I changed the Window Class Style by removing the backdrop shadow of my child window by adding "CS_DROPSHADOW" style and calling SystemParametersInfoA method.
It worked. However the problem now is I don’t know how to set it back to default. The code implementation is as shown below:
child.style = CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS | CS_DROPSHADOW; child.lpfnWndProc = WndProcChild; child.cbClsExtra = 0; child.cbWndExtra = 0; child.hInstance = hInstance; child.hIcon = NULL; child.hCursor = LoadCursor(NULL, IDC_ARROW); child.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1); child.lpszMenuName = NULL; child.lpszClassName = _T("ChildWindow"); child.hIconSm = NULL; SystemParametersInfoA(SPI_SETDROPSHADOW, 0, (PVOID)FALSE, 0);
Source: Windows Questions C++