/// Resolve an eye position.
 ///
 /// \param stamp Position in frame.
 vec3 resolveEye(unsigned stamp) const
 {
   return m_eye.resolvePosition(stamp + m_offset);
 }
 /// Resolve a camera position.
 ///
 /// \param stamp Position in frames.
 vec3 resolveCamera(unsigned stamp) const
 {
   return m_camera.resolvePosition(stamp + m_offset);
 }