Man pages matching name get_x_rotate_matrix in section 3alleg4:

get_x_rotate_matrix.3alleg4.en	debian 10 / allegro4-doc
get_x_rotate_matrix.3alleg4.en	debian 11 / allegro4-doc
get_x_rotate_matrix.3alleg4.en	debian 12 / allegro4-doc
get_x_rotate_matrix.3alleg4.en	debian 13 / allegro4-doc