expand

function StrExpand(trgt_pos: Integer; s1, s2, str: string): string;
var
  l, p, start, finish, s1L, s2L: Integer;
  tmp: string;
begin
  Result := '';
  l := Length(str);
  s1L := Length(s1);
  s2L := Length(s2);
  if (((s1L + s2L) <= l) and (s1L > 0) and (s2L > 0) and (trgt_pos <= l) and (trgt_pos > 0)) then
  begin
    p := 0;
    start := 0;
    finish := PosEx(s2, str, trgt_pos);
    if ((finish < 1) or (finish = trgt_pos)) then
      Exit;
    tmp := Copy(str, 1, trgt_pos);
    repeat
      p := PosEx(s1, tmp, (p + 1));
      if (p > 0) then
        start := p;
    until (p <= 0);
    if ((start <> trgt_pos) and (start > 0) and (finish > 0) and (start < finish)) then
      Result := Copy(str, (start + s1L), ((finish - start) - 1));
  end;
end;

var
  str: string;

begin
  str := 'C:\Simba\Includes\SPS\img\runescape_surface\air_altar_path.png';
  WriteLn(StrExpand((Length(str) - 4), '\', '.png', str));
end.