apply_quat - Man Page

#include <allegro.h>

void apply_quat(const QUAT *q, float x, y, z, *xout, *yout, *zout);

Multiplies the point (x, y, z) by the quaternion q, storing the result in  (*xout, *yout, *zout). This is quite a bit slower than apply_matrix_f(),  so only use it to translate a few points. If you have many points, it is  much more efficient to call quat_to_matrix() and then use  apply_matrix_f().