🚀 go-pugleaf

I'm trying to use SetPortBits to draw off screen so I can then use
CopyBits to dump on the screen.  However, when I try to set the active
port back to the window, I can't draw anything new in it.  Basically the
procedure is as follows:

procedure UpKeep;
var
  UPDRect,ARect : Rect;
  WinBits,OldPtr   : BitPtr;
  SavePort  : GrafPtr;
begin
  GetPort(SavePort);
  UPDRect:=SavePort^.portRect;
  New(WinBits);
  WinBits^.rowBytes:=SavePort^.portBits.rowBytes;
  WinBits^.bounds:=SavePort^.portBits.bounds;
  OldPtr:=@SavePort^.portBits;
  SetPortBits(WinBits^);
  SetPortBits(OldPtr^);  <<<<

   ...  draw stuff - it never appears??  ...

If I take out the line with "<<<<" the picture gets drawn to the screen
as expected.  I've tried setting OldPtr to everything I can think of, but
I never seem to be able to get back to the original screen.  Help!!!!!!!
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