imgui/examples/imgui_impl_win32.cpp

// dear imgui: Platform Binding for Windows (standard windows API for 32 and 64 bits applications)
// This needs to be used along with a Renderer (e.g. DirectX11, OpenGL3, Vulkan..)

// Implemented features:
//  [X] Platform: Clipboard support (for Win32 this is actually part of core imgui)
//  [X] Platform: Mouse cursor shape and visibility. Disable with 'io.ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange'.
//  [X] Platform: Keyboard arrays indexed using VK_* Virtual Key Codes, e.g. ImGui::IsKeyPressed(VK_SPACE).
//  [X] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
// Missing features:
//  [ ] Platform: Gamepad support (best leaving it to user application to fill io.NavInputs[] with gamepad inputs from their source of choice).

#include "imgui.h"
#include "imgui_impl_win32.h"
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#include <tchar.h>

// 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.
//  2018-11-30: Misc: Setting up io.BackendPlatformName so it can be displayed in the About Window.
//  2018-06-29: Inputs: Added support for the ImGuiMouseCursor_Hand cursor.
//  2018-06-10: Inputs: Fixed handling of mouse wheel messages to support fine position messages (typically sent by track-pads).
//  2018-06-08: Misc: Extracted imgui_impl_win32.cpp/.h away from the old combined DX9/DX10/DX11/DX12 examples.
//  2018-03-20: Misc: Setup io.BackendFlags ImGuiBackendFlags_HasMouseCursors and ImGuiBackendFlags_HasSetMousePos flags + honor ImGuiConfigFlags_NoMouseCursorChange flag.
//  2018-02-20: Inputs: Added support for mouse cursors (ImGui::GetMouseCursor() value and WM_SETCURSOR message handling).
//  2018-02-06: Inputs: Added mapping for ImGuiKey_Space.
//  2018-02-06: Inputs: Honoring the io.WantSetMousePos by repositioning the mouse (when using navigation and ImGuiConfigFlags_NavMoveMouse is set).
//  2018-02-06: Misc: Removed call to ImGui::Shutdown() which is not available from 1.60 WIP, user needs to call CreateContext/DestroyContext themselves.
//  2018-01-20: Inputs: Added Horizontal Mouse Wheel support.
//  2018-01-08: Inputs: Added mapping for ImGuiKey_Insert.
//  2018-01-05: Inputs: Added WM_LBUTTONDBLCLK double-click handlers for window classes with the CS_DBLCLKS flag.
//  2017-10-23: Inputs: Added WM_SYSKEYDOWN / WM_SYSKEYUP handlers so e.g. the VK_MENU key can be read.
//  2017-10-23: Inputs: Using Win32 ::SetCapture/::GetCapture() to retrieve mouse positions outside the client area when dragging. 
//  2016-11-12: Inputs: Only call Win32 ::SetCursor(NULL) when io.MouseDrawCursor is set.

// Win32 Data
static HWND                 g_hWnd = 0;
static INT64                g_Time = 0;
static INT64                g_TicksPerSecond = 0;
static ImGuiMouseCursor     g_LastMouseCursor = ImGuiMouseCursor_COUNT;
static bool                 g_WantUpdateMonitors = true;

// Forward Declarations
static void ImGui_ImplWin32_InitPlatformInterface();
static void ImGui_ImplWin32_ShutdownPlatformInterface();
static void ImGui_ImplWin32_UpdateMonitors();

// Functions
bool    ImGui_ImplWin32_Init(void* hwnd)
{
    if (!::QueryPerformanceFrequency((LARGE_INTEGER *)&g_TicksPerSecond))
        return false;
    if (!::QueryPerformanceCounter((LARGE_INTEGER *)&g_Time))
        return false;

    // Setup back-end capabilities flags
    ImGuiIO& io = ImGui::GetIO();
    io.BackendFlags |= ImGuiBackendFlags_HasMouseCursors;         // We can honor GetMouseCursor() values (optional)
    io.BackendFlags |= ImGuiBackendFlags_HasSetMousePos;          // We can honor io.WantSetMousePos requests (optional, rarely used)
    io.BackendFlags |= ImGuiBackendFlags_PlatformHasViewports;    // We can create multi-viewports on the Platform side (optional)
    io.BackendFlags |= ImGuiBackendFlags_HasMouseHoveredViewport; // We can set io.MouseHoveredViewport correctly (optional, not easy)
    io.BackendPlatformName = "imgui_impl_win32";

    // Our mouse update function expect PlatformHandle to be filled for the main viewport
    g_hWnd = (HWND)hwnd;
    ImGuiViewport* main_viewport = ImGui::GetMainViewport();
    main_viewport->PlatformHandle = (void*)g_hWnd;
    if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
        ImGui_ImplWin32_InitPlatformInterface();

    // Keyboard mapping. ImGui will use those indices to peek into the io.KeysDown[] array that we will update during the application lifetime.
    io.KeyMap[ImGuiKey_Tab] = VK_TAB;
    io.KeyMap[ImGuiKey_LeftArrow] = VK_LEFT;
    io.KeyMap[ImGuiKey_RightArrow] = VK_RIGHT;
    io.KeyMap[ImGuiKey_UpArrow] = VK_UP;
    io.KeyMap[ImGuiKey_DownArrow] = VK_DOWN;
    io.KeyMap[ImGuiKey_PageUp] = VK_PRIOR;
    io.KeyMap[ImGuiKey_PageDown] = VK_NEXT;
    io.KeyMap[ImGuiKey_Home] = VK_HOME;
    io.KeyMap[ImGuiKey_End] = VK_END;
    io.KeyMap[ImGuiKey_Insert] = VK_INSERT;
    io.KeyMap[ImGuiKey_Delete] = VK_DELETE;
    io.KeyMap[ImGuiKey_Backspace] = VK_BACK;
    io.KeyMap[ImGuiKey_Space] = VK_SPACE;
    io.KeyMap[ImGuiKey_Enter] = VK_RETURN;
    io.KeyMap[ImGuiKey_Escape] = VK_ESCAPE;
    io.KeyMap[ImGuiKey_A] = 'A';
    io.KeyMap[ImGuiKey_C] = 'C';
    io.KeyMap[ImGuiKey_V] = 'V';
    io.KeyMap[ImGuiKey_X] = 'X';
    io.KeyMap[ImGuiKey_Y] = 'Y';
    io.KeyMap[ImGuiKey_Z] = 'Z';

    return true;
}

void    ImGui_ImplWin32_Shutdown()
{
    ImGui_ImplWin32_ShutdownPlatformInterface();
    g_hWnd = (HWND)0;
}

static bool ImGui_ImplWin32_UpdateMouseCursor()
{
    ImGuiIO& io = ImGui::GetIO();
    if (io.ConfigFlags & ImGuiConfigFlags_NoMouseCursorChange)
        return false;

    ImGuiMouseCursor imgui_cursor = ImGui::GetMouseCursor();
    if (imgui_cursor == ImGuiMouseCursor_None || io.MouseDrawCursor)
    {
        // Hide OS mouse cursor if imgui is drawing it or if it wants no cursor
        ::SetCursor(NULL);
    }
    else
    {
        // Show OS mouse cursor
        LPTSTR win32_cursor = IDC_ARROW;
        switch (imgui_cursor)
        {
        case ImGuiMouseCursor_Arrow:        win32_cursor = IDC_ARROW; break;
        case ImGuiMouseCursor_TextInput:    win32_cursor = IDC_IBEAM; break;
        case ImGuiMouseCursor_ResizeAll:    win32_cursor = IDC_SIZEALL; break;
        case ImGuiMouseCursor_ResizeEW:     win32_cursor = IDC_SIZEWE; break;
        case ImGuiMouseCursor_ResizeNS:     win32_cursor = IDC_SIZENS; break;
        case ImGuiMouseCursor_ResizeNESW:   win32_cursor = IDC_SIZENESW; break;
        case ImGuiMouseCursor_ResizeNWSE:   win32_cursor = IDC_SIZENWSE; break;
        case ImGuiMouseCursor_Hand:         win32_cursor = IDC_HAND; break;
        }
        ::SetCursor(::LoadCursor(NULL, win32_cursor));
    }
    return true;
}

// This code supports multi-viewports (multiple OS Windows mapped into different Dear ImGui viewports)
// Because of that, it is a little more complicated than your typical single-viewport binding code!
static void ImGui_ImplWin32_UpdateMousePos()
{
    ImGuiIO& io = ImGui::GetIO();

    // 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 (io.WantSetMousePos)
    {
        POINT pos = { (int)io.MousePos.x, (int)io.MousePos.y };
        if ((io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) == 0)
            ::ClientToScreen(g_hWnd, &pos);
        ::SetCursorPos(pos.x, pos.y);
    }

    io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
    io.MouseHoveredViewport = 0;

    // Set imgui mouse position
    POINT mouse_screen_pos;
    if (!::GetCursorPos(&mouse_screen_pos))
        return;
    if (HWND focused_hwnd = ::GetActiveWindow())
    {
        if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
        {
            // Multi-viewport mode: mouse position in OS absolute coordinates (io.MousePos is (0,0) when the mouse is on the upper-left of the primary monitor)
            // This is the position you can get with GetCursorPos(). In theory adding viewport->Pos is also the reverse operation of doing ScreenToClient().
            if (ImGui::FindViewportByPlatformHandle((void*)focused_hwnd) != NULL)
                io.MousePos = ImVec2((float)mouse_screen_pos.x, (float)mouse_screen_pos.y);
        }
        else
        {
            // Single viewport mode: mouse position in client window coordinates (io.MousePos is (0,0) when the mouse is on the upper-left corner of the app window.)
            // This is the position you can get with GetCursorPos() + ScreenToClient() or from WM_MOUSEMOVE.
            if (focused_hwnd == g_hWnd)
            {
                POINT mouse_client_pos = mouse_screen_pos;
                ::ScreenToClient(focused_hwnd, &mouse_client_pos);
                io.MousePos = ImVec2((float)mouse_client_pos.x, (float)mouse_client_pos.y);
            }
        }
    }

    // (Optional) When using multiple viewports: set io.MouseHoveredViewport to the viewport the OS mouse cursor is hovering.
    // Important: this information is not easy to provide and many high-level windowing library won't be able to provide it correctly, because
    // - This is _ignoring_ viewports with the ImGuiViewportFlags_NoInputs flag (pass-through windows).
    // - This is _regardless_ of whether another viewport is focused or being dragged from.
    // If ImGuiBackendFlags_HasMouseHoveredViewport is not set by the back-end, imgui will ignore this field and infer the information by relying on the
    // rectangles and last focused time of every viewports it knows about. It will be unaware of foreign windows that may be sitting between or over your windows.
    if (HWND hovered_hwnd = ::WindowFromPoint(mouse_screen_pos))
        if (ImGuiViewport* viewport = ImGui::FindViewportByPlatformHandle((void*)hovered_hwnd))
            if ((viewport->Flags & ImGuiViewportFlags_NoInputs) == 0) // FIXME: We still get our NoInputs window with WM_NCHITTEST/HTTRANSPARENT code when decorated?
                io.MouseHoveredViewport = viewport->ID;
}

void    ImGui_ImplWin32_NewFrame()
{
    ImGuiIO& io = ImGui::GetIO();
    IM_ASSERT(io.Fonts->IsBuilt() && "Font atlas not built! It is generally built by the renderer back-end. Missing call to renderer _NewFrame() function? e.g. ImGui_ImplOpenGL3_NewFrame().");

    // Setup display size (every frame to accommodate for window resizing)
    RECT rect;
    ::GetClientRect(g_hWnd, &rect);
    io.DisplaySize = ImVec2((float)(rect.right - rect.left), (float)(rect.bottom - rect.top));
    if (g_WantUpdateMonitors)
        ImGui_ImplWin32_UpdateMonitors();

    // Setup time step
    INT64 current_time;
    ::QueryPerformanceCounter((LARGE_INTEGER *)&current_time);
    io.DeltaTime = (float)(current_time - g_Time) / g_TicksPerSecond;
    g_Time = current_time;

    // Read keyboard modifiers inputs
    io.KeyCtrl = (::GetKeyState(VK_CONTROL) & 0x8000) != 0;
    io.KeyShift = (::GetKeyState(VK_SHIFT) & 0x8000) != 0;
    io.KeyAlt = (::GetKeyState(VK_MENU) & 0x8000) != 0;
    io.KeySuper = false;
    // io.KeysDown[], io.MousePos, io.MouseDown[], io.MouseWheel: filled by the WndProc handler below.

    // Update OS mouse position
    ImGui_ImplWin32_UpdateMousePos();

    // Update OS mouse cursor with the cursor requested by imgui
    ImGuiMouseCursor mouse_cursor = io.MouseDrawCursor ? ImGuiMouseCursor_None : ImGui::GetMouseCursor();
    if (g_LastMouseCursor != mouse_cursor)
    {
        g_LastMouseCursor = mouse_cursor;
        ImGui_ImplWin32_UpdateMouseCursor();
    }
}

// Allow compilation with old Windows SDK. MinGW doesn't have default _WIN32_WINNT/WINVER versions.
#ifndef WM_MOUSEHWHEEL
#define WM_MOUSEHWHEEL 0x020E
#endif

// Process Win32 mouse/keyboard inputs. 
// 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.
// PS: In this Win32 handler, we use the capture API (GetCapture/SetCapture/ReleaseCapture) to be able to read mouse coordinations when dragging mouse outside of our window bounds.
// PS: We treat DBLCLK messages as regular mouse down messages, so this code will work on windows classes that have the CS_DBLCLKS flag set. Our own example app code doesn't set this flag.
IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    if (ImGui::GetCurrentContext() == NULL)
        return 0;

    ImGuiIO& io = ImGui::GetIO();
    switch (msg)
    {
    case WM_LBUTTONDOWN: case WM_LBUTTONDBLCLK:
    case WM_RBUTTONDOWN: case WM_RBUTTONDBLCLK:
    case WM_MBUTTONDOWN: case WM_MBUTTONDBLCLK:
    {
        int button = 0;
        if (msg == WM_LBUTTONDOWN || msg == WM_LBUTTONDBLCLK) button = 0;
        if (msg == WM_RBUTTONDOWN || msg == WM_RBUTTONDBLCLK) button = 1;
        if (msg == WM_MBUTTONDOWN || msg == WM_MBUTTONDBLCLK) button = 2;
        if (!ImGui::IsAnyMouseDown() && ::GetCapture() == NULL)
            ::SetCapture(hwnd);
        io.MouseDown[button] = true;
        return 0;
    }
    case WM_LBUTTONUP:
    case WM_RBUTTONUP:
    case WM_MBUTTONUP:
    {
        int button = 0;
        if (msg == WM_LBUTTONUP) button = 0;
        if (msg == WM_RBUTTONUP) button = 1;
        if (msg == WM_MBUTTONUP) button = 2;
        io.MouseDown[button] = false;
        if (!ImGui::IsAnyMouseDown() && ::GetCapture() == hwnd)
            ::ReleaseCapture();
        return 0;
    }
    case WM_MOUSEWHEEL:
        io.MouseWheel += (float)GET_WHEEL_DELTA_WPARAM(wParam) / (float)WHEEL_DELTA;
        return 0;
    case WM_MOUSEHWHEEL:
        io.MouseWheelH += (float)GET_WHEEL_DELTA_WPARAM(wParam) / (float)WHEEL_DELTA;
        return 0;
    case WM_KEYDOWN:
    case WM_SYSKEYDOWN:
        if (wParam < 256)
            io.KeysDown[wParam] = 1;
        return 0;
    case WM_KEYUP:
    case WM_SYSKEYUP:
        if (wParam < 256)
            io.KeysDown[wParam] = 0;
        return 0;
    case WM_CHAR:
        // You can also use ToAscii()+GetKeyboardState() to retrieve characters.
        if (wParam > 0 && wParam < 0x10000)
            io.AddInputCharacter((unsigned short)wParam);
        return 0;
    case WM_SETCURSOR:
        if (LOWORD(lParam) == HTCLIENT && ImGui_ImplWin32_UpdateMouseCursor())
            return 1;
        return 0;
    case WM_DISPLAYCHANGE:
        g_WantUpdateMonitors = true;
        return 0;
    }
    return 0;
}

//--------------------------------------------------------------------------------------------------------
// DPI handling
// Those in theory should be simple calls but Windows has multiple ways to handle DPI, and most of them
// require recent Windows versions at runtime or recent Windows SDK at compile-time. Neither we want to depend on.
// So we dynamically select and load those functions to avoid dependencies. This is the scheme successfully 
// used by GLFW (from which we borrowed some of the code here) and other applications aiming to be portable.
//---------------------------------------------------------------------------------------------------------
// At this point ImGui_ImplWin32_EnableDpiAwareness() is just a helper called by main.cpp, we don't call it automatically.
//---------------------------------------------------------------------------------------------------------

static BOOL IsWindowsVersionOrGreater(WORD major, WORD minor, WORD sp)
{
    OSVERSIONINFOEXW osvi = { sizeof(osvi), major, minor, 0, 0,{ 0 }, sp };
    DWORD mask = VER_MAJORVERSION | VER_MINORVERSION | VER_SERVICEPACKMAJOR;
    ULONGLONG cond = VerSetConditionMask(0, VER_MAJORVERSION, VER_GREATER_EQUAL);
    cond = VerSetConditionMask(cond, VER_MINORVERSION, VER_GREATER_EQUAL);
    cond = VerSetConditionMask(cond, VER_SERVICEPACKMAJOR, VER_GREATER_EQUAL);
    return VerifyVersionInfoW(&osvi, mask, cond);
}
#define IsWindows8Point1OrGreater()  IsWindowsVersionOrGreater(HIBYTE(0x0602), LOBYTE(0x0602), 0) // _WIN32_WINNT_WINBLUE
#define IsWindows10OrGreater()       IsWindowsVersionOrGreater(HIBYTE(0x0A00), LOBYTE(0x0A00), 0) // _WIN32_WINNT_WIN10

#ifndef DPI_ENUMS_DECLARED
typedef enum { PROCESS_DPI_UNAWARE = 0, PROCESS_SYSTEM_DPI_AWARE = 1, PROCESS_PER_MONITOR_DPI_AWARE = 2 } PROCESS_DPI_AWARENESS;
typedef enum { MDT_EFFECTIVE_DPI = 0, MDT_ANGULAR_DPI = 1, MDT_RAW_DPI = 2, MDT_DEFAULT = MDT_EFFECTIVE_DPI } MONITOR_DPI_TYPE;
#endif
#ifndef _DPI_AWARENESS_CONTEXTS_
DECLARE_HANDLE(DPI_AWARENESS_CONTEXT);
#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE    (DPI_AWARENESS_CONTEXT)-3
#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 (DPI_AWARENESS_CONTEXT)-4
#endif
typedef HRESULT(WINAPI * PFN_SetProcessDpiAwareness)(PROCESS_DPI_AWARENESS);                     // Shcore.lib+dll, Windows 8.1
typedef HRESULT(WINAPI * PFN_GetDpiForMonitor)(HMONITOR, MONITOR_DPI_TYPE, UINT*, UINT*);        // Shcore.lib+dll, Windows 8.1
typedef DPI_AWARENESS_CONTEXT(WINAPI * PFN_SetThreadDpiAwarenessContext)(DPI_AWARENESS_CONTEXT); // User32.lib+dll, Windows 10 v1607 (Creators Update)

void ImGui_ImplWin32_EnableDpiAwareness()
{
    // if (IsWindows10OrGreater()) // FIXME-DPI: This needs a manifest to succeed. Instead we try to grab the function pointer.
    {
        static HINSTANCE user32_dll = ::LoadLibraryA("user32.dll"); // Reference counted per-process
        if (PFN_SetThreadDpiAwarenessContext SetThreadDpiAwarenessContextFn = (PFN_SetThreadDpiAwarenessContext)::GetProcAddress(user32_dll, "SetThreadDpiAwarenessContext"))
        {
            SetThreadDpiAwarenessContextFn(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
            return;
        }
    }
    if (IsWindows8Point1OrGreater())
    {
        static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process
        if (PFN_SetProcessDpiAwareness SetProcessDpiAwarenessFn = (PFN_SetProcessDpiAwareness)::GetProcAddress(shcore_dll, "SetProcessDpiAwareness"))
            SetProcessDpiAwarenessFn(PROCESS_PER_MONITOR_DPI_AWARE);
    }
    else
    {
        SetProcessDPIAware();
    }
}

float ImGui_ImplWin32_GetDpiScaleForMonitor(void* monitor)
{
    UINT xdpi = 96, ydpi = 96;
    if (::IsWindows8Point1OrGreater())
    {
        static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process
        if (PFN_GetDpiForMonitor GetDpiForMonitorFn = (PFN_GetDpiForMonitor)::GetProcAddress(shcore_dll, "GetDpiForMonitor"))
            GetDpiForMonitorFn((HMONITOR)monitor, MDT_EFFECTIVE_DPI, &xdpi, &ydpi);
    }
    else
    {
        const HDC dc = ::GetDC(NULL);
        xdpi = ::GetDeviceCaps(dc, LOGPIXELSX);
        ydpi = ::GetDeviceCaps(dc, LOGPIXELSY);
        ::ReleaseDC(NULL, dc);
    }
    IM_ASSERT(xdpi == ydpi); // Please contact me if you hit this assert!
    return xdpi / 96.0f;
}

float ImGui_ImplWin32_GetDpiScaleForHwnd(void* hwnd)
{
    HMONITOR monitor = ::MonitorFromWindow((HWND)hwnd, MONITOR_DEFAULTTONEAREST);
    return ImGui_ImplWin32_GetDpiScaleForMonitor(monitor);
}

//--------------------------------------------------------------------------------------------------------
// IME (Input Method Editor) basic support for e.g. Asian language users
//--------------------------------------------------------------------------------------------------------

#if defined(_WIN32) && !defined(IMGUI_DISABLE_WIN32_FUNCTIONS) && !defined(IMGUI_DISABLE_WIN32_DEFAULT_IME_FUNCTIONS) && !defined(__GNUC__)
#define HAS_WIN32_IME   1
#include <imm.h>
#ifdef _MSC_VER
#pragma comment(lib, "imm32")
#endif
static void ImGui_ImplWin32_SetImeInputPos(ImGuiViewport* viewport, ImVec2 pos)
{
    COMPOSITIONFORM cf = { CFS_FORCE_POSITION,{ (LONG)(pos.x - viewport->Pos.x), (LONG)(pos.y - viewport->Pos.y) },{ 0, 0, 0, 0 } };
    if (HWND hwnd = (HWND)viewport->PlatformHandle)
        if (HIMC himc = ::ImmGetContext(hwnd))
        {
            ::ImmSetCompositionWindow(himc, &cf);
            ::ImmReleaseContext(hwnd, himc);
        }
}
#else
#define HAS_WIN32_IME   0
#endif

//--------------------------------------------------------------------------------------------------------
// 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 ImGuiViewportDataWin32
{
    HWND    Hwnd;
    bool    HwndOwned;
    DWORD   DwStyle;
    DWORD   DwExStyle;

    ImGuiViewportDataWin32() { Hwnd = NULL; HwndOwned = false;  DwStyle = DwExStyle = 0; }
    ~ImGuiViewportDataWin32() { IM_ASSERT(Hwnd == NULL); }
};

static void ImGui_ImplWin32_GetWin32StyleFromViewportFlags(ImGuiViewportFlags flags, DWORD* out_style, DWORD* out_ex_style)
{
    if (flags & ImGuiViewportFlags_NoDecoration)
        *out_style = WS_POPUP;
    else
        *out_style = WS_OVERLAPPEDWINDOW;

    if (flags & ImGuiViewportFlags_NoTaskBarIcon)
        *out_ex_style = WS_EX_TOOLWINDOW;
    else
        *out_ex_style = WS_EX_APPWINDOW;

    if (flags & ImGuiViewportFlags_TopMost)
        *out_ex_style |= WS_EX_TOPMOST;
}

static void ImGui_ImplWin32_CreateWindow(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = IM_NEW(ImGuiViewportDataWin32)();
    viewport->PlatformUserData = data;

    // Select style and parent window
    ImGui_ImplWin32_GetWin32StyleFromViewportFlags(viewport->Flags, &data->DwStyle, &data->DwExStyle);
    HWND parent_window = NULL;
    if (viewport->ParentViewportId != 0)
        if (ImGuiViewport* parent_viewport = ImGui::FindViewportByID(viewport->ParentViewportId))
            parent_window = (HWND)parent_viewport->PlatformHandle;

    // Create window
    RECT rect = { (LONG)viewport->Pos.x, (LONG)viewport->Pos.y, (LONG)(viewport->Pos.x + viewport->Size.x), (LONG)(viewport->Pos.y + viewport->Size.y) };
    ::AdjustWindowRectEx(&rect, data->DwStyle, FALSE, data->DwExStyle);
    data->Hwnd = ::CreateWindowEx(
        data->DwExStyle, _T("ImGui Platform"), _T("Untitled"), data->DwStyle,   // Style, class name, window name
        rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top,    // Window area
        parent_window, NULL, ::GetModuleHandle(NULL), NULL);                    // Parent window, Menu, Instance, Param
    data->HwndOwned = true;
    viewport->PlatformRequestResize = false;
    viewport->PlatformHandle = data->Hwnd;
}

static void ImGui_ImplWin32_DestroyWindow(ImGuiViewport* viewport)
{
    if (ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData)
    {
        if (::GetCapture() == data->Hwnd)
        {
            // Transfer capture so if we started dragging from a window that later disappears, we'll still receive the MOUSEUP event.
            ::ReleaseCapture();
            ::SetCapture(g_hWnd);
        }
        if (data->Hwnd && data->HwndOwned)
            ::DestroyWindow(data->Hwnd);
        data->Hwnd = NULL;
        IM_DELETE(data);
    }
    viewport->PlatformUserData = viewport->PlatformHandle = NULL;
}

static void ImGui_ImplWin32_ShowWindow(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    if (viewport->Flags & ImGuiViewportFlags_NoFocusOnAppearing)
        ::ShowWindow(data->Hwnd, SW_SHOWNA);
    else
        ::ShowWindow(data->Hwnd, SW_SHOW);
}

static void ImGui_ImplWin32_UpdateWindow(ImGuiViewport* viewport)
{
    // (Optional) Update Win32 style if it changed _after_ creation. 
    // Generally they won't change unless configuration flags are changed, but advanced uses (such as manually rewriting viewport flags) make this useful.
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    DWORD new_style;
    DWORD new_ex_style;
    ImGui_ImplWin32_GetWin32StyleFromViewportFlags(viewport->Flags, &new_style, &new_ex_style);

    // Only reapply the flags that have been changed from our point of view (as other flags are being modified by Windows)
    if (data->DwStyle != new_style || data->DwExStyle != new_ex_style)
    {
        data->DwStyle = new_style;
        data->DwExStyle = new_ex_style;
        ::SetWindowLong(data->Hwnd, GWL_STYLE, data->DwStyle);
        ::SetWindowLong(data->Hwnd, GWL_EXSTYLE, data->DwExStyle);
        RECT rect = { (LONG)viewport->Pos.x, (LONG)viewport->Pos.y, (LONG)(viewport->Pos.x + viewport->Size.x), (LONG)(viewport->Pos.y + viewport->Size.y) };
        ::AdjustWindowRectEx(&rect, data->DwStyle, FALSE, data->DwExStyle); // Client to Screen
        ::SetWindowPos(data->Hwnd, NULL, rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top, SWP_NOZORDER | SWP_NOACTIVATE | SWP_FRAMECHANGED);
        ::ShowWindow(data->Hwnd, SW_SHOWNA); // This is necessary when we alter the style
        viewport->PlatformRequestMove = viewport->PlatformRequestResize = true;
    }
}

static ImVec2 ImGui_ImplWin32_GetWindowPos(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    POINT pos = { 0, 0 };
    ::ClientToScreen(data->Hwnd, &pos);
    return ImVec2((float)pos.x, (float)pos.y);
}

static void ImGui_ImplWin32_SetWindowPos(ImGuiViewport* viewport, ImVec2 pos)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    RECT rect = { (LONG)pos.x, (LONG)pos.y, (LONG)pos.x, (LONG)pos.y };
    ::AdjustWindowRectEx(&rect, data->DwStyle, FALSE, data->DwExStyle);
    ::SetWindowPos(data->Hwnd, NULL, rect.left, rect.top, 0, 0, SWP_NOZORDER | SWP_NOSIZE | SWP_NOACTIVATE);
}

static ImVec2 ImGui_ImplWin32_GetWindowSize(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    RECT rect;
    ::GetClientRect(data->Hwnd, &rect);
    return ImVec2(float(rect.right - rect.left), float(rect.bottom - rect.top));
}

static void ImGui_ImplWin32_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    RECT rect = { 0, 0, (LONG)size.x, (LONG)size.y };
    ::AdjustWindowRectEx(&rect, data->DwStyle, FALSE, data->DwExStyle); // Client to Screen
    ::SetWindowPos(data->Hwnd, NULL, 0, 0, rect.right - rect.left, rect.bottom - rect.top, SWP_NOZORDER | SWP_NOMOVE | SWP_NOACTIVATE);
}

static void ImGui_ImplWin32_SetWindowFocus(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    ::BringWindowToTop(data->Hwnd);
    ::SetForegroundWindow(data->Hwnd);
    ::SetFocus(data->Hwnd);
}

static bool ImGui_ImplWin32_GetWindowFocus(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    return ::GetActiveWindow() == data->Hwnd;
}

static bool ImGui_ImplWin32_GetWindowMinimized(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    return ::IsIconic(data->Hwnd) != 0;
}

static void ImGui_ImplWin32_SetWindowTitle(ImGuiViewport* viewport, const char* title)
{
    // ::SetWindowTextA() doesn't properly handle UTF-8 so we explicitely convert our string.
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    int n = ::MultiByteToWideChar(CP_UTF8, 0, title, -1, NULL, 0);
    ImVector<wchar_t> title_w;
    title_w.resize(n);
    ::MultiByteToWideChar(CP_UTF8, 0, title, -1, title_w.Data, n);
    ::SetWindowTextW(data->Hwnd, title_w.Data);
}

static void ImGui_ImplWin32_SetWindowAlpha(ImGuiViewport* viewport, float alpha)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    IM_ASSERT(alpha >= 0.0f && alpha <= 1.0f);
    if (alpha < 1.0f)
    {
        DWORD style = ::GetWindowLongW(data->Hwnd, GWL_EXSTYLE) | WS_EX_LAYERED;
        ::SetWindowLongW(data->Hwnd, GWL_EXSTYLE, style);
        ::SetLayeredWindowAttributes(data->Hwnd, 0, (BYTE)(255 * alpha), LWA_ALPHA);
    }
    else
    {
        DWORD style = ::GetWindowLongW(data->Hwnd, GWL_EXSTYLE) & ~WS_EX_LAYERED;
        ::SetWindowLongW(data->Hwnd, GWL_EXSTYLE, style);
    }
}

static float ImGui_ImplWin32_GetWindowDpiScale(ImGuiViewport* viewport)
{
    ImGuiViewportDataWin32* data = (ImGuiViewportDataWin32*)viewport->PlatformUserData;
    IM_ASSERT(data->Hwnd != 0);
    return ImGui_ImplWin32_GetDpiScaleForHwnd(data->Hwnd);
}

// FIXME-DPI: Testing DPI related ideas
static void ImGui_ImplWin32_OnChangedViewport(ImGuiViewport* viewport)
{
    (void)viewport;
#if 0
    ImGuiStyle default_style;
    //default_style.WindowPadding = ImVec2(0, 0);
    //default_style.WindowBorderSize = 0.0f;
    //default_style.ItemSpacing.y = 3.0f;
    //default_style.FramePadding = ImVec2(0, 0);
    default_style.ScaleAllSizes(viewport->DpiScale);
    ImGuiStyle& style = ImGui::GetStyle();
    style = default_style;
#endif
}

static LRESULT CALLBACK ImGui_ImplWin32_WndProcHandler_PlatformWindow(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    if (ImGui_ImplWin32_WndProcHandler(hWnd, msg, wParam, lParam))
        return true;

    if (ImGuiViewport* viewport = ImGui::FindViewportByPlatformHandle((void*)hWnd))
    {
        switch (msg)
        {
        case WM_CLOSE:
            viewport->PlatformRequestClose = true;
            return 0;
        case WM_MOVE:
            viewport->PlatformRequestMove = true;
            break;
        case WM_SIZE:
            viewport->PlatformRequestResize = true;
            break;
        case WM_NCHITTEST:
            // Let mouse pass-through the window. This will allow the back-end to set io.MouseHoveredViewport properly (which is OPTIONAL).
            // The ImGuiViewportFlags_NoInputs flag is set while dragging a viewport, as want to detect the window behind the one we are dragging.
            // If you cannot easily access those viewport flags from your windowing/event code: you may manually synchronize its state e.g. in
            // your main loop after calling UpdatePlatformWindows(). Iterate all viewports/platform windows and pass the flag to your windowing system.
            if (viewport->Flags & ImGuiViewportFlags_NoInputs)
                return HTTRANSPARENT;
            break;
        }
    }

    return DefWindowProc(hWnd, msg, wParam, lParam);
}

static BOOL CALLBACK ImGui_ImplWin32_UpdateMonitors_EnumFunc(HMONITOR monitor, HDC, LPRECT, LPARAM)
{
    MONITORINFO info = { 0 };
    info.cbSize = sizeof(MONITORINFO);
    if (!::GetMonitorInfo(monitor, &info))
        return TRUE;
    ImGuiPlatformMonitor imgui_monitor;
    imgui_monitor.MainPos = ImVec2((float)info.rcMonitor.left, (float)info.rcMonitor.top);
    imgui_monitor.MainSize = ImVec2((float)(info.rcMonitor.right - info.rcMonitor.left), (float)(info.rcMonitor.bottom - info.rcMonitor.top));
    imgui_monitor.WorkPos = ImVec2((float)info.rcWork.left, (float)info.rcWork.top);
    imgui_monitor.WorkSize = ImVec2((float)(info.rcWork.right - info.rcWork.left), (float)(info.rcWork.bottom - info.rcWork.top));
    imgui_monitor.DpiScale = ImGui_ImplWin32_GetDpiScaleForMonitor(monitor);
    ImGuiPlatformIO& io = ImGui::GetPlatformIO();
    if (info.dwFlags & MONITORINFOF_PRIMARY)
        io.Monitors.push_front(imgui_monitor);
    else
        io.Monitors.push_back(imgui_monitor);
    return TRUE;
}

static void ImGui_ImplWin32_UpdateMonitors()
{
    ImGui::GetPlatformIO().Monitors.resize(0);
    ::EnumDisplayMonitors(NULL, NULL, ImGui_ImplWin32_UpdateMonitors_EnumFunc, NULL);
    g_WantUpdateMonitors = false;
}

static void ImGui_ImplWin32_InitPlatformInterface()
{
    WNDCLASSEX wcex;
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = ImGui_ImplWin32_WndProcHandler_PlatformWindow;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = ::GetModuleHandle(NULL);
    wcex.hIcon = NULL;
    wcex.hCursor = NULL;
    wcex.hbrBackground = (HBRUSH)(COLOR_BACKGROUND + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = _T("ImGui Platform");
    wcex.hIconSm = NULL;
    ::RegisterClassEx(&wcex);

    ImGui_ImplWin32_UpdateMonitors();

    // Register platform interface (will be coupled with a renderer interface)
    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
    platform_io.Platform_CreateWindow = ImGui_ImplWin32_CreateWindow;
    platform_io.Platform_DestroyWindow = ImGui_ImplWin32_DestroyWindow;
    platform_io.Platform_ShowWindow = ImGui_ImplWin32_ShowWindow;
    platform_io.Platform_SetWindowPos = ImGui_ImplWin32_SetWindowPos;
    platform_io.Platform_GetWindowPos = ImGui_ImplWin32_GetWindowPos;
    platform_io.Platform_SetWindowSize = ImGui_ImplWin32_SetWindowSize;
    platform_io.Platform_GetWindowSize = ImGui_ImplWin32_GetWindowSize;
    platform_io.Platform_SetWindowFocus = ImGui_ImplWin32_SetWindowFocus;
    platform_io.Platform_GetWindowFocus = ImGui_ImplWin32_GetWindowFocus;
    platform_io.Platform_GetWindowMinimized = ImGui_ImplWin32_GetWindowMinimized;
    platform_io.Platform_SetWindowTitle = ImGui_ImplWin32_SetWindowTitle;
    platform_io.Platform_SetWindowAlpha = ImGui_ImplWin32_SetWindowAlpha;
    platform_io.Platform_UpdateWindow = ImGui_ImplWin32_UpdateWindow;
    platform_io.Platform_GetWindowDpiScale = ImGui_ImplWin32_GetWindowDpiScale; // FIXME-DPI
    platform_io.Platform_OnChangedViewport = ImGui_ImplWin32_OnChangedViewport; // FIXME-DPI
#if HAS_WIN32_IME
    platform_io.Platform_SetImeInputPos = ImGui_ImplWin32_SetImeInputPos;
#endif

    // Register main window handle (which is owned by the main application, not by us)
    ImGuiViewport* main_viewport = ImGui::GetMainViewport();
    ImGuiViewportDataWin32* data = IM_NEW(ImGuiViewportDataWin32)();
    data->Hwnd = g_hWnd;
    data->HwndOwned = false;
    main_viewport->PlatformUserData = data;
    main_viewport->PlatformHandle = (void*)g_hWnd;
}

static void ImGui_ImplWin32_ShutdownPlatformInterface()
{
    ::UnregisterClass(_T("ImGui Platform"), ::GetModuleHandle(NULL));
}