Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!uunet!mcsun!hp4nl!eutrc3!tuewsd!wsinpp
From: wsinpp@lso.win.tue.nl (Peter Peters)
Newsgroups: comp.lang.pascal
Subject: TP BUG
Keywords: TP,BUG,WINDOWS
Message-ID: <822@tuewsd.lso.win.tue.nl>
Date: 24 Jan 90 09:46:43 GMT
Organization: Eindhoven University of Technology, The Netherlands
Lines: 87

Fellow TP pascal users,

I did some more testing on the window bug I claimed to have found.
The next program will show what I've come up with so far. Any
comments (about the problem) are welcome....

			Peter.


-----------------------------------------------------------------
{$define test}
Program BugAgain;

(*
 * Demonstrate a bug which was present in TP 3.x (I patched it there)
 * Was corrected in TP 4.x and seems to be present again in TP 5.x
 *)

Uses
  Dos,Crt;

Const
  Xloc   = 10;
  Yloc   = 10;
  Width  = 5;
  Height = 1;   (* This is a troublesome value !!! *)

Var
  i : Word;
  R : Registers;

Begin
  ClrScr;
  For i := 1 To 80*24-1 Do Write('-');
  Window(Xloc,Yloc,Xloc-1+Width,Yloc-1+Height);
  ClrScr;
  For i := 1 To Width-1 Do Write('a');

  (*
   * Here comes trouble...
   * somewhere in the next write('a'), scrolling is done via the bios
   * INT 10h with register AX set to $0601. The $01 in register AL is
   * the number of empty lines to move in.
   * Apparently this goes wrong as can be shown by replacing the
   * write('a') statement by the alternative piece of code.
   * Watch what happens when this window scrolls !!!
   *)

{$ifdef test}

  Write('a');

{$else}

  (*
   * This is an exact functional copy of what the TP compiler generates
   * to scroll a window up !!
   *)

  R.ax:=$0601;
  R.bh:=TextAttr;
  R.cx:=WindMin;
  R.dx:=WindMax;
  Intr($10,R);

{$endif}

 (*
  * Now this could be called :
  *
  * 1 - a bios bug.
  * 2 - a TP bug.
  *
  * Scrolling up a 1 line window should be the same as clearing it !.
  * If all bios-es are like the one in my machine, (showing the same
  * erroneous scroll in the example above) I tend to calling this a
  * TP bug, because they (Borland) should have known this bios-"feature"
  *)
End.

---------------------------------------------------------------------

-- 
| Peter Peters                              | UUCP : wsinpp@lso.win.tue.nl  |
| Eindhoven University of Technology (TUE)  | SURF : heithe5::wsdcpp        |
| Dept. of Mathematics and Computer Science | VHF  : PA0PPE                 |
| Disclaimer : I said WHAT ???              | TUE  : HG 8.86 tst. 4283      |