al_set_d3d_device_release_callback - Man Page

#include <allegro5/allegro_direct3d.h>

void al_set_d3d_device_release_callback(
   void (*callback)(ALLEGRO_DISPLAY *display))

The callback will be called whenever a D3D device is reset (minimize, toggle fullscreen window, etc). In the callback you should release any d3d resources you have created yourself. The callback receives the affected display as a parameter.

Pass NULL to disable the callback.

5.1.0