フローティング中のツールバーを斜めにサイズ変更できるようにする

ツールバーなどのコントロールバーはフローティング中、
通常縦横にしかサイズ変更ができません。
カーソルをあわせても斜めのカーソルがでません。
まずはそれを修正します。

コントロールバーがフローティングを実現する時には、
CMiniDockFrameWndというクラスのウィンドウの
子（孫）ウィンドウになっています。
このCMiniDockFrameWndがカーソルを制御しています。

下記のCMiniDockFrameWndの派生元クラス
CMiniFrameWndのOnNcHitTestの部分で
縦横にしかカーソルがでないようにしています。

	if (dwStyle & MFS_4THICKFRAME)
	{
		switch (nHit)
		{
		case HTTOPLEFT:
			return point.y < rectWindow.top ? HTTOP : HTLEFT;
		case HTTOPRIGHT:
			return point.y < rectWindow.top ? HTTOP : HTRIGHT;
		case HTBOTTOMLEFT:
			return point.y > rectWindow.bottom ? HTBOTTOM : HTLEFT;
		case HTGROWBOX:
		case HTBOTTOMRIGHT:
			return point.y > rectWindow.bottom ? HTBOTTOM : HTRIGHT;
		}
	}

ですので、CMiniDockFrameWndのウィンドウスタイルから
MFS_4THICKFRAMEを消してしまいましょう。
CControlBarから継承したクラスCMyControlBarに
以下の二つの関数を追加すればOKです。

CMiniDockFrameWnd* CMyControlBar::GetMiniDockFrameWnd()
{
	CWnd				*pWnd;


	if( m_hWnd )
	{
		if( pWnd = GetParent() )
		{
			if( pWnd = pWnd->GetParent() )
			{
				if( pWnd->IsKindOf( RUNTIME_CLASS( CMiniDockFrameWnd ) ) )
				{
					return (CMiniDockFrameWnd*)pWnd;
				}
			}
		}
	}

	return 0;
}

void CMyControlBar::OnSize(UINT nType, int cx, int cy) 
{
	CControlBar::OnSize(nType, cx, cy);

	if( GetMiniDockFrameWnd() )
	{
		GetMiniDockFrameWnd()->ModifyStyle( MFS_4THICKFRAME, 0 );
	}
}

これで斜めにもカーソルがでるようになります。
…が、まだサイズ変更はできません。
この原因を確かめるべく、
CMiniDockFrameWndのOnNcLButtonDownから追っていくと、

pBar->m_pDockContext->StartResize(nHitTest, point);
↓
Stretch(pt);

という関数のこの部分

	if (m_nHitTest == HTLEFT || m_nHitTest == HTRIGHT)
	{
		if (m_nHitTest == HTLEFT)
			m_rectRequestedSize.left += ptOffset.x;
		else
			m_rectRequestedSize.right += ptOffset.x;
		nLength = m_rectRequestedSize.Width();
	}
	else
	{
		dwMode |= LM_LENGTHY;
		if (m_nHitTest == HTTOP)
			m_rectRequestedSize.top += ptOffset.y;
		else
			m_rectRequestedSize.bottom += ptOffset.y;
		nLength = m_rectRequestedSize.Height();
	}

このように上下左右しか扱っていません。
なので、HitTestが斜めの時は斜めに操作できるように
処理を奪い取りましょう。

アプリケーションクラスに以下の処理を追加してください。
長いですが。

BOOL CMyApp::PreTranslateMessage(MSG* pMsg)
{
	CMiniDockFrameWnd	*pMiniWnd = 0;
	BOOL				bMiniWnd;
	CPoint				pos;


	switch( pMsg->message )
	{
	case WM_NCLBUTTONDOWN:
		pMiniWnd	= m_myBar.GetMiniDockFrameWnd();
		if( pMiniWnd && pMiniWnd->m_hWnd == pMsg->hwnd )
		{
			switch( pMsg->wParam )
			{
			case HTTOPLEFT:
			case HTTOPRIGHT:
			case HTBOTTOMLEFT:
			case HTBOTTOMRIGHT:
				pos.x	= (LONG)pMsg->lParam & 0xFFFF;
				pos.y	= (LONG)pMsg->lParam >> 16;
				StretchWnd( pMiniWnd, (int)pMsg->wParam, pos );
				return TRUE;
			}
		}
		break;
	}

	return CWinApp::PreTranslateMessage(pMsg);
}

#define m_rectRequestedSize     m_rectDragHorz
#define m_rectActualSize        m_rectDragVert
#define m_rectActualFrameSize   m_rectFrameDragHorz
#define m_rectFrameBorders      m_rectFrameDragVert
struct AUX_DATA
{
	// system metrics
	int cxVScroll, cyHScroll;
	int cxIcon, cyIcon;

	int cxBorder2, cyBorder2;

	// device metrics for screen
	int cxPixelsPerInch, cyPixelsPerInch;

	// convenient system color
	HBRUSH hbrWindowFrame;
	HBRUSH hbrBtnFace;

	// color values of system colors used for CToolBar
	COLORREF clrBtnFace, clrBtnShadow, clrBtnHilite;
	COLORREF clrBtnText, clrWindowFrame;

	// standard cursors
	HCURSOR hcurWait;
	HCURSOR hcurArrow;
	HCURSOR hcurHelp;       // cursor used in Shift+F1 help

	// special GDI objects allocated on demand
	HFONT   hStatusFont;
	HFONT   hToolTipsFont;
	HBITMAP hbmMenuDot;

	// other system information
	BOOL    bWin95;         // TRUE if Windows 95 (not NT)

// Implementation
	AUX_DATA();
	~AUX_DATA();
	void UpdateSysColors();
	void UpdateSysMetrics();
};
extern AUX_DATA afxData;

void CMyApp::StretchWnd( CMiniDockFrameWnd *pMiniWnd, int nHitTest, CPoint pt )
{
	int nPos = 1;
	CControlBar* pBar = NULL;
	while(pBar == NULL && nPos < pMiniWnd->m_wndDockBar.m_arrBars.GetSize())
	{
		CControlBar* pResult = (CControlBar*)pMiniWnd->m_wndDockBar.m_arrBars[nPos];
		if (DWORD_PTR(pResult) <= 0xffff)
			pBar	= NULL;
		else
			pBar	= pResult;
	}

	ASSERT(pBar != NULL);
	ASSERT_KINDOF(CControlBar, pBar);
	ASSERT(pBar->m_pDockContext != NULL);

	// CBRS_SIZE_DYNAMIC toolbars cannot have the CBRS_FLOAT_MULTI style
	ASSERT((pMiniWnd->m_wndDockBar.m_dwStyle & CBRS_FLOAT_MULTI) == 0);
	ASSERT_VALID(pBar->m_pDockContext->m_pBar);
	ASSERT(pBar->m_pDockContext->m_pBar->m_dwStyle & CBRS_SIZE_DYNAMIC);
	pBar->m_pDockContext->m_bDragging = FALSE;

	pBar->m_pDockContext->InitLoop();

	// GetWindowRect returns screen coordinates(not mirrored)
	// So if the desktop is mirrored then turn off mirroring
	// for the desktop dc so that we draw correct focus rect 

	if (pBar->m_pDockContext->m_pDC->GetLayout() & LAYOUT_RTL)
		pBar->m_pDockContext->m_pDC->SetLayout(LAYOUT_LTR);

	// get true bar size (including borders)
	CRect rect;
	pBar->m_pDockContext->m_pBar->GetWindowRect(rect);
	pBar->m_pDockContext->m_ptLast = pt;
	pBar->m_pDockContext->m_nHitTest = nHitTest;

	CSize size = pBar->m_pDockContext->m_pBar->CalcDynamicLayout(0, LM_HORZ | LM_MRUWIDTH);
	pBar->m_pDockContext->m_rectRequestedSize = CRect(rect.TopLeft(), size);
	pBar->m_pDockContext->m_rectActualSize = CRect(rect.TopLeft(), size);
	pBar->m_pDockContext->m_rectActualFrameSize = CRect(rect.TopLeft(), size);

	// calculate frame rectangle
	CMiniFrameWnd::CalcBorders(&pBar->m_pDockContext->m_rectActualFrameSize);
	pBar->m_pDockContext->m_rectActualFrameSize.InflateRect(-afxData.cxBorder2, -afxData.cyBorder2);

	pBar->m_pDockContext->m_rectFrameBorders = CRect(CPoint(0,0),
		pBar->m_pDockContext->m_rectActualFrameSize.Size() - pBar->m_pDockContext->m_rectActualSize.Size());

	// initialize tracking state and enter tracking loop
	pBar->m_pDockContext->m_dwOverDockStyle = 0;
	StretchMiniWnd( pBar, pt );
	TrackMiniWnd( pBar );

	return;
}

void CMyApp::StretchMiniWnd( CControlBar* pBar, CPoint pt )
{
	CPoint ptOffset = pt - pBar->m_pDockContext->m_ptLast;

	// offset all drag rects to new position
	int nLength = 0;
	DWORD dwMode = LM_HORZ;

	switch( pBar->m_pDockContext->m_nHitTest )
	{
	case HTTOPLEFT:
		pBar->m_pDockContext->m_rectRequestedSize.left	+= ptOffset.x;
		pBar->m_pDockContext->m_rectRequestedSize.top	+= ptOffset.y;
		break;
	case HTTOPRIGHT:
		pBar->m_pDockContext->m_rectRequestedSize.top	+= ptOffset.y;
		pBar->m_pDockContext->m_rectRequestedSize.right	+= ptOffset.x;
		break;
	case HTBOTTOMLEFT:
		pBar->m_pDockContext->m_rectRequestedSize.left	+= ptOffset.x;
		pBar->m_pDockContext->m_rectRequestedSize.bottom	+= ptOffset.y;
		break;
	case HTBOTTOMRIGHT:
		pBar->m_pDockContext->m_rectRequestedSize.right	+= ptOffset.x;
		pBar->m_pDockContext->m_rectRequestedSize.bottom	+= ptOffset.y;
		break;
	}

	CSize	size;
	nLength = pBar->m_pDockContext->m_rectRequestedSize.Width();
	nLength = (nLength >= 0) ? nLength : 0;
	size = pBar->m_pDockContext->m_pBar->CalcDynamicLayout(nLength, dwMode);
	dwMode |= LM_LENGTHY;
	nLength = pBar->m_pDockContext->m_rectRequestedSize.Height();
	nLength = (nLength >= 0) ? nLength : 0;
	size = pBar->m_pDockContext->m_pBar->CalcDynamicLayout(nLength, dwMode);

	CRect rectDesk;
	HWND hWndDesk = ::GetDesktopWindow();
	::GetWindowRect(hWndDesk, &rectDesk);
	CRect rectTemp = pBar->m_pDockContext->m_rectActualFrameSize;

	CRect rect;
	switch( pBar->m_pDockContext->m_nHitTest )
	{
	case HTTOPLEFT:
		rectTemp.left = rectTemp.right - (size.cx + pBar->m_pDockContext->m_rectFrameBorders.Width());
		rectTemp.top = rectTemp.bottom - (size.cy + pBar->m_pDockContext->m_rectFrameBorders.Height());
		if (rect.IntersectRect(rectDesk, rectTemp))
		{
			pBar->m_pDockContext->m_rectActualSize.left = pBar->m_pDockContext->m_rectActualSize.right - size.cx;
			pBar->m_pDockContext->m_rectActualSize.top = pBar->m_pDockContext->m_rectActualSize.bottom - size.cy;
			pBar->m_pDockContext->m_rectActualFrameSize.left = rectTemp.left;
			pBar->m_pDockContext->m_rectActualFrameSize.top = rectTemp.top;
		}
		break;
	case HTTOPRIGHT:
		rectTemp.right = rectTemp.left + (size.cx + pBar->m_pDockContext->m_rectFrameBorders.Width());
		rectTemp.top = rectTemp.bottom - (size.cy + pBar->m_pDockContext->m_rectFrameBorders.Height());
		if (rect.IntersectRect(rectDesk, rectTemp))
		{
			pBar->m_pDockContext->m_rectActualSize.top = pBar->m_pDockContext->m_rectActualSize.bottom - size.cy;
			pBar->m_pDockContext->m_rectActualSize.right = pBar->m_pDockContext->m_rectActualSize.left + size.cx;
			pBar->m_pDockContext->m_rectActualFrameSize.top = rectTemp.top;
			pBar->m_pDockContext->m_rectActualFrameSize.right = rectTemp.right;
		}
		break;
	case HTBOTTOMLEFT:
		rectTemp.left = rectTemp.right - (size.cx + pBar->m_pDockContext->m_rectFrameBorders.Width());
		rectTemp.bottom = rectTemp.top + (size.cy + pBar->m_pDockContext->m_rectFrameBorders.Height());
		if (rect.IntersectRect(rectDesk, rectTemp))
		{
			pBar->m_pDockContext->m_rectActualSize.left = pBar->m_pDockContext->m_rectActualSize.right - size.cx;
			pBar->m_pDockContext->m_rectActualSize.bottom = pBar->m_pDockContext->m_rectActualSize.top + size.cy;
			pBar->m_pDockContext->m_rectActualFrameSize.left = rectTemp.left;
			pBar->m_pDockContext->m_rectActualFrameSize.bottom = rectTemp.bottom;
		}
		break;
	case HTBOTTOMRIGHT:
		rectTemp.right = rectTemp.left + (size.cx + pBar->m_pDockContext->m_rectFrameBorders.Width());
		rectTemp.bottom = rectTemp.top + (size.cy + pBar->m_pDockContext->m_rectFrameBorders.Height());
		if (rect.IntersectRect(rectDesk, rectTemp))
		{
			pBar->m_pDockContext->m_rectActualSize.right = pBar->m_pDockContext->m_rectActualSize.left + size.cx;
			pBar->m_pDockContext->m_rectActualSize.bottom = pBar->m_pDockContext->m_rectActualSize.top + size.cy;
			pBar->m_pDockContext->m_rectActualFrameSize.right = rectTemp.right;
			pBar->m_pDockContext->m_rectActualFrameSize.bottom = rectTemp.bottom;
		}
		break;
	}
	
	pBar->m_pDockContext->m_ptLast = pt;

	// update feedback
	pBar->m_pDockContext->DrawFocusRect();

}

BOOL CMyApp::TrackMiniWnd( CControlBar *pBar )
{
	// don't handle if capture already set
	if (::GetCapture() != NULL)
		return FALSE;

	// set capture to the window which received this message
	pBar->m_pDockContext->m_pBar->SetCapture();
	ASSERT(pBar->m_pDockContext->m_pBar == CWnd::GetCapture());

	// get messages until capture lost or cancelled/accepted
	while (CWnd::GetCapture() == pBar->m_pDockContext->m_pBar)
	{
		MSG msg;
		if (!::GetMessage(&msg, NULL, 0, 0))
		{
			AfxPostQuitMessage((int)msg.wParam);
			break;
		}

		switch (msg.message)
		{
		case WM_LBUTTONUP:
			if (pBar->m_pDockContext->m_bDragging)
				pBar->m_pDockContext->EndDrag();
			else
				pBar->m_pDockContext->EndResize();
			return TRUE;
		case WM_MOUSEMOVE:
			if (pBar->m_pDockContext->m_bDragging)
				pBar->m_pDockContext->Move(msg.pt);
			else
				StretchMiniWnd( pBar, msg.pt);
			break;
		case WM_KEYUP:
			if (pBar->m_pDockContext->m_bDragging)
				pBar->m_pDockContext->OnKey((int)msg.wParam, FALSE);
			break;
		case WM_KEYDOWN:
			if (pBar->m_pDockContext->m_bDragging)
				pBar->m_pDockContext->OnKey((int)msg.wParam, TRUE);
			if (msg.wParam == VK_ESCAPE)
			{
				pBar->m_pDockContext->CancelLoop();
				return FALSE;
			}
			break;
		case WM_RBUTTONDOWN:
			pBar->m_pDockContext->CancelLoop();
			return FALSE;

		// just dispatch rest of the messages
		default:
			DispatchMessage(&msg);
			break;
		}
	}

	pBar->m_pDockContext->CancelLoop();

	return FALSE;
}

ヘッダにもちゃんと上記で作成した関数の定義を
書いておいてください。
長いですがこれで完成です。

時間と機能があまりにも割に合わない作業でした…。