//
        //  The camera is placed in such a way
        //  it can display the content of the BBox
        //  In all regards, it is also placed along the negative Z axis
        //  Looking towards the positive Z axis
        //  with a (0,1,0) Up vector
        //
        public override void LookAt(BoundingBox BBox, LookAtDirection dir = LookAtDirection.POSITIVE_Z)
        {
            Reset();

            _bbox = BBox;

            _center = (BBox.Maximum + BBox.Minimum) / 2;
            Vector3 LMax = BBox.Maximum - BBox.Minimum;
            float lmax = Math.Max(LMax.Z, Math.Max(LMax.X, LMax.Y));

            Vector3 translation = _center;
            translation.Z = -(lmax / (float)Math.Tan(_camera.Fov) + lmax / 2 + _center.Z);

            _cameraWorldTransform = Matrix.Translation(translation);
            _camera.WorldTransform = _cameraWorldTransform;

            Matrix r = Matrix.Identity;
            if (dir == LookAtDirection.POSITIVE_Z)
            {
                r = Matrix.Identity;
            }
            else if (dir == LookAtDirection.NEGATIVE_Z)
            {
                r = Matrix.RotationY((float)Math.PI);
            }
            else if (dir == LookAtDirection.POSITIVE_X)
            {
                r = Matrix.RotationY((float)Math.PI / 2f);
            }
            else if (dir == LookAtDirection.NEGATIVE_X)
            {
                r = Matrix.RotationY(-(float)Math.PI / 2f);
            }
            else if (dir == LookAtDirection.POSITIVE_Y)
            {
                r = Matrix.Translation(-_center) * Matrix.RotationX(-(float)Math.PI / 2f) * Matrix.Translation(_center);
            }
            else if (dir == LookAtDirection.NEGATIVE_Y)
            {
                r = Matrix.Translation(-_center) * Matrix.RotationX((float)Math.PI / 2f) * Matrix.Translation(_center);
            }

            _cameraWorldTransform = Matrix.Translation(translation) * r;
            _camera.WorldTransform = _cameraWorldTransform;
        }
 public abstract void LookAt(BoundingBox BBox, LookAtDirection dir = LookAtDirection.POSITIVE_Z);