiConfigFlags_NavEnableGamepad is set).
//  [ ] Platform: Multi-viewport + Minimized windows seems to break mouse wheel events (at least under Windows).

// You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
// If you are new to dear imgui, read examples/README.txt and read the documentation at the top of imgui.cpp.
// https://github.com/ocornut/imgui

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
//  2018-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
//  2018-11-14: Changed the signature of ImGui_ImplSDL2_ProcessEvent() to take a 'const SDL_Event*'.
//  2018-08-01: Inputs: Workaround for Emscripten which doesn't seem to handle focus related calls.
//  2018-06-29: Inputs: Added support for the ImGuiMouseCursor_Hand cursor.
//  2018-06-08: Misc: Extracted imgui_impl_sdl.cpp/.h away from the old combined SDL2+OpenGL/Vulkan examples.
//  2018-06-08: Misc: ImGui_ImplSDL2_InitForOpenGL() now takes a SDL_GLContext parameter. 
//  2018-05-09: Misc: Fixed clipboard paste memory leak (we didn't call SDL_FreeMemory on the data returned by SDL_GetClipboardText).
//  2018-03-20: Misc: Setup io.BackendFlags ImGuiBackendFlags_HasMouseCursors flag + honor ImGuiConfigFlags_NoMouseCursorChange flag.
//  2018-02-16: Inputs: Added support for mouse cursors, honoring ImGui::GetMouseCursor() value.
//  2018-02-06: Misc: Removed call to ImGui::Shutdown() which is not available from 1.60 WIP, user needs to call CreateContext/DestroyContext themselves.
//  2018-02-06: Inputs: Added mapping for ImGuiKey_Space.
//  2018-02-05: Misc: Using SDL_GetPerformanceCounter() instead of SDL_GetTicks() to be able to handle very high framerate (1000+ FPS).
//  2018-02-05: Inputs: Keyboard mapping is using scancodes everywhere instead of a confusing mixture of keycodes and scancodes. 
//  2018-01-20: Inputs: Added Horizontal Mouse Wheel support.
//  2018-01-19: Inputs: When available (SDL 2.0.4+) using SDL_CaptureMouse() to retrieve coordinates outside of client area when dragging. Otherwise (SDL 2.0.3 and before) testing for SDL_WINDOW_INPUT_FOCUS instead of SDL_WINDOW_MOUSE_FOCUS.
//  2018-01-18: Inputs: Added mapping for ImGuiKey_Insert.
//  2017-08-25: Inputs: MousePos set to -FLT_MAX,-FLT_MAX when mouse is unavailable/missing (instead of -1,-1).
//  2016-10-15: Misc: Added a void* user_data parameter to Clipboard function handlers.

#include "imgui.h"
#include "imgui_impl_sdl.h"

// SDL
// (the multi-viewports feature requires SDL features supported from SDL 2.0.5+)
#include <SDL.h>
#include <SDL_syswm.h>
#define SDL_HAS_WARP_MOUSE_GLOBAL           SDL_VERSION_ATLEAST(2,0,4)
#define SDL_HAS_CAPTURE_MOUSE               SDL_VERSION_ATLEAST(2,0,4)
#define SDL_HAS_WINDOW_OPACITY              SDL_VERSION_ATLEAST(2,0,5)
#define SDL_HAS_ALWAYS_ON_TOP               SDL_VERSION_ATLEAST(2,0,5)
#define SDL_HAS_USABLE_DISPLAY_BOUNDS       SDL_VERSION_ATLEAST(2,0,5)
#define SDL_HAS_PER_MONITOR_DPI             SDL_VERSION_ATLEAST(2,0,4)
#define SDL_HAS_VULKAN                      SDL_VERSION_ATLEAST(2,0,6)
#define SDL_HAS_MOUSE_FOCUS_CLICKTHROUGH    SDL_VERSION_ATLEAST(2,0,5)
#if !SDL_HAS_VULKAN
static const Uint32 SDL_WINDOW_VULKAN = 0x10000000;
#endif

// Data
static SDL_Window*  g_Window = NULL;
static Uint64       g_Time = 0;
static bool         g_MousePressed[3] = { false, false, false };
static SDL_Cursor*  g_MouseCursors[ImGuiMouseCursor_COUNT] = { 0 };
static char*        g_ClipboardTextData = NULL;

// Forward Declarations
static void ImGui_ImplSDL2_InitPlatformInterface(SDL_Window* window, void* sdl_gl_context);
static void ImGui_ImplSDL2_ShutdownPlatformInterface();

static const char* ImGui_ImplSDL2_GetClipboardText(void*)
{
    if (g_ClipboardTextData)
        SDL_free(g_ClipboardTextData);
    g_ClipboardTextData = SDL_GetClipboardText();
    return g_ClipboardTextData;
}

static void ImGui_ImplSDL2_SetClipboardText(void*, const char* text)
{
    SDL_SetClipboardText(text);
}

// 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.
// If you have multiple SDL events and some of them are not meant to be used by dear imgui, you may need to filter events based on their windowID field.
bool ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event)
{
    ImGuiIO& io = ImGui::GetIO();
    switch (event->type)
    {
    case SDL_MOUSEWHEEL:
        {
            if (event->wheel.x > 0) io.MouseWheelH += 1;
            if (event->wheel.x < 0) io.MouseWheelH -= 1;
            if (event->wheel.y > 0) io.MouseWheel += 1;
            if (event->wheel.y < 0) io.MouseWheel -= 1;
            return true;
        }
    case SDL_MOUSEBUTTONDOWN:
        {
            if (event->button.button == SDL_BUTTON_LEFT) g_MousePressed[0] = true;
            if (event->button.button == SDL_BUTTON_RIGHT) g_MousePressed[1] = true;
            if (event->button.button == SDL_BUTTON_MIDDLE) g_MousePressed[2] = true;
            return true;
        }
    case SDL_TEXTINPUT:
        {
            io.AddInputCharactersUTF8(event->text.text);
            return true;
        }
    case SDL_KEYDOWN:
    case SDL_KEYUP:
        {
            int key = event->key.keysym.scancode;
            IM_ASSERT(key >= 0 && key < IM_ARRAYSIZE(io.KeysDown));
            io.KeysDown[key] = (event->type == SDL_KEYDOWN);
            io.KeyShift = ((SDL_GetModState() & KMOD_SHIFT) != 0);
            io.KeyCtrl = ((SDL_GetModState() & KMOD_CTRL) != 0);
            io.KeyAlt = ((SDL_GetModState() & KMOD_ALT) != 0);
            io.KeySuper = ((SDL_GetModState() & KMOD_GUI) != 0);
            return true;
        }
    // Multi-viewport support
    case SDL_WINDOWEVENT:
        Uint8 window_event = event->window.event;
        if (window_event == SDL_WINDOWEVENT_CLOSE || window_event == SDL_WINDOWEVENT_MOVED || window_event == SDL_WINDOWEVENT_RESIZED)
            if (ImGuiViewport* viewport = ImGui::FindViewportByPlatformHandle((void*)SDL_GetWindowFromID(event->window.windowID)))
            {
                if (window_event == SDL_WINDOWEVENT_CLOSE)
                    viewport->PlatformRequestClose = true;
                if (window_event == SDL_WINDOWEVENT_MOVED)
                    viewport->PlatformRequestMove = true;
                if (window_event == SDL_WINDOWEVENT_RESIZED)
                    viewport->PlatformRequestResize = true;
                return true;
            }
        break;
    }
    return false;
}

static bool ImGui_ImplSDL2_Init(SDL_Window* window, void* sdl_gl_context)
{
    g_Window = window;

    // Setup back-end capabilities flags
    ImGuiIO& io = ImGui::GetIO();
    io.BackendFlags |= ImGuiBackendFlags_HasMouseCursors;       // We can honor GetMouseCursor() values (optional)
#if SDL_HAS_WARP_MOUSE_GLOBAL
    io.BackendFlags |= ImGuiBackendFlags_HasSetMousePos;        // We can honor io.WantSetMousePos requests (optional, rarely used)
#endif
#if SDL_HAS_CAPTURE_MOUSE
    io.BackendFlags |= ImGuiBackendFlags_PlatformHasViewports;  // We can create multi-viewports on the Platform side (optional)
#endif

    // Keyboard mapping. ImGui will use those indices to peek into the io.KeysDown[] array.
    io.KeyMap[ImGuiKey_Tab] = SDL_SCANCODE_TAB;
    io.KeyMap[ImGuiKey_LeftArrow] = SDL_SCANCODE_LEFT;
    io.KeyMap[ImGuiKey_RightArrow] = SDL_SCANCODE_RIGHT;
    io.KeyMap[ImGuiKey_UpArrow] = SDL_SCANCODE_UP;
    io.KeyMap[ImGuiKey_DownArrow] = SDL_SCANCODE_DOWN;
    io.KeyMap[ImGuiKey_PageUp] = SDL_SCANCODE_PAGEUP;
    io.KeyMap[ImGuiKey_PageDown] = SDL_SCANCODE_PAGEDOWN;
    io.KeyMap[ImGuiKey_Home] = SDL_SCANCODE_HOME;
    io.KeyMap[ImGuiKey_End] = SDL_SCANCODE_END;
    io.KeyMap[ImGuiKey_Insert] = SDL_SCANCODE_INSERT;
    io.KeyMap[ImGuiKey_Delete] = SDL_SCANCODE_DELETE;
    io.KeyMap[ImGuiKey_Backspace] = SDL_SCANCODE_BACKSPACE;
    io.KeyMap[ImGuiKey_Space] = SDL_SCANCODE_SPACE;
    io.KeyMap[ImGuiKey_Enter] = SDL_SCANCODE_RETURN;
    io.KeyMap[ImGuiKey_Escape] = SDL_SCANCODE_ESCAPE;
    io.KeyMap[ImGuiKey_A] = SDL_SCANCODE_A;
    io.KeyMap[ImGuiKey_C] = SDL_SCANCODE_C;
    io.KeyMap[ImGuiKey_V] = SDL_SCANCODE_V;
    io.KeyMap[ImGuiKey_X] = SDL_SCANCODE_X;
    io.KeyMap[ImGuiKey_Y] = SDL_SCANCODE_Y;
    io.KeyMap[ImGuiKey_Z] = SDL_SCANCODE_Z;

    io.SetClipboardTextFn = ImGui_ImplSDL2_SetClipboardText;
    io.GetClipboardTextFn = ImGui_ImplSDL2_GetClipboardText;
    io.ClipboardUserData = NULL;

    g_MouseCursors[ImGuiMouseCursor_Arrow] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_ARROW);
    g_MouseCursors[ImGuiMouseCursor_TextInput] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_IBEAM);
    g_MouseCursors[ImGuiMouseCursor_ResizeAll] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_SIZEALL);
    g_MouseCursors[ImGuiMouseCursor_ResizeNS] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_SIZENS);
    g_MouseCursors[ImGuiMouseCursor_ResizeEW] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_SIZEWE);
    g_MouseCursors[ImGuiMouseCursor_ResizeNESW] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_SIZENESW);
    g_MouseCursors[ImGuiMouseCursor_ResizeNWSE] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_SIZENWSE);
    g_MouseCursors[ImGuiMouseCursor_Hand] = SDL_CreateSystemCursor(SDL_SYSTEM_CURSOR_HAND);

    // Our mouse update function expect PlatformHandle to be filled for the main viewport
    ImGuiViewport* main_viewport = ImGui::GetMainViewport();
    main_viewport->PlatformHandle = (void*)window;

    // We need SDL_CaptureMouse(), SDL_GetGlobalMouseState() from SDL 2.0.4+ to support multiple viewports.
    // We left the call to ImGui_ImplSDL2_InitPlatformInterface() outside of #ifdef to avoid unused-function warnings.
    if ((io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) && (io.BackendFlags & ImGuiBackendFlags_PlatformHasViewports))
        ImGui_ImplSDL2_InitPlatformInterface(window, sdl_gl_context);

    return true;
}

bool ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context)
{
    (void)sdl_gl_context; // Viewport branch will need this.
    return ImGui_ImplSDL2_Init(window, sdl_gl_context);
}

bool ImGui_ImplSDL2_InitForVulkan(SDL_Window* window)
{
    #if !SDL_HAS_VULKAN
    IM_ASSERT(0 && "Unsupported");
    #endif
    return ImGui_ImplSDL2_Init(window, NULL);
}

void ImGui_ImplSDL2_Shutdown()
{
    ImGui_ImplSDL2_ShutdownPlatformInterface();
    g_Window = NULL;

    // Destroy last known clipboard data
    if (g_ClipboardTextData)
        SDL_free(g_ClipboardTextData);
    g_ClipboardTextData = NULL;

    // Destroy SDL mouse cursors
    for (ImGuiMouseCursor cursor_n = 0; cursor_n < ImGuiMouseCursor_COUNT; cursor_n++)
        SDL_FreeCursor(g_MouseCursors[cursor_n]);
    memset(g_MouseCursors, 0, sizeof(g_MouseCursors));
}

static void ImGui_ImplSDL2_UpdateMousePosAndButtons()
{
    ImGuiIO& io = ImGui::GetIO();
    io.MouseHoveredViewport = 0;

    // Set OS mouse position if requested (rarely used, only when ImGuiConfigFlags_NavEnableSetMousePos is enabled by user)
    // (When multi-viewports are enabled, all imgui positions are same as OS positions.)
#if SDL_HAS_WARP_MOUSE_GLOBAL
    if (!io.WantSetMousePos)
        io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
    else if ((io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) == 0)
        SDL_WarpMouseInWindow(g_Window, (int)io.MousePos.x, (int)io.MousePos.y);
    else
        SDL_WarpMouseGlobal((int)io.MousePos.x, (int)io.MousePos.y);
#else
    io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
#endif

    int mx, my;
    Uint32 mouse_buttons = SDL_GetMouseState(&mx, &my);
    io.MouseDown[0] = g_MousePressed[0] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0;  // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
    io.MouseDown[1] = g_MousePressed[1] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_RIGHT)) != 0;
    io.MouseDown[2] = g_MousePressed[2] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_MIDDLE)) != 0;
    g_MousePressed[0] = g_MousePressed[1] = g_MousePressed[2] = false;

#if SDL_HAS_CAPTURE_MOUSE && !defined(__EMSCRIPTEN__)
    SDL_Window* focused_window = SDL_GetKeyboardFocus();
    if (focused_window)
    {
        // SDL_GetMouseState() gives mouse position seemingly based on the last window entered/focused(?)
        // The creation of new windows at runtime and SDL_CaptureMouse both seems to severely mess up with that, so we retrieve that position globally.
        int wx, wy;
        SDL_GetWindowPosition(focused_window, &wx, &wy);
        SDL_GetGlobalMouseState(&mx, &my);
        mx -= wx;
        my -= wy;
    }
    if (ImGuiViewport* viewport = ImGui::FindViewportByPlatformHandle((void*)focused_window))
        io.MousePos = ImVec2(viewport->Pos.x + (float)mx, viewport->Pos.y + (float)my);

    // We already retrieve global mouse position, SDL_CaptureMouse() also let the OS know e.g. that our imgui drag outside the SDL window boundaries shouldn't trigger the OS window resize cursor
    // The function is only supported from SDL 2.0.4 (released Jan 2016)
    bool any_mouse_button_down = ImGui::IsAnyMouseDown();
    SDL_CaptureMouse(any_mouse_button_down ? SDL_TRUE : SDL_FALSE);
#else
    if (SDL_GetWindowFlags(g_Window) & SDL_WINDOW_INPUT_FOCUS)
        io.MousePos = ImVec2((float)mx, (float)my);
#endif
}

static void ImGui_ImplSDL2_UpdateMouseCursor()
{
    ImGuiIO& io = ImGui::GetIO();
    if (io.ConfigFlags & ImGuiConfigFlags_NoMouseCursorChange)
        return;

    ImGuiMouseCursor imgui_cursor = ImGui::GetMouseCursor();
    if (io.MouseDrawCursor || imgui_cursor == ImGuiMouseCursor_None)
    {
        // Hide OS mouse cursor if imgui is drawing it or if it wants no cursor
        SDL_ShowCursor(SDL_FALSE);
    }
    else
    {
        // Show OS mouse cursor
        SDL_SetCursor(g_MouseCursors[imgui_cursor] ? g_MouseCursors[imgui_cursor] : g_MouseCursors[ImGuiMouseCursor_Arrow]);
        SDL_ShowCursor(SDL_TRUE);
    }
}

void ImGui_ImplSDL2_NewFrame(SDL_Window* window)
{
    ImGuiIO& io = ImGui::GetIO();
    IM_ASSERT(io.Fonts->IsBuilt());     // Font atlas needs to be built, call renderer _NewFrame() function e.g. ImGui_ImplOpenGL3_NewFrame() 

    // Setup display size (every frame to accommodate for window resizing)
    int w, h;
    int display_w, display_h;
    SDL_GetWindowSize(window, &w, &h);
    SDL_GL_GetDrawableSize(window, &display_w, &display_h);
    io.DisplaySize = ImVec2((float)w, (float)h);
    io.DisplayFramebufferScale = ImVec2(w > 0 ? ((float)display_w / w) : 0, h > 0 ? ((float)display_h / h) : 0);

    // Setup time step (we don't use SDL_GetTicks() because it is using millisecond resolution)
    static Uint64 frequency = SDL_GetPerformanceFrequency();
    Uint64 current_time = SDL_GetPerformanceCounter();
    io.DeltaTime = g_Time > 0 ? (float)((double)(current_time - g_Time) / frequency) : (float)(1.0f / 60.0f);
    g_Time = current_time;

    ImGui_ImplSDL2_UpdateMousePosAndButtons();
    ImGui_ImplSDL2_UpdateMouseCursor();
}

//--------------------------------------------------------------------------------------------------------
// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
//--------------------------------------------------------------------------------------------------------

struct ImGuiViewportDataSDL2
{
    SDL_Window*     Window;
    Uint32          WindowID;
    bool            WindowOwned;
    SDL_GLContext   GLContext;

    ImGuiViewportDataSDL2() { Window = NULL; WindowID = 0; WindowOwned = false; GLContext = NULL; }
    ~ImGuiViewportDataSDL2() { IM_ASSERT(Window == NULL && GLContext == NULL); }
};

static void ImGui_ImplSDL2_CreateWindow(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = IM_NEW(ImGuiViewportDataSDL2)();
    viewport->PlatformUserData = data;

    ImGuiViewport* main_viewport = ImGui::GetMainViewport();
    ImGuiViewportDataSDL2* main_viewport_data = (ImGuiViewportDataSDL2*)main_viewport->PlatformUserData;

    // Share GL resources with main context
    bool use_opengl = (main_viewport_data->GLContext != NULL);
    SDL_GLContext backup_context = NULL;
    if (use_opengl)
    {
        backup_context = SDL_GL_GetCurrentContext();
        SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1);
        SDL_GL_MakeCurrent(main_viewport_data->Window, main_viewport_data->GLContext);
    }

    // We don't enable SDL_WINDOW_RESIZABLE because it enforce windows decorations
    Uint32 sdl_flags = 0;
    sdl_flags |= use_opengl ? SDL_WINDOW_OPENGL : SDL_WINDOW_VULKAN;
    sdl_flags |= SDL_WINDOW_HIDDEN;
    sdl_flags |= (viewport->Flags & ImGuiViewportFlags_NoDecoration) ? SDL_WINDOW_BORDERLESS : 0;
    sdl_flags |= (viewport->Flags & ImGuiViewportFlags_NoDecoration) ? 0 : SDL_WINDOW_RESIZABLE;
#if SDL_HAS_ALWAYS_ON_TOP
    sdl_flags |= (viewport->Flags & ImGuiViewportFlags_TopMost) ? SDL_WINDOW_ALWAYS_ON_TOP : 0;
#endif
    data->Window = SDL_CreateWindow("No Title Yet", (int)viewport->Pos.x, (int)viewport->Pos.y, (int)viewport->Size.x, (int)viewport->Size.y, sdl_flags);
    data->WindowOwned = true; 
    if (use_opengl)
    {
        data->GLContext = SDL_GL_CreateContext(data->Window);
        SDL_GL_SetSwapInterval(0);
    }
    if (use_opengl && backup_context)
        SDL_GL_MakeCurrent(data->Window, backup_context);
    viewport->PlatformHandle = (void*)data->Window;
}

static void ImGui_ImplSDL2_DestroyWindow(ImGuiViewport* viewport)
{
    if (ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData)
    {
        if (data->GLContext && data->WindowOwned)
            SDL_GL_DeleteContext(data->GLContext);
        if (data->Window && data->WindowOwned)
            SDL_DestroyWindow(data->Window);
        data->GLContext = NULL;
        data->Window = NULL;
        IM_DELETE(data);
    }
    viewport->PlatformUserData = viewport->PlatformHandle = NULL;
}

static void ImGui_ImplSDL2_ShowWindow(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
#if defined(_WIN32)
    SDL_SysWMinfo info;
    SDL_VERSION(&info.version);
    if (SDL_GetWindowWMInfo(data->Window, &info))
    {
        HWND hwnd = info.info.win.window;

        // SDL hack: Hide icon from task bar
        // Note: SDL 2.0.6+ has a SDL_WINDOW_SKIP_TASKBAR flag which is supported under Windows but the way it create the window breaks our seamless transition.
        if (viewport->Flags & ImGuiViewportFlags_NoTaskBarIcon)
        {
            LONG ex_style = ::GetWindowLong(hwnd, GWL_EXSTYLE);
            ex_style &= ~WS_EX_APPWINDOW;
            ex_style |= WS_EX_TOOLWINDOW;
            ::SetWindowLong(hwnd, GWL_EXSTYLE, ex_style);
        }

        // SDL hack: SDL always activate/focus windows :/
        if (viewport->Flags & ImGuiViewportFlags_NoFocusOnAppearing)
        {
            ::ShowWindow(hwnd, SW_SHOWNA);
            return;
        }
    }
#endif

    SDL_ShowWindow(data->Window);
}

static ImVec2 ImGui_ImplSDL2_GetWindowPos(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    int x = 0, y = 0;
    SDL_GetWindowPosition(data->Window, &x, &y);
    return ImVec2((float)x, (float)y);
}

static void ImGui_ImplSDL2_SetWindowPos(ImGuiViewport* viewport, ImVec2 pos)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    SDL_SetWindowPosition(data->Window, (int)pos.x, (int)pos.y);
}

static ImVec2 ImGui_ImplSDL2_GetWindowSize(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    int w = 0, h = 0;
    SDL_GetWindowSize(data->Window, &w, &h);
    return ImVec2((float)w, (float)h);
}

static void ImGui_ImplSDL2_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    SDL_SetWindowSize(data->Window, (int)size.x, (int)size.y);
}

static void ImGui_ImplSDL2_SetWindowTitle(ImGuiViewport* viewport, const char* title)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    SDL_SetWindowTitle(data->Window, title);
}

static void ImGui_ImplSDL2_SetWindowFocus(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    SDL_RaiseWindow(data->Window);
}

static bool ImGui_ImplSDL2_GetWindowFocus(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    return (SDL_GetWindowFlags(data->Window) & SDL_WINDOW_INPUT_FOCUS) != 0;
}

static bool ImGui_ImplSDL2_GetWindowMinimized(ImGuiViewport* viewport)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    return (SDL_GetWindowFlags(data->Window) & SDL_WINDOW_MINIMIZED) != 0;
}

static void ImGui_ImplSDL2_RenderWindow(ImGuiViewport* viewport, void*)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    if (data->GLContext)
        SDL_GL_MakeCurrent(data->Window, data->GLContext);
}

static void ImGui_ImplSDL2_SwapBuffers(ImGuiViewport* viewport, void*)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    if (data->GLContext)
    {
        SDL_GL_MakeCurrent(data->Window, data->GLContext);
        SDL_GL_SwapWindow(data->Window);
    }
}

// Vulkan support (the Vulkan renderer needs to call a platform-side support function to create the surface)
// SDL is graceful enough to _not_ need <vulkan/vulkan.h> so we can safely include this.
#if SDL_HAS_VULKAN
#include <SDL_vulkan.h>
static int ImGui_ImplSDL2_CreateVkSurface(ImGuiViewport* viewport, ImU64 vk_instance, const void* vk_allocator, ImU64* out_vk_surface)
{
    ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
    (void)vk_allocator;
    SDL_bool ret = SDL_Vulkan_CreateSurface(data->Window, (VkInstance)vk_instance, (VkSurfaceKHR*)out_vk_surface);
    return ret ? 0 : 1; // ret ? VK_SUCCESS : VK_NOT_READY 
}
#endif // SDL_HAS_VULKAN

// FIXME-PLATFORM: SDL doesn't have an event to notify the application of display/monitor changes
static void ImGui_ImplSDL2_UpdateMonitors()
{
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    platform_io.Monitors.resize(0);
    int display_count = SDL_GetNumVideoDisplays();
    for (int n = 0; n < display_count; n++)
    {
        // Warning: the validity of monitor DPI information on Windows depends on the application DPI awareness settings, which generally needs to be set in the manifest or at runtime.
        ImGuiPlatformMonitor monitor;
        SDL_Rect r;
        SDL_GetDisplayBounds(n, &r);
        monitor.MainPos = monitor.WorkPos = ImVec2((float)r.x, (float)r.y);
        monitor.MainSize = monitor.WorkSize = ImVec2((float)r.w, (float)r.h);
#if SDL_HAS_USABLE_DISPLAY_BOUNDS
        SDL_GetDisplayUsableBounds(n, &r);
        monitor.WorkPos = ImVec2((float)r.x, (float)r.y);
        monitor.WorkSize = ImVec2((float)r.w, (float)r.h);
#endif
#if SDL_HAS_PER_MONITOR_DPI
        float dpi = 0.0f;
        if (!SDL_GetDisplayDPI(n, &dpi, NULL, NULL))
            monitor.DpiScale = dpi / 96.0f;
#endif
        platform_io.Monitors.push_back(monitor);
    }
}

static void ImGui_ImplSDL2_InitPlatformInterface(SDL_Window* window, void* sdl_gl_context)
{
    // Register platform interface (will be coupled with a renderer interface)
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    platform_io.Platform_CreateWindow = ImGui_ImplSDL2_CreateWindow;
    platform_io.Platform_DestroyWindow = ImGui_ImplSDL2_DestroyWindow;
    platform_io.Platform_ShowWindow = ImGui_ImplSDL2_ShowWindow;
    platform_io.Platform_SetWindowPos = ImGui_ImplSDL2_SetWindowPos;
    platform_io.Platform_GetWindowPos = ImGui_ImplSDL2_GetWindowPos;
    platform_io.Platform_SetWindowSize = ImGui_ImplSDL2_SetWindowSize;
    platform_io.Platform_GetWindowSize = ImGui_ImplSDL2_GetWindowSize;
    platform_io.Platform_SetWindowFocus = ImGui_ImplSDL2_SetWindowFocus;
    platform_io.Platform_GetWindowFocus = ImGui_ImplSDL2_GetWindowFocus;
    platform_io.Platform_GetWindowMinimized = ImGui_ImplSDL2_GetWindowMinimized;
    platform_io.Platform_SetWindowTitle = ImGui_ImplSDL2_SetWindowTitle;
    platform_io.Platform_RenderWindow = ImGui_ImplSDL2_RenderWindow;
    platform_io.Platform_SwapBuffers = ImGui_ImplSDL2_SwapBuffers;
#if SDL_HAS_VULKAN
    platform_io.Platform_CreateVkSurface = ImGui_ImplSDL2_CreateVkSurface;
#endif

    // SDL2 by default doesn't pass mouse clicks to the application when the click focused a window. This is getting in the way of our interactions and we disable that behavior.
#if SDL_HAS_MOUSE_FOCUS_CLICKTHROUGH
    SDL_SetHint(SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH, "1");
#endif

    ImGui_ImplSDL2_UpdateMonitors();

    // Register main window handle (which is owned by the main application, not by us)
    ImGuiViewport* main_viewport = ImGui::GetMainViewport();
    ImGuiViewportDataSDL2* data = IM_NEW(ImGuiViewportDataSDL2)();
    data->Window = window;
    data->WindowID = SDL_GetWindowID(window);
    data->WindowOwned = false;
    data->GLContext = sdl_gl_context;
    main_viewport->PlatformUserData = data;
    main_viewport->PlatformHandle = data->Window;
}

static void ImGui_ImplSDL2_ShutdownPlatformInterface()
{
}