public Vector2 GetIntersectionDepth(ICollider a, ICollider b)
        {
            Vector2 direction = b.Particle.Position - a.Particle.Position;
            float   distance  = direction.Length();

            direction.Normalize();
            float depth = (a.GetRadius() + b.GetRadius()) - distance;

            return(depth > 0 ? depth * direction : Vector2.Zero);
        }