imgui/backends/imgui_impl_win32.cpp

// dear imgui: Platform Backend 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 dear 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: Gamepad support. Enabled with 'io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad'.

// You can copy and use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
// Read online: https://github.com/ocornut/imgui/tree/master/docs

#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>
#include <dwmapi.h>

// Configuration flags to add in your imconfig.h file:
//#define IMGUI_IMPL_WIN32_DISABLE_GAMEPAD              // Disable gamepad support (this used to be meaningful before <1.81) but we know load XInput dynamically so the option is less relevant now.

// Using XInput for gamepad (will load DLL dynamically)
#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
#include <XInput.h>
typedef DWORD (WINAPI *PFN_XInputGetCapabilities)(DWORD, DWORD, XINPUT_CAPABILITIES*);
typedef DWORD (WINAPI *PFN_XInputGetState)(DWORD, XINPUT_STATE*);
#endif

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
//  2021-02-18: Added ImGui_ImplWin32_EnableAlphaCompositing(). Non Visual Studio users will need to link with dwmapi.lib (MinGW/gcc: use -ldwmapi).
//  2021-02-17: Fixed ImGui_ImplWin32_EnableDpiAwareness() attempting to get SetProcessDpiAwareness from shcore.dll on Windows 8 whereas it is only supported on Windows 8.1.
//  2021-01-25: Inputs: Dynamically loading XInput DLL.
//  2020-12-04: Misc: Fixed setting of io.DisplaySize to invalid/uninitialized data when after hwnd has been closed.
//  2020-03-03: Inputs: Calling AddInputCharacterUTF16() to support surrogate pairs leading to codepoint >= 0x10000 (for more complete CJK inputs)
//  2020-02-17: Added ImGui_ImplWin32_EnableDpiAwareness(), ImGui_ImplWin32_GetDpiScaleForHwnd(), ImGui_ImplWin32_GetDpiScaleForMonitor() helper functions.
//  2020-01-14: Inputs: Added support for #define IMGUI_IMPL_WIN32_DISABLE_GAMEPAD/IMGUI_IMPL_WIN32_DISABLE_LINKING_XINPUT.
//  2019-12-05: Inputs: Added support for ImGuiMouseCursor_NotAllowed mouse cursor.
//  2019-05-11: Inputs: Don't filter value from WM_CHAR before calling AddInputCharacter().
//  2019-01-17: Misc: Using GetForegroundWindow()+IsChild() instead of GetActiveWindow() to be compatible with windows created in a different thread or parent.
//  2019-01-17: Inputs: Added support for mouse buttons 4 and 5 via WM_XBUTTON* messages.
//  2019-01-15: Inputs: Added support for XInput gamepads (if ImGuiConfigFlags_NavEnableGamepad is set by user application).
//  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 = NULL;
static INT64                g_Time = 0;
static INT64                g_TicksPerSecond = 0;
static ImGuiMouseCursor     g_LastMouseCursor = ImGuiMouseCursor_COUNT;
static bool                 g_HasGamepad = false;
static bool                 g_WantUpdateHasGamepad = true;

// XInput DLL and functions
#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
static HMODULE                      g_XInputDLL = NULL;
static PFN_XInputGetCapabilities    g_XInputGetCapabilities = NULL;
static PFN_XInputGetState           g_XInputGetState = NULL;
#endif

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

    // Setup backend capabilities flags
    g_hWnd = (HWND)hwnd;
    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.BackendPlatformName = "imgui_impl_win32";
    io.ImeWindowHandle = hwnd;

    // Keyboard mapping. Dear 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_KeyPadEnter] = VK_RETURN;
    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';

    // Dynamically load XInput library
#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
    const char* xinput_dll_names[] =
    {
        "xinput1_4.dll",   // Windows 8+
        "xinput1_3.dll",   // DirectX SDK
        "xinput9_1_0.dll", // Windows Vista, Windows 7
        "xinput1_2.dll",   // DirectX SDK
        "xinput1_1.dll"    // DirectX SDK
    };
    for (int n = 0; n < IM_ARRAYSIZE(xinput_dll_names); n++)
        if (HMODULE dll = ::LoadLibraryA(xinput_dll_names[n]))
        {
            g_XInputDLL = dll;
            g_XInputGetCapabilities = (PFN_XInputGetCapabilities)::GetProcAddress(dll, "XInputGetCapabilities");
            g_XInputGetState = (PFN_XInputGetState)::GetProcAddress(dll, "XInputGetState");
            break;
        }
#endif // IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
    
    return true;
}

void    ImGui_ImplWin32_Shutdown()
{
    // Unload XInput library
#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
    if (g_XInputDLL)
        ::FreeLibrary(g_XInputDLL);
    g_XInputDLL = NULL;
    g_XInputGetCapabilities = NULL;
    g_XInputGetState = NULL;
#endif // IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
    
    g_hWnd = NULL;
    g_Time = 0;
    g_TicksPerSecond = 0;
    g_LastMouseCursor = ImGuiMouseCursor_COUNT;
    g_HasGamepad = false;
    g_WantUpdateHasGamepad = true;
}

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;
        case ImGuiMouseCursor_NotAllowed:   win32_cursor = IDC_NO; break;
        }
        ::SetCursor(::LoadCursor(NULL, win32_cursor));
    }
    return true;
}

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

    // Set mouse position
    io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
    POINT pos;
    if (HWND active_window = ::GetForegroundWindow())
        if (active_window == g_hWnd || ::IsChild(active_window, g_hWnd))
            if (::GetCursorPos(&pos) && ::ScreenToClient(g_hWnd, &pos))
                io.MousePos = ImVec2((float)pos.x, (float)pos.y);
}

// Gamepad navigation mapping
static void ImGui_ImplWin32_UpdateGamepads()
{
#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
    ImGuiIO& io = ImGui::GetIO();
    memset(io.NavInputs, 0, sizeof(io.NavInputs));
    if ((io.ConfigFlags & ImGuiConfigFlags_NavEnableGamepad) == 0)
        return;

    // Calling XInputGetState() every frame on disconnected gamepads is unfortunately too slow.
    // Instead we refresh gamepad availability by calling XInputGetCapabilities() _only_ after receiving WM_DEVICECHANGE.
    if (g_WantUpdateHasGamepad)
    {
        XINPUT_CAPABILITIES caps;
        g_HasGamepad = g_XInputGetCapabilities ? (g_XInputGetCapabilities(0, XINPUT_FLAG_GAMEPAD, &caps) == ERROR_SUCCESS) : false;
        g_WantUpdateHasGamepad = false;
    }

    io.BackendFlags &= ~ImGuiBackendFlags_HasGamepad;
    XINPUT_STATE xinput_state;
    if (g_HasGamepad && g_XInputGetState && g_XInputGetState(0, &xinput_state) == ERROR_SUCCESS)
    {
        const XINPUT_GAMEPAD& gamepad = xinput_state.Gamepad;
        io.BackendFlags |= ImGuiBackendFlags_HasGamepad;

        #define MAP_BUTTON(NAV_NO, BUTTON_ENUM)     { io.NavInputs[NAV_NO] = (gamepad.wButtons & BUTTON_ENUM) ? 1.0f : 0.0f; }
        #define MAP_ANALOG(NAV_NO, VALUE, V0, V1)   { float vn = (float)(VALUE - V0) / (float)(V1 - V0); if (vn > 1.0f) vn = 1.0f; if (vn > 0.0f && io.NavInputs[NAV_NO] < vn) io.NavInputs[NAV_NO] = vn; }
        MAP_BUTTON(ImGuiNavInput_Activate,      XINPUT_GAMEPAD_A);              // Cross / A
        MAP_BUTTON(ImGuiNavInput_Cancel,        XINPUT_GAMEPAD_B);              // Circle / B
        MAP_BUTTON(ImGuiNavInput_Menu,          XINPUT_GAMEPAD_X);              // Square / X
        MAP_BUTTON(ImGuiNavInput_Input,         XINPUT_GAMEPAD_Y);              // Triangle / Y
        MAP_BUTTON(ImGuiNavInput_DpadLeft,      XINPUT_GAMEPAD_DPAD_LEFT);      // D-Pad Left
        MAP_BUTTON(ImGuiNavInput_DpadRight,     XINPUT_GAMEPAD_DPAD_RIGHT);     // D-Pad Right
        MAP_BUTTON(ImGuiNavInput_DpadUp,        XINPUT_GAMEPAD_DPAD_UP);        // D-Pad Up
        MAP_BUTTON(ImGuiNavInput_DpadDown,      XINPUT_GAMEPAD_DPAD_DOWN);      // D-Pad Down
        MAP_BUTTON(ImGuiNavInput_FocusPrev,     XINPUT_GAMEPAD_LEFT_SHOULDER);  // L1 / LB
        MAP_BUTTON(ImGuiNavInput_FocusNext,     XINPUT_GAMEPAD_RIGHT_SHOULDER); // R1 / RB
        MAP_BUTTON(ImGuiNavInput_TweakSlow,     XINPUT_GAMEPAD_LEFT_SHOULDER);  // L1 / LB
        MAP_BUTTON(ImGuiNavInput_TweakFast,     XINPUT_GAMEPAD_RIGHT_SHOULDER); // R1 / RB
        MAP_ANALOG(ImGuiNavInput_LStickLeft,    gamepad.sThumbLX,  -XINPUT_GAMEPAD_LEFT_THUMB_DEADZONE, -32768);
        MAP_ANALOG(ImGuiNavInput_LStickRight,   gamepad.sThumbLX,  +XINPUT_GAMEPAD_LEFT_THUMB_DEADZONE, +32767);
        MAP_ANALOG(ImGuiNavInput_LStickUp,      gamepad.sThumbLY,  +XINPUT_GAMEPAD_LEFT_THUMB_DEADZONE, +32767);
        MAP_ANALOG(ImGuiNavInput_LStickDown,    gamepad.sThumbLY,  -XINPUT_GAMEPAD_LEFT_THUMB_DEADZONE, -32767);
        #undef MAP_BUTTON
        #undef MAP_ANALOG
    }
#endif // #ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
}

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

    // Setup display size (every frame to accommodate for window resizing)
    RECT rect = { 0, 0, 0, 0 };
    ::GetClientRect(g_hWnd, &rect);
    io.DisplaySize = ImVec2((float)(rect.right - rect.left), (float)(rect.bottom - rect.top));

    // Setup time step
    INT64 current_time = 0;
    ::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();
    }

    // Update game controllers (if enabled and available)
    ImGui_ImplWin32_UpdateGamepads();
}

// Allow compilation with old Windows SDK. MinGW doesn't have default _WIN32_WINNT/WINVER versions.
#ifndef WM_MOUSEHWHEEL
#define WM_MOUSEHWHEEL 0x020E
#endif
#ifndef DBT_DEVNODES_CHANGED
#define DBT_DEVNODES_CHANGED 0x0007
#endif

// Win32 message handler (process Win32 mouse/keyboard inputs, etc.)
// Call from your application's message handler.
// When implementing your own backend, 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 coordinates 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.
#if 0
// Copy this line into your .cpp file to forward declare the function.
extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
#endif
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:
    case WM_XBUTTONDOWN: case WM_XBUTTONDBLCLK:
    {
        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 (msg == WM_XBUTTONDOWN || msg == WM_XBUTTONDBLCLK) { button = (GET_XBUTTON_WPARAM(wParam) == XBUTTON1) ? 3 : 4; }
        if (!ImGui::IsAnyMouseDown() && ::GetCapture() == NULL)
            ::SetCapture(hwnd);
        io.MouseDown[button] = true;
        return 0;
    }
    case WM_LBUTTONUP:
    case WM_RBUTTONUP:
    case WM_MBUTTONUP:
    case WM_XBUTTONUP:
    {
        int button = 0;
        if (msg == WM_LBUTTONUP) { button = 0; }
        if (msg == WM_RBUTTONUP) { button = 1; }
        if (msg == WM_MBUTTONUP) { button = 2; }
        if (msg == WM_XBUTTONUP) { button = (GET_XBUTTON_WPARAM(wParam) == XBUTTON1) ? 3 : 4; }
        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.AddInputCharacterUTF16((unsigned short)wParam);
        return 0;
    case WM_SETCURSOR:
        if (LOWORD(lParam) == HTCLIENT && ImGui_ImplWin32_UpdateMouseCursor())
            return 1;
        return 0;
    case WM_DEVICECHANGE:
        if ((UINT)wParam == DBT_DEVNODES_CHANGED)
            g_WantUpdateHasGamepad = true;
        return 0;
    }
    return 0;
}


//--------------------------------------------------------------------------------------------------------
// DPI-related helpers (optional)
//--------------------------------------------------------------------------------------------------------
// - Use to enable DPI awareness without having to create an application manifest.
// - Your own app may already do this via a manifest or explicit calls. This is mostly useful for our examples/ apps.
// - In theory we could call simple functions from Windows SDK such as SetProcessDPIAware(), SetProcessDpiAwareness(), etc.
//   but most of the functions provided by Microsoft require Windows 8.1/10+ SDK at compile time and Windows 8/10+ at runtime,
//   neither we want to require the user to have. 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) and other apps aiming to be highly portable.
// ImGui_ImplWin32_EnableDpiAwareness() is just a helper called by main.cpp, we don't call it automatically.
// If you are trying to implement your own backend for your own engine, you may ignore that noise.
//---------------------------------------------------------------------------------------------------------

// Implement some of the functions and types normally declared in recent Windows SDK.
#if !defined(_versionhelpers_H_INCLUDED_) && !defined(_INC_VERSIONHELPERS)
static BOOL IsWindowsVersionOrGreater(WORD major, WORD minor, WORD sp)
{
    OSVERSIONINFOEXW osvi = { sizeof(osvi), major, minor, 0, 0, { 0 }, sp, 0, 0, 0, 0 };
    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 IsWindowsVistaOrGreater()   IsWindowsVersionOrGreater(HIBYTE(0x0600), LOBYTE(0x0600), 0) // _WIN32_WINNT_VISTA
#define IsWindows8OrGreater()       IsWindowsVersionOrGreater(HIBYTE(0x0602), LOBYTE(0x0602), 0) // _WIN32_WINNT_WIN8
#define IsWindows8Point1OrGreater() IsWindowsVersionOrGreater(HIBYTE(0x0603), LOBYTE(0x0603), 0) // _WIN32_WINNT_WINBLUE
#endif

#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
#endif
#ifndef DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2
#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)

// Helper function to enable DPI awareness without setting up a manifest
void ImGui_ImplWin32_EnableDpiAwareness()
{
    // if (IsWindows10OrGreater()) // 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);
            return;
        }
    }
#if _WIN32_WINNT >= 0x0600
    ::SetProcessDPIAware();
#endif
}

#if defined(_MSC_VER) && !defined(NOGDI)
#pragma comment(lib, "gdi32")   // Link with gdi32.lib for GetDeviceCaps(). MinGW will require linking with '-lgdi32'
#endif

float ImGui_ImplWin32_GetDpiScaleForMonitor(void* monitor)
{
    UINT xdpi = 96, ydpi = 96;
    static BOOL bIsWindows8Point1OrGreater = IsWindows8Point1OrGreater();
    if (bIsWindows8Point1OrGreater)
    {
        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);
    }
#ifndef NOGDI
    else
    {
        const HDC dc = ::GetDC(NULL);
        xdpi = ::GetDeviceCaps(dc, LOGPIXELSX);
        ydpi = ::GetDeviceCaps(dc, LOGPIXELSY);
        ::ReleaseDC(NULL, dc);
    }
#endif
    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);
}

//---------------------------------------------------------------------------------------------------------
// Transparency related helpers (optional)
//--------------------------------------------------------------------------------------------------------

#if defined(_MSC_VER)
#pragma comment(lib, "dwmapi")  // Link with dwmapi.lib. MinGW will require linking with '-ldwmapi'
#endif

// [experimental]
// Borrowed from GLFW's function updateFramebufferTransparency() in src/win32_window.c
// (the Dwm* functions are Vista era functions but we are borrowing logic from GLFW)
void ImGui_ImplWin32_EnableAlphaCompositing(void* hwnd)
{
    if (!IsWindowsVistaOrGreater())
        return;

    BOOL composition;
    if (FAILED(::DwmIsCompositionEnabled(&composition)) || !composition)
        return;

    BOOL opaque;
    DWORD color;
    if (IsWindows8OrGreater() || (SUCCEEDED(::DwmGetColorizationColor(&color, &opaque)) && !opaque))
    {
        HRGN region = ::CreateRectRgn(0, 0, -1, -1);
        DWM_BLURBEHIND bb = {};
        bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
        bb.hRgnBlur = region;
        bb.fEnable = TRUE;
        ::DwmEnableBlurBehindWindow((HWND)hwnd, &bb);
        ::DeleteObject(region);
    }
    else
    {
        DWM_BLURBEHIND bb = {};
        bb.dwFlags = DWM_BB_ENABLE;
        ::DwmEnableBlurBehindWindow((HWND)hwnd, &bb);
    }
}

//---------------------------------------------------------------------------------------------------------