Fix offscreen rendering mode

--HG--
branch : develop

code/nel/src/3d/driver/opengl/driver_opengl_window.cpp

@@ -627,9 +627,11 @@ bool CDriverGL::setDisplay(nlWindow wnd, const GfxMode &mode, bool show, bool re
 	// Offscreen mode ?
 	if (_CurrentMode.OffScreen)
 	{
-#if 0
 		if (!createWindow(mode))
 			return false;
+		HWND tmpHWND = _win;
+		int width = mode.Width;
+		int height = mode.Height;
 
 		// resize the window
 		RECT rc;
@@ -908,7 +910,6 @@ bool CDriverGL::setDisplay(nlWindow wnd, const GfxMode &mode, bool show, bool re
 			_hDC = NULL;
 			return false;
 		}
-#endif
 	}
 	else
 	{
@@ -1437,8 +1438,17 @@ bool CDriverGL::createWindow(const GfxMode &mode)
 #ifdef NL_OS_WINDOWS
 
 	// create the OpenGL window
-	window = CreateWindowW(L"NLClass", L"NeL Window", WS_OVERLAPPEDWINDOW|WS_CLIPCHILDREN|WS_CLIPSIBLINGS,
-		CW_USEDEFAULT, CW_USEDEFAULT, mode.Width, mode.Height, HWND_DESKTOP, NULL, GetModuleHandle(NULL), NULL);
+	DWORD dwStyle = WS_OVERLAPPEDWINDOW|WS_CLIPCHILDREN|WS_CLIPSIBLINGS;
+	int pos = CW_USEDEFAULT;
+	HWND hwndParent = HWND_DESKTOP;
+	if (mode.OffScreen)
+	{
+		dwStyle &= ~WS_VISIBLE;
+		pos = 0;
+		hwndParent = NULL;
+	}
+	window = CreateWindowW(L"NLClass", L"NeL Window", dwStyle, 
+		pos, pos, mode.Width, mode.Height, hwndParent, NULL, GetModuleHandle(NULL), NULL);
 
 	if (window == EmptyWindow)
 	{