Fix annotation moving to the left when X axis PV changes

app/rtplot/src/main/java/org/csstudio/javafx/rtplot/data/PlotDataSearch.java

@@ -7,6 +7,9 @@
  ******************************************************************************/
 package org.csstudio.javafx.rtplot.data;
 
+import java.util.Date;
+import java.time.Instant;
+
 /** Search for samples in a haystack.
  *  @author Kay Kasemir
  */
@@ -125,4 +128,67 @@ final public int findSampleGreaterThan(final PlotDataProvider<XTYPE> data, final
         }
         return -1;
     }
+
+    /** Find the sample closest to the given value.
+     * @param data Data, must already be locked
+     * @param x The value to look for.
+     * @return Index of sample closest to x, or -1 if data is empty or type unsupported.
+     */
+    public int findClosestSample(final PlotDataProvider<XTYPE> data, final XTYPE x) {
+        int low = 0;
+        int high = data.size() - 1;
+
+        if (high < 0) return -1;
+
+        int bestIndex = -1;
+        double bestDistance = Double.MAX_VALUE;
+
+        double target;
+        try {
+            target = toDouble(x);
+        } catch (IllegalArgumentException e) {
+            return -1;
+        }
+
+        double distance;
+
+        while (low <= high) {
+            int mid = (low + high) / 2;
+            PlotDataItem<XTYPE> sample = data.get(mid);
+            XTYPE sampleX = sample.getPosition();
+            int cmp = sampleX.compareTo(x);
+
+            try{
+                distance = Math.abs(toDouble(sampleX) - target);
+            } catch (IllegalArgumentException e) {
+                return -1;
+            }
+
+            if (distance < bestDistance) {
+                bestDistance = distance;
+                bestIndex = mid;
+            }
+
+            if (cmp == 0) {
+                return mid;
+            } else if (cmp < 0) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+
+        return bestIndex;
+    }
+
+    /** Convert supported XTYPE to double for distance comparison */
+    private double toDouble(XTYPE x) {
+        if (x instanceof Number)
+            return ((Number) x).doubleValue();
+        if (x instanceof Instant)
+            return ((Instant) x).toEpochMilli();
+        if (x instanceof Date)
+            return ((Date) x).getTime();
+        throw new IllegalArgumentException("Unsupported XTYPE: " + x.getClass());
+    }
 }

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.findSampleLessOrEqual(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);