Using TrackMouseEvent to find out when the mouse leaves your window

Using TrackMouseEvent is pretty simple. When the mouse enters the
window you want to track, you call track mouse event telling it to
inform you when the mouse leaves. When it does, it will send a
WM_MOUSELEAVE message to that window.

If you add this code to any of your existing view classes (or any CWnd
derived class), you will see a drag rectangle that follows the mouse
cursor around. If you move the mouse outside the window, it will
disappear. If you move the mouse back into the window, it will


// TrackView.h changes

class CTrackView : public CView
// Add data members
	CRect m_rectLast;	//** Added line
	BOOL m_bMouseTracking;	//** Added line

// Add message handler prototype
	afx_msg LRESULT OnMouseLeave(WPARAM wParam, LPARAM lParam);	//** Added line



// TrackView.cpp changes

// Add message handler
	ON_MESSAGE(WM_MOUSELEAVE, OnMouseLeave)	//** Added line

	m_bMouseTracking = FALSE;	//** Added line

// CTrackView message handlers

//** Added function
LRESULT CTrackView::OnMouseLeave(WPARAM wParam, LPARAM lParam)
	// Draw last rect, but no new one (erase old rect)
	CClientDC dc(this);
	dc.DrawDragRect(CRect(0,0,0,0), CSize(0,0), m_rectLast, CSize(2,2));
	m_rectLast = CRect(0,0,0,0);

	m_bMouseTracking = FALSE;
	return TRUE;

void CTrackView::OnMouseMove(UINT nFlags, CPoint point)
	// Calc new rectangle
	CRect rectNew(point.x-20, point.y-20, point.x+20, point.y+20);
	CClientDC dc(this);

	// WM_MOUSEMOVE + !m_bMouseTracking becomes the equivalent of
	// WM_MOUSEENTER of which there is no such thing.
	if (!m_bMouseTracking)
		tme.cbSize = sizeof(TRACKMOUSEEVENT);
		tme.dwFlags = TME_LEAVE;
		tme.hwndTrack = this->m_hWnd;

		if (::_TrackMouseEvent(&tme))
			m_bMouseTracking = TRUE;

			// Draw new rect, but no last rect as we are starting anew
			dc.DrawDragRect(rectNew, CSize(2,2), NULL, CSize(0,0));
		// Draw new rect and erase old rect
		dc.DrawDragRect(rectNew, CSize(2,2), m_rectLast, CSize(2,2));

	// Remember where we drew this rectangle
	m_rectLast = rectNew;

	CView::OnMouseMove(nFlags, point);


Here’s a helper class I use to make it a little simpler:

class CTrackMouseEvent : public tagTRACKMOUSEEVENT
	CTrackMouseEvent(CWnd* pWnd, DWORD dwFlags = TME_LEAVE, DWORD dwHoverTime = HOVER_DEFAULT)

		this->cbSize = sizeof(TRACKMOUSEEVENT);
		this->dwFlags = dwFlags;
		this->hwndTrack = pWnd->m_hWnd;
		this->dwHoverTime = dwHoverTime;

	BOOL Track()
		{ return _TrackMouseEvent(this); }

You can start tracking like this:

if (!m_bMouseTracking)
	m_bMouseTracking = CTrackMouseEvent(this).Track();

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