void b2BuoyancyController::Step(const b2TimeStep& step)
{
B2_NOT_USED(step);
if(!m_bodyList)
return;
if(useWorldGravity){
gravity = m_world->GetGravity();
}
for(b2ControllerEdge *i=m_bodyList;i;i=i->nextBody){
b2Body* body = i->body;
if(body->IsSleeping()){
//Buoyancy force is just a function of position,
//so unlike most forces, it is safe to ignore sleeping bodes
continue;
}
b2Vec2 areac(0,0);
b2Vec2 massc(0,0);
float32 area = 0;
float32 mass = 0;
for(b2Shape* shape=body->GetShapeList();shape;shape=shape->GetNext()){
b2Vec2 sc(0,0);
float32 sarea = shape->ComputeSubmergedArea(normal,offset,body->GetXForm(),&sc);
area += sarea;
areac.x += sarea * sc.x;
areac.y += sarea * sc.y;
float shapeDensity = 0;
if(useDensity){
//TODO: Expose density publicly
shapeDensity=shape->GetDensity();
}else{
shapeDensity = 1;
}
mass += sarea*shapeDensity;
massc.x += sarea * sc.x * shapeDensity;
massc.y += sarea * sc.y * shapeDensity;
}
areac.x/=area;
areac.y/=area;
b2Vec2 localCentroid = b2MulT(body->GetXForm(),areac);
massc.x/=mass;
massc.y/=mass;
if(area<B2_FLT_EPSILON)
continue;
//Buoyancy
b2Vec2 buoyancyForce = -density*area*gravity;
body->ApplyForce(buoyancyForce,massc);
//Linear drag
b2Vec2 dragForce = body->GetLinearVelocityFromWorldPoint(areac) - velocity;
dragForce *= -linearDrag*area;
body->ApplyForce(dragForce,areac);
//Angular drag
//TODO: Something that makes more physical sense?
body->ApplyTorque(-body->GetInertia()/body->GetMass()*area*body->GetAngularVelocity()*angularDrag);
}
}
bool LH_b2BuoyancyController::ApplyToFixture(b2Fixture* f)
{
b2Body* body = f->GetBody();
b2Vec2 areac(0,0);
b2Vec2 massc(0,0);
float32 area = 0;
float32 mass = 0;
b2Shape* shape = f->GetShape();
b2Vec2 sc(0,0);
float32 sarea = ComputeSubmergedArea(shape,
normal,
offset,
body->GetTransform(),
&sc,
f->GetDensity());
area += sarea;
areac.x += sarea * sc.x;
areac.y += sarea * sc.y;
float shapeDensity = useDensity ? f->GetDensity() : 1;
mass += sarea * shapeDensity;
massc.x += sarea * sc.x * shapeDensity;
massc.y += sarea * sc.y * shapeDensity;
areac.x /= area;
areac.y /= area;
massc.x /= mass;
massc.y /= mass;
if(area < FLT_EPSILON) {
return false;
}
//Buoyancy
b2Vec2 buoyancyForce = -density*area*gravity;
body->ApplyForce(buoyancyForce,massc);
//Linear drag
b2Vec2 dragForce = body->GetLinearVelocityFromWorldPoint(areac) - velocity;
dragForce *= -linearDrag*area;
body->ApplyForce(dragForce,areac);
//Angular drag
//TODO: Something that makes more physical sense?
body->ApplyTorque(-body->GetInertia()/body->GetMass()*area*body->GetAngularVelocity()*angularDrag);
return true;
}
