Give the possibility to supply a custom label generator for pie charts

xchart-demo/src/main/java/org/knowm/xchart/demo/charts/pie/PieChart02.java

@@ -1,10 +1,14 @@
 package org.knowm.xchart.demo.charts.pie;
 
 import java.awt.Color;
+import java.util.Collection;
+
 import org.knowm.xchart.PieChart;
 import org.knowm.xchart.PieChartBuilder;
+import org.knowm.xchart.PieSeries;
 import org.knowm.xchart.SwingWrapper;
 import org.knowm.xchart.demo.charts.ExampleChart;
+import org.knowm.xchart.style.LabelGenerator;
 import org.knowm.xchart.style.PieStyler.LabelType;
 
 /**
@@ -16,6 +20,7 @@
  *   <li>Pie Chart
  *   <li>PieChartBuilder
  *   <li>Custom series palette
+ *   <li>Custom label type
  *   <li>Value Annotations
  *   <li>Tooltips
  */
@@ -35,6 +40,13 @@ public PieChart getChart() {
     PieChart chart =
         new PieChartBuilder().width(800).height(600).title(getClass().getSimpleName()).build();
 
+    // Series
+    chart.addSeries("Gold", 24);
+    chart.addSeries("Silver", 21);
+    chart.addSeries("Platinum", 39);
+    chart.addSeries("Copper", 17);
+    chart.addSeries("Zinc", 40);
+
     // Customize Chart
     Color[] sliceColors =
         new Color[] {
@@ -45,18 +57,12 @@ public PieChart getChart() {
           new Color(246, 199, 182)
         };
     chart.getStyler().setSeriesColors(sliceColors);
-    chart.getStyler().setLabelType(LabelType.Value);
+    chart.getStyler().setLabelType(LabelType.Custom);
+    chart.getStyler().setLabelGenerator(new CustomLabelGenerator(chart.getSeriesMap().values()));
     // chart.getStyler().setDecimalPattern("#0.000");
     chart.getStyler().setToolTipsEnabled(true);
     //    chart.getStyler().setToolTipsAlwaysVisible(true);
 
-    // Series
-    chart.addSeries("Gold", 24);
-    chart.addSeries("Silver", 21);
-    chart.addSeries("Platinum", 39);
-    chart.addSeries("Copper", 17);
-    chart.addSeries("Zinc", 40);
-
     return chart;
   }
 
@@ -65,4 +71,21 @@ public String getExampleChartName() {
 
     return getClass().getSimpleName() + " - Pie Chart Custom Color Palette";
   }
+
+  private static class CustomLabelGenerator implements LabelGenerator {
+
+    private final double total;
+
+    public CustomLabelGenerator(Collection<PieSeries> values) {
+
+      this.total = values.stream().map(PieSeries::getValue).mapToDouble(Number::doubleValue).sum();
+    }
+
+    @Override
+    public String generateSeriesLabel(PieSeries series) {
+
+      double percent = (series.getValue().doubleValue() / total) * 100;
+      return String.format("%s (%.2f%%)", series.getValue(), percent);
+    }
+  }
 }

xchart/src/main/java/org/knowm/xchart/internal/chartpart/PlotContent_Pie.java

@@ -290,6 +290,8 @@ private void paintLabels(Graphics2D g, Rectangle2D pieBounds, double total, doub
           } else {
             label = series.getName() + " (" + y.toString() + ")";
           }
+        } else if (pieStyler.getLabelType() == LabelType.Custom) {
+          label = pieStyler.getLabelGenerator().generateSeriesLabel(series);
         }
 
         TextLayout textLayout =

xchart/src/main/java/org/knowm/xchart/style/LabelGenerator.java

@@ -0,0 +1,7 @@
+package org.knowm.xchart.style;
+
+import org.knowm.xchart.PieSeries;
+
+public interface LabelGenerator {
+    String generateSeriesLabel(PieSeries series);
+}

xchart/src/main/java/org/knowm/xchart/style/PieStyler.java

@@ -26,6 +26,7 @@ public class PieStyler extends Styler {
   private Color labelsFontColor;
   private double labelsDistance;
   private LabelType labelType;
+  private LabelGenerator labelGenerator;
   private boolean isForceAllLabelsVisible;
   private boolean isLabelsFontColorAutomaticEnabled;
   private Color labelsFontColorAutomaticLight;
@@ -143,6 +144,23 @@ public PieStyler setLabelType(LabelType labelType) {
     return this;
   }
 
+  public LabelGenerator getLabelGenerator() {
+
+    return labelGenerator;
+  }
+
+  /**
+   * Sets the Pie custom label generator
+   *
+   * @param labelGenerator
+   */
+  public PieStyler setLabelGenerator(LabelGenerator labelGenerator) {
+
+    this.labelType = LabelType.Custom;
+    this.labelGenerator = labelGenerator;
+    return this;
+  }
+
   public boolean isForceAllLabelsVisible() {
 
     return isForceAllLabelsVisible;
@@ -361,7 +379,8 @@ public enum LabelType {
     Percentage,
     Name,
     NameAndPercentage,
-    NameAndValue
+    NameAndValue,
+    Custom
   }
 
   public enum ClockwiseDirectionType {