OpenEuphoria

Re: weird bug?

• Posted by Talvitie <smtoa at SAUNALAHTI.FI> Oct 10, 1999
• 636 views

>Weird bugs like this are almost always due to
>your program writing into areas of memory that
>don't belong to it. Whether you add a dummy statement or
>a whole extra include file is largely irrelevant. The point is
>that you are changing the memory addresses and contents,
>so the bug might just go away by luck.
>
>To debug this, you should copy euphoria\include\safe.e into
>your working directory, then rename safe.e as machine.e.
>safe.e provides safer versions of the routines in
>machine.e such as poke() and mem_copy().
>Run the program again. It will say
>"Using Debug Version of machine.e". The routines
>in safe.e will often catch the bug. If they don't, it's still probably
>a memory-related bug in your program (or in Neil) -
>interpreter bugs are very rare compared to application bugs.
>Of course, if you can clearly demonstrate that it's the
>interpreter at fault, I'll be glad to look at it.
>
>Regards,
>     Rob Craig


Bad news: I removed Neil from my engine so it won't use machine.e or =
display graphics anymore. The bug stays! I have two almost identical =
subroutines in my engine: Gouraud and Flat. Gouraud does it well, but =
Flat crashes. Also if I remove this line: "   ZBuffer[CamZB][pl+2]=3Dz  =
"  from Flat's command lines it doesn't do anything weird. But, cause =
Flat and Gouraud are identical in this point, it means that I'm not =
writing to a bad place (ie. ZBuffer[-1][-5]) either. I'm not using any =
machine language, so this just migth be a interpreter bug.

From Flat:

  if ZBuffer[CamZB][pl+2]>z then
   TileBuffer[CamTile][pl+2]=3Drgb
   --!!!!!!!!!! HERE'S THE BUG !!!!!!!!!!!!! comment the next line and =
the program will crash!
   if pl<1 or pl>2+640*480 then end if
    -- if you comment the next line then  the program will run just =
nice, and you don't need the=20
    --previous one either to prevent crash
   ZBuffer[CamZB][pl+2]=3Dz
  end if

From Gouraud:

  if ZBuffer[CamZB][pl+2]>z then
   TileBuffer[CamTile][pl+2]=3Dfloor(rgbIn*(x-x1)+rgb1)
    --This works just fine!
   ZBuffer[CamZB][pl+2]=3Dz
  end if

If you like Rob, I can send you the source so that you may check it.

--Talvitie