zoom help please

Christian,

I am drawing lines, rectangles etc by MM_TEXT in my view derived from
CScrollView. my default doc size (logical units) is CSize (1000, 1000)

What I understand is ..

=> to Zoom In - ViewportExt > WinExt
=> to Zoom out - ViewportExt < WinExt
=> to Fit - ViewportExt = View Client Size.

Now in OnLButtonView, I check if current mode is zoomin or zoomout
accordingly set the zoom scale (+ /-) and call OnPrepareDC.
Following code works fine but I want to the zooming to be centered on
the given point (not sure if viewport or windowext org has to be
shifted and where)

I wanted my zoom to be centered on the given point (so scrollbars need
to be moved at the correct location so this area is visible).

User may zoom in or out, and he may not come back to default zoom. So
he would draw next rectangles and lines at that zoom level in the view.
But
other view whose zoom level is not changed should display it correctly.
I am not able to do this correctly. How may I achive this. How the
mechanism of storing point should be in the zoomed view.

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

int nExtentX;
int nExtentY;
CSize sizeDoc;
CRect rectClient;

pDC->SetMapMode(MM_ANISOTROPIC);

// Get pertinent rectangle data
GetClientRect(&rectClient);
sizeDoc=GetDocument()->GetDocSize();

sizeDoc.cy=(-sizeDoc.cy); // Y goes down as it increments
pDC->SetWindowExt(sizeDoc);

if(theApp.m_currentCommand == FITCMD)
{
nExtentX=(int)(rectClient.Width());
nExtentY=(int)(-rectClient.Height());
}
else
{
// Calculate viewport extent
// Current scale is 3, in zoom in its increased by 1 and in zoom
// out its decreased by 1.
double scl = (double)GetScale()/3;
nExtentX=(int)(scl*sizeDoc.cx);
nExtentY=(int)(scl*sizeDoc.cy);
}

// What kind of device context do we have?
if (pDC->IsPrinting()==TRUE)
{
// Printer Context. Allow printing to edge of context. No scaling.
Margins?
pDC->SetViewportExt(pDC->GetDeviceCaps(LOGPIXELSX),-pDC->GetDeviceCaps(LOGPIXELSY));

pDC->SetROP2(R2_BLACK );
}
else
{
// Context is for screen
pDC->SetViewportExt(nExtentX,nExtentY);

}

}

void CCadView::OnLButtonDown(UINT nFlags, CPoint point)
{
...
...
if(theApp.m_currentCommand == ZOOMINCMD)
{
if (GetScale() {
pivot_point = point;
Invalidate();
SetScrollSizes(MM_TEXT,CSize(1000,1000));
}
}
else if(theApp.m_currentCommand == ZOOMOUTCMD)
{
if (GetScale()>=2) SetScale(GetScale()-1);
{
pivot_point = point;
Invalidate();
SetScrollSizes(MM_TEXT,CSize(1000,1000));
}
}

...
...
}

I am really stuck in the middle here.
Hope someone helps me in detail and make my life easy.

Thank you.

Leya