/// <summary>
/// given the relative velocity between the two objects and the MTV this method modifies the relativeVelocity to make it a collision
/// response.
/// </summary>
/// <param name="relativeVelocity">Relative velocity.</param>
/// <param name="minimumTranslationVector">Minimum translation vector.</param>
void calculateResponseVelocity(ref Vector2 relativeVelocity, ref Vector2 minimumTranslationVector, out Vector2 responseVelocity)
{
// first, we get the normalized MTV in the opposite direction: the surface normal
var inverseMTV = minimumTranslationVector * -1f;
Vector2 normal;
VectorExtensions.Normalize(ref inverseMTV, out normal);
// the velocity is decomposed along the normal of the collision and the plane of collision.
// The elasticity will affect the response along the normal (normalVelocityComponent) and the friction will affect
// the tangential component of the velocity (tangentialVelocityComponent)
float n;
VectorExtensions.Dot(ref relativeVelocity, ref normal, out n);
var normalVelocityComponent = normal * n;
var tangentialVelocityComponent = relativeVelocity - normalVelocityComponent;
if (n > 0.0f)
{
normalVelocityComponent = Vector2.zero;
}
// if the squared magnitude of the tangential component is less than glue then we bump up the friction to the max
var coefficientOfFriction = _friction;
if (tangentialVelocityComponent.LengthSquared() < _glue)
{
coefficientOfFriction = 1.01f;
}
// elasticity affects the normal component of the velocity and friction affects the tangential component
responseVelocity = -(1.0f + _elasticity) * normalVelocityComponent - coefficientOfFriction * tangentialVelocityComponent;
}