void VectorMem::allocateData(int size)
{
vertexBuffer = new float[size * 2];
colorBuffer = new float[size * 4];
vertexBufferSize = sizeof(float) * 2 * size;
colorBufferSize = sizeof(float) * 4 * size;
allocateParticles();
}
void RungeKuttaIntegrator::step( const float &deltaT )
{
allocateParticles();
/////////////////////////////////////////////////////////
// save original position and velocities
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
originalPositions[i]= ( p->position );
originalVelocities[i]=( p->velocity );
}
p->force=Vec3f(0,0,0); // and clear the forces
}
////////////////////////////////////////////////////////
// get all the k1 values
s->applyForces();
// save the intermediate forces
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
k1Forces[i]= p->force ;
k1Velocities[i]= p->velocity ;
}
p->force=Vec3f(0,0,0); // and clear the forces
}
////////////////////////////////////////////////////////////////
// get k2 values
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
Vec3f originalPosition = originalPositions[i];
Vec3f k1Velocity = k1Velocities[i];
p->position= originalPosition + (k1Velocity * (0.5f * deltaT)) ;
Vec3f originalVelocity = originalVelocities[i];
Vec3f k1Force = k1Forces[i];
p->velocity= originalVelocity + k1Force * 0.5f * deltaT / p->mass ;
}
}
s->applyForces();
// save the intermediate forces
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
k2Forces[i]= ( p->force );
k2Velocities[i]= ( p->velocity );
}
p->force=Vec3f(0,0,0); // and clear the forces now that we are done with them
}
/////////////////////////////////////////////////////
// get k3 values
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
Vec3f originalPosition = originalPositions[i];
Vec3f k2Velocity = k2Velocities[i];
p->position= ( originalPosition + k2Velocity * 0.5f * deltaT );
Vec3f originalVelocity = originalVelocities[i];
Vec3f k2Force = k2Forces[i];
p->velocity= ( originalVelocity + k2Force * 0.5f * deltaT / p->mass );
}
}
s->applyForces();
// save the intermediate forces
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
k3Forces[i]= ( p->force );
k3Velocities[i]= ( p->velocity );
}
p->force=Vec3f(0,0,0); // and clear the forces now that we are done with them
}
//////////////////////////////////////////////////
// get k4 values
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
Vec3f originalPosition = originalPositions[i];
Vec3f k3Velocity = k3Velocities[i];
p->position= ( originalPosition + k3Velocity * deltaT);
Vec3f originalVelocity = originalVelocities[i];
Vec3f k3Force = k3Forces[i];
p->velocity= ( originalVelocity + k3Force * deltaT / p->mass );
}
}
s->applyForces();
// save the intermediate forces
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
if ( !p->fixed )
{
k4Forces[i]= ( p->force );
k4Velocities[i]= ( p->velocity );
}
}
/////////////////////////////////////////////////////////////
// put them all together and what do you get?
for ( size_t i = 0; i < s->particles.size(); ++i )
{
Particle* p = s->particles[i];
p->age += deltaT;
if ( !p->fixed )
{
// update position
Vec3f originalPosition = originalPositions[i];
Vec3f k1Velocity = k1Velocities[i];
Vec3f k2Velocity = k2Velocities[i];
Vec3f k3Velocity = k3Velocities[i];
Vec3f k4Velocity = k4Velocities[i];
p->position= ( originalPosition + deltaT / 6.0f * ( k1Velocity + 2.0f*k2Velocity + 2.0f*k3Velocity + k4Velocity ) );
// update velocity
Vec3f originalVelocity = originalVelocities[i];
Vec3f k1Force = k1Forces[i];
Vec3f k2Force = k2Forces[i];
Vec3f k3Force = k3Forces[i];
Vec3f k4Force = k4Forces[i];
p->velocity= ( originalVelocity + deltaT / ( 6.0f * p->mass ) * ( k1Force + 2.0f*k2Force + 2.0f*k3Force + k4Force ) );
}
}
}
