viewport origin,mapping mode, etc

Hi,

I am using a CScrollView as the base class for my view
and want to use MM_LOENGLISH as the mapping mode.
I want to change the origin from top-left to bottom-left.
I also need to draw a set of axes at the origin. I am really
confused with device coordinates, logical coordinates,
setting the viewport origin, and how these things work
together when drawing on the screen (in MM_LOENGLISH mode).
Any help is appreciated.

override OnPrepareDC in your view class.


void CGridView::OnPrepareDC(CDC* pDC,CPrintInfo* pInfo)
{
pDC->SetMapMode(MM_LOENGLISH);

CRect clientRect;
GetClientRect(clientRect); // Find size of client view are in device pixels

CSize size=GetTotalSize(); // Find size of ScrollView in device pixels
size.cx=max(size.cx,clientRect.Width()); // use the larger of the client width or scroll width
size.cy=max(size.cy,clientRect.Height()); // use the larger of the client height or scroll height

CRect rect(CPoint(0,0),size); // create a view rectangle (if using a scroll coordinate it will be larger than the viewable area)
pDC->DPtoLP(&rect); // convert the rectangle from device pixels to logical pixels

pDC->SetWindowOrg(CPoint(0,-rect.Height())); // move the window origin down the height of the view (not always the same as viewable area)
}

I'm having a problem with scrolling in which the rectangles I have drawn will incorrectly draw over the already existing rectangles when I scroll in either direction. Also, the visible rectangles are completely redrawn when I minimize and then restore the window but as if the origin moved upon scrolling. My code to draw the rectangles is

CRect TempRect = pDoc->GetNode(i); // The points for the rectangle
OnPrepareDC(pDC);
pDC->DPtoLP(&TempRect);
pDC->Rectangle(TempRect);

And I used the code provided in OnPrepareDC but the problem didn't change. Any ideas?