Fix the svg:use. For a svg:use, it is a group which include the content it reference. It means that we can not tween it to its origin object directly. Instead, we need to ungroup it and then use the result matrix to generate the tweened transformation matrix. Therefore, we need to concate its matrix to the referenced object. Ad center object when the bbox-x is not available.

#ifndef __MB_BACKEND_UTILS_H_
#define __MB_BACKEND_UTILS_H_

#include "mb_backend.h"
#include "mb_timer.h"

/*! \brief A facotry of timer manager implemented with mb_tman_t.
 */
extern mb_timer_factory_t tman_timer_factory;
extern mb_tman_t *tman_timer_man_get_tman(mb_timer_man_t *tm_man);

#endif /* __MB_BACKEND_UTILS_H_ */