org.zkoss.ztl.jna.User32Extra.INSTANCE.GetClientRect(hWnd, bounds);
int width = bounds.right - bounds.left;
int height = bounds.bottom - bounds.top;
HBITMAP hBitmap = GDI32.INSTANCE.CreateCompatibleBitmap(hdcWindow, width, height);
HANDLE hOld = GDI32.INSTANCE.SelectObject(hdcMemDC, hBitmap);
GDI32Extra.INSTANCE.BitBlt(hdcMemDC, 0, 0, width, height, hdcWindow, 0, 0, WinGDIExtra.SRCCOPY);
GDI32.INSTANCE.SelectObject(hdcMemDC, hOld);