ALLEGRO_DISPLAY *al_create_display(int w, int h)
Create a display, or window, with the specified dimensions. The parameters of the display are determined by the last calls to al_set_new_display_*. Default parameters are used if none are set explicitly. Creating a new display will automatically make it the active one, with the backbuffer selected for drawing.
Returns NULL on error.
Each display that uses OpenGL as a backend has a distinct OpenGL rendering context associated with it. See al_set_target_bitmap(3alleg5) for the discussion about rendering contexts.