introduction of a zero lag mode when pilots are synched in time, eg using ntp.

src/AIModel/AIMultiplayer.cxx

@@ -50,6 +50,12 @@ FGAIMultiplayer::FGAIMultiplayer() :
    lastUpdateTime = 0;
    playerLag = 0.03;
    compensateLag = 1;
+   realTime = false;
+   lastTime=0.0;
+   lagPpsAveraged = 1.0;
+   rawLag = 0.0;
+   rawLagMod = 0.0;
+   lagModAveraged = 0.0;
    _searchOrder = PREFER_DATA;
 }
 
@@ -152,10 +158,27 @@ void FGAIMultiplayer::update(double dt)
   // requested time to the most recent available packet. This is the
   // target we want to reach in average.
   double lag = it->second.lag;
+
+  rawLag = curentPkgTime - curtime;
+  realTime = false; //default behaviour
+
   if (!mTimeOffsetSet) {
     mTimeOffsetSet = true;
     mTimeOffset = curentPkgTime - curtime - lag;
+    lastTime = curentPkgTime;
+    lagModAveraged = remainder((curentPkgTime - curtime), 3600.0);
+    props->setDoubleValue("lag/pps-averaged", lagPpsAveraged);
+    props->setDoubleValue("lag/lag-mod-averaged", lagModAveraged);
   } else {
+      if ((curentPkgTime - lastTime) != 0) {
+        lagPpsAveraged = 0.99 * lagPpsAveraged + 0.01 * fabs( 1 / (lastTime - curentPkgTime));
+        lastTime = curentPkgTime;
+        rawLagMod = remainder(rawLag, 3600.0);
+        lagModAveraged = lagModAveraged *0.99 + 0.01 * rawLagMod;
+        props->setDoubleValue("lag/pps-averaged", lagPpsAveraged);
+        props->setDoubleValue("lag/lag-mod-averaged", lagModAveraged);
+      }
+
       double offset = 0.0;
 
         //spectator mode, more late to be in the interpolation zone
@@ -166,8 +189,15 @@ void FGAIMultiplayer::update(double dt)
 
     // using the prediction mode to display the mpaircraft in the futur/past with given playerlag value
     //currently compensatelag = 2
+    } else if (fabs(lagModAveraged) < 0.3) {
+        mTimeOffset = (round(rawLag/3600))*3600; //real time mode if close enough
+        realTime = true;
+
     } else { offset = curentPkgTime - curtime + 0.48*lag + playerLag;
     }
+
+    if (!realTime) {
+
       if ((!mAllowExtrapolation && offset + lag < mTimeOffset)
             || (offset - 10 > mTimeOffset)) {
         mTimeOffset = offset;
@@ -181,7 +211,6 @@ void FGAIMultiplayer::update(double dt)
           // arriving packets will pessimize the overall lag much more than
           // early packets will shorten the overall lag
         double sysSpeed;
-
           //trying to slow the rudderlag phenomenon thus using more the prediction system
           //if we are off by less than 1.5s, do a little correction, and bigger step above 1.5s
         if (fabs(err) < 1.5) {
@@ -217,7 +246,7 @@ void FGAIMultiplayer::update(double dt)
              << fabs(norm(it->second.linearVel)*systemIncrement));
       }
     }
-
+  }
 
   // Compute the time in the feeders time scale which fits the current time
   // we need to
@@ -227,9 +256,10 @@ void FGAIMultiplayer::update(double dt)
   SGQuatf ecOrient;
   SGVec3f ecLinearVel;
 
-  if (tInterp <= curentPkgTime) {
+  if (tInterp < curentPkgTime) {
     // Ok, we need a time prevous to the last available packet,
     // that is good ...
+    // the case tInterp = curentPkgTime need to be in the interpolation, to avoid a bug zeroing the position
 
     // Find the first packet before the target time
     MotionInfo::iterator nextIt = mMotionInfo.upper_bound(tInterp);

src/AIModel/AIMultiplayer.hxx

@@ -86,11 +86,15 @@ private:
   typedef std::map<unsigned, SGSharedPtr<SGPropertyNode> > PropertyMap;
   PropertyMap mPropertyMap;
 
-  double mTimeOffset;
   bool mTimeOffsetSet;
-  double playerLag;
+  bool realTime;
   int compensateLag;
+  double playerLag;
+  double mTimeOffset;
   double lastUpdateTime;
+  double lastTime;
+  double lagPpsAveraged;
+  double rawLag, rawLagMod, lagModAveraged;
 
   /// Properties which are for now exposed for testing
   bool mAllowExtrapolation;