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Re: Only one trace appears in gnuplot

From: John W. Eaton
Subject: Re: Only one trace appears in gnuplot
Date: Thu, 8 Jul 1999 12:09:51 -0500 (CDT)

On 30-Jun-1999, Kai Mueller <address@hidden> wrote:

| On Tue, Jun 29, 1999 at 03:06:37PM -0700, Robert D. Penny wrote:
| > I have just compiled and installed octave-2.0.14 on a Redhat 6.0 system.
| > I've encountered a small glitch in plotting two traces on the same
| > figure.  It appears that the problem occurs when gnuplot is only sent a 
| > amount of data.
| [snip]
| I had some discussion with Gnuplot developers on this problem a year
| ago. This behavior is not related to Octave or Linux, because it
| can be observed also with a standalone Gnuplot on DEC Alpha with DUNIX.
| Sometimes the first plot on an X-window is corrupted. After a "replot"
| the plot looks ok. We didn't found a solution but it seems that
| the problem has something to do with the way gnuplot creates the
| X-window plot. Gnuplot draws on the background-pixmap, and an
| exposure event (or other events) should make the drawings visible.
| While this seems to be ok it does not always work. Maybe it's a
| problem with X-windows.

I think the ultimate cause of the problem is that gnuplot's outboard
X11 driver expects to be able to call select to find out if additional
input is available to read, but it also calls fgets, which may buffer
input, causing select to think that there is no more input available
even when actually there is.

I debugged this quite some time ago and sent a patch to the gnuplot
people, but nothing happened.  You can find a copy of my patch at  It
is relative to gnuplot 3.6 beta 340, but it should not be too hard to
apply to gnuplot 3.7.


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