Alternate between less-or-equal and greater-or-equal sample searches

That is possibly easier solution - instead of searching closest sample
every update call we first search for less-or-equal sample
and then greater-or-equal.
Thanks to that we should keep more or less the same position as in the
beginning.

Author: Mateusz Nabywaniec

app/rtplot/src/main/java/org/csstudio/javafx/rtplot/internal/AnnotationImpl.java

@@ -43,6 +43,8 @@ public class AnnotationImpl<XTYPE extends Comparable<XTYPE>> extends Annotation<
 
     private static final Stroke DASH = new BasicStroke(1.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER, 10.0f, new float[] { 3f, 3f }, 1.0f);
 
+    private boolean searchLessOrEqual;
+
     /** What part of this annotation has been selected by the mouse? */
     public static enum Selection
     {   /** Nothing */
@@ -65,6 +67,7 @@ public static enum Selection
     public AnnotationImpl(final boolean internal, final Trace<XTYPE> trace, final XTYPE position, final double value, final Point2D offset, final String text)
     {
         super(internal, trace, position, value, offset, text);
+        searchLessOrEqual = true;
     }
 
     /** Set to new position
@@ -179,7 +182,15 @@ boolean updateValue(final XTYPE location) throws Exception
             throw new TimeoutException("Cannot update annotation, no lock on " + data);
         try
         {
-            final int index = search.findClosestSample(data, location);
+            final int index;
+            if (searchLessOrEqual){
+                index = search.findSampleLessOrEqual(data, location);
+            }
+            else{
+                index = search.findSampleGreaterOrEqual(data, location);
+            }
+            searchLessOrEqual = !searchLessOrEqual;
+
             if (index < 0)
                 return false;
             final PlotDataItem<XTYPE> sample = data.get(index);