al_get_haptic_from_touch_input man page
al_get_haptic_from_touch_input — Allegro 5 API
#include <allegro5/allegro.h> ALLEGRO_HAPTIC *al_get_haptic_from_touch_input(ALLEGRO_TOUCH_INPUT *dev)
If the touch input device has haptic capabilities, returns the associated haptic device handle. Otherwise returns NULL.
[Unstable API]: Perhaps could be simplified due to limited support for all the exposed features across all of the platforms. Awaiting feedback from users.