CZoomView

void CTrafficView::OnPrepareDC(CDC *pDC, CPrintInfo *pInfo)
{
	CScrollView::OnPrepareDC(pDC, pInfo);

	pDC->SetMapMode(MM_ANISOTROPIC);	// for scaling
	pDC->SetWindowExt(m_DrawArea);		// in logical units

	int xExtent = m_Scale * m_DrawArea.cx;
	int yExtent = m_Scale * m_DrawArea.cy;
	pDC->SetViewportExt(xExtent, yExtent);

	// keep the road divider in the centre of screen
	// by moving the viewport origin
	GetClientRect(&m_ClientRect);	// the height of the window
	CPoint viewOrg;
	viewOrg.y = m_ClientRect.Height()/2;
	viewOrg.x = m_Border_Lhs*m_Scale;

	viewOrg -= GetDeviceScrollPosition();	// so scrolling accounted for
	pDC->SetViewportOrg(viewOrg);
}

void CTrafficView::ResetScrollBars()
{
	// set up device context and new scroll sizes
	CClientDC aDC(this);
	OnPrepareDC(&aDC);
	CSize temp = m_DrawArea;	// since we don't want drawArea changed
	aDC.LPtoDP(&temp);
	SetScrollSizes(MM_TEXT, temp);
}

void CTrafficView::OnToolsZoomin() 
{
	// move scrolls bars to centre of logical view
	CPoint pt;
	GetClientRect(&m_ClientRect);
        pt.x = (m_ClientRect.Width()  / 2);
        pt.y = (m_ClientRect.Height() / 2);
	
	CClientDC aDC(this);
	OnPrepareDC(&aDC);
	CPoint vp = aDC.GetViewportOrg();

	pt = pt - vp;	// adjust device point to viewport point

	CScrollView::ScrollToPosition(pt);	// scroll to viewport point

	m_Scale += 0.2;				// MAGIC NUMBER - should it be an option?
	ResetScrollBars();
	
	Invalidate();	// draw it
}

void CTrafficView::OnPrepareDC(CDC *pDC, CPrintInfo *pInfo)
{
	CScrollView::OnPrepareDC(pDC, pInfo);

	pDC->SetMapMode(MM_ANISOTROPIC);	// for scaling
	pDC->SetWindowExt(m_DrawArea);		// in logical units

	int xExtent = m_Scale * m_DrawArea.cx;
	int yExtent = m_Scale * m_DrawArea.cy;
	pDC->SetViewportExt(xExtent, yExtent);

	// keep the road divider in the centre of screen
	// by moving the viewport origin
	GetClientRect(&m_ClientRect);	// the height of the window
	CPoint viewOrg;
	viewOrg.y = m_ClientRect.Height()/2;    // move centre of road to middle of screen
	viewOrg.x = m_Border_Lhs*m_Scale;       // a left border
	
	viewOrg -= GetDeviceScrollPosition();	// so scrolling accounted for
	pDC->SetViewportOrg(viewOrg);
}

// note this function sets the new m_Scale so call it as follows
// SetZoomScale(m_Scale + 0.2) for example
// do not set m_Scale and then call the function!!!
void CTrafficView::SetZoomScale(double newScale)
{
	if(newScale > 0.1)
	{
		double oldZoomFactor = m_Scale;
		
		CPoint centerScrollPosition = GetScrollPosition();
		CRect ClientRect(0,0,0,0);
		centerScrollPosition.x += m_ClientRect.right/2;
		centerScrollPosition.y += m_ClientRect.bottom/2;

		m_Scale = newScale;
		
		CSize displaySize;
		displaySize.cx = Round(m_DrawArea.cx * m_Scale);
		displaySize.cy = Round(m_DrawArea.cy * m_Scale);
		SetScrollSizes(MM_TEXT,displaySize);
		
		int newXScrollPosition = Round((centerScrollPosition.x / oldZoomFactor) * m_Scale);    // I think this is the magic bit!
		int newYScrollPosition = Round((centerScrollPosition.y / oldZoomFactor) * m_Scale);

		newXScrollPosition -= m_ClientRect.right/2;
		newYScrollPosition -= m_ClientRect.bottom/2;
		ScrollToPosition(CPoint(newXScrollPosition,newYScrollPosition));
	}
	else
		MessageBox("You cannot zoom out any further - minimum view scale is 0.1.", "Traffic", MB_OK|MB_ICONWARNING);

	Invalidate(FALSE);
}

void CTrafficView::initRoad() // called whenever a "road" parameter changes - updates data behind objects to be drawn
{
        // some other initilisation code here

        // the new road draw area dimensions
	m_DrawArea.cy =  m_Border_Top + m_Border_Btm + m_RoadWidth;
	m_DrawArea.cx =  m_Border_Lhs + m_Border_Rhs + m_RoadLength;

	CSize scrolls;
	scrolls.cx = m_DrawArea.cx*m_Scale;	// when scale is not 1.0 so user can alter road parameters
	scrolls.cy = m_DrawArea.cy*m_Scale;     // when zoomed in and not see a radical change in scroll bars
 	CScrollView::SetScrollSizes(MM_TEXT, scrolls);
}

int CZoomView::SetMapMode(CDC* pDC)<br />
{<br />
...<br />
pDC->SetViewport(FlatToInt(100*m_xZoomFactor), FloatToInt(100*m_yZoomFactor));<br />
...<br />
}