Attraction and Repulsion Force for Games in Unity

Example of an simple attraction and repulsion force for games

Methods

First, we calculate the object direction to center. Where D is the vector direction, P is the object and C is the center.

Then, we calculate the force proportional to distance from object to center. Where F is the proportional force, F_max is the maximum force and D is the distance from the object to the center.

Finally, we calculate the vector force according to the attraction or repulsion function. Where f is the vector force applied to the object, σ is the type of (none, repulsion or attraction) and m is the mass of the object.

Code

Basic code created from equations

public class Force : MonoBehaviour
{
    public enum ForceType { Repulsion = -1, None = 0, Attraction = 1 }
    public ForceType m_Type;
    public Transform m_Pivot;
    public float m_Radius;
    public float m_StopRadius;
    public float m_Force;
    public LayerMask m_Layers;

    private void FixedUpdate()
    {
        Collider[] colliders = Physics.OverlapSphere(m_Pivot.position, m_Radius, m_Layers);

        float signal = (float)m_Type;

        foreach (var collider in colliders)
        {
            Rigidbody body = collider.GetComponent<Rigidbody>();
            if (body == null) 
                continue;

            Vector3 direction = m_Pivot.position - body.position;

            float distance = direction.magnitude;

            direction = direction.normalized;

            if (distance < m_StopRadius) 
                continue;

            float forceRate = (m_Force / distance);

            body.AddForce(direction * (forceRate / body.mass) * signal);
        }
    }
}

License

Copyright 2019 Kleber de Oliveira Andrade

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