fixed the flickering issue with tail update, bug 3378

Change-Id: Ib52197191537d1dc8de1c704b6b23d9b2f3e1ff3

java/com.sap.sailing.gwt.ui/src/main/java/com/sap/sailing/gwt/ui/client/shared/racemap/FixesAndTails.java

@@ -12,6 +12,7 @@ import java.util.Map;
 import java.util.Set;
 
 import com.google.gwt.maps.client.base.LatLng;
+import com.google.gwt.maps.client.mvc.MVCArray;
 import com.google.gwt.maps.client.overlays.Polyline;
 import com.google.gwt.user.client.Timer;
 import com.google.gwt.user.client.rpc.AsyncCallback;
@@ -47,22 +48,23 @@ public class FixesAndTails {
     private final Map<CompetitorDTO, List<GPSFixDTO>> fixes;
     
     /**
-     * Tails of competitors currently displayed as overlays on the map.
+     * Tails of competitors currently displayed as overlays on the map. A tail may have an {@link MVCArray#getLength()
+     * empty} {@link Polyline#getPath()}. In this case, {@link #firstShownFix} and {@link #lastShownFix} will hold
+     * <code>-1</code> for that competitor key.
      */
     private final Map<CompetitorDTO, Polyline> tails;
 
-
     /**
-     * Key set is equal to that of {@link #tails} and tells what the index in in {@link #fixes} of the first fix shown
+     * Key set is equal to that of {@link #tails} and tells what the index in {@link #fixes} of the first fix shown
      * in {@link #tails} is. If a key is contained in this map, it is also contained in {@link #lastShownFix} and vice
-     * versa.
+     * versa. If a tail is present but has an empty path, this map contains <code>-1</code> for that competitor.
      */
     private final Map<CompetitorDTO, Integer> firstShownFix;
 
     /**
-     * Key set is equal to that of {@link #tails} and tells what the index in in {@link #fixes} of the last fix shown in
+     * Key set is equal to that of {@link #tails} and tells what the index in {@link #fixes} of the last fix shown in
      * {@link #tails} is. If a key is contained in this map, it is also contained in {@link #firstShownFix} and vice
-     * versa.
+     * versa. If a tail is present but has an empty path, this map contains <code>-1</code> for that competitor.
      */
     private final Map<CompetitorDTO, Integer> lastShownFix;
 
@@ -129,7 +131,9 @@ public class FixesAndTails {
      * Creates a polyline for the competitor represented by <code>competitorDTO</code>, taking the fixes from
      * {@link #fixes fixes.get(competitorDTO)} and using the fixes starting at time point <code>from</code> (inclusive)
      * up to the last fix with time point before <code>to</code>. The polyline is returned. Updates are applied to
-     * {@link #lastShownFix}, {@link #firstShownFix} and {@link #tails}.
+     * {@link #lastShownFix}, {@link #firstShownFix} and {@link #tails}.<p>
+     * 
+     * Precondition: <code>tails.containsKey(competitorDTO) == false</code>
      */
     protected Polyline createTailAndUpdateIndices(final CompetitorDTO competitorDTO, Date from, Date to, TailFactory tailFactory) {
         List<LatLng> points = new ArrayList<LatLng>();
@@ -199,10 +203,19 @@ public class FixesAndTails {
      *            longer tail itself), such that the second request that uses the <em>same</em> map will be considered
      *            having an overlap now, not leading to a replacement of the previous update originating from the same
      *            request.
+     * @return 
+     * 
+     * @return a {@link Runnable} for each competitor that the caller must invoke before starting to create or update
+     *         the key competitor's tail. The object returned may be a no-op, but it may also clear an existing tail if
+     *         necessary. The reason why this is not executed immediately is that there may be a transition-based delay
+     *         with which the tails are updated. In this case we would be producing severe flicker. By delaying the
+     *         command to the point when the update is applied should avoid such flicker.
      */
-    protected void updateFixes(Map<CompetitorDTO, List<GPSFixDTO>> fixesForCompetitors,
+    protected Map<CompetitorDTO, Runnable> updateFixes(Map<CompetitorDTO, List<GPSFixDTO>> fixesForCompetitors,
             Map<CompetitorDTO, Boolean> overlapsWithKnownFixes, TailFactory tailFactory, long timeForPositionTransitionMillis) {
-        for (Map.Entry<CompetitorDTO, List<GPSFixDTO>> e : fixesForCompetitors.entrySet()) {
+        final Map<CompetitorDTO, Runnable> result = new HashMap<>();
+        final Runnable noOp = new Runnable() { @Override public void run() {} };
+        for (final Map.Entry<CompetitorDTO, List<GPSFixDTO>> e : fixesForCompetitors.entrySet()) {
             if (e.getValue() != null && !e.getValue().isEmpty()) {
                 List<GPSFixDTO> fixesForCompetitor = fixes.get(e.getKey());
                 if (fixesForCompetitor == null) {
@@ -214,14 +227,18 @@ public class FixesAndTails {
                     fixesForCompetitor.clear();
                     // to re-establish the invariants for tails, firstShownFix and lastShownFix, we now need to remove
                     // all points from the competitor's polyline and clear the entries in firstShownFix and lastShownFix
-                    removeTail(e.getKey());
+                    result.put(e.getKey(), new Runnable() { @Override public void run() { clearTail(e.getKey()); } });
                     fixesForCompetitor.addAll(e.getValue());
                     overlapsWithKnownFixes.put(e.getKey(), true); // In case this was only one part of a split request, the next request *does* have an overlap
                 } else {
                     mergeFixes(e.getKey(), e.getValue(), timeForPositionTransitionMillis);
+                    result.put(e.getKey(), noOp);
+                }
+            } else {
+                result.put(e.getKey(), noOp);
             }
         }
-        }
+        return result;
     }
 
     /**
@@ -299,6 +316,7 @@ public class FixesAndTails {
             } else {
                 intoThis.add(intoThisIndex, mergeThisFix);
                 if (tail != null && intoThisIndex >= indexOfFirstShownFix && intoThisIndex <= indexOfLastShownFix) {
+                    // fix inserted at a position currently visualized by tail
                     tail.getPath().insertAt(intoThisIndex - indexOfFirstShownFix, coordinateSystem.toLatLng(mergeThisFix.position));
                 }
                 if (intoThisIndex < indexOfFirstShownFix) {
@@ -364,12 +382,19 @@ public class FixesAndTails {
      * @param delayForTailChangeInMillis
      *            the time in milliseconds after which to actually draw the tail update, or <code>-1</code> to perform
      *            the update immediately
+     * @param tailPreparer
+     *            will be {@link Runnable#run} just before the updates are applied to the <code>tail</code>. In
+     *            particular, if a transition is active, the effect of running this preparer will be held back until the
+     *            transition applies. May be <code>null</code> in which case simply no preparer is run.
      */
     protected void updateTail(final Polyline tail, final  CompetitorDTO competitorDTO,
-            final Date from, final Date to, final int delayForTailChangeInMillis) {
+            final Date from, final Date to, final int delayForTailChangeInMillis, final Runnable tailPreparer) {
         Timer delayedOrImmediateExecutor = new Timer() {
             @Override
             public void run() {
+                if (tailPreparer != null) {
+                    tailPreparer.run();
+                }
                 int vertexCount = tail.getPath().getLength();
                 final List<GPSFixDTO> fixesForCompetitor = getFixes(competitorDTO);
                 int indexOfFirstShownFix = firstShownFix.get(competitorDTO) == null ? -1 : firstShownFix
@@ -391,7 +416,7 @@ public class FixesAndTails {
                     tail.getPath().insertAt(0, coordinateSystem.toLatLng(fix.position));
                     vertexCount++;
                 }
-                // now adjust the polylines tail: remove excess vertices that are after "to"
+                // now adjust the polyline's tail: remove excess vertices that are after "to"
                 int indexOfLastShownFix = lastShownFix.get(competitorDTO) == null ? -1 : lastShownFix
                         .get(competitorDTO);
                 while (indexOfLastShownFix != -1 && vertexCount > 0
@@ -410,6 +435,9 @@ public class FixesAndTails {
                     indexOfLastShownFix++;
                     GPSFixDTO fix = fixesForCompetitor.get(indexOfLastShownFix);
                     tail.getPath().insertAt(vertexCount++, coordinateSystem.toLatLng(fix.position));
+                    if (indexOfFirstShownFix < 0) { // empty tail before?
+                        indexOfFirstShownFix = indexOfLastShownFix; // set to the first vertex inserted into tail
+                    }
                 }
                 firstShownFix.put(competitorDTO, indexOfFirstShownFix);
                 lastShownFix.put(competitorDTO, indexOfLastShownFix);
@@ -439,6 +467,19 @@ public class FixesAndTails {
         lastShownFix.remove(competitor);
     }
     
+    /**
+     * Leaves the tail on the map and empties its path {@link Polyline#getPath()}. Correspondingly, the
+     * {@link #firstShownFix} and {@link #lastShownFix} entries for <code>competitor</code> are set to <code>-1</code>.
+     */
+    private void clearTail(CompetitorDTO competitor) {
+        Polyline tail = tails.get(competitor);
+        if (tail != null) {
+            tail.getPath().clear();
+            firstShownFix.put(competitor, -1);
+            lastShownFix.put(competitor, -1);
+        }
+    }
+
     /**
      * From {@link #fixes} as well as the selection of {@link #getCompetitorsToShow competitors to show}, computes the
      * from/to times for which to request GPS fixes from the server. No update is performed here to {@link #fixes}. The

java/com.sap.sailing.gwt.ui/src/main/java/com/sap/sailing/gwt/ui/client/shared/racemap/RaceMap.java

@@ -1008,8 +1008,9 @@ public class RaceMap extends AbsolutePanel implements TimeListener, CompetitorSe
     private void updateBoatPositions(final Date newTime, final long transitionTimeInMillis,
             final Map<CompetitorDTO, Boolean> hasTailOverlapForCompetitor,
             final Iterable<CompetitorDTO> competitorsToShow, Map<CompetitorDTO, List<GPSFixDTO>> boatData, boolean updateTailsOnly) {
+        final Map<CompetitorDTO, Runnable> tailPreparersPerCompetitor =
                 fixesAndTails.updateFixes(boatData, hasTailOverlapForCompetitor, RaceMap.this, transitionTimeInMillis);
-        showBoatsOnMap(newTime, transitionTimeInMillis, competitorsToShow, updateTailsOnly);
+        showBoatsOnMap(newTime, transitionTimeInMillis, competitorsToShow, updateTailsOnly, tailPreparersPerCompetitor);
         if (!updateTailsOnly) {
             showCompetitorInfoOnMap(newTime, transitionTimeInMillis, competitorSelection.getSelectedFilteredCompetitors());
             // even though the wind data is retrieved by a separate call, re-draw the advantage line because it needs to
@@ -1220,9 +1221,15 @@ public class RaceMap extends AbsolutePanel implements TimeListener, CompetitorSe
     }
     
     /**
-     * @param updateTailsOnly if <code>false</code>, tails of competitors not in <code>competitorsToShow</code> are removed from the map
+     * @param updateTailsOnly
+     *            if <code>false</code>, tails of competitors not in <code>competitorsToShow</code> are removed from the
+     *            map
+     * @param tailPreparersPerCompetitor
+     *            executed before creating or updating the respective competitor's tail
      */
-    private void showBoatsOnMap(final Date newTime, final long timeForPositionTransitionMillis, final Iterable<CompetitorDTO> competitorsToShow, boolean updateTailsOnly) {
+    private void showBoatsOnMap(final Date newTime, final long timeForPositionTransitionMillis,
+            final Iterable<CompetitorDTO> competitorsToShow, boolean updateTailsOnly,
+            Map<CompetitorDTO, Runnable> tailPreparersPerCompetitor) {
         if (map != null) {
             Date tailsFromTime = new Date(newTime.getTime() - settings.getEffectiveTailLengthInMilliseconds());
             Date tailsToTime = newTime;
@@ -1233,13 +1240,15 @@ public class RaceMap extends AbsolutePanel implements TimeListener, CompetitorSe
                 competitorDTOsOfUnusedBoatCanvases.addAll(boatOverlays.keySet());
             }
             for (CompetitorDTO competitorDTO : competitorsToShow) {
+                Runnable tailPreparer = tailPreparersPerCompetitor.get(competitorDTO);
                 if (fixesAndTails.hasFixesFor(competitorDTO)) {
                     Polyline tail = fixesAndTails.getTail(competitorDTO);
                     if (tail == null) {
+                        tailPreparer.run(); // presumably a no-op, but you never know...
                         tail = fixesAndTails.createTailAndUpdateIndices(competitorDTO, tailsFromTime, tailsToTime, this);
                     } else {
                         fixesAndTails.updateTail(tail, competitorDTO, tailsFromTime, tailsToTime,
-                                (int) (timeForPositionTransitionMillis==-1?-1:timeForPositionTransitionMillis/2));
+                                (int) (timeForPositionTransitionMillis==-1?-1:timeForPositionTransitionMillis/2), tailPreparer);
                         if (!updateTailsOnly) {
                             competitorDTOsOfUnusedTails.remove(competitorDTO);
                         }