Can I make a Win32 child window show under the parent window? - windows

Question

I want to add a child window to a parent window,make the content of child window is below the parent window(Z order).just like compose two layer,not replacement.Because I want some UI element in parent window can be seen within the child window's area,but not cover all of the child window.The child window should be a window,so I can't just using parent window's UI system to implement the child window's UI.
Is there any api to achieve this?
I found something like "UpdateLayeredWindow",But I failed to create a layer child window,CreateWindowEx return NULL and GetLastError return 0.This code was copy from Windows's example.and the demo project (DirectCompositionLayeredChildWindow) works well.
HRESULT hr = S_OK;
// Register the window class.
WNDCLASSEX wc = { 0 };
wc.cbSize = sizeof(wc);
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = WindowProc;
wc.hInstance = hInstance;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = static_cast<HBRUSH>(GetStockObject(BLACK_BRUSH));
wc.lpszClassName = L"DirectComposition Window Class";
RegisterClassEx(&wc);
// Creates the m_hMainWindow window.
HWND m_hMainWindow = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW| WS_EX_COMPOSITED, // Extended window style
wc.lpszClassName, // Name of window class
L"DirectComposition Layered Child Window Sample", // Title-bar string
WS_OVERLAPPED | WS_SYSMENU, // Top-level window
CW_USEDEFAULT, // Horizontal position
CW_USEDEFAULT, // Vertical position
1000, // Width
700, // Height
NULL, // Parent
NULL, // Class menu
GetModuleHandle(NULL), // Handle to application instance
NULL // Window-creation data
);
if (!m_hMainWindow)
{
hr = HRESULT_FROM_WIN32(GetLastError());
}
if (SUCCEEDED(hr))
{
ShowWindow(m_hMainWindow, SW_SHOWDEFAULT);
}
WNDCLASSEX wcex = { 0 };
wcex.cbSize = sizeof(wcex);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WindowProc;
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.lpszClassName = L"DirectCompositionChildWindow-Child";
RegisterClassEx(&wcex);
// !!! m_hControlChildWindow is always NULL
HWND m_hControlChildWindow = CreateWindowEx(WS_EX_LAYERED, // Extended window style
wcex.lpszClassName, // Name of window class
NULL, // Title-bar string
WS_CHILD, // Child window
30,30, 100, 100, // Window will be resized via MoveWindow
m_hMainWindow, // Parent
NULL, // Class menu
GetModuleHandle(NULL), // Handle to application instance
NULL); // Window-creation data
if (!m_hControlChildWindow)
{
hr = HRESULT_FROM_WIN32(GetLastError());
}
ShowWindow(m_hControlChildWindow, nCmdShow);
UpdateWindow(m_hControlChildWindow);

Answer 1

This cannot be done, as explained here:
No part of a child window ever appears outside the borders of its parent window.
Also:
A child window is grouped with its parent in z-order.
In other words: You cannot create a child window that's either outside the parent window's client area, or underneath the parent window in Z-order.