透明窗口问题

如何让一个窗口实现淡入淡出效果或者半透明效果呢？
codeproject的这边文章挺不错的，转链在这里。

http://www.codeproject.com/w2k/QDWndTransparency.asp


/**************************************************************
* MakeWindowTrasparent(window, factor)
*
* A function that will try to make a window transparent
* (layered) under versions of Windows that support that kind
* of thing. Gracefully fails on versions of Windows that
* don't.
*
* Returns FALSE if the operation fails.
*/

typedef DWORD (WINAPI *PSLWA)(HWND, DWORD, BYTE, DWORD);

static PSLWA pSetLayeredWindowAttributes = NULL;
static BOOL initialized = FALSE;

BOOL MakeWindowTransparent(HWND hWnd, unsigned char factor)
{
/* First, see if we can get the API call we need. If we've tried
* once, we don't need to try again. */
if (!initialized)
{
HMODULE hDLL = LoadLibrary ("user32");

pSetLayeredWindowAttributes =
(PSLWA) GetProcAddress(hDLL, "SetLayeredWindowAttributes");

initialized = TRUE;
}

if (pSetLayeredWindowAttributes == NULL)
return FALSE;

/* Windows need to be layered to be made transparent. This is done
* by modifying the extended style bits to contain WS_EX_LAYARED. */
SetLastError(0);

SetWindowLong(hWnd,
GWL_EXSTYLE ,
GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);

if (GetLastError())
return FALSE;

/* Now, we need to set the 'layered window attributes'. This
* is where the alpha values get set. */
return pSetLayeredWindowAttributes (hWnd,
RGB(255,255,255),
factor,
LWA_COLORKEY|LWA_ALPHA);
}