update method
Implementation
Vec2 update(double dt, Vec2 target) {
_force
..setFrom(target)
..sub(pos)
..scale(stiffness);
_force.x -= velocity.x * damping;
_force.y -= velocity.y * damping;
velocity.x += _force.x * dt;
velocity.y += _force.y * dt;
pos.x += velocity.x * dt;
pos.y += velocity.y * dt;
return pos;
}