--- a/flys-artifacts/ChangeLog	Thu Jan 12 16:01:01 2012 +0000
+++ b/flys-artifacts/ChangeLog	Thu Jan 12 16:49:00 2012 +0000
@@ -1,3 +1,9 @@
+2011-01-12	Sascha L. Teichmann	<sascha.teichmann@intevation.de>
+
+	* src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java:
+	  Added code to calculate the area of the generated polygons.
+	  TODO: Render the generated area sum to the plot.
+
 2011-01-12	Sascha L. Teichmann	<sascha.teichmann@intevation.de>
 
 	 * src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java:

--- a/flys-artifacts/src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java	Thu Jan 12 16:01:01 2012 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/jfree/StableXYDifferenceRenderer.java	Thu Jan 12 16:49:00 2012 +0000
@@ -137,6 +137,12 @@
 
     private static Logger log = Logger.getLogger(StableXYDifferenceRenderer.class);
 
+    public static final int CALCULATE_NO_AREA       = 0;
+    public static final int CALCULATE_POSITIVE_AREA = 1;
+    public static final int CALCULATE_NEGATIVE_AREA = 2;
+    public static final int CALCULATE_ALL_AREA =
+                            CALCULATE_POSITIVE_AREA | CALCULATE_NEGATIVE_AREA;
+
     /** For serialization. */
     private static final long serialVersionUID = -8447915602375584857L;
 
@@ -163,7 +169,11 @@
 
     protected boolean drawOriginalSeries;
 
-    //private XYDatasetToZeroMapper mapper;
+    protected int areaCalculationMode;
+
+    protected double positiveArea;
+    protected double negativeArea;
+
 
     /**
      * This flag controls whether or not the x-coordinates (in Java2D space)
@@ -183,6 +193,11 @@
         this(Color.green, Color.red, false /*,  null */);
     }
 
+    public StableXYDifferenceRenderer(Paint positivePaint, Paint negativePaint,
+                                boolean shapes) {
+        this(positivePaint, negativePaint, shapes, CALCULATE_NO_AREA);
+    }
+
     /**
      * Creates a new renderer.
      *
@@ -193,7 +208,7 @@
      * @param shapes  draw shapes?
      */
     public StableXYDifferenceRenderer(Paint positivePaint, Paint negativePaint,
-                                boolean shapes) {
+                                boolean shapes, int areaCalculationMode) {
         if (positivePaint == null) {
             throw new IllegalArgumentException(
                     "Null 'positivePaint' argument.");
@@ -211,8 +226,22 @@
         this.outlineStroke = new BasicStroke(1);
         this.outlinePaint  = Color.black;
         this.drawOriginalSeries = false;
+        this.areaCalculationMode = areaCalculationMode;
     }
 
+    public int getAreaCalculationMode() {
+        return areaCalculationMode;
+    }
+
+    public void setAreaCalculationMode(int areaCalculationMode) {
+        this.areaCalculationMode = areaCalculationMode;
+    }
+
+
+
+    public double getCalculatedArea() {
+        return positiveArea + negativeArea;
+    }
 
     /**
      * Sets color that is used if drawOutline is true.
@@ -1405,6 +1434,23 @@
                 || (l_subtrahendLast < l_minuendFirst));
     }
 
+    public static double calculateArea(Object [] xValues, Object [] yValues) {
+        double area = 0d;
+
+        for (int i = 0, N = xValues.length; i < N; ++i) {
+            int j = (i + 1) % N;
+            double xi = ((Double)xValues[i]).doubleValue();
+            double yi = ((Double)yValues[i]).doubleValue();
+            double xj = ((Double)xValues[j]).doubleValue();
+            double yj = ((Double)yValues[j]).doubleValue();
+
+            area += xi*yj;
+            area -= xj*yi;
+        }
+
+        return 0.5d*area;
+    }
+
     /**
      * Draws the visual representation of a polygon
      *
@@ -1437,6 +1483,20 @@
         Object[] l_xValues = x_xValues.toArray();
         Object[] l_yValues = x_yValues.toArray();
 
+        int acm = areaCalculationMode;
+
+        if (acm != CALCULATE_NO_AREA) {
+            if ((x_positive && ((acm|CALCULATE_POSITIVE_AREA)
+                    == CALCULATE_POSITIVE_AREA))
+            || (!x_positive && ((acm|CALCULATE_NEGATIVE_AREA)
+                    == CALCULATE_NEGATIVE_AREA))
+            ) {
+                double area = calculateArea(l_xValues, l_yValues);
+                if (x_positive) positiveArea += area;
+                else            negativeArea += area;
+            }
+        }
+
         GeneralPath l_path = new GeneralPath();
 
         if (PlotOrientation.VERTICAL == l_orientation) {