Add fill_min_y and fill_max_y options.

These options allow restricting the fill region in the y range when
filling between curves.  Furthermore, these options can be combined with
the fill_min and fill_max options to restrict the fill region to a
rectangle.

Author: drgrice1

lib/Plots/JSXGraph.pm

@@ -326,6 +326,8 @@ sub add_curve {
 			if ($curve_name) {
 				my $fill_min    = $data->str_to_real($data->style('fill_min'));
 				my $fill_max    = $data->str_to_real($data->style('fill_max'));
+				my $fill_min_y  = $data->str_to_real($data->style('fill_min_y'));
+				my $fill_max_y  = $data->str_to_real($data->style('fill_max_y'));
 				my $fill_layer  = $self->get_layer($data, 1) // $self->get_layer($data);
 				my $fillOptions = Mojo::JSON::encode_json({
 					strokeWidth => 0,
@@ -361,12 +363,24 @@ sub add_curve {
 							".filter(p => {"
 							. "return p.usrCoords[1] >= $fill_min && p.usrCoords[1] <= $fill_max ? true : false" . "})";
 					}
+					if ($fill_min_y ne '' && $fill_max_y ne '') {
+						$self->{JS} .=
+							".filter(p => {"
+							. "return p.usrCoords[2] >= $fill_min_y && p.usrCoords[2] <= $fill_max_y ? true : false"
+							. "})";
+					}
 					$self->{JS} .= ";const points2 = curve_${fill}.points";
 					if ($fill_min ne '' && $fill_max ne '') {
 						$self->{JS} .=
 							".filter(p => {"
 							. "return p.usrCoords[1] >= $fill_min && p.usrCoords[1] <= $fill_max ? true : false" . "})";
 					}
+					if ($fill_min_y ne '' && $fill_max_y ne '') {
+						$self->{JS} .=
+							".filter(p => {"
+							. "return p.usrCoords[2] >= $fill_min_y && p.usrCoords[2] <= $fill_max_y ? true : false"
+							. "})";
+					}
 					$self->{JS} .=
 						";this.dataX = points1.map( p => p.usrCoords[1] ).concat("
 						. "points2.map( p => p.usrCoords[1] ).reverse());"

lib/Plots/Tikz.pm

@@ -685,18 +685,26 @@ sub draw {
 				# Make sure this is the name from the data style attribute, and not an internal name.
 				my $name = $data->style('name');
 				if ($name) {
-					my $opacity  = $data->style('fill_opacity') || 0.5;
-					my $fill_min = $data->style('fill_min');
-					my $fill_max = $data->style('fill_max');
+					my $opacity    = $data->style('fill_opacity') || 0.5;
+					my $fill_min   = $data->style('fill_min');
+					my $fill_max   = $data->style('fill_max');
+					my $fill_min_y = $data->style('fill_min_y');
+					my $fill_max_y = $data->style('fill_max_y');
 					my $fill_range =
-						$fill_min ne '' && $fill_max ne '' ? ", soft clip={domain=$fill_min:$fill_max}" : '';
+						$fill_min ne '' && $fill_max ne '' && $fill_min_y ne '' && $fill_max_y ne ''
+						? ", soft clip={($fill_min, $fill_min_y) rectangle ($fill_max, $fill_max_y)}"
+						: $fill_min ne ''   && $fill_max ne ''   ? ", soft clip={domain=$fill_min:$fill_max}"
+						: $fill_min_y ne '' && $fill_max_y ne '' ? ", soft clip={domain y=$fill_min_y:$fill_max_y}"
+						:                                          '';
 					my $fill_layer = $data->style('fill_layer') || $layer;
+					my $reverse    = $data->style('fill_reverse') ? ', reverse' : '';
 					$tikzCode .=
 						"\\begin{scope}[/tikz/fill between/on layer=$fill_layer]\\begin{pgfonlayer}{$fill_layer}"
 						. "\\clip\\axisclippath;\n"
 						if $fill_layer;
 					$tikzCode .=
-						"\\addplot[$fill_color, fill opacity=$opacity] fill between[of=$name and $fill$fill_range];\n";
+						"\\addplot[$fill_color, fill opacity=$opacity] "
+						. "fill between[of=$name and $fill$fill_range$reverse];\n";
 					$tikzCode .= "\\end{pgfonlayer}\\end{scope}\n" if $fill_layer;
 				} else {
 					warn q{Unable to create fill. Missing 'name' attribute.};

macros/graph/plots.pl

@@ -473,6 +473,23 @@ =head2 DATASET OPTIONS
         fill_opacity => 0.2,
     );
 
+The following fills the area between the two curves x = 4 - y^2 and x = y^2 - 4,
+and only fills in the area between y=-2 and y=2:
+
+    $plot->add_function(['4 - y^2', 'y'], 'y', -3, 3,
+        color => 'blue',
+        name  => 'A'
+    );
+    $plot->add_function(['y^2 - 4', 'y'] 'y', -3, 3,
+        color        => 'blue',
+        name         => 'B',
+        fill         => 'A',
+        fill_min_y   => -2,
+        fill_max_y   => 2,
+        fill_color   => 'green',
+        fill_opacity => 0.2,
+    );
+
 =item fill_color
 
 The color used when filling the region. Default: C<color>
@@ -487,6 +504,26 @@ =head2 DATASET OPTIONS
 not defined, then the fill will use the full domain of the function.
 Default: undefined
 
+=item fill_min_y, fill_max_y
+
+The minimum and maximum y-values to fill between. If either of these are
+not defined, then the fill will use the full y range of the function.
+Default: undefined
+
+Note that fill_min, fill_max, fill_min_y, and fill_max_y can be defined, and
+this will result in the region filled being restricted to the rectangle defined
+by those ranges.
+
+=item fill_reverse
+
+This reverses the fill for TikZ output if it is set to 1.  This should only be
+used if the TikZ output is filling the wrong side of one of the curves.  By
+default the pgfplots fillbetween library attempts to autodetect if one of the
+curves needs to be reversed in order to obtain the fill region between the
+curves. However, sometimes the autodetection is wrong. So set this option to 1.
+If the correct region is being filled as compared to the JSXGraph output, then
+leave this at 0.
+
 =item layer
 
 The layer to draw on. Available layers are "axis background", "axis grid",