src/video/windows/SDL_windowswindow.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "../../SDL_internal.h"

#if SDL_VIDEO_DRIVER_WINDOWS

#include "../../core/windows/SDL_windows.h"

#include "SDL_assert.h"
#include "../SDL_sysvideo.h"
#include "../SDL_pixels_c.h"
#include "../../events/SDL_keyboard_c.h"
#include "../../events/SDL_mouse_c.h"

#include "SDL_windowsvideo.h"
#include "SDL_windowswindow.h"
#include "SDL_hints.h"

/* Dropfile support */
#include <shellapi.h>

/* This is included after SDL_windowsvideo.h, which includes windows.h */
#include "SDL_syswm.h"

/* Windows CE compatibility */
#ifndef SWP_NOCOPYBITS
#define SWP_NOCOPYBITS 0
#endif

/* Fake window to help with DirectInput events. */
HWND SDL_HelperWindow = NULL;
static WCHAR *SDL_HelperWindowClassName = TEXT("SDLHelperWindowInputCatcher");
static WCHAR *SDL_HelperWindowName = TEXT("SDLHelperWindowInputMsgWindow");
static ATOM SDL_HelperWindowClass = 0;

#define STYLE_BASIC         (WS_CLIPSIBLINGS | WS_CLIPCHILDREN)
#define STYLE_FULLSCREEN    (WS_POPUP)
#define STYLE_BORDERLESS    (WS_POPUP)
#define STYLE_NORMAL        (WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX)
#define STYLE_RESIZABLE     (WS_THICKFRAME | WS_MAXIMIZEBOX)
#define STYLE_MASK          (STYLE_FULLSCREEN | STYLE_BORDERLESS | STYLE_NORMAL | STYLE_RESIZABLE)

static DWORD
GetWindowStyle(SDL_Window * window)
{
    DWORD style = 0;

    if (window->flags & SDL_WINDOW_FULLSCREEN) {
        style |= STYLE_FULLSCREEN;
    } else {
        if (window->flags & SDL_WINDOW_BORDERLESS) {
            style |= STYLE_BORDERLESS;
        } else {
            style |= STYLE_NORMAL;
        }
        if (window->flags & SDL_WINDOW_RESIZABLE) {
            style |= STYLE_RESIZABLE;
        }
    }
    return style;
}

static void
WIN_SetWindowPositionInternal(_THIS, SDL_Window * window, UINT flags)
{
    SDL_WindowData *data = (SDL_WindowData *)window->driverdata;
    HWND hwnd = data->hwnd;
    RECT rect;
    DWORD style;
    HWND top;
    BOOL menu;
    int x, y;
    int w, h;

    /* Figure out what the window area will be */
    if (SDL_ShouldAllowTopmost() && (window->flags & (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) == (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) {
        top = HWND_TOPMOST;
    } else {
        top = HWND_NOTOPMOST;
    }
    style = GetWindowLong(hwnd, GWL_STYLE);
    rect.left = 0;
    rect.top = 0;
    rect.right = window->w;
    rect.bottom = window->h;
    menu = (style & WS_CHILDWINDOW) ? FALSE : (GetMenu(hwnd) != NULL);
    AdjustWindowRectEx(&rect, style, menu, 0);
    w = (rect.right - rect.left);
    h = (rect.bottom - rect.top);
    x = window->x + rect.left;
    y = window->y + rect.top;

    data->expected_resize = SDL_TRUE;
    SetWindowPos(hwnd, top, x, y, w, h, flags);
    data->expected_resize = SDL_FALSE;
}

static int
SetupWindowData(_THIS, SDL_Window * window, HWND hwnd, SDL_bool created)
{
    SDL_VideoData *videodata = (SDL_VideoData *) _this->driverdata;
    SDL_WindowData *data;

    /* Allocate the window data */
    data = (SDL_WindowData *) SDL_calloc(1, sizeof(*data));
    if (!data) {
        return SDL_OutOfMemory();
    }
    data->window = window;
    data->hwnd = hwnd;
    data->hdc = GetDC(hwnd);
    data->created = created;
    data->mouse_button_flags = 0;
    data->videodata = videodata;
    data->initializing = SDL_TRUE;

    window->driverdata = data;

    /* Associate the data with the window */
    if (!SetProp(hwnd, TEXT("SDL_WindowData"), data)) {
        ReleaseDC(hwnd, data->hdc);
        SDL_free(data);
        return WIN_SetError("SetProp() failed");
    }

    /* Set up the window proc function */
#ifdef GWLP_WNDPROC
    data->wndproc = (WNDPROC) GetWindowLongPtr(hwnd, GWLP_WNDPROC);
    if (data->wndproc == WIN_WindowProc) {
        data->wndproc = NULL;
    } else {
        SetWindowLongPtr(hwnd, GWLP_WNDPROC, (LONG_PTR) WIN_WindowProc);
    }
#else
    data->wndproc = (WNDPROC) GetWindowLong(hwnd, GWL_WNDPROC);
    if (data->wndproc == WIN_WindowProc) {
        data->wndproc = NULL;
    } else {
        SetWindowLong(hwnd, GWL_WNDPROC, (LONG_PTR) WIN_WindowProc);
    }
#endif

    /* Fill in the SDL window with the window data */
    {
        RECT rect;
        if (GetClientRect(hwnd, &rect)) {
            int w = rect.right;
            int h = rect.bottom;
            if ((window->w && window->w != w) || (window->h && window->h != h)) {
                /* We tried to create a window larger than the desktop and Windows didn't allow it.  Override! */
                RECT rect;
                DWORD style;
                BOOL menu;
                int x, y;
                int w, h;

                /* Figure out what the window area will be */
                style = GetWindowLong(hwnd, GWL_STYLE);
                rect.left = 0;
                rect.top = 0;
                rect.right = window->w;
                rect.bottom = window->h;
                menu = (style & WS_CHILDWINDOW) ? FALSE : (GetMenu(hwnd) != NULL);
                AdjustWindowRectEx(&rect, style, menu, 0);
                w = (rect.right - rect.left);
                h = (rect.bottom - rect.top);
                x = window->x + rect.left;
                y = window->y + rect.top;

                SetWindowPos(hwnd, HWND_NOTOPMOST, x, y, w, h, SWP_NOCOPYBITS | SWP_NOZORDER | SWP_NOACTIVATE);
            } else {
                window->w = w;
                window->h = h;
            }
        }
    }
    {
        POINT point;
        point.x = 0;
        point.y = 0;
        if (ClientToScreen(hwnd, &point)) {
            window->x = point.x;
            window->y = point.y;
        }
    }
    {
        DWORD style = GetWindowLong(hwnd, GWL_STYLE);
        if (style & WS_VISIBLE) {
            window->flags |= SDL_WINDOW_SHOWN;
        } else {
            window->flags &= ~SDL_WINDOW_SHOWN;
        }
        if (style & (WS_BORDER | WS_THICKFRAME)) {
            window->flags &= ~SDL_WINDOW_BORDERLESS;
        } else {
            window->flags |= SDL_WINDOW_BORDERLESS;
        }
        if (style & WS_THICKFRAME) {
            window->flags |= SDL_WINDOW_RESIZABLE;
        } else {
            window->flags &= ~SDL_WINDOW_RESIZABLE;
        }
#ifdef WS_MAXIMIZE
        if (style & WS_MAXIMIZE) {
            window->flags |= SDL_WINDOW_MAXIMIZED;
        } else
#endif
        {
            window->flags &= ~SDL_WINDOW_MAXIMIZED;
        }
#ifdef WS_MINIMIZE
        if (style & WS_MINIMIZE) {
            window->flags |= SDL_WINDOW_MINIMIZED;
        } else
#endif
        {
            window->flags &= ~SDL_WINDOW_MINIMIZED;
        }
    }
    if (GetFocus() == hwnd) {
        window->flags |= SDL_WINDOW_INPUT_FOCUS;
        SDL_SetKeyboardFocus(data->window);

        if (window->flags & SDL_WINDOW_INPUT_GRABBED) {
            RECT rect;
            GetClientRect(hwnd, &rect);
            ClientToScreen(hwnd, (LPPOINT) & rect);
            ClientToScreen(hwnd, (LPPOINT) & rect + 1);
            ClipCursor(&rect);
        }
    }

    /* Enable multi-touch */
    if (videodata->RegisterTouchWindow) {
        videodata->RegisterTouchWindow(hwnd, (TWF_FINETOUCH|TWF_WANTPALM));
    }

    /* Enable dropping files */
    DragAcceptFiles(hwnd, TRUE);

    data->initializing = SDL_FALSE;

    /* All done! */
    return 0;
}

int
WIN_CreateWindow(_THIS, SDL_Window * window)
{
    HWND hwnd;
    RECT rect;
    DWORD style = STYLE_BASIC;
    int x, y;
    int w, h;

    style |= GetWindowStyle(window);

    /* Figure out what the window area will be */
    rect.left = window->x;
    rect.top = window->y;
    rect.right = window->x + window->w;
    rect.bottom = window->y + window->h;
    AdjustWindowRectEx(&rect, style, FALSE, 0);
    x = rect.left;
    y = rect.top;
    w = (rect.right - rect.left);
    h = (rect.bottom - rect.top);

    hwnd =
        CreateWindow(SDL_Appname, TEXT(""), style, x, y, w, h, NULL, NULL,
                     SDL_Instance, NULL);
    if (!hwnd) {
        return WIN_SetError("Couldn't create window");
    }

    WIN_PumpEvents(_this);

    if (SetupWindowData(_this, window, hwnd, SDL_TRUE) < 0) {
        DestroyWindow(hwnd);
        return -1;
    }

#if SDL_VIDEO_OPENGL_WGL
    /* We need to initialize the extensions before deciding how to create ES profiles */
    if (window->flags & SDL_WINDOW_OPENGL) {
        WIN_GL_InitExtensions(_this);
    }
#endif

#if SDL_VIDEO_OPENGL_ES2
    if ((window->flags & SDL_WINDOW_OPENGL) &&
        _this->gl_config.profile_mask == SDL_GL_CONTEXT_PROFILE_ES
#if SDL_VIDEO_OPENGL_WGL           
        && (!_this->gl_data || !_this->gl_data->HAS_WGL_EXT_create_context_es2_profile)
#endif  
        ) {
#if SDL_VIDEO_OPENGL_EGL  
        if (WIN_GLES_SetupWindow(_this, window) < 0) {
            WIN_DestroyWindow(_this, window);
            return -1;
        }
#else
        return SDL_SetError("Could not create GLES window surface (no EGL support available)");
#endif /* SDL_VIDEO_OPENGL_EGL */
    } else 
#endif /* SDL_VIDEO_OPENGL_ES2 */

#if SDL_VIDEO_OPENGL_WGL
    if (window->flags & SDL_WINDOW_OPENGL) {
        if (WIN_GL_SetupWindow(_this, window) < 0) {
            WIN_DestroyWindow(_this, window);
            return -1;
        }
    }
#endif

    return 0;
}

int
WIN_CreateWindowFrom(_THIS, SDL_Window * window, const void *data)
{
    HWND hwnd = (HWND) data;
    LPTSTR title;
    int titleLen;

    /* Query the title from the existing window */
    titleLen = GetWindowTextLength(hwnd);
    title = SDL_stack_alloc(TCHAR, titleLen + 1);
    if (title) {
        titleLen = GetWindowText(hwnd, title, titleLen);
    } else {
        titleLen = 0;
    }
    if (titleLen > 0) {
        window->title = WIN_StringToUTF8(title);
    }
    if (title) {
        SDL_stack_free(title);
    }

    if (SetupWindowData(_this, window, hwnd, SDL_FALSE) < 0) {
        return -1;
    }

#if SDL_VIDEO_OPENGL_WGL
    {
        const char *hint = SDL_GetHint(SDL_HINT_VIDEO_WINDOW_SHARE_PIXEL_FORMAT);
        if (hint) {
            /* This hint is a pointer (in string form) of the address of
               the window to share a pixel format with
            */
            SDL_Window *otherWindow = NULL;
            SDL_sscanf(hint, "%p", (void**)&otherWindow);

            /* Do some error checking on the pointer */
            if (otherWindow != NULL && otherWindow->magic == &_this->window_magic)
            {
                /* If the otherWindow has SDL_WINDOW_OPENGL set, set it for the new window as well */
                if (otherWindow->flags & SDL_WINDOW_OPENGL)
                {
                    window->flags |= SDL_WINDOW_OPENGL;
                    if(!WIN_GL_SetPixelFormatFrom(_this, otherWindow, window)) {
                        return -1;
                    }
                }
            }
        }
    }
#endif
    return 0;
}

void
WIN_SetWindowTitle(_THIS, SDL_Window * window)
{
    HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
    LPTSTR title = WIN_UTF8ToString(window->title);
    SetWindowText(hwnd, title);
    SDL_free(title);
}

void
WIN_SetWindowIcon(_THIS, SDL_Window * window, SDL_Surface * icon)
{
    HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
    HICON hicon = NULL;
    BYTE *icon_bmp;
    int icon_len, y;
    SDL_RWops *dst;

    /* Create temporary bitmap buffer */
    icon_len = 40 + icon->h * icon->w * 4;
    icon_bmp = SDL_stack_alloc(BYTE, icon_len);
    dst = SDL_RWFromMem(icon_bmp, icon_len);
    if (!dst) {
        SDL_stack_free(icon_bmp);
        return;
    }

    /* Write the BITMAPINFO header */
    SDL_WriteLE32(dst, 40);
    SDL_WriteLE32(dst, icon->w);
    SDL_WriteLE32(dst, icon->h * 2);
    SDL_WriteLE16(dst, 1);
    SDL_WriteLE16(dst, 32);
    SDL_WriteLE32(dst, BI_RGB);
    SDL_WriteLE32(dst, icon->h * icon->w * 4);
    SDL_WriteLE32(dst, 0);
    SDL_WriteLE32(dst, 0);
    SDL_WriteLE32(dst, 0);
    SDL_WriteLE32(dst, 0);

    /* Write the pixels upside down into the bitmap buffer */
    SDL_assert(icon->format->format == SDL_PIXELFORMAT_ARGB8888);
    y = icon->h;
    while (y--) {
        Uint8 *src = (Uint8 *) icon->pixels + y * icon->pitch;
        SDL_RWwrite(dst, src, icon->pitch, 1);
    }

    hicon = CreateIconFromResource(icon_bmp, icon_len, TRUE, 0x00030000);

    SDL_RWclose(dst);
    SDL_stack_free(icon_bmp);

    /* Set the icon for the window */
    SendMessage(hwnd, WM_SETICON, ICON_SMALL, (LPARAM) hicon);

    /* Set the icon in the task manager (should we do this?) */
    SendMessage(hwnd, WM_SETICON, ICON_BIG, (LPARAM) hicon);
}

void
WIN_SetWindowPosition(_THIS, SDL_Window * window)
{
    WIN_SetWindowPositionInternal(_this, window, SWP_NOCOPYBITS | SWP_NOSIZE | SWP_NOACTIVATE);
}

void
WIN_SetWindowSize(_THIS, SDL_Window * window)
{
    WIN_SetWindowPositionInternal(_this, window, SWP_NOCOPYBITS | SWP_NOMOVE | SWP_NOACTIVATE);
}

void
WIN_ShowWindow(_THIS, SDL_Window * window)
{
    HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
    ShowWindow(hwnd, SW_SHOW);
}

void
WIN_HideWindow(_THIS, SDL_Window * window)
{
    HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
    ShowWindow(hwnd, SW_HIDE);
}

void
WIN_RaiseWindow(_THIS, SDL_Window * window)
{
    WIN_SetWindowPositionInternal(_this, window, SWP_NOCOPYBITS | SWP_NOMOVE | SWP_NOSIZE);
}

void
WIN_MaximizeWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *)window->driverdata;
    HWND hwnd = data->hwnd;
    data->expected_resize = SDL_TRUE;
    ShowWindow(hwnd, SW_MAXIMIZE);
    data->expected_resize = SDL_FALSE;
}

void
WIN_MinimizeWindow(_THIS, SDL_Window * window)
{
    HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
    ShowWindow(hwnd, SW_MINIMIZE);
}

void
WIN_SetWindowBordered(_THIS, SDL_Window * window, SDL_bool bordered)
{
    SDL_WindowData *data = (SDL_WindowData *)window->driverdata;
    HWND hwnd = data->hwnd;
    DWORD style = GetWindowLong(hwnd, GWL_STYLE);

    if (bordered) {
        style &= ~STYLE_BORDERLESS;
        style |= STYLE_NORMAL;
    } else {
        style &= ~STYLE_NORMAL;
        style |= STYLE_BORDERLESS;
    }

    data->in_border_change = SDL_TRUE;
    SetWindowLong(hwnd, GWL_STYLE, style);
    WIN_SetWindowPositionInternal(_this, window, SWP_NOCOPYBITS | SWP_FRAMECHANGED | SWP_NOZORDER | SWP_NOACTIVATE);
    data->in_border_change = SDL_FALSE;
}

void
WIN_RestoreWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *)window->driverdata;
    HWND hwnd = data->hwnd;
    data->expected_resize = SDL_TRUE;
    ShowWindow(hwnd, SW_RESTORE);
    data->expected_resize = SDL_FALSE;
}

void
WIN_SetWindowFullscreen(_THIS, SDL_Window * window, SDL_VideoDisplay * display, SDL_bool fullscreen)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    HWND hwnd = data->hwnd;
    RECT rect;
    SDL_Rect bounds;
    DWORD style;
    HWND top;
    BOOL menu;
    int x, y;
    int w, h;

    if (SDL_ShouldAllowTopmost() && (window->flags & (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) == (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) {
        top = HWND_TOPMOST;
    } else {
        top = HWND_NOTOPMOST;
    }

    style = GetWindowLong(hwnd, GWL_STYLE);
    style &= ~STYLE_MASK;
    style |= GetWindowStyle(window);

    WIN_GetDisplayBounds(_this, display, &bounds);

    if (fullscreen) {
        x = bounds.x;
        y = bounds.y;
        w = bounds.w;
        h = bounds.h;

        /* Unset the maximized flag.  This fixes
           https://bugzilla.libsdl.org/show_bug.cgi?id=3215
        */
        if (style & WS_MAXIMIZE) {
            data->windowed_mode_was_maximized = SDL_TRUE;
            style &= ~WS_MAXIMIZE;
        }
    } else {
        /* Restore window-maximization state, as applicable.
           Special care is taken to *not* do this if and when we're
           alt-tab'ing away (to some other window; as indicated by
           in_window_deactivation), otherwise
           https://bugzilla.libsdl.org/show_bug.cgi?id=3215 can reproduce!
        */
        if (data->windowed_mode_was_maximized && !data->in_window_deactivation) {
            style |= WS_MAXIMIZE;
            data->windowed_mode_was_maximized = SDL_FALSE;
        }
        rect.left = 0;
        rect.top = 0;
        rect.right = window->windowed.w;
        rect.bottom = window->windowed.h;
        menu = (style & WS_CHILDWINDOW) ? FALSE : (GetMenu(hwnd) != NULL);
        AdjustWindowRectEx(&rect, style, menu, 0);
        w = (rect.right - rect.left);
        h = (rect.bottom - rect.top);
        x = window->windowed.x + rect.left;
        y = window->windowed.y + rect.top;
    }
    SetWindowLong(hwnd, GWL_STYLE, style);
    data->expected_resize = SDL_TRUE;
    SetWindowPos(hwnd, top, x, y, w, h, SWP_NOCOPYBITS | SWP_NOACTIVATE);
    data->expected_resize = SDL_FALSE;
}

int
WIN_SetWindowGammaRamp(_THIS, SDL_Window * window, const Uint16 * ramp)
{
    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
    SDL_DisplayData *data = (SDL_DisplayData *) display->driverdata;
    HDC hdc;
    BOOL succeeded = FALSE;

    hdc = CreateDC(data->DeviceName, NULL, NULL, NULL);
    if (hdc) {
        succeeded = SetDeviceGammaRamp(hdc, (LPVOID)ramp);
        if (!succeeded) {
            WIN_SetError("SetDeviceGammaRamp()");
        }
        DeleteDC(hdc);
    }
    return succeeded ? 0 : -1;
}

int
WIN_GetWindowGammaRamp(_THIS, SDL_Window * window, Uint16 * ramp)
{
    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
    SDL_DisplayData *data = (SDL_DisplayData *) display->driverdata;
    HDC hdc;
    BOOL succeeded = FALSE;

    hdc = CreateDC(data->DeviceName, NULL, NULL, NULL);
    if (hdc) {
        succeeded = GetDeviceGammaRamp(hdc, (LPVOID)ramp);
        if (!succeeded) {
            WIN_SetError("GetDeviceGammaRamp()");
        }
        DeleteDC(hdc);
    }
    return succeeded ? 0 : -1;
}

void
WIN_SetWindowGrab(_THIS, SDL_Window * window, SDL_bool grabbed)
{
    WIN_UpdateClipCursor(window);

    if (window->flags & SDL_WINDOW_FULLSCREEN) {
        UINT flags = SWP_NOCOPYBITS | SWP_NOMOVE | SWP_NOSIZE;

        if (!(window->flags & SDL_WINDOW_SHOWN)) {
            flags |= SWP_NOACTIVATE;
        }
        WIN_SetWindowPositionInternal(_this, window, flags);
    }
}

void
WIN_DestroyWindow(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;

    if (data) {
        ReleaseDC(data->hwnd, data->hdc);
        RemoveProp(data->hwnd, TEXT("SDL_WindowData"));
        if (data->created) {
            DestroyWindow(data->hwnd);
        } else {
            /* Restore any original event handler... */
            if (data->wndproc != NULL) {
#ifdef GWLP_WNDPROC
                SetWindowLongPtr(data->hwnd, GWLP_WNDPROC,
                                 (LONG_PTR) data->wndproc);
#else
                SetWindowLong(data->hwnd, GWL_WNDPROC,
                              (LONG_PTR) data->wndproc);
#endif
            }
        }
        SDL_free(data);
    }
    window->driverdata = NULL;
}

SDL_bool
WIN_GetWindowWMInfo(_THIS, SDL_Window * window, SDL_SysWMinfo * info)
{
    const SDL_WindowData *data = (const SDL_WindowData *) window->driverdata;
    if (info->version.major <= SDL_MAJOR_VERSION) {
        info->subsystem = SDL_SYSWM_WINDOWS;
        info->info.win.window = data->hwnd;
        info->info.win.hdc = data->hdc;
        return SDL_TRUE;
    } else {
        SDL_SetError("Application not compiled with SDL %d.%d\n",
                     SDL_MAJOR_VERSION, SDL_MINOR_VERSION);
        return SDL_FALSE;
    }
}


/*
 * Creates a HelperWindow used for DirectInput events.
 */
int
SDL_HelperWindowCreate(void)
{
    HINSTANCE hInstance = GetModuleHandle(NULL);
    WNDCLASS wce;

    /* Make sure window isn't created twice. */
    if (SDL_HelperWindow != NULL) {
        return 0;
    }

    /* Create the class. */
    SDL_zero(wce);
    wce.lpfnWndProc = DefWindowProc;
    wce.lpszClassName = (LPCWSTR) SDL_HelperWindowClassName;
    wce.hInstance = hInstance;

    /* Register the class. */
    SDL_HelperWindowClass = RegisterClass(&wce);
    if (SDL_HelperWindowClass == 0 && GetLastError() != ERROR_CLASS_ALREADY_EXISTS) {
        return WIN_SetError("Unable to create Helper Window Class");
    }

    /* Create the window. */
    SDL_HelperWindow = CreateWindowEx(0, SDL_HelperWindowClassName,
                                      SDL_HelperWindowName,
                                      WS_OVERLAPPED, CW_USEDEFAULT,
                                      CW_USEDEFAULT, CW_USEDEFAULT,
                                      CW_USEDEFAULT, HWND_MESSAGE, NULL,
                                      hInstance, NULL);
    if (SDL_HelperWindow == NULL) {
        UnregisterClass(SDL_HelperWindowClassName, hInstance);
        return WIN_SetError("Unable to create Helper Window");
    }

    return 0;
}


/*
 * Destroys the HelperWindow previously created with SDL_HelperWindowCreate.
 */
void
SDL_HelperWindowDestroy(void)
{
    HINSTANCE hInstance = GetModuleHandle(NULL);

    /* Destroy the window. */
    if (SDL_HelperWindow != NULL) {
        if (DestroyWindow(SDL_HelperWindow) == 0) {
            WIN_SetError("Unable to destroy Helper Window");
            return;
        }
        SDL_HelperWindow = NULL;
    }

    /* Unregister the class. */
    if (SDL_HelperWindowClass != 0) {
        if ((UnregisterClass(SDL_HelperWindowClassName, hInstance)) == 0) {
            WIN_SetError("Unable to destroy Helper Window Class");
            return;
        }
        SDL_HelperWindowClass = 0;
    }
}

void WIN_OnWindowEnter(_THIS, SDL_Window * window)
{
#ifdef WM_MOUSELEAVE
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    TRACKMOUSEEVENT trackMouseEvent;

    if (!data || !data->hwnd) {
        /* The window wasn't fully initialized */
        return;
    }

    trackMouseEvent.cbSize = sizeof(TRACKMOUSEEVENT);
    trackMouseEvent.dwFlags = TME_LEAVE;
    trackMouseEvent.hwndTrack = data->hwnd;

    TrackMouseEvent(&trackMouseEvent);
#endif /* WM_MOUSELEAVE */
}

void
WIN_UpdateClipCursor(SDL_Window *window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    SDL_Mouse *mouse = SDL_GetMouse();

    if (data->focus_click_pending) {
        return;
    }

    if ((mouse->relative_mode || (window->flags & SDL_WINDOW_INPUT_GRABBED)) &&
        (window->flags & SDL_WINDOW_INPUT_FOCUS)) {
        if (mouse->relative_mode && !mouse->relative_mode_warp) {
            LONG cx, cy;
            RECT rect;
            GetWindowRect(data->hwnd, &rect);

            cx = (rect.left + rect.right) / 2;
            cy = (rect.top + rect.bottom) / 2;

            /* Make an absurdly small clip rect */
            rect.left = cx - 1;
            rect.right = cx + 1;
            rect.top = cy - 1;
            rect.bottom = cy + 1;

            ClipCursor(&rect);
        } else {
            RECT rect;
            if (GetClientRect(data->hwnd, &rect) && !IsRectEmpty(&rect)) {
                ClientToScreen(data->hwnd, (LPPOINT) & rect);
                ClientToScreen(data->hwnd, (LPPOINT) & rect + 1);
                ClipCursor(&rect);
            }
        }
    } else {
        ClipCursor(NULL);
    }
}

int
WIN_SetWindowHitTest(SDL_Window *window, SDL_bool enabled)
{
    return 0;  /* just succeed, the real work is done elsewhere. */
}

int
WIN_SetWindowOpacity(_THIS, SDL_Window * window, float opacity)
{
    const SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    const HWND hwnd = data->hwnd;
    const LONG style = GetWindowLong(hwnd, GWL_EXSTYLE);

    SDL_assert(style != 0);

    if (opacity == 1.0f) {
        /* want it fully opaque, just mark it unlayered if necessary. */
        if (style & WS_EX_LAYERED) {
            if (SetWindowLong(hwnd, GWL_EXSTYLE, style & ~WS_EX_LAYERED) == 0) {
                return WIN_SetError("SetWindowLong()");
            }
        }
    } else {
        const BYTE alpha = (BYTE) ((int) (opacity * 255.0f));
        /* want it transparent, mark it layered if necessary. */
        if ((style & WS_EX_LAYERED) == 0) {
            if (SetWindowLong(hwnd, GWL_EXSTYLE, style | WS_EX_LAYERED) == 0) {
                return WIN_SetError("SetWindowLong()");
            }
        }

        if (SetLayeredWindowAttributes(hwnd, 0, alpha, LWA_ALPHA) == 0) {
            return WIN_SetError("SetLayeredWindowAttributes()");
        }
    }

    return 0;
}

#endif /* SDL_VIDEO_DRIVER_WINDOWS */

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