Fix bug in (error) point reduction

When reducing the points, the reducer would for some reason swap the
positive and negative error for the last point. When no actual reduction
is taking place, this leads to the values actually having the same value
which would give strange results in the error bars/surfaces.

This commit removes the swapping of the errors of the last point.

The error surface renderer would also swap these points again before
rendering, so this is also removed with this commit.

To ease testing, an option to enable/disable parallel point caching in
the renderer was added to the ErrorDataSetRendererStylingSample.

chartfx-chart/src/main/java/de/gsi/chart/renderer/datareduction/DefaultDataReducer.java

@@ -2,11 +2,12 @@
 
 import java.security.InvalidParameterException;
 
+import javafx.beans.property.IntegerProperty;
+import javafx.beans.property.SimpleIntegerProperty;
+
 import de.gsi.chart.renderer.RendererDataReducer;
 import de.gsi.dataset.utils.AssertUtils;
 import de.gsi.dataset.utils.ProcessingProfiler;
-import javafx.beans.property.IntegerProperty;
-import javafx.beans.property.SimpleIntegerProperty;
 
 /**
  * Default data reduction algorithm implementation for the ErrorDataSet Renderer <br>
@@ -17,7 +18,6 @@
  * @author rstein
  */
 public class DefaultDataReducer implements RendererDataReducer {
-
     protected IntegerProperty minPointPixelDistance = new SimpleIntegerProperty(this, "minPixelDistance", 6) {
         @Override
         public void set(final int value) {
@@ -218,8 +218,8 @@ private int reducePointsInternal(final double[] xValues, final double[] yValues,
         yValues[count] = yValues[indexMax - 1];
         xPointErrorsNeg[count] = xPointErrorsPos[indexMax - 1];
         xPointErrorsPos[count] = xPointErrorsNeg[indexMax - 1];
-        yPointErrorsNeg[count] = yPointErrorsPos[indexMax - 1];
-        yPointErrorsPos[count] = yPointErrorsNeg[indexMax - 1];
+        yPointErrorsNeg[count] = yPointErrorsNeg[indexMax - 1];
+        yPointErrorsPos[count] = yPointErrorsPos[indexMax - 1];
         pointSelected[count] = pointSelected[indexMax - 1];
         styles[count] = styles[indexMax - 1];
         count++;
@@ -480,5 +480,4 @@ private int reducePointsInternal(final double[] xValues, final double[] yValues,
     public final void setMinPointPixelDistance(final int minPixelDistance) {
         minPointPixelDistanceProperty().setValue(minPixelDistance);
     }
-
 }

chartfx-chart/src/main/java/de/gsi/chart/renderer/spi/ErrorDataSetRenderer.java

@@ -1,12 +1,7 @@
 package de.gsi.chart.renderer.spi;
 
 import java.security.InvalidParameterException;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-import java.util.Locale;
-import java.util.Map;
-import java.util.Optional;
+import java.util.*;
 
 import javafx.collections.ObservableList;
 import javafx.geometry.Orientation;
@@ -493,12 +488,6 @@ protected void drawErrorSurface(final GraphicsContext gc, final CachedDataPoints
             xValuesSurface[xend - i] = localCachedPoints.xValues[i];
             yValuesSurface[xend - i] = localCachedPoints.errorYPos[i];
         }
-        // swap y coordinates at mid-point
-        if (nDataCount > 4) {
-            final double yTmp = yValuesSurface[nDataCount - 1];
-            yValuesSurface[nDataCount - 1] = yValuesSurface[xend - nDataCount + 1];
-            yValuesSurface[xend - nDataCount + 1] = yTmp;
-        }
 
         gc.setFillRule(FillRule.EVEN_ODD);
         gc.fillPolygon(xValuesSurface, yValuesSurface, nPolygoneEdges);

chartfx-samples/src/main/java/de/gsi/chart/samples/ErrorDataSetRendererStylingSample.java

@@ -360,6 +360,12 @@ private ParameterTab getRendererTab(final XYChart chart, final ErrorDataSetRende
         assumeSorted.selectedProperty().addListener((ch, old, selected) -> chart.requestLayout());
         pane.addToParameterPane("Assume sorted data: ", assumeSorted);
 
+        pane.addToParameterPane(" ", null);
+        final CheckBox cacheParallel = new CheckBox();
+        cacheParallel.selectedProperty().bindBidirectional(errorRenderer.parallelImplementationProperty());
+        cacheParallel.selectedProperty().addListener((ch, old, selected) -> chart.requestLayout());
+        pane.addToParameterPane("   Point cache parallel: ", cacheParallel);
+
         return pane;
     }