private void EvolveForTimestep(GravityEngine ge, double physicsDt)
{
// if everything is on rails, can just jump to the end time
if (onRails)
{
time += physicsDt;
MoveFixedBodies(time);
// Keep these up-to-date so can flip to off-rails if needed
physicalTime[(int)Evolvers.MASSIVE] = time;
physicalTime[(int)Evolvers.MASSLESS] = time;
physicalTime[(int)Evolvers.PARTICLES] = time;
return;
}
// Objective is to keep physical time proportional to game time
// Each integrator will run for at least as long as it is told but may overshoot
// so correct time on next iteration.
//
// Keep the current physical time each integrator has reached in physicalTime[integrator_type]
//
double engineDt = ge.engineDt;
if (physicsDt < engineDt)
{
return;
}
double timeEvolved = 0;
// Need to move the integrators forward concurrently in steps matching the engineDt
// - Hermite may be using a different timestep than this
// - particles likely use a much longer timestep
while (timeEvolved < physicsDt)
{
//==============================
// Massive bodies
//==============================
// evolve all the massive game objects
double massiveDt = 0.0;
if (numBodies > fixedBodiesInIntegrator)
{
// typical path - have massive bodies: use NBody integration
massiveDt = integrator.Evolve(engineDt, this, ref info);
physicalTime[(int)Evolvers.MASSIVE] += massiveDt;
timeEvolved += massiveDt;
}
else
{
// all Kepler mode: skip integration
physicalTime[(int)Evolvers.MASSIVE] += engineDt;
timeEvolved += engineDt;
}
//==============================
// Fixed Bodies
//==============================
// Update fixed update objects (if any)
// Evolution is to a specific time - so use massive object physical time
MoveFixedBodies(physicalTime[(int)Evolvers.MASSIVE]);
// Debug.Log(string.Format("gameDt={0} integated={1} ptime={2} wtime={3}", gameDt, dt, physicalTime, worldTime));
// LF is built in to particles and massless routines. They have their own DT built in
// these run on a fixed timestep (if it is varied energy conservation is wrecked)
// Track their evolution vs wall clock time seperately
//==============================
// Particles (should only be present in worldState)
//==============================
if (gravityParticles.Count > 0)
{
double particle_dt = ge.GetParticleDt();
if (physicalTime[(int)GravityState.Evolvers.PARTICLES] <
physicalTime[(int)GravityState.Evolvers.MASSIVE])
{
double evolvedFor = 0.0;
if (forceDelegate != null)
{
foreach (GravityParticles nbp in gravityParticles)
{
evolvedFor = nbp.EvolveWithForce(particle_dt, numBodies, this,
ref size2, ref info, forceDelegate);
}
}
else
{
foreach (GravityParticles nbp in gravityParticles)
{
evolvedFor = nbp.Evolve(particle_dt, numBodies, this, ref size2, ref info);
}
}
physicalTime[(int)Evolvers.PARTICLES] += evolvedFor;
}
}
//==============================
// Massless
//==============================
if (masslessEngine != null && masslessEngine.NumBodies() > 0)
{
// rockets need the time
if (physicalTime[(int)Evolvers.MASSLESS] <
physicalTime[(int)Evolvers.MASSIVE])
{
if (forceDelegate != null)
{
physicalTime[(int)Evolvers.MASSLESS] +=
masslessEngine.EvolveWithForce(engineDt, time, numBodies, this, ref info, forceDelegate);
}
else
{
physicalTime[(int)Evolvers.MASSLESS] +=
masslessEngine.Evolve(engineDt, time, numBodies, this, ref info);
}
}
}
// must update time so trajectory times are up to date
time = physicalTime[(int)Evolvers.MASSIVE];
if (hasTrajectories)
{
ge.UpdateTrajectories();
}
} // while
}