void DynamicBody::CalcExternalForce()
{
// gravity
if (!GetFrame()) return; // no external force if not in a frame
Body *body = GetFrame()->GetBody();
if (body && !body->IsType(Object::SPACESTATION)) { // they ought to have mass though...
vector3d b1b2 = GetPosition();
double m1m2 = GetMass() * body->GetMass();
double invrsqr = 1.0 / b1b2.LengthSqr();
double force = G*m1m2 * invrsqr;
m_externalForce = -b1b2 * sqrt(invrsqr) * force;
}
else m_externalForce = vector3d(0.0);
m_gravityForce = m_externalForce;
// atmospheric drag
if (body && GetFrame()->IsRotFrame() && body->IsType(Object::PLANET))
{
Planet *planet = static_cast<Planet*>(body);
double dist = GetPosition().Length();
double speed = m_vel.Length();
double pressure, density;
planet->GetAtmosphericState(dist, &pressure, &density);
const double radius = GetClipRadius(); // bogus, preserving behaviour
const double AREA = radius;
// ^^^ yes that is as stupid as it looks
const double DRAG_COEFF = 0.1; // 'smooth sphere'
vector3d dragDir = -m_vel.NormalizedSafe();
vector3d fDrag = 0.5*density*speed*speed*AREA*DRAG_COEFF*dragDir;
// make this a bit less daft at high time accel
// only allow atmosForce to increase by .1g per frame
vector3d f1g = m_atmosForce + dragDir * GetMass();
if (fDrag.LengthSqr() > f1g.LengthSqr()) m_atmosForce = f1g;
else m_atmosForce = fDrag;
m_externalForce += m_atmosForce;
}
else m_atmosForce = vector3d(0.0);
// centrifugal and coriolis forces for rotating frames
if (GetFrame()->IsRotFrame()) {
vector3d angRot(0, GetFrame()->GetAngSpeed(), 0);
m_externalForce -= m_mass * angRot.Cross(angRot.Cross(GetPosition())); // centrifugal
m_externalForce -= 2 * m_mass * angRot.Cross(GetVelocity()); // coriolis
}
}
void DynamicsSystem::update(ent_ptr<EntityManager> em, ent_ptr<EventManager> events, double dt)
{
for (auto entity : em->entities_with_components<DynamicsComponent>()) {
ent_ptr<DynamicsComponent> dc = entity.component<DynamicsComponent>();
ent_ptr<PosOrientComponent> poc = entity.component<PosOrientComponent>();
ent_ptr<MassComponent> mc = entity.component<MassComponent>();
SDL_assert(poc);
SDL_assert(mc);
//save previous
//poc->oldPos = poc->pos;
//poc->oldAngDisplacement = dc->angVel * dt;
dc->force += dc->externalForce;
dc->vel += dt * dc->force * (1.0 / mc->mass);
dc->angVel += dt * dc->torque * (1.0 / dc->angInertia);
//update pos
poc->pos += dc->vel * dt;
//update orient
double len = dc->angVel.Length();
if (len > 1e-16) {
vector3d axis = dc->angVel * (1.0 / len);
matrix3x3d r = matrix3x3d::Rotate(len * dt, axis);
poc->orient = r * poc->orient;
}
dc->force = vector3d(0.0);
dc->torque = vector3d(0.0);
//calculate external forces
//- gravity
//- atmospheric drag
//- centrifugal/coriolis force
auto fc = entity.component<FrameComponent>();
if (fc) {
if (fc->frame->IsRotFrame()) {
vector3d angRot(0, fc->frame->GetAngSpeed(), 0);
dc->externalForce -= mc->mass * angRot.Cross(angRot.Cross(poc->pos)); // centrifugal
dc->externalForce -= 2 * mc->mass * angRot.Cross(dc->vel); // coriolis
}
}
}
}
void DynamicBody::CalcExternalForce()
{
// gravity
if (!GetFrame()) return; // no external force if not in a frame
Body *body = GetFrame()->GetBody();
if (body && !body->IsType(Object::SPACESTATION)) { // they ought to have mass though...
vector3d b1b2 = GetPosition();
double m1m2 = GetMass() * body->GetMass();
double invrsqr = 1.0 / b1b2.LengthSqr();
double force = G*m1m2 * invrsqr;
m_externalForce = -b1b2 * sqrt(invrsqr) * force;
}
else m_externalForce = vector3d(0.0);
m_gravityForce = m_externalForce;
// atmospheric drag
if (body && GetFrame()->IsRotFrame() && body->IsType(Object::PLANET))
{
vector3d dragDir = -m_vel.NormalizedSafe();
vector3d fDrag = CalcAtmosphericForce(m_dragCoeff)*dragDir;
// make this a bit less daft at high time accel
// only allow atmosForce to increase by .1g per frame
vector3d f1g = m_atmosForce + dragDir * GetMass();
if (fDrag.LengthSqr() > f1g.LengthSqr()) m_atmosForce = f1g;
else m_atmosForce = fDrag;
m_externalForce += m_atmosForce;
}
else m_atmosForce = vector3d(0.0);
// centrifugal and coriolis forces for rotating frames
if (GetFrame()->IsRotFrame()) {
vector3d angRot(0, GetFrame()->GetAngSpeed(), 0);
m_externalForce -= m_mass * angRot.Cross(angRot.Cross(GetPosition())); // centrifugal
m_externalForce -= 2 * m_mass * angRot.Cross(GetVelocity()); // coriolis
}
}
