--- a/flys-artifacts/ChangeLog	Thu Nov 03 10:25:23 2011 +0000
+++ b/flys-artifacts/ChangeLog	Thu Nov 03 10:32:17 2011 +0000
@@ -33,6 +33,18 @@
 
 2011-11-03  Sascha L. Teichmann <sascha.teichmann@intevation.de>
 
+	* src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java:
+	  New. At the moment a pure copy of JFreeChart's XYDifferenceRenderer.
+	  Needs to be refactored to cope with its limitations:
+
+	  - Series numbers need to be zero based. We have more than two series
+	    in our diagrams.
+
+	  - Cannot handle definition holes indicated by NaNs. We have these
+	    cases e.g. more than one "Fliessbereich".
+
+2011-11-03  Sascha L. Teichmann <sascha.teichmann@intevation.de>
+
 	* src/main/java/de/intevation/flys/artifacts/charts/CrossSectionApp.java:
 	  Reenabled dumping data to disk.
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java	Thu Nov 03 10:32:17 2011 +0000
@@ -0,0 +1,1242 @@
+/* ===========================================================
+ * JFreeChart : a free chart library for the Java(tm) platform
+ * ===========================================================
+ *
+ * (C) Copyright 2000-2008, by Object Refinery Limited and Contributors.
+ *
+ * Project Info:  http://www.jfree.org/jfreechart/index.html
+ *
+ * This library is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ *
+ * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
+ * in the United States and other countries.]
+ *
+ * -------------------------
+ * StableXYDifferenceRenderer.java
+ * -------------------------
+ * (C) Copyright 2003-2008, by Object Refinery Limited and Contributors.
+ *
+ * Original Author:  David Gilbert (for Object Refinery Limited);
+ * Contributor(s):   Richard West, Advanced Micro Devices, Inc. (major rewrite
+ *                   of difference drawing algorithm);
+ *
+ * Changes:
+ * --------
+ * 30-Apr-2003 : Version 1 (DG);
+ * 30-Jul-2003 : Modified entity constructor (CZ);
+ * 20-Aug-2003 : Implemented Cloneable and PublicCloneable (DG);
+ * 16-Sep-2003 : Changed ChartRenderingInfo --> PlotRenderingInfo (DG);
+ * 09-Feb-2004 : Updated to support horizontal plot orientation (DG);
+ * 10-Feb-2004 : Added default constructor, setter methods and updated
+ *               Javadocs (DG);
+ * 25-Feb-2004 : Replaced CrosshairInfo with CrosshairState (DG);
+ * 30-Mar-2004 : Fixed bug in getNegativePaint() method (DG);
+ * 15-Jul-2004 : Switched getX() with getXValue() and getY() with
+ *               getYValue() (DG);
+ * 25-Aug-2004 : Fixed a bug preventing the use of crosshairs (DG);
+ * 11-Nov-2004 : Now uses ShapeUtilities to translate shapes (DG);
+ * 19-Jan-2005 : Now accesses only primitive values from dataset (DG);
+ * 22-Feb-2005 : Override getLegendItem(int, int) to return "line" items (DG);
+ * 13-Apr-2005 : Fixed shape positioning bug (id = 1182062) (DG);
+ * 20-Apr-2005 : Use generators for legend tooltips and URLs (DG);
+ * 04-May-2005 : Override equals() method, renamed get/setPlotShapes() -->
+ *               get/setShapesVisible (DG);
+ * 09-Jun-2005 : Updated equals() to handle GradientPaint (DG);
+ * 16-Jun-2005 : Fix bug (1221021) affecting stroke used for each series (DG);
+ * ------------- JFREECHART 1.0.x ---------------------------------------------
+ * 24-Jan-2007 : Added flag to allow rounding of x-coordinates, and fixed
+ *               bug in clone() (DG);
+ * 05-Feb-2007 : Added an extra call to updateCrosshairValues() in
+ *               drawItemPass1(), to fix bug 1564967 (DG);
+ * 06-Feb-2007 : Fixed bug 1086307, crosshairs with multiple axes (DG);
+ * 08-Mar-2007 : Fixed entity generation (DG);
+ * 20-Apr-2007 : Updated getLegendItem() for renderer change (DG);
+ * 23-Apr-2007 : Rewrite of difference drawing algorithm to allow use of
+ *               series with disjoint x-values (RW);
+ * 04-May-2007 : Set processVisibleItemsOnly flag to false (DG);
+ * 17-May-2007 : Set datasetIndex and seriesIndex in getLegendItem() (DG);
+ * 18-May-2007 : Set dataset and seriesKey for LegendItem (DG);
+ * 05-Nov-2007 : Draw item labels if visible (RW);
+ * 17-Jun-2008 : Apply legend shape, font and paint attributes (DG);
+ *
+ */
+
+package org.jfree.chart.renderer.xy;
+
+import java.awt.Color;
+import java.awt.Graphics2D;
+import java.awt.Paint;
+import java.awt.Shape;
+import java.awt.Stroke;
+import java.awt.geom.GeneralPath;
+import java.awt.geom.Line2D;
+import java.awt.geom.Rectangle2D;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.Collections;
+import java.util.LinkedList;
+
+import org.jfree.chart.LegendItem;
+import org.jfree.chart.axis.ValueAxis;
+import org.jfree.chart.entity.EntityCollection;
+import org.jfree.chart.entity.XYItemEntity;
+import org.jfree.chart.event.RendererChangeEvent;
+import org.jfree.chart.labels.XYToolTipGenerator;
+import org.jfree.chart.plot.CrosshairState;
+import org.jfree.chart.plot.PlotOrientation;
+import org.jfree.chart.plot.PlotRenderingInfo;
+import org.jfree.chart.plot.XYPlot;
+import org.jfree.chart.urls.XYURLGenerator;
+import org.jfree.data.xy.XYDataset;
+import org.jfree.io.SerialUtilities;
+import org.jfree.ui.RectangleEdge;
+import org.jfree.util.PaintUtilities;
+import org.jfree.util.PublicCloneable;
+import org.jfree.util.ShapeUtilities;
+
+/**
+ * A renderer for an {@link XYPlot} that highlights the differences between two
+ * series.  The example shown here is generated by the
+ * <code>DifferenceChartDemo1.java</code> program included in the JFreeChart
+ * demo collection:
+ * <br><br>
+ * <img src="../../../../../images/StableXYDifferenceRendererSample.png"
+ * alt="StableXYDifferenceRendererSample.png" />
+ */
+public class StableXYDifferenceRenderer extends AbstractXYItemRenderer
+        implements XYItemRenderer, PublicCloneable {
+
+    /** For serialization. */
+    private static final long serialVersionUID = -8447915602375584857L;
+
+    /** The paint used to highlight positive differences (y(0) > y(1)). */
+    private transient Paint positivePaint;
+
+    /** The paint used to highlight negative differences (y(0) < y(1)). */
+    private transient Paint negativePaint;
+
+    /** Display shapes at each point? */
+    private boolean shapesVisible;
+
+    /** The shape to display in the legend item. */
+    private transient Shape legendLine;
+
+    /**
+     * This flag controls whether or not the x-coordinates (in Java2D space)
+     * are rounded to integers.  When set to true, this can avoid the vertical
+     * striping that anti-aliasing can generate.  However, the rounding may not
+     * be appropriate for output in high resolution formats (for example,
+     * vector graphics formats such as SVG and PDF).
+     *
+     * @since 1.0.4
+     */
+    private boolean roundXCoordinates;
+
+    /**
+     * Creates a new renderer with default attributes.
+     */
+    public StableXYDifferenceRenderer() {
+        this(Color.green, Color.red, false);
+    }
+
+    /**
+     * Creates a new renderer.
+     *
+     * @param positivePaint  the highlight color for positive differences
+     *                       (<code>null</code> not permitted).
+     * @param negativePaint  the highlight color for negative differences
+     *                       (<code>null</code> not permitted).
+     * @param shapes  draw shapes?
+     */
+    public StableXYDifferenceRenderer(Paint positivePaint, Paint negativePaint,
+                                boolean shapes) {
+        if (positivePaint == null) {
+            throw new IllegalArgumentException(
+                    "Null 'positivePaint' argument.");
+        }
+        if (negativePaint == null) {
+            throw new IllegalArgumentException(
+                    "Null 'negativePaint' argument.");
+        }
+        this.positivePaint = positivePaint;
+        this.negativePaint = negativePaint;
+        this.shapesVisible = shapes;
+        this.legendLine = new Line2D.Double(-7.0, 0.0, 7.0, 0.0);
+        this.roundXCoordinates = false;
+    }
+
+    /**
+     * Returns the paint used to highlight positive differences.
+     *
+     * @return The paint (never <code>null</code>).
+     *
+     * @see #setPositivePaint(Paint)
+     */
+    public Paint getPositivePaint() {
+        return this.positivePaint;
+    }
+
+    /**
+     * Sets the paint used to highlight positive differences and sends a
+     * {@link RendererChangeEvent} to all registered listeners.
+     *
+     * @param paint  the paint (<code>null</code> not permitted).
+     *
+     * @see #getPositivePaint()
+     */
+    public void setPositivePaint(Paint paint) {
+        if (paint == null) {
+            throw new IllegalArgumentException("Null 'paint' argument.");
+        }
+        this.positivePaint = paint;
+        fireChangeEvent();
+    }
+
+    /**
+     * Returns the paint used to highlight negative differences.
+     *
+     * @return The paint (never <code>null</code>).
+     *
+     * @see #setNegativePaint(Paint)
+     */
+    public Paint getNegativePaint() {
+        return this.negativePaint;
+    }
+
+    /**
+     * Sets the paint used to highlight negative differences.
+     *
+     * @param paint  the paint (<code>null</code> not permitted).
+     *
+     * @see #getNegativePaint()
+     */
+    public void setNegativePaint(Paint paint) {
+        if (paint == null) {
+            throw new IllegalArgumentException("Null 'paint' argument.");
+        }
+        this.negativePaint = paint;
+        notifyListeners(new RendererChangeEvent(this));
+    }
+
+    /**
+     * Returns a flag that controls whether or not shapes are drawn for each
+     * data value.
+     *
+     * @return A boolean.
+     *
+     * @see #setShapesVisible(boolean)
+     */
+    public boolean getShapesVisible() {
+        return this.shapesVisible;
+    }
+
+    /**
+     * Sets a flag that controls whether or not shapes are drawn for each
+     * data value, and sends a {@link RendererChangeEvent} to all registered
+     * listeners.
+     *
+     * @param flag  the flag.
+     *
+     * @see #getShapesVisible()
+     */
+    public void setShapesVisible(boolean flag) {
+        this.shapesVisible = flag;
+        fireChangeEvent();
+    }
+
+    /**
+     * Returns the shape used to represent a line in the legend.
+     *
+     * @return The legend line (never <code>null</code>).
+     *
+     * @see #setLegendLine(Shape)
+     */
+    public Shape getLegendLine() {
+        return this.legendLine;
+    }
+
+    /**
+     * Sets the shape used as a line in each legend item and sends a
+     * {@link RendererChangeEvent} to all registered listeners.
+     *
+     * @param line  the line (<code>null</code> not permitted).
+     *
+     * @see #getLegendLine()
+     */
+    public void setLegendLine(Shape line) {
+        if (line == null) {
+            throw new IllegalArgumentException("Null 'line' argument.");
+        }
+        this.legendLine = line;
+        fireChangeEvent();
+    }
+
+    /**
+     * Returns the flag that controls whether or not the x-coordinates (in
+     * Java2D space) are rounded to integer values.
+     *
+     * @return The flag.
+     *
+     * @since 1.0.4
+     *
+     * @see #setRoundXCoordinates(boolean)
+     */
+    public boolean getRoundXCoordinates() {
+        return this.roundXCoordinates;
+    }
+
+    /**
+     * Sets the flag that controls whether or not the x-coordinates (in
+     * Java2D space) are rounded to integer values, and sends a
+     * {@link RendererChangeEvent} to all registered listeners.
+     *
+     * @param round  the new flag value.
+     *
+     * @since 1.0.4
+     *
+     * @see #getRoundXCoordinates()
+     */
+    public void setRoundXCoordinates(boolean round) {
+        this.roundXCoordinates = round;
+        fireChangeEvent();
+    }
+
+    /**
+     * Initialises the renderer and returns a state object that should be
+     * passed to subsequent calls to the drawItem() method.  This method will
+     * be called before the first item is rendered, giving the renderer an
+     * opportunity to initialise any state information it wants to maintain.
+     * The renderer can do nothing if it chooses.
+     *
+     * @param g2  the graphics device.
+     * @param dataArea  the area inside the axes.
+     * @param plot  the plot.
+     * @param data  the data.
+     * @param info  an optional info collection object to return data back to
+     *              the caller.
+     *
+     * @return A state object.
+     */
+    public XYItemRendererState initialise(Graphics2D g2,
+                                          Rectangle2D dataArea,
+                                          XYPlot plot,
+                                          XYDataset data,
+                                          PlotRenderingInfo info) {
+
+        XYItemRendererState state = super.initialise(g2, dataArea, plot, data,
+                info);
+        state.setProcessVisibleItemsOnly(false);
+        return state;
+
+    }
+
+    /**
+     * Returns <code>2</code>, the number of passes required by the renderer.
+     * The {@link XYPlot} will run through the dataset this number of times.
+     *
+     * @return The number of passes required by the renderer.
+     */
+    public int getPassCount() {
+        return 2;
+    }
+
+    /**
+     * Draws the visual representation of a single data item.
+     *
+     * @param g2  the graphics device.
+     * @param state  the renderer state.
+     * @param dataArea  the area within which the data is being drawn.
+     * @param info  collects information about the drawing.
+     * @param plot  the plot (can be used to obtain standard color
+     *              information etc).
+     * @param domainAxis  the domain (horizontal) axis.
+     * @param rangeAxis  the range (vertical) axis.
+     * @param dataset  the dataset.
+     * @param series  the series index (zero-based).
+     * @param item  the item index (zero-based).
+     * @param crosshairState  crosshair information for the plot
+     *                        (<code>null</code> permitted).
+     * @param pass  the pass index.
+     */
+    public void drawItem(Graphics2D g2,
+                         XYItemRendererState state,
+                         Rectangle2D dataArea,
+                         PlotRenderingInfo info,
+                         XYPlot plot,
+                         ValueAxis domainAxis,
+                         ValueAxis rangeAxis,
+                         XYDataset dataset,
+                         int series,
+                         int item,
+                         CrosshairState crosshairState,
+                         int pass) {
+
+        if (pass == 0) {
+            drawItemPass0(g2, dataArea, info, plot, domainAxis, rangeAxis,
+                    dataset, series, item, crosshairState);
+        }
+        else if (pass == 1) {
+            drawItemPass1(g2, dataArea, info, plot, domainAxis, rangeAxis,
+                    dataset, series, item, crosshairState);
+        }
+
+    }
+
+    /**
+     * Draws the visual representation of a single data item, first pass.
+     *
+     * @param x_graphics  the graphics device.
+     * @param x_dataArea  the area within which the data is being drawn.
+     * @param x_info  collects information about the drawing.
+     * @param x_plot  the plot (can be used to obtain standard color
+     *                information etc).
+     * @param x_domainAxis  the domain (horizontal) axis.
+     * @param x_rangeAxis  the range (vertical) axis.
+     * @param x_dataset  the dataset.
+     * @param x_series  the series index (zero-based).
+     * @param x_item  the item index (zero-based).
+     * @param x_crosshairState  crosshair information for the plot
+     *                          (<code>null</code> permitted).
+     */
+    protected void drawItemPass0(Graphics2D x_graphics,
+                                 Rectangle2D x_dataArea,
+                                 PlotRenderingInfo x_info,
+                                 XYPlot x_plot,
+                                 ValueAxis x_domainAxis,
+                                 ValueAxis x_rangeAxis,
+                                 XYDataset x_dataset,
+                                 int x_series,
+                                 int x_item,
+                                 CrosshairState x_crosshairState) {
+
+        if (!((0 == x_series) && (0 == x_item))) {
+            return;
+        }
+
+        boolean b_impliedZeroSubtrahend = (1 == x_dataset.getSeriesCount());
+
+        // check if either series is a degenerate case (i.e. less than 2 points)
+        if (isEitherSeriesDegenerate(x_dataset, b_impliedZeroSubtrahend)) {
+            return;
+        }
+
+        // check if series are disjoint (i.e. domain-spans do not overlap)
+        if (!b_impliedZeroSubtrahend && areSeriesDisjoint(x_dataset)) {
+            return;
+        }
+
+        // polygon definitions
+        LinkedList l_minuendXs    = new LinkedList();
+        LinkedList l_minuendYs    = new LinkedList();
+        LinkedList l_subtrahendXs = new LinkedList();
+        LinkedList l_subtrahendYs = new LinkedList();
+        LinkedList l_polygonXs    = new LinkedList();
+        LinkedList l_polygonYs    = new LinkedList();
+
+        // state
+        int l_minuendItem      = 0;
+        int l_minuendItemCount = x_dataset.getItemCount(0);
+        Double l_minuendCurX   = null;
+        Double l_minuendNextX  = null;
+        Double l_minuendCurY   = null;
+        Double l_minuendNextY  = null;
+        double l_minuendMaxY   = Double.NEGATIVE_INFINITY;
+        double l_minuendMinY   = Double.POSITIVE_INFINITY;
+
+        int l_subtrahendItem      = 0;
+        int l_subtrahendItemCount = 0; // actual value set below
+        Double l_subtrahendCurX   = null;
+        Double l_subtrahendNextX  = null;
+        Double l_subtrahendCurY   = null;
+        Double l_subtrahendNextY  = null;
+        double l_subtrahendMaxY   = Double.NEGATIVE_INFINITY;
+        double l_subtrahendMinY   = Double.POSITIVE_INFINITY;
+
+        // if a subtrahend is not specified, assume it is zero
+        if (b_impliedZeroSubtrahend) {
+            l_subtrahendItem      = 0;
+            l_subtrahendItemCount = 2;
+            l_subtrahendCurX      = new Double(x_dataset.getXValue(0, 0));
+            l_subtrahendNextX     = new Double(x_dataset.getXValue(0,
+                    (l_minuendItemCount - 1)));
+            l_subtrahendCurY      = new Double(0.0);
+            l_subtrahendNextY     = new Double(0.0);
+            l_subtrahendMaxY      = 0.0;
+            l_subtrahendMinY      = 0.0;
+
+            l_subtrahendXs.add(l_subtrahendCurX);
+            l_subtrahendYs.add(l_subtrahendCurY);
+        }
+        else {
+            l_subtrahendItemCount = x_dataset.getItemCount(1);
+        }
+
+        boolean b_minuendDone           = false;
+        boolean b_minuendAdvanced       = true;
+        boolean b_minuendAtIntersect    = false;
+        boolean b_minuendFastForward    = false;
+        boolean b_subtrahendDone        = false;
+        boolean b_subtrahendAdvanced    = true;
+        boolean b_subtrahendAtIntersect = false;
+        boolean b_subtrahendFastForward = false;
+        boolean b_colinear              = false;
+
+        boolean b_positive;
+
+        // coordinate pairs
+        double l_x1 = 0.0, l_y1 = 0.0; // current minuend point
+        double l_x2 = 0.0, l_y2 = 0.0; // next minuend point
+        double l_x3 = 0.0, l_y3 = 0.0; // current subtrahend point
+        double l_x4 = 0.0, l_y4 = 0.0; // next subtrahend point
+
+        // fast-forward through leading tails
+        boolean b_fastForwardDone = false;
+        while (!b_fastForwardDone) {
+            // get the x and y coordinates
+            l_x1 = x_dataset.getXValue(0, l_minuendItem);
+            l_y1 = x_dataset.getYValue(0, l_minuendItem);
+            l_x2 = x_dataset.getXValue(0, l_minuendItem + 1);
+            l_y2 = x_dataset.getYValue(0, l_minuendItem + 1);
+
+            l_minuendCurX  = new Double(l_x1);
+            l_minuendCurY  = new Double(l_y1);
+            l_minuendNextX = new Double(l_x2);
+            l_minuendNextY = new Double(l_y2);
+
+            if (b_impliedZeroSubtrahend) {
+                l_x3 = l_subtrahendCurX.doubleValue();
+                l_y3 = l_subtrahendCurY.doubleValue();
+                l_x4 = l_subtrahendNextX.doubleValue();
+                l_y4 = l_subtrahendNextY.doubleValue();
+            }
+            else {
+                l_x3 = x_dataset.getXValue(1, l_subtrahendItem);
+                l_y3 = x_dataset.getYValue(1, l_subtrahendItem);
+                l_x4 = x_dataset.getXValue(1, l_subtrahendItem + 1);
+                l_y4 = x_dataset.getYValue(1, l_subtrahendItem + 1);
+
+                l_subtrahendCurX  = new Double(l_x3);
+                l_subtrahendCurY  = new Double(l_y3);
+                l_subtrahendNextX = new Double(l_x4);
+                l_subtrahendNextY = new Double(l_y4);
+            }
+
+            if (l_x2 <= l_x3) {
+                // minuend needs to be fast forwarded
+                l_minuendItem++;
+                b_minuendFastForward = true;
+                continue;
+            }
+
+            if (l_x4 <= l_x1) {
+                // subtrahend needs to be fast forwarded
+                l_subtrahendItem++;
+                b_subtrahendFastForward = true;
+                continue;
+            }
+
+            // check if initial polygon needs to be clipped
+            if ((l_x3 < l_x1) && (l_x1 < l_x4)) {
+                // project onto subtrahend
+                double l_slope   = (l_y4 - l_y3) / (l_x4 - l_x3);
+                l_subtrahendCurX = l_minuendCurX;
+                l_subtrahendCurY = new Double((l_slope * l_x1)
+                        + (l_y3 - (l_slope * l_x3)));
+
+                l_subtrahendXs.add(l_subtrahendCurX);
+                l_subtrahendYs.add(l_subtrahendCurY);
+            }
+
+            if ((l_x1 < l_x3) && (l_x3 < l_x2)) {
+                // project onto minuend
+                double l_slope = (l_y2 - l_y1) / (l_x2 - l_x1);
+                l_minuendCurX  = l_subtrahendCurX;
+                l_minuendCurY  = new Double((l_slope * l_x3)
+                        + (l_y1 - (l_slope * l_x1)));
+
+                l_minuendXs.add(l_minuendCurX);
+                l_minuendYs.add(l_minuendCurY);
+            }
+
+            l_minuendMaxY    = l_minuendCurY.doubleValue();
+            l_minuendMinY    = l_minuendCurY.doubleValue();
+            l_subtrahendMaxY = l_subtrahendCurY.doubleValue();
+            l_subtrahendMinY = l_subtrahendCurY.doubleValue();
+
+            b_fastForwardDone = true;
+        }
+
+        // start of algorithm
+        while (!b_minuendDone && !b_subtrahendDone) {
+            if (!b_minuendDone && !b_minuendFastForward && b_minuendAdvanced) {
+                l_x1 = x_dataset.getXValue(0, l_minuendItem);
+                l_y1 = x_dataset.getYValue(0, l_minuendItem);
+                l_minuendCurX = new Double(l_x1);
+                l_minuendCurY = new Double(l_y1);
+
+                if (!b_minuendAtIntersect) {
+                    l_minuendXs.add(l_minuendCurX);
+                    l_minuendYs.add(l_minuendCurY);
+                }
+
+                l_minuendMaxY = Math.max(l_minuendMaxY, l_y1);
+                l_minuendMinY = Math.min(l_minuendMinY, l_y1);
+
+                l_x2 = x_dataset.getXValue(0, l_minuendItem + 1);
+                l_y2 = x_dataset.getYValue(0, l_minuendItem + 1);
+                l_minuendNextX = new Double(l_x2);
+                l_minuendNextY = new Double(l_y2);
+            }
+
+            // never updated the subtrahend if it is implied to be zero
+            if (!b_impliedZeroSubtrahend && !b_subtrahendDone
+                    && !b_subtrahendFastForward && b_subtrahendAdvanced) {
+                l_x3 = x_dataset.getXValue(1, l_subtrahendItem);
+                l_y3 = x_dataset.getYValue(1, l_subtrahendItem);
+                l_subtrahendCurX = new Double(l_x3);
+                l_subtrahendCurY = new Double(l_y3);
+
+                if (!b_subtrahendAtIntersect) {
+                    l_subtrahendXs.add(l_subtrahendCurX);
+                    l_subtrahendYs.add(l_subtrahendCurY);
+                }
+
+                l_subtrahendMaxY = Math.max(l_subtrahendMaxY, l_y3);
+                l_subtrahendMinY = Math.min(l_subtrahendMinY, l_y3);
+
+                l_x4 = x_dataset.getXValue(1, l_subtrahendItem + 1);
+                l_y4 = x_dataset.getYValue(1, l_subtrahendItem + 1);
+                l_subtrahendNextX = new Double(l_x4);
+                l_subtrahendNextY = new Double(l_y4);
+            }
+
+            // deassert b_*FastForward (only matters for 1st time through loop)
+            b_minuendFastForward    = false;
+            b_subtrahendFastForward = false;
+
+            Double l_intersectX = null;
+            Double l_intersectY = null;
+            boolean b_intersect = false;
+
+            b_minuendAtIntersect    = false;
+            b_subtrahendAtIntersect = false;
+
+            // check for intersect
+            if ((l_x2 == l_x4) && (l_y2 == l_y4)) {
+                // check if line segments are colinear
+                if ((l_x1 == l_x3) && (l_y1 == l_y3)) {
+                    b_colinear = true;
+                }
+                else {
+                    // the intersect is at the next point for both the minuend
+                    // and subtrahend
+                    l_intersectX = new Double(l_x2);
+                    l_intersectY = new Double(l_y2);
+
+                    b_intersect             = true;
+                    b_minuendAtIntersect    = true;
+                    b_subtrahendAtIntersect = true;
+                 }
+            }
+            else {
+                // compute common denominator
+                double l_denominator = ((l_y4 - l_y3) * (l_x2 - l_x1))
+                        - ((l_x4 - l_x3) * (l_y2 - l_y1));
+
+                // compute common deltas
+                double l_deltaY = l_y1 - l_y3;
+                double l_deltaX = l_x1 - l_x3;
+
+                // compute numerators
+                double l_numeratorA = ((l_x4 - l_x3) * l_deltaY)
+                        - ((l_y4 - l_y3) * l_deltaX);
+                double l_numeratorB = ((l_x2 - l_x1) * l_deltaY)
+                        - ((l_y2 - l_y1) * l_deltaX);
+
+                // check if line segments are colinear
+                if ((0 == l_numeratorA) && (0 == l_numeratorB)
+                        && (0 == l_denominator)) {
+                    b_colinear = true;
+                }
+                else {
+                    // check if previously colinear
+                    if (b_colinear) {
+                        // clear colinear points and flag
+                        l_minuendXs.clear();
+                        l_minuendYs.clear();
+                        l_subtrahendXs.clear();
+                        l_subtrahendYs.clear();
+                        l_polygonXs.clear();
+                        l_polygonYs.clear();
+
+                        b_colinear = false;
+
+                        // set new starting point for the polygon
+                        boolean b_useMinuend = ((l_x3 <= l_x1)
+                                && (l_x1 <= l_x4));
+                        l_polygonXs.add(b_useMinuend ? l_minuendCurX
+                                : l_subtrahendCurX);
+                        l_polygonYs.add(b_useMinuend ? l_minuendCurY
+                                : l_subtrahendCurY);
+                    }
+
+                    // compute slope components
+                    double l_slopeA = l_numeratorA / l_denominator;
+                    double l_slopeB = l_numeratorB / l_denominator;
+
+                    // check if the line segments intersect
+                    if ((0 < l_slopeA) && (l_slopeA <= 1) && (0 < l_slopeB)
+                            && (l_slopeB <= 1)) {
+                        // compute the point of intersection
+                        double l_xi = l_x1 + (l_slopeA * (l_x2 - l_x1));
+                        double l_yi = l_y1 + (l_slopeA * (l_y2 - l_y1));
+
+                        l_intersectX            = new Double(l_xi);
+                        l_intersectY            = new Double(l_yi);
+                        b_intersect             = true;
+                        b_minuendAtIntersect    = ((l_xi == l_x2)
+                                && (l_yi == l_y2));
+                        b_subtrahendAtIntersect = ((l_xi == l_x4)
+                                && (l_yi == l_y4));
+
+                        // advance minuend and subtrahend to intesect
+                        l_minuendCurX    = l_intersectX;
+                        l_minuendCurY    = l_intersectY;
+                        l_subtrahendCurX = l_intersectX;
+                        l_subtrahendCurY = l_intersectY;
+                    }
+                }
+            }
+
+            if (b_intersect) {
+                // create the polygon
+                // add the minuend's points to polygon
+                l_polygonXs.addAll(l_minuendXs);
+                l_polygonYs.addAll(l_minuendYs);
+
+                // add intersection point to the polygon
+                l_polygonXs.add(l_intersectX);
+                l_polygonYs.add(l_intersectY);
+
+                // add the subtrahend's points to the polygon in reverse
+                Collections.reverse(l_subtrahendXs);
+                Collections.reverse(l_subtrahendYs);
+                l_polygonXs.addAll(l_subtrahendXs);
+                l_polygonYs.addAll(l_subtrahendYs);
+
+                // create an actual polygon
+                b_positive = (l_subtrahendMaxY <= l_minuendMaxY)
+                        && (l_subtrahendMinY <= l_minuendMinY);
+                createPolygon(x_graphics, x_dataArea, x_plot, x_domainAxis,
+                        x_rangeAxis, b_positive, l_polygonXs, l_polygonYs);
+
+                // clear the point vectors
+                l_minuendXs.clear();
+                l_minuendYs.clear();
+                l_subtrahendXs.clear();
+                l_subtrahendYs.clear();
+                l_polygonXs.clear();
+                l_polygonYs.clear();
+
+                // set the maxY and minY values to intersect y-value
+                double l_y       = l_intersectY.doubleValue();
+                l_minuendMaxY    = l_y;
+                l_subtrahendMaxY = l_y;
+                l_minuendMinY    = l_y;
+                l_subtrahendMinY = l_y;
+
+                // add interection point to new polygon
+                l_polygonXs.add(l_intersectX);
+                l_polygonYs.add(l_intersectY);
+            }
+
+            // advance the minuend if needed
+            if (l_x2 <= l_x4) {
+                l_minuendItem++;
+                b_minuendAdvanced = true;
+            }
+            else {
+                b_minuendAdvanced = false;
+            }
+
+            // advance the subtrahend if needed
+            if (l_x4 <= l_x2) {
+                l_subtrahendItem++;
+                b_subtrahendAdvanced = true;
+            }
+            else {
+                b_subtrahendAdvanced = false;
+            }
+
+            b_minuendDone    = (l_minuendItem == (l_minuendItemCount - 1));
+            b_subtrahendDone = (l_subtrahendItem == (l_subtrahendItemCount
+                    - 1));
+        }
+
+        // check if the final polygon needs to be clipped
+        if (b_minuendDone && (l_x3 < l_x2) && (l_x2 < l_x4)) {
+            // project onto subtrahend
+            double l_slope    = (l_y4 - l_y3) / (l_x4 - l_x3);
+            l_subtrahendNextX = l_minuendNextX;
+            l_subtrahendNextY = new Double((l_slope * l_x2)
+                    + (l_y3 - (l_slope * l_x3)));
+        }
+
+        if (b_subtrahendDone && (l_x1 < l_x4) && (l_x4 < l_x2)) {
+            // project onto minuend
+            double l_slope = (l_y2 - l_y1) / (l_x2 - l_x1);
+            l_minuendNextX = l_subtrahendNextX;
+            l_minuendNextY = new Double((l_slope * l_x4)
+                    + (l_y1 - (l_slope * l_x1)));
+        }
+
+        // consider last point of minuend and subtrahend for determining
+        // positivity
+        l_minuendMaxY    = Math.max(l_minuendMaxY,
+                l_minuendNextY.doubleValue());
+        l_subtrahendMaxY = Math.max(l_subtrahendMaxY,
+                l_subtrahendNextY.doubleValue());
+        l_minuendMinY    = Math.min(l_minuendMinY,
+                l_minuendNextY.doubleValue());
+        l_subtrahendMinY = Math.min(l_subtrahendMinY,
+                l_subtrahendNextY.doubleValue());
+
+        // add the last point of the minuned and subtrahend
+        l_minuendXs.add(l_minuendNextX);
+        l_minuendYs.add(l_minuendNextY);
+        l_subtrahendXs.add(l_subtrahendNextX);
+        l_subtrahendYs.add(l_subtrahendNextY);
+
+        // create the polygon
+        // add the minuend's points to polygon
+        l_polygonXs.addAll(l_minuendXs);
+        l_polygonYs.addAll(l_minuendYs);
+
+        // add the subtrahend's points to the polygon in reverse
+        Collections.reverse(l_subtrahendXs);
+        Collections.reverse(l_subtrahendYs);
+        l_polygonXs.addAll(l_subtrahendXs);
+        l_polygonYs.addAll(l_subtrahendYs);
+
+        // create an actual polygon
+        b_positive = (l_subtrahendMaxY <= l_minuendMaxY)
+                && (l_subtrahendMinY <= l_minuendMinY);
+        createPolygon(x_graphics, x_dataArea, x_plot, x_domainAxis,
+                x_rangeAxis, b_positive, l_polygonXs, l_polygonYs);
+    }
+
+    /**
+     * Draws the visual representation of a single data item, second pass.  In
+     * the second pass, the renderer draws the lines and shapes for the
+     * individual points in the two series.
+     *
+     * @param x_graphics  the graphics device.
+     * @param x_dataArea  the area within which the data is being drawn.
+     * @param x_info  collects information about the drawing.
+     * @param x_plot  the plot (can be used to obtain standard color
+     *         information etc).
+     * @param x_domainAxis  the domain (horizontal) axis.
+     * @param x_rangeAxis  the range (vertical) axis.
+     * @param x_dataset  the dataset.
+     * @param x_series  the series index (zero-based).
+     * @param x_item  the item index (zero-based).
+     * @param x_crosshairState  crosshair information for the plot
+     *                          (<code>null</code> permitted).
+     */
+    protected void drawItemPass1(Graphics2D x_graphics,
+                                 Rectangle2D x_dataArea,
+                                 PlotRenderingInfo x_info,
+                                 XYPlot x_plot,
+                                 ValueAxis x_domainAxis,
+                                 ValueAxis x_rangeAxis,
+                                 XYDataset x_dataset,
+                                 int x_series,
+                                 int x_item,
+                                 CrosshairState x_crosshairState) {
+
+        Shape l_entityArea = null;
+        EntityCollection l_entities = null;
+        if (null != x_info) {
+            l_entities = x_info.getOwner().getEntityCollection();
+        }
+
+        Paint l_seriesPaint   = getItemPaint(x_series, x_item);
+        Stroke l_seriesStroke = getItemStroke(x_series, x_item);
+        x_graphics.setPaint(l_seriesPaint);
+        x_graphics.setStroke(l_seriesStroke);
+
+        PlotOrientation l_orientation      = x_plot.getOrientation();
+        RectangleEdge l_domainAxisLocation = x_plot.getDomainAxisEdge();
+        RectangleEdge l_rangeAxisLocation  = x_plot.getRangeAxisEdge();
+
+        double l_x0 = x_dataset.getXValue(x_series, x_item);
+        double l_y0 = x_dataset.getYValue(x_series, x_item);
+        double l_x1 = x_domainAxis.valueToJava2D(l_x0, x_dataArea,
+                l_domainAxisLocation);
+        double l_y1 = x_rangeAxis.valueToJava2D(l_y0, x_dataArea,
+                l_rangeAxisLocation);
+
+        if (getShapesVisible()) {
+            Shape l_shape = getItemShape(x_series, x_item);
+            if (l_orientation == PlotOrientation.HORIZONTAL) {
+                l_shape = ShapeUtilities.createTranslatedShape(l_shape,
+                        l_y1, l_x1);
+            }
+            else {
+                l_shape = ShapeUtilities.createTranslatedShape(l_shape,
+                        l_x1, l_y1);
+            }
+            if (l_shape.intersects(x_dataArea)) {
+                x_graphics.setPaint(getItemPaint(x_series, x_item));
+                x_graphics.fill(l_shape);
+            }
+            l_entityArea = l_shape;
+        }
+
+        // add an entity for the item...
+        if (null != l_entities) {
+            if (null == l_entityArea) {
+                l_entityArea = new Rectangle2D.Double((l_x1 - 2), (l_y1 - 2),
+                        4, 4);
+            }
+            String l_tip = null;
+            XYToolTipGenerator l_tipGenerator = getToolTipGenerator(x_series,
+                    x_item);
+            if (null != l_tipGenerator) {
+                l_tip = l_tipGenerator.generateToolTip(x_dataset, x_series,
+                        x_item);
+            }
+            String l_url = null;
+            XYURLGenerator l_urlGenerator = getURLGenerator();
+            if (null != l_urlGenerator) {
+                l_url = l_urlGenerator.generateURL(x_dataset, x_series,
+                        x_item);
+            }
+            XYItemEntity l_entity = new XYItemEntity(l_entityArea, x_dataset,
+                    x_series, x_item, l_tip, l_url);
+            l_entities.add(l_entity);
+        }
+
+        // draw the item label if there is one...
+        if (isItemLabelVisible(x_series, x_item)) {
+            drawItemLabel(x_graphics, l_orientation, x_dataset, x_series,
+                          x_item, l_x1, l_y1, (l_y1 < 0.0));
+        }
+
+        int l_domainAxisIndex = x_plot.getDomainAxisIndex(x_domainAxis);
+        int l_rangeAxisIndex  = x_plot.getRangeAxisIndex(x_rangeAxis);
+        updateCrosshairValues(x_crosshairState, l_x0, l_y0, l_domainAxisIndex,
+                              l_rangeAxisIndex, l_x1, l_y1, l_orientation);
+
+        if (0 == x_item) {
+            return;
+        }
+
+        double l_x2 = x_domainAxis.valueToJava2D(x_dataset.getXValue(x_series,
+                (x_item - 1)), x_dataArea, l_domainAxisLocation);
+        double l_y2 = x_rangeAxis.valueToJava2D(x_dataset.getYValue(x_series,
+                (x_item - 1)), x_dataArea, l_rangeAxisLocation);
+
+        Line2D l_line = null;
+        if (PlotOrientation.HORIZONTAL == l_orientation) {
+            l_line = new Line2D.Double(l_y1, l_x1, l_y2, l_x2);
+        }
+        else if (PlotOrientation.VERTICAL == l_orientation) {
+            l_line = new Line2D.Double(l_x1, l_y1, l_x2, l_y2);
+        }
+
+        if ((null != l_line) && l_line.intersects(x_dataArea)) {
+            x_graphics.setPaint(getItemPaint(x_series, x_item));
+            x_graphics.setStroke(getItemStroke(x_series, x_item));
+            x_graphics.draw(l_line);
+        }
+    }
+
+    /**
+     * Determines if a dataset is degenerate.  A degenerate dataset is a
+     * dataset where either series has less than two (2) points.
+     *
+     * @param x_dataset  the dataset.
+     * @param x_impliedZeroSubtrahend  if false, do not check the subtrahend
+     *
+     * @return true if the dataset is degenerate.
+     */
+    private boolean isEitherSeriesDegenerate(XYDataset x_dataset,
+            boolean x_impliedZeroSubtrahend) {
+
+        if (x_impliedZeroSubtrahend) {
+            return (x_dataset.getItemCount(0) < 2);
+        }
+
+        return ((x_dataset.getItemCount(0) < 2)
+                || (x_dataset.getItemCount(1) < 2));
+    }
+
+    /**
+     * Determines if the two (2) series are disjoint.
+     * Disjoint series do not overlap in the domain space.
+     *
+     * @param x_dataset  the dataset.
+     *
+     * @return true if the dataset is degenerate.
+     */
+    private boolean areSeriesDisjoint(XYDataset x_dataset) {
+
+        int l_minuendItemCount = x_dataset.getItemCount(0);
+        double l_minuendFirst  = x_dataset.getXValue(0, 0);
+        double l_minuendLast   = x_dataset.getXValue(0, l_minuendItemCount - 1);
+
+        int l_subtrahendItemCount = x_dataset.getItemCount(1);
+        double l_subtrahendFirst  = x_dataset.getXValue(1, 0);
+        double l_subtrahendLast   = x_dataset.getXValue(1,
+                l_subtrahendItemCount - 1);
+
+        return ((l_minuendLast < l_subtrahendFirst)
+                || (l_subtrahendLast < l_minuendFirst));
+    }
+
+    /**
+     * Draws the visual representation of a polygon
+     *
+     * @param x_graphics  the graphics device.
+     * @param x_dataArea  the area within which the data is being drawn.
+     * @param x_plot  the plot (can be used to obtain standard color
+     *                information etc).
+     * @param x_domainAxis  the domain (horizontal) axis.
+     * @param x_rangeAxis  the range (vertical) axis.
+     * @param x_positive  indicates if the polygon is positive (true) or
+     *                    negative (false).
+     * @param x_xValues  a linked list of the x values (expects values to be
+     *                   of type Double).
+     * @param x_yValues  a linked list of the y values (expects values to be
+     *                   of type Double).
+     */
+    private void createPolygon (Graphics2D x_graphics,
+                                Rectangle2D x_dataArea,
+                                XYPlot x_plot,
+                                ValueAxis x_domainAxis,
+                                ValueAxis x_rangeAxis,
+                                boolean x_positive,
+                                LinkedList x_xValues,
+                                LinkedList x_yValues) {
+
+        PlotOrientation l_orientation      = x_plot.getOrientation();
+        RectangleEdge l_domainAxisLocation = x_plot.getDomainAxisEdge();
+        RectangleEdge l_rangeAxisLocation  = x_plot.getRangeAxisEdge();
+
+        Object[] l_xValues = x_xValues.toArray();
+        Object[] l_yValues = x_yValues.toArray();
+
+        GeneralPath l_path = new GeneralPath();
+
+        if (PlotOrientation.VERTICAL == l_orientation) {
+            double l_x = x_domainAxis.valueToJava2D((
+                    (Double) l_xValues[0]).doubleValue(), x_dataArea,
+                    l_domainAxisLocation);
+            if (this.roundXCoordinates) {
+                l_x = Math.rint(l_x);
+            }
+
+            double l_y = x_rangeAxis.valueToJava2D((
+                    (Double) l_yValues[0]).doubleValue(), x_dataArea,
+                    l_rangeAxisLocation);
+
+            l_path.moveTo((float) l_x, (float) l_y);
+            for (int i = 1; i < l_xValues.length; i++) {
+                l_x = x_domainAxis.valueToJava2D((
+                        (Double) l_xValues[i]).doubleValue(), x_dataArea,
+                        l_domainAxisLocation);
+                if (this.roundXCoordinates) {
+                    l_x = Math.rint(l_x);
+                }
+
+                l_y = x_rangeAxis.valueToJava2D((
+                        (Double) l_yValues[i]).doubleValue(), x_dataArea,
+                        l_rangeAxisLocation);
+                l_path.lineTo((float) l_x, (float) l_y);
+            }
+            l_path.closePath();
+        }
+        else {
+            double l_x = x_domainAxis.valueToJava2D((
+                    (Double) l_xValues[0]).doubleValue(), x_dataArea,
+                    l_domainAxisLocation);
+            if (this.roundXCoordinates) {
+                l_x = Math.rint(l_x);
+            }
+
+            double l_y = x_rangeAxis.valueToJava2D((
+                    (Double) l_yValues[0]).doubleValue(), x_dataArea,
+                    l_rangeAxisLocation);
+
+            l_path.moveTo((float) l_y, (float) l_x);
+            for (int i = 1; i < l_xValues.length; i++) {
+                l_x = x_domainAxis.valueToJava2D((
+                        (Double) l_xValues[i]).doubleValue(), x_dataArea,
+                        l_domainAxisLocation);
+                if (this.roundXCoordinates) {
+                    l_x = Math.rint(l_x);
+                }
+
+                l_y = x_rangeAxis.valueToJava2D((
+                        (Double) l_yValues[i]).doubleValue(), x_dataArea,
+                        l_rangeAxisLocation);
+                l_path.lineTo((float) l_y, (float) l_x);
+            }
+            l_path.closePath();
+        }
+
+        if (l_path.intersects(x_dataArea)) {
+            x_graphics.setPaint(x_positive ? getPositivePaint()
+                    : getNegativePaint());
+            x_graphics.fill(l_path);
+        }
+    }
+
+    /**
+     * Returns a default legend item for the specified series.  Subclasses
+     * should override this method to generate customised items.
+     *
+     * @param datasetIndex  the dataset index (zero-based).
+     * @param series  the series index (zero-based).
+     *
+     * @return A legend item for the series.
+     */
+    public LegendItem getLegendItem(int datasetIndex, int series) {
+        LegendItem result = null;
+        XYPlot p = getPlot();
+        if (p != null) {
+            XYDataset dataset = p.getDataset(datasetIndex);
+            if (dataset != null) {
+                if (getItemVisible(series, 0)) {
+                    String label = getLegendItemLabelGenerator().generateLabel(
+                            dataset, series);
+                    String description = label;
+                    String toolTipText = null;
+                    if (getLegendItemToolTipGenerator() != null) {
+                        toolTipText
+                            = getLegendItemToolTipGenerator().generateLabel(
+                                    dataset, series);
+                    }
+                    String urlText = null;
+                    if (getLegendItemURLGenerator() != null) {
+                        urlText = getLegendItemURLGenerator().generateLabel(
+                                dataset, series);
+                    }
+                    Paint paint = lookupSeriesPaint(series);
+                    Stroke stroke = lookupSeriesStroke(series);
+                    Shape line = getLegendLine();
+                    result = new LegendItem(label, description,
+                            toolTipText, urlText, line, stroke, paint);
+                    result.setLabelFont(lookupLegendTextFont(series));
+                    Paint labelPaint = lookupLegendTextPaint(series);
+                    if (labelPaint != null) {
+                        result.setLabelPaint(labelPaint);
+                    }
+                    result.setDataset(dataset);
+                    result.setDatasetIndex(datasetIndex);
+                    result.setSeriesKey(dataset.getSeriesKey(series));
+                    result.setSeriesIndex(series);
+                }
+            }
+
+        }
+
+        return result;
+
+    }
+
+    /**
+     * Tests this renderer for equality with an arbitrary object.
+     *
+     * @param obj  the object (<code>null</code> permitted).
+     *
+     * @return A boolean.
+     */
+    public boolean equals(Object obj) {
+        if (obj == this) {
+            return true;
+        }
+        if (!(obj instanceof StableXYDifferenceRenderer)) {
+            return false;
+        }
+        if (!super.equals(obj)) {
+            return false;
+        }
+        StableXYDifferenceRenderer that = (StableXYDifferenceRenderer) obj;
+        if (!PaintUtilities.equal(this.positivePaint, that.positivePaint)) {
+            return false;
+        }
+        if (!PaintUtilities.equal(this.negativePaint, that.negativePaint)) {
+            return false;
+        }
+        if (this.shapesVisible != that.shapesVisible) {
+            return false;
+        }
+        if (!ShapeUtilities.equal(this.legendLine, that.legendLine)) {
+            return false;
+        }
+        if (this.roundXCoordinates != that.roundXCoordinates) {
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * Returns a clone of the renderer.
+     *
+     * @return A clone.
+     *
+     * @throws CloneNotSupportedException  if the renderer cannot be cloned.
+     */
+    public Object clone() throws CloneNotSupportedException {
+        StableXYDifferenceRenderer clone = (StableXYDifferenceRenderer) super.clone();
+        clone.legendLine = ShapeUtilities.clone(this.legendLine);
+        return clone;
+    }
+
+    /**
+     * Provides serialization support.
+     *
+     * @param stream  the output stream.
+     *
+     * @throws IOException  if there is an I/O error.
+     */
+    private void writeObject(ObjectOutputStream stream) throws IOException {
+        stream.defaultWriteObject();
+        SerialUtilities.writePaint(this.positivePaint, stream);
+        SerialUtilities.writePaint(this.negativePaint, stream);
+        SerialUtilities.writeShape(this.legendLine, stream);
+    }
+
+    /**
+     * Provides serialization support.
+     *
+     * @param stream  the input stream.
+     *
+     * @throws IOException  if there is an I/O error.
+     * @throws ClassNotFoundException  if there is a classpath problem.
+     */
+    private void readObject(ObjectInputStream stream)
+        throws IOException, ClassNotFoundException {
+        stream.defaultReadObject();
+        this.positivePaint = SerialUtilities.readPaint(stream);
+        this.negativePaint = SerialUtilities.readPaint(stream);
+        this.legendLine = SerialUtilities.readShape(stream);
+    }
+}
+