ExpandPoly v

//forumla by Garrett
function ExpandPoly(poly:TPointArray; incr:Int32): TPointArray;
var
  i,j,size: Int32;
  x,y,r: Double;
  b,m: array of Double;
begin
  SetLength(B, Length(poly));
  SetLength(M, Length(poly));

  size := Length(poly);
  for i:=0 to size-1 do
  begin
    j := (i+1) mod size;
    r := incr / Hypot(poly[i].x-poly[j].x, poly[i].y-poly[j].y);
    x := r * (poly[j].y - poly[i].y);
    y := r * (poly[i].x - poly[j].x);
    m[i] := ((poly[j].y + y) - (poly[i].y + y)) / ((poly[j].x + x) - (poly[i].x + x)); //fix me vertical lines
    b[i] := (poly[i].y + y) - (m[i] * (poly[i].x + x));
  end;

  SetLength(Result, Length(poly));
  for i:=0 to size-1 do
  begin
    j := (i+1) mod size;
    x := (b[j] - b[i]) / (m[i] - m[j]);
    Result[i].x := Round(x);
    Result[i].y := Round((x * m[i]) + b[i]);
  end;
end;