[Lazarus] External SigFPE

[Dave Coventry]

I have a Procedure as follows.


procedure TForm_DB.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
var
  xr,yr: Real;
  dx,dy: integer;
  SrcRect,DestRect: TRect;
begin
  if iScale=0 then exit;<- External SigFPE occurs here.
  mousePos.x:=X;
  mousePos.y:=Y;
  xr:=trunc(x/iScale+PanVect.x);
  yr:=trunc(y/iScale+PanVect.y);
  if middleDown=1 then
  begin
    SrcRect:=Rect(0,0,ImageWidth,ImageHeight);
    dx:=X-MouseClkDn.x;
    dy:=Y-MouseClkDn.y;
    DestRect:=Rect(dx,dy,ImageWidth+dx,ImageHeight+dy);
    Image1.Canvas.CopyRect(DestRect,ImageBuffer.Canvas,SrcRect);
  end;
end;

Mostly it works as expected.

However, after some reasonably complex computing, mostly involving
TStringLists, it throws up an error:

"Project project1 raised exception class 'External SigFPE'
in file 'unit5.pas' at line 435:
 if iScale=0 then exit;"

The iScale variable at this point is 1.1394385252832742, so clearly the
debugger is not actually indicating the correct cause of the exception.

Can anyone offer a way to try to seek out the cause?

Many thanks,

Dave Coventry
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