public static void Update(EntityCollection entities)
{
// The state of collisions (positions, etc.) may change between
// iterations of FindCollisions. To make this clear, we've opted
// for a callback function instead of an IEnumerable return value
// to indicate collisions.
//
// For example, four balls are colliding. Each ball, after being
// notified of a collision, moves itself so that it does not
// collide with any of the other balls.
//
// If we collected collisions before-hand, handling them later, we
// would fire 4*3 = 12 collision events.
//
// If we collected and handled collisions as they were detected, we
// would fire at only three collisions.
FindCollisions(entities.EntitiesWith<ICollidable>(), entities, Intersected);
}