--- loncom/xml/lonplot.pm	2004/05/26 19:44:20	1.96
+++ loncom/xml/lonplot.pm	2004/08/17 17:37:56	1.100
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # Dynamic plot
 #
-# $Id: lonplot.pm,v 1.96 2004/05/26 19:44:20 matthew Exp $
+# $Id: lonplot.pm,v 1.100 2004/08/17 17:37:56 matthew Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -36,8 +36,17 @@ use Apache::response;
 use Apache::lonxml;
 use Apache::edit;
 
+use vars qw/$weboutputformat $versionstring/;
+
 BEGIN {
-  &Apache::lonxml::register('Apache::lonplot',('gnuplot'));
+    &Apache::lonxml::register('Apache::lonplot',('gnuplot'));
+    #
+    # Determine the version of GNUPLOT
+    $weboutputformat = 'gif';
+    $versionstring = `gnuplot --version 2>/dev/null`;
+    if ($versionstring =~ /^gnuplot 4/) {
+        $weboutputformat = 'png';
+    }
 }
 
 ## 
@@ -302,7 +311,7 @@ my %tic_defaults =
      minorfreq => {
 	 default => '0',
 	 test => $int_test,
-	 description => 'Number of minor tics between major tic marks',
+	 description => 'Number of minor tics per major tic mark',
 	 edit_type   => 'entry',
 	 size        => '10'
 	 },         
@@ -460,7 +469,7 @@ sub end_gnuplot {
 	## return image tag for the plot
 	if ($target eq 'web') {
 	    $result .= <<"ENDIMAGE";
-<img src    = "/cgi-bin/plot.gif?file=$filename.data&output=gif" 
+<img src    = "/cgi-bin/plot.gif?file=$filename.data&output=$weboutputformat" 
      width  = "$plot{'width'}"
      height = "$plot{'height'}"
      align  = "$plot{'align'}"
@@ -945,6 +954,24 @@ sub write_gnuplot_file {
     my $gnuplot_input = '';
     my $curve;
     my $pt = $plot{'texfont'};
+    #
+    # Check to be sure we do not have any empty curves
+    my @curvescopy;
+    foreach my $curve (@curves) {
+        if (exists($curve->{'function'})) {
+            if ($curve->{'function'} !~ /^\s*$/) {
+                push(@curvescopy,$curve);
+            }
+        } elsif (exists($curve->{'data'})) {
+            foreach my $data (@{$curve->{'data'}}) {
+                if (scalar(@$data) > 0) {
+                    push(@curvescopy,$curve);
+                    last;
+                }
+            }
+        }
+    }
+    @curves = @curvescopy;
     # Collect all the colors
     my @Colors;
     push @Colors, $plot{'bgcolor'};