Can't create child windows

OnionKnight · 11-30-2006, 07:04 PM

I am trying to make one main window and inside that one I want to have one window that renders OpenGL stuff and another one that is an edit control. So I made this:

Code:

const char wndclass[] = "OpenGL Program";
const char oglclass[] = "OpenGL Renderer";
WNDPROC oldconproc;
HWND window;

int WINAPI WinMain (HINSTANCE inst, HINSTANCE pinst, char* args, int show)
{
	WNDCLASSEX wc;
	WNDCLASSEX oc;
	MSG msg;

	ZeroMemory(&wc, sizeof(wc));
	wc.cbSize        = sizeof(wc);
	wc.lpfnWndProc   = wndproc;
	wc.hInstance     = inst;
	wc.hbrBackground = COLOR_WINDOW;
	wc.lpszClassName = wndclass;

	ZeroMemory(&oc, sizeof(oc));
	oc.cbSize        = sizeof(oc);
	oc.style         = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
	oc.lpfnWndProc   = oglproc;
	oc.hInstance     = inst;
	oc.hbrBackground = COLOR_WINDOW;
	oc.lpszClassName = oglclass;

	if (!RegisterClassEx(&wc) || !RegisterClassEx(&oc)) {
		Error();
		return 1;
	}
	window = CreateWindowEx(WS_EX_CLIENTEDGE, wndclass, "OpenGL", WS_OVERLAPPEDWINDOW,
	                        CW_USEDEFAULT, CW_USEDEFAULT, 640, 480, NULL, NULL, inst, NULL);
	if (window == NULL) {
		Error();
		return 1;
	}
	ShowWindow(window, show);
	UpdateWindow(window);

	while (GetMessage(&msg, NULL, 0, 0) > 0) {
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	return msg.wParam;
}

This part of the code runs fine, but when it gets to WM_CREATE for the window I just made it throws me an error because it couldn't create neither of the two child windows with the error message "Cannot create a top-level child window.".

The wndproc function, cut off to show the important parts:

Code:

LRESULT CALLBACK wndproc (HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
	static HWND ogl;
	static HWND con;
	static int fonth;

	switch (msg) {
		case WM_CREATE:
		{
			HFONT font, oldfont;
			HDC condc;
			TEXTMETRIC tm;

			font = CreateFont(-MulDiv(12, GetDeviceCaps(GetDC(hwnd), LOGPIXELSY), 72), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, TEXT("MS Shell Dlg"));
			/*Here comes the trouble makers*/
			ogl = CreateWindowEx(0, oglclass, TEXT(""), WS_CHILD | WS_CLIPCHILDREN | WS_CLIPSIBLINGS, 0, 0, 0, 0, window, NULL, GetModuleHandle(NULL), NULL);
			con = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("EDIT"), TEXT(""), WS_CHILD | WS_VISIBLE | ES_AUTOHSCROLL, 0, 0, 0, 0, window, NULL, GetModuleHandle(NULL), NULL);
			if (font == NULL || ogl == NULL || con == NULL) { /*End of the line*/
				Error();
				PostQuitMessage(1);
				break;
			}
			oldconproc = SetWindowLongPtr(con, GWLP_WNDPROC, (LONG_PTR) conproc);
			SendMessage(con, WM_SETFONT, (WPARAM) font, MAKELPARAM(FALSE, 0));
			condc = GetDC(con);
			oldfont = SelectObject(condc, font);
			GetTextMetrics(condc, &tm);
			SelectObject(condc, oldfont);
			ReleaseDC(con, condc);
			fonth = tm.tmHeight;
			break;
		}

'ogl' is the child window that is to draw the OpenGL stuff and 'con', for console, is the edit control.
Looking up the error message doesn't help me solve my problem, "As part of its user interface, an application has tried to create a child window at an inappropriate level.", what are these "levels" to begin with?

**Ken Fitlike** · 11-30-2006, 08:05 PM

The variable window isn't a valid window handle until CreateWindowEx returns (recall that a WM_CREATE message is issued during system processing of that api function) so the child windows essentially have a NULL handle as a parent. A top-level window is a non-child window, like your main window.

Just use the HWND parameter passed to the window procedure in the WM_CREATE handler as the parent handle when creating the child windows .

OnionKnight · 11-30-2006, 08:11 PM

You're right, I had forgotten about that, even though I copypasted stuff from another program which used hwnd instead. :|
Now it works fine, except that the OpenGL window isn't showing anything. EDIT: Forgot WS_VISIBLE. Now everything's like it should.

11-30-2006, 08:05 PM	#2
Ken Fitlike erstwhile Join Date: Jan 2002 Posts: 2,223	The variable window isn't a valid window handle until CreateWindowEx returns (recall that a WM_CREATE message is issued during system processing of that api function) so the child windows essentially have a NULL handle as a parent. A top-level window is a non-child window, like your main window. Just use the HWND parameter passed to the window procedure in the WM_CREATE handler as the parent handle when creating the child windows . __________________ CProgramming FAQ Caution: this person may be a carrier of the misinformation virus.
Ken Fitlike is offline

11-30-2006, 08:11 PM	#3
OnionKnight Mad Join Date: Jan 2005 Location: Umeå, Sweden Posts: 555	You're right, I had forgotten about that, even though I copypasted stuff from another program which used hwnd instead. :\| Now it works fine, except that the OpenGL window isn't showing anything. EDIT: Forgot WS_VISIBLE. Now everything's like it should. Last edited by OnionKnight; 11-30-2006 at 08:15 PM.
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