public void updateModelView(ref Matrix4 modelViewMatrix) { Quaternion quat = modelViewMatrix.ExtractRotation().Inverted(); Vector3 euler = OpenTKHelper.QuaternionToEuler(ref quat); Vector3 baseVec = new Vector3(euler.X + 0.5f * (float)Math.PI, euler.Y, euler.Z); orientationMin = baseVec + new Vector3((float)Math.PI / 8f, 0f, 0f); orientationMax = baseVec + new Vector3((float)Math.PI * 3f / 8f, 2f * (float)Math.PI, 0f); }