C / C++ / MFC

void CImageControl::OnLButtonDown(UINT nFlags, CPoint point) 
{
	m_down = true;
	pDC = new CClientDC(this);
	pDC->DPtoLP(&point);
	m_currentpoint = m_newpoint = point;

	CStatic::OnLButtonDown(nFlags, point);
}

void CImageControl::OnLButtonUp(UINT nFlags, CPoint point) 
{
	if (m_draw)
	{
		pDC->DPtoLP(&point);
		pDC->SetROP2(R2_NOTXORPEN);
		pDC->Rectangle(m_currentpoint.x, m_currentpoint.y, m_newpoint.x, m_newpoint.y);
		CStatic::OnLButtonUp(nFlags, point);
		pDC->SelectObject(oldpen);
		m_draw = false;
		ReleaseDC(pDC);
	}
}

void CImageControl::OnMouseMove(UINT nFlags, CPoint point) 
{
	if (m_down && nFlags == MK_LBUTTON)
	{
		m_draw = true;
		pDC->DPtoLP(&point);
		oldpen = pDC->SelectObject(boxpen);
		pDC->SetROP2(R2_NOTXORPEN);
		pDC->Rectangle(m_currentpoint.x, m_currentpoint.y, m_newpoint.x, m_newpoint.y);
		m_newpoint = point;
		pDC->Rectangle(m_currentpoint.x, m_currentpoint.y, m_newpoint.x, m_newpoint.y);
	}
	CStatic::OnMouseMove(nFlags, point);
}