UpdateLayeredWindow方式实现异型窗口

使用该种方法要注意几个问题：

1. 窗口属性必须是Top Window，子窗口（Win8之前的操作系统）不支持实现异形窗口

2. Layer Window没有WM_PAINT消息，需要自己调用OnPaint

3. 窗口属性可设置为

WS_POPUP | WS_VISIBLE, WS_EX_TOOLWINDOW | WS_EX_LAYERED

实现代码：

CDC hdc = GetDC();  // Get the display device context (DC)
CDC hdcSrc = CreateCompatibleDC(hdc); // creates a memory device context (DC) compatible with the display device context

CRect rc;
GetClientRect(&rc);

// 创建DIB
BITMAPINFO    bmInfo;
ZeroMemory (&bmInfo, sizeof(bmInfo));
bmInfo.bmiHeader.biSize		= sizeof(BITMAPINFOHEADER);
bmInfo.bmiHeader.biWidth	= rc.Width();
bmInfo.bmiHeader.biHeight	= rc.Height();
bmInfo.bmiHeader.biPlanes	= 1;
bmInfo.bmiHeader.biBitCount = 32;

UINT* pBits = NULL;
CBitmap hBmp = CreateDIBSection (hdcSrc, (BITMAPINFO*)&bmInfo, DIB_RGB_COLORS, (void**)&pBits, NULL, 0);
HBITMAP hBmpOld = hdcSrc.SelectBitmap(hBmp);
RECT rcDraw = {0, 0, c_n_popwnd_width, c_n_popwnd_height};

BLENDFUNCTION blendFunction;
blendFunction.AlphaFormat = AC_SRC_ALPHA;
blendFunction.BlendFlags = 0;
blendFunction.BlendOp = AC_SRC_OVER;
blendFunction.SourceConstantAlpha = 255;
POINT pptDst = {m_ptWnd.x, m_ptWnd.y};
SIZE pDesSize = {c_n_popwnd_width, c_n_popwnd_height};
POINT ptSrc = { 0, 0 };
////////////////////////////////

m_bmpBkg.StretchBlt(hdcSrc, 0, 0, rc.Width(), rc.Height(), 0);  // 这里是要绘制的异形窗口背景
BOOL bRet = ::UpdateLayeredWindow(m_hWnd, NULL, &pptDst, &pDesSize, hdcSrc, &ptSrc, CLR_NONE, &blendFunction, ULW_ALPHA);
hdcSrc.SelectBitmap(hBmpOld);
ReleaseDC(hdc);