func (p *particle) treeForce(tree node) vect.V {
if tree == nil {
return vect.V{}
}
switch n := tree.(type) {
case *quad:
dist := p.position.Dst(n.position)
size := n.Size()
if size/dist < THETA {
return p.force(n)
} else {
force := vect.V{}
for _, child := range n.children {
force = force.Add(p.treeForce(child))
}
return force
}
case *particle:
if n == p {
return vect.V{}
}
return p.force(n)
default:
panic(fmt.Errorf("treeForce: bad argument type - %T", tree))
}
}
func (q *quad) recalculate() {
var (
pos vect.V
mass float64
)
for _, n := range q.children {
if n == nil {
continue
}
pos = pos.Add(n.Position().Mul(n.Mass()))
mass += n.Mass()
}
q.position = pos.Div(mass)
q.mass = mass
}