纯win32实现PNG图片透明窗体

#include <windows.h>
#include <gdiplus.h>

/*  GDI+ startup token */
ULONG_PTR gdiplusStartupToken;

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

// UpdateLayeredWindow Defination
typedef BOOL(*UPDATELAYEREDWINDOWFUNCTION)(HWND,HDC,POINT*,SIZE*,HDC,POINT*,COLORREF,BLENDFUNCTION*,DWORD);

/*  Make the class name into a global variable  */
char szClassName[ ] = "PNGDialog";

int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{

    /**/
    Gdiplus::GdiplusStartupInput gdiInput;
    Gdiplus::GdiplusStartup(&gdiplusStartupToken,&gdiInput,NULL);
    /**/
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;//+-69+
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (
           WS_EX_LAYERED|WS_EX_TOPMOST|WS_EX_TOOLWINDOW,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           "PNGDialog Example Application",       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           500,                 /* The programs width */
           500,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    /* Make the window visible on the screen */
    ShowWindow (hwnd, nCmdShow);
    LONG style = ::GetWindowLong(hwnd,GWL_STYLE);
    if(style&WS_CAPTION)
        style^=WS_CAPTION;
    if(style&WS_THICKFRAME)
        style^=WS_THICKFRAME;
    if(style&WS_SYSMENU)
        style^=WS_SYSMENU;
    ::SetWindowLong(hwnd,GWL_STYLE,style);

    style = ::GetWindowLong(hwnd,GWL_EXSTYLE);
    if(style&WS_EX_APPWINDOW)
        style^=WS_EX_APPWINDOW;
    ::SetWindowLong(hwnd,GWL_EXSTYLE,style);

    /********************************************
    *   step 1.
    *   Using Gdiplus to load the image
    ********************************************/
    RECT wndRect;
    ::GetWindowRect(hwnd,&wndRect);
    SIZE wndSize = {wndRect.right-wndRect.left,wndRect.bottom-wndRect.top};
    HDC hdc = ::GetDC(hwnd);
    HDC memDC = ::CreateCompatibleDC(hdc);
    HBITMAP memBitmap = ::CreateCompatibleBitmap(hdc,wndSize.cx,wndSize.cy);
    ::SelectObject(memDC,memBitmap);

    Gdiplus::Image image(L"pic.png");
    Gdiplus::Graphics graphics(memDC);
    graphics.DrawImage(&image,0,0,wndSize.cx,wndSize.cy);
    /********************************************
    *   step 2.
    *   Get "UpdateLayeredWindow" function's
    *   proc address.
    ********************************************/
    HMODULE hUser32 = ::LoadLibrary("User32.dll");
    if(!hUser32)
    {
        return FALSE;
    }
    UPDATELAYEREDWINDOWFUNCTION UpdateLayeredWindow = (UPDATELAYEREDWINDOWFUNCTION)::GetProcAddress(hUser32,"UpdateLayeredWindow");
    if(!UpdateLayeredWindow)
    {
        return FALSE;
    }
    // get screen dc
    HDC screenDC = GetDC(NULL);
    POINT ptSrc = {0,0};

    /*********************************************
    *   step 3.
    *   Use UpdateLayeredWindow to Draw the Window
    *
    *********************************************/
    BLENDFUNCTION blendFunction;
    blendFunction.AlphaFormat = AC_SRC_ALPHA;
    blendFunction.BlendFlags = 0;
    blendFunction.BlendOp = AC_SRC_OVER;
    blendFunction.SourceConstantAlpha = 255;
    UpdateLayeredWindow(hwnd,screenDC,&ptSrc,&wndSize,memDC,&ptSrc,0,&blendFunction,2);

    ::DeleteDC(memDC);
    ::DeleteObject(memBitmap);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }
    Gdiplus::GdiplusShutdown(gdiplusStartupToken);
    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}


/*  This function is called by the Windows function DispatchMessage()  */

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY:
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;
        case WM_LBUTTONDOWN:
            //::SendMessage(hwnd,WM_HIT)
            break;
        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }
    return 0;
}

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