// Map produces a vector that is within the bounds of the
// rectangular manifold of toroidal space, given a vector
// that is on the torus but may be outside these bounds.
func (t Torus) Map(v *mat64.Vector) {
x := v.At(0, 0)
y := v.At(1, 0)
remx := x
right := t.W / 2
if math.Abs(x) > right {
remx = math.Mod(t.W, -x)
}
remy := y
top := t.H / 2
if math.Abs(y) > top {
remy = math.Mod(t.H, -y)
}
v.SetVec(0, remx)
v.SetVec(1, remy)
}