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From: oivindt@ulrik.uio.no (Oivind Toien)
Newsgroups: comp.lang.pascal
Subject: Bug in TurboHALO Graphics Kernel?
Message-ID: <OIVINDT.90Feb17234034@ulrik.uio.no>
Date: 17 Feb 90 22:40:34 GMT
Sender: oivindt@ulrik.uio.no (Oivind Toien)
Distribution: comp
Organization: University of Oslo, Norway
Lines: 49

I have a problem that may interest TurboHALO users as well as those
only using Turbo Pascal: I have written a plotting routine that is
plotting lines or points at very short intervals using
world-coordinates. It is used in a data acquisition routine to display
the input on the A/D converter variable plotted against time.  After
some samples, however, the x-coordinate is at certain intervals not
plotted correctly, but is plotted with a x-value 1-3 pixels lower than
it is supposed to.  When input to the routine is obtained from a
sine-wave equation, it results in a jagged appearance. The effect is
especially present when the distance between data-points is very short
on the X-axis.  However, the numbers passed to TurboHALO are correct!
It is the address of the variables that is passed from Turbo Pascal to
the TurboHALO routines. The error occurs when using the procedures:
LnAbs, MoveAbs+PtAbs and PolyLnAbs. The problems are present with all
versions of Turbo Pascal >= 3.0.

Finally I detected a way to make the error appear and disappear:

  X         : real; { x-coordinate}
  XInterval : real; { interval between points on x-axis}
  n         : Integer; {counter variable}

1)It is present in the test routine if the X-value is calculated the
following way:

  X:=X+Xinterval;

2)It is not present if the X-value is calculated this way:
  
  n:=n+1;
  X:=n*Xinterval;

But I have still not been able to eliminate it in the routine used in
the program, in spite of avoiding the no.1) approach. Something is
still screwing up the system. (The source is to long to post).
	
Has anyone out there had similar problems?  I can E-mail source of
test-routine if interest, I am especially interested if the problems
exists with **HALO 88** which is an updated version of the same
graphics kernel.

I will be very pleased for any response. If you E-mail I will summarize.

--
Oivind Toien  <oivindt@ulrik.uio.no>
Div. of General Physiology, Dept. of Biology, Univ. of Oslo
P.O. Box 1051, N-0316 Oslo 3, NORWAY  
Phone+47-2-454732  Fax+47-2-454726