Windows API:UpdateLayeredWindow返回值

Question

我的程序中有一个分层窗口,看起来(视觉上)工作正常,但返回代码UpdateLayeredWindow应该是成功时的非零值.在我的例子中,它是0,并GetLastError返回87,即不正确的参数.如果我的设置有任何问题,有人可以告诉我吗？这是完整的功能,窗口样式是WS_EX_LAYERED|WS_EX_TOPMOST和WS_POPUP.

bool SplashScreen(HWND hwnd, HINSTANCE m_hinstance)
{
    HBITMAP hBitmap = (HBITMAP)LoadImage(m_hinstance, "splash.bmp", IMAGE_BITMAP, 640, 640, LR_LOADFROMFILE);
    PAINTSTRUCT     ps;
    HDC             hdc;
    BITMAP          bitmap;
    HDC             hdcMem;
    HGDIOBJ         oldBitmap;
    int result=0;

    if(!SetLayeredWindowAttributes(hwnd, 0, (255 * 100) / 100, LWA_ALPHA))
    {
        char msg[255];
        sprintf(msg,"Error SetLayeredWindowAttributes: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    hdc = BeginPaint(hwnd, &ps);
    if(!hdc)
    {
        char msg[255];
        sprintf(msg,"Error BeginPaint: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    hdcMem = CreateCompatibleDC(hdc);
    if(!hdcMem)
    {
        char msg[255];
        sprintf(msg,"Error CreateCompatibleDC: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    oldBitmap = SelectObject(hdcMem, hBitmap);

    GetObject(hBitmap, sizeof(bitmap), &bitmap);
    result=BitBlt(hdc, 0, 0, 640, 640, hdcMem, 0, 0, SRCCOPY);
    if(result==0)
    {
        char msg[255];
        sprintf(msg,"Error BitBlt: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    BLENDFUNCTION blend = { 0 };
    blend.BlendOp = AC_SRC_OVER;
    blend.SourceConstantAlpha = 255;
    blend.AlphaFormat = AC_SRC_ALPHA;

    result=UpdateLayeredWindow(hwnd,GetDC(NULL),NULL,NULL,hdcMem,NULL, RGB(0,0,0),&blend, ULW_ALPHA);// Returns non-zero on success(!), in reality works when 0 is returned.
    if(result==0)
    {
        char msg[255];
        sprintf(msg,"Error UpdateLayeredWindow: %d",GetLastError());// Error UpdateLayeredWindow: 87
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    result=SetLayeredWindowAttributes(hwnd, RGB(255,255,255), 0, ULW_COLORKEY);
    if(result==0)
    {
        char msg[255];
        sprintf(msg,"Error SetLayeredWindowAttributes: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    result=EndPaint(hwnd, &ps);
    if(result==0)
    {
        char msg[255];
        sprintf(msg,"Error EndPaint: %d",GetLastError());
        MessageBox(hwnd,msg,"System",MB_OK);
        return false;
    }

    SelectObject(hdcMem, oldBitmap);
    DeleteDC(hdc);
    DeleteObject(hdcMem);
    return true;
}

Answer 1

你在SetLayeredWindowAttributes()和UpdateLayeredWindow()同一个HWND 打电话.这不起作用,文档非常明确:

http://msdn.microsoft.com/en-us/library/windows/desktop/ms633540(v=vs.85).aspx

请注意,一旦为分层窗口调用了SetLayeredWindowAttributes,后续UpdateLayeredWindow调用将失败,直到清除分层样式位并再次设置.

不要使用SetLayeredWindowAttributes()和UpdateLayeredWindow()在一起.它们是非常不同的方法.可以SetLayeredWindowAttributes()与传统WM_PAINT绘图一起使用,也可以UpdateLayeredWindow()与内存中的位图一起使用.不要同时使用两者.根据您展示的内容,您应该单独使用UpdateLayeredWindow().它将位图设置为窗口内容并同时设置窗口的透明度/ alpha.

并且不要Begin/EndPaint()在WM_PAINT处理程序之外使用.