void GLWidget::rotateView(const QPoint& newPos) {
float dx = (float)(newPos.x() - _oldMousePos.x()) / (float)_width;
float dy = (float)(newPos.y() - _oldMousePos.y()) / (float)_height;
_oldMousePos = newPos;
updateDir();
// rotate eye around center
_eye.rotate(_center, _dirx, -dx * PI );
_eye.rotate(_center, _diry, dy*PI );
// now calculate the new up-vector
P3<float> upCenter = _center + _up;
upCenter.rotate( _center , _diry, dy*PI);
_up = upCenter - _center;
_up *= 1.0/_up.norm();
updateGL();
}
