flightgear/src/AIModel/AIMultiplayer.cxx

// FGAIMultiplayer - FGAIBase-derived class creates an AI multiplayer aircraft
//
// Based on FGAIAircraft
// Written by David Culp, started October 2003.
// Also by Gregor Richards, started December 2005.
//
// Copyright (C) 2003  David P. Culp - davidculp2@comcast.net
// Copyright (C) 2005  Gregor Richards
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <string>

#include "AIMultiplayer.hxx"

// #define SG_DEBUG SG_ALERT

FGAIMultiplayer::FGAIMultiplayer() : FGAIBase(otMultiplayer) {
   no_roll = false;

   mTimeOffsetSet = false;
   mAllowExtrapolation = true;
   mLagAdjustSystemSpeed = 10;
}


FGAIMultiplayer::~FGAIMultiplayer() {
}

bool FGAIMultiplayer::init() {
   return FGAIBase::init();
}

void FGAIMultiplayer::bind() {
    FGAIBase::bind();

#define AIMPROProp(type, name) \
SGRawValueMethods<FGAIMultiplayer, type>(*this, &FGAIMultiplayer::get##name)

#define AIMPRWProp(type, name) \
SGRawValueMethods<FGAIMultiplayer, type>(*this, \
      &FGAIMultiplayer::get##name, &FGAIMultiplayer::set##name)

    props->tie("callsign", AIMPROProp(const char *, CallSign));

    props->tie("controls/allow-extrapolation",
               AIMPRWProp(bool, AllowExtrapolation));
    props->tie("controls/lag-adjust-system-speed",
               AIMPRWProp(double, LagAdjustSystemSpeed));

#undef AIMPROProp
#undef AIMPRWProp
}

void FGAIMultiplayer::unbind() {
    FGAIBase::unbind();

    props->untie("callsign");
    props->untie("controls/allow-extrapolation");
    props->untie("controls/lag-adjust-system-speed");
}

void FGAIMultiplayer::update(double dt)
{
  if (dt <= 0)
    return;

  FGAIBase::update(dt);

  // Check if we already got data
  if (mMotionInfo.empty())
    return;

  // The current simulation time we need to update for,
  // note that the simulation time is updated before calling all the
  // update methods. Thus it contains the time intervals *end* time
  double curtime = globals->get_sim_time_sec();

  // Get the last available time
  MotionInfo::reverse_iterator it = mMotionInfo.rbegin();
  double curentPkgTime = it->second.time;

  // Dynamically optimize the time offset between the feeder and the client
  // Well, 'dynamically' means that the dynamic of that update must be very
  // slow. You would otherwise notice huge jumps in the multiplayer models.
  // The reason is that we want to avoid huge extrapolation times since
  // extrapolation is highly error prone. For that we need something
  // approaching the average latency of the packets. This first order lag
  // component will provide this. We just take the error of the currently
  // requested time to the most recent available packet. This is the
  // target we want to reach in average.
  double lag = it->second.lag;
  if (!mTimeOffsetSet) {
    mTimeOffsetSet = true;
    mTimeOffset = curentPkgTime - curtime - lag;
  } else {
    double offset = curentPkgTime - curtime - lag;
    if (!mAllowExtrapolation && offset + lag < mTimeOffset) {
      mTimeOffset = offset;
      SG_LOG(SG_GENERAL, SG_DEBUG, "Resetting time offset adjust system to "
             "avoid extrapolation: time offset = " << mTimeOffset);
    } else {
      // the error of the offset, respectively the negative error to avoid
      // a minus later ...
      double err = offset - mTimeOffset;
      // limit errors leading to shorter lag values somehow, that is late
      // arriving packets will pessimize the overall lag much more than
      // early packets will shorten the overall lag
      double sysSpeed;
      if (err < 0) {
        // Ok, we have some very late packets and nothing newer increase the
        // lag by the given speedadjust
        sysSpeed = mLagAdjustSystemSpeed*err;
      } else {
        // We have a too pessimistic display delay shorten that a small bit
        sysSpeed = SGMiscd::min(0.1*err*err, 0.5);
      }

      // simple euler integration for that first order system including some
      // overshooting guard to prevent to aggressive system speeds
      // (stiff systems) to explode the systems state
      double systemIncrement = dt*sysSpeed;
      if (fabs(err) < fabs(systemIncrement))
        systemIncrement = err;
      mTimeOffset += systemIncrement;
      
      SG_LOG(SG_GENERAL, SG_DEBUG, "Offset adjust system: time offset = "
             << mTimeOffset << ", expected longitudinal position error due to "
             " current adjustment of the offset: "
             << fabs(norm(it->second.linearVel)*systemIncrement));
    }
  }


  // Compute the time in the feeders time scale which fits the current time
  // we need to 
  double tInterp = curtime + mTimeOffset;

  SGVec3d ecPos;
  SGQuatf ecOrient;
  if (tInterp <= curentPkgTime) {
    // Ok, we need a time prevous to the last available packet,
    // that is good ...

    // Find the first packet before the target time
    MotionInfo::iterator nextIt = mMotionInfo.upper_bound(tInterp);
    if (nextIt == mMotionInfo.begin()) {
      SG_LOG(SG_GENERAL, SG_DEBUG, "Taking oldest packet!");
      // We have no packet before the target time, just use the first one
      MotionInfo::iterator firstIt = mMotionInfo.begin();
      ecPos = firstIt->second.position;
      ecOrient = firstIt->second.orientation;

      std::vector<FGFloatPropertyData>::const_iterator firstPropIt;
      std::vector<FGFloatPropertyData>::const_iterator firstPropItEnd;
      firstPropIt = firstIt->second.properties.begin();
      firstPropItEnd = firstIt->second.properties.end();
      while (firstPropIt != firstPropItEnd) {
        float val = firstPropIt->value;
        PropertyMap::iterator pIt = mPropertyMap.find(firstPropIt->id);
        if (pIt != mPropertyMap.end())
          pIt->second->setFloatValue(val);
        ++firstPropIt;
      }

    } else {
      // Ok, we have really found something where our target time is in between
      // do interpolation here
      MotionInfo::iterator prevIt = nextIt;
      --prevIt;

      // Interpolation coefficient is between 0 and 1
      double intervalStart = prevIt->second.time;
      double intervalEnd = nextIt->second.time;
      double intervalLen = intervalEnd - intervalStart;
      double tau = (tInterp - intervalStart)/intervalLen;

      SG_LOG(SG_GENERAL, SG_DEBUG, "Multiplayer vehicle interpolation: ["
             << intervalStart << ", " << intervalEnd << "], intervalLen = "
             << intervalLen << ", interpolation parameter = " << tau);

      // Here we do just linear interpolation on the position
      ecPos = ((1-tau)*prevIt->second.position + tau*nextIt->second.position);
      ecOrient = interpolate((float)tau, prevIt->second.orientation,
                             nextIt->second.orientation);

      if (prevIt->second.properties.size()
          == nextIt->second.properties.size()) {
        std::vector<FGFloatPropertyData>::const_iterator prevPropIt;
        std::vector<FGFloatPropertyData>::const_iterator prevPropItEnd;
        std::vector<FGFloatPropertyData>::const_iterator nextPropIt;
        std::vector<FGFloatPropertyData>::const_iterator nextPropItEnd;
        prevPropIt = prevIt->second.properties.begin();
        prevPropItEnd = prevIt->second.properties.end();
        nextPropIt = nextIt->second.properties.begin();
        nextPropItEnd = nextIt->second.properties.end();
        while (prevPropIt != prevPropItEnd) {
          float val = (1-tau)*prevPropIt->value + tau*nextPropIt->value;
          PropertyMap::iterator pIt = mPropertyMap.find(prevPropIt->id);
          if (pIt != mPropertyMap.end())
            pIt->second->setFloatValue(val);
          ++prevPropIt;
          ++nextPropIt;
        }
      }

      // Now throw away too old data
      if (prevIt != mMotionInfo.begin()) {
        --prevIt;
        mMotionInfo.erase(mMotionInfo.begin(), prevIt);
      }
    }
  } else {
    // Ok, we need to predict the future, so, take the best data we can have
    // and do some eom computation to guess that for now.
    FGExternalMotionData motionInfo = it->second;

    // The time to predict, limit to 5 seconds
    double t = tInterp - motionInfo.time;
    t = SGMisc<double>::min(t, 5);

    SG_LOG(SG_GENERAL, SG_DEBUG, "Multiplayer vehicle extrapolation: "
           "extrapolation time = " << t);

    // Do a few explicit euler steps with the constant acceleration's
    // This must be sufficient ...
    ecPos = motionInfo.position;
    ecOrient = motionInfo.orientation;
    SGVec3f linearVel = motionInfo.linearVel;
    SGVec3f angularVel = motionInfo.angularVel;
    while (0 < t) {
      double h = 1e-1;
      if (t < h)
        h = t;

      SGVec3d ecVel = toVec3d(ecOrient.backTransform(linearVel));
      ecPos += h*ecVel;
      ecOrient += h*ecOrient.derivative(angularVel);

      linearVel += h*(cross(linearVel, angularVel) + motionInfo.linearAccel);
      angularVel += h*motionInfo.angularAccel;
      
      t -= h;
    }

    std::vector<FGFloatPropertyData>::const_iterator firstPropIt;
    std::vector<FGFloatPropertyData>::const_iterator firstPropItEnd;
    firstPropIt = it->second.properties.begin();
    firstPropItEnd = it->second.properties.end();
    while (firstPropIt != firstPropItEnd) {
      float val = firstPropIt->value;
      PropertyMap::iterator pIt = mPropertyMap.find(firstPropIt->id);
      if (pIt != mPropertyMap.end())
        pIt->second->setFloatValue(val);
      ++firstPropIt;
    }
  }
  
  // extract the position
  SGGeod geod = ecPos;
  pos.setlat(geod.getLatitudeDeg());
  pos.setlon(geod.getLongitudeDeg());
  pos.setelev(geod.getElevationM());
  
  // The quaternion rotating from the earth centered frame to the
  // horizontal local frame
  SGQuatf qEc2Hl = SGQuatf::fromLonLat((float)geod.getLongitudeRad(),
                                       (float)geod.getLatitudeRad());
  // The orientation wrt the horizontal local frame
  SGQuatf hlOr = conj(qEc2Hl)*ecOrient;
  float hDeg, pDeg, rDeg;
  hlOr.getEulerDeg(hDeg, pDeg, rDeg);
  hdg = hDeg;
  roll = rDeg;
  pitch = pDeg;

  SG_LOG(SG_GENERAL, SG_DEBUG, "Multiplayer position and orientation: "
         << geod << ", " << hlOr);

  //###########################//
  // do calculations for radar //
  //###########################//
  UpdateRadar(manager);

  Transform();
}

void
FGAIMultiplayer::addMotionInfo(const FGExternalMotionData& motionInfo,
                               long stamp)
{
  mLastTimestamp = stamp;
  // Drop packets arriving out of order
  if (!mMotionInfo.empty() && motionInfo.time < mMotionInfo.rbegin()->first)
    return;
  mMotionInfo[motionInfo.time] = motionInfo;
}

void
FGAIMultiplayer::setDoubleProperty(const std::string& prop, double val)
{
  SGPropertyNode* pNode = props->getChild(prop.c_str(), true);
  pNode->setDoubleValue(val);
}