//pass in the amount of time you want to simulate
//in real time, this is the delta time between called to update
//in simulation time, this can be any amount -- but this function won't return until all updates are processed
//so it holds up the thread
int IESoRWorld::updateWorld(double msUpdate)
{
msUpdate = 4*msUpdate;
//we'll keep track of the number of times we simulated during this update
int stepCount = 0;
//# of seconds since last time
double frameTime = msUpdate/1000.0f;
//maximum frame time, to prevent what is called the spiral of death
if (frameTime > .35)
frameTime = .35;
//we accumulate all the time we haven't rendered things in
this->accumulator += frameTime;
//as long as we have a chunk of time to simulate, we need to do the simulation
while (accumulator >= simulationRate)
{
//how many times did we run this loop, we shoudl keep track --
//that's the number of times we ran the physics engine
stepCount++;
//move the muscles quicker using this toggle
float speedup = 3;
//we loop through all our muscles, and update the lengths associated with the connectionsj
for (std::vector<Muscle*>::iterator it = muscleList.begin() ; it != muscleList.end(); ++it)
{
//grab our muscle pointer from the list
Muscle* muscle = *it;
//get our distance joint -- holder of physical joint info
b2DistanceJoint* dJoint = (b2DistanceJoint*)muscle->GetJoint();
//Javascript version
//muscle.SetLength(muscle.m_length + muscle.amplitude/this.scale*Math.cos(rad + muscle.phase*2*Math.PI));
//double lengthCalc = (dJoint->GetLength() + muscle->GetAmplitude()*cos(radians + muscle->GetPhase() * 2 * M_PI));
//fetch the original length of the distance joint, and add some fraction of that amount to the length
//depending on the current location in the muscle cycle
double lengthCalc = (1.0 + muscle->GetAmplitude() * cos(radians + muscle->GetPhase() * 2 * M_PI)) * muscle->GetOriginalLength();
//we set our length as the calculate value
dJoint->SetLength(lengthCalc);
}
//step the physics world
this->world->Step(
this->simulationRate //frame-rate
, 10 //velocity iterations
, 10 //position iterations
);
//manually clear forces when doing fixed time steps,
//NOTE: that we disabled auto clear after step inside of the b2World
this->world->ClearForces();
//increment the radians for the muscles
radians += speedup * this->simulationRate;
//decrement the accumulator - we ran a chunk just now!
accumulator -= this->simulationRate;
}
//interpolation is basically a measure of how far into the next step we should have simulated
//it's meant to ease the drawing stages
//(you linearly interpolate the last frame and the current frame using this value)
this->interpolation = accumulator / this->simulationRate;
//how many times did we run the simulator?
return stepCount;
}
