利用UpdateLayeredWindow函数制作透明窗口时BMP的Alpha通道的问题

void CDigitalClock::Update()
{
	// Create the alpha blending bitmap
	BITMAPINFO bmi;        // bitmap header
	ZeroMemory(&bmi, sizeof(BITMAPINFO));
	bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmi.bmiHeader.biWidth = m_Width;
	bmi.bmiHeader.biHeight = m_Height;
	bmi.bmiHeader.biPlanes = 1;
	bmi.bmiHeader.biBitCount = 32;   // four 8-bit components
	bmi.bmiHeader.biCompression = BI_RGB;
	bmi.bmiHeader.biSizeImage = m_Width * m_Height * 4;
	
	BYTE *pvBits;          // pointer to DIB section
	HBITMAP hbitmap = CreateDIBSection(NULL, &bmi, DIB_RGB_COLORS, 
		(void **)&pvBits, NULL, 0);
	ZeroMemory(pvBits, bmi.bmiHeader.biSizeImage);
	HDC hMemDC = CreateCompatibleDC(GetDC(m_hWnd));
	HBITMAP hOriBmp = (HBITMAP)SelectObject(hMemDC, hbitmap);
	
	HFONT *oldFont=NULL;
	static char str_time[10]={""};
	CTime t=CTime::GetCurrentTime();
	sprintf(str_time,"%02d:%02d.%02d",
	    t.GetHour(),t.GetMinute(),t.GetSecond());
	CRect rt;
	GetClientRect(m_hWnd, &rt);
	
	oldFont = (HFONT*)SelectObject(hMemDC,g_this->GetFont());
	SetBkColor(hMemDC,RGB(0,0,0));
	SetBkMode(hMemDC,TRANSPARENT);
	GetClientRect(m_hWnd, &rt);
	FillRect(hMemDC,&rt,CBrush(RGB(128,128,128)));
	SetTextColor(hMemDC,RGB(255,255,255));
	DrawText(hMemDC, str_time,strlen(str_time), &rt, 
		DT_CENTER|DT_VCENTER|DT_SINGLELINE);
	
	GetWindowRect(m_hWnd,rt);
	POINT ptDst = {rt.left,rt.top};
	POINT ptSrc = {0, 0};
	SIZE WndSize = {m_Width, m_Height};
	//ULW_COLORKEY  1  ULW_ALPHA     2 ULW_OPAQUE    4
	//AC_SRC_OVER   0  AC_SRC_ALPHA  1
	BLENDFUNCTION blendPixelFunction={AC_SRC_OVER, 0, 
	    m_iSourceConstantAlpha,AC_SRC_ALPHA };
		
	//在这里设置BMP的Alpha值
	//内存中的数据格式为 RR GG BB AL
	for(int m=3;m<m_Width * m_Height * 4;m+=4)
		*(pvBits+m)=(BYTE)m_iImageAlpha;
	
	HDC hdcScreen=::GetDC (m_hWnd);
	BOOL bRet =_UpdateLayeredWindow(m_hWnd, hdcScreen, &ptDst, &WndSize, 
		hMemDC,
		&ptSrc, RGB(0,0,0), &blendPixelFunction, 2);
	//_ASSERT(bRet); // something was wrong....
	// Delete used resources
	SelectObject(hMemDC,oldFont);
	SelectObject(hMemDC, hOriBmp);
	DeleteObject(hbitmap);
	DeleteDC(hMemDC);
}
下载源码