al_apply_window_constraints - Allegro 5 API

       Enable or disable previously set constraints by al_set_window_constraints(3alleg5) function.

       If  enabled,  the  specified display will be automatically resized to new sizes to conform constraints in
       next cases:

       • The specified display is resizable, not maximized and is not in fullscreen mode.

       • If the appropriate current display size (width or  height)  is  less  than  the  value  of  constraint.
         Applied to minimum constraints.

       • If  the  appropriate  current  display  size (width or height) is greater than the value of constraint.
         Applied to maximum constraints.

       Constrains are not applied when a display is toggle from windowed to maximized or fullscreen modes.  When
       a display is toggle from maximized/fullscreen to windowed mode,  then  the  display  may  be  resized  as
       described above.  The later case is also possible when a user drags the maximized display via mouse.

       If disabled, the specified display will stop using constraints.

       al_apply_window_constraints - Allegro 5 API

al_get_window_constraints(3alleg5), al_set_window_constraints(3alleg5)

Allegro reference manual                                                    al_apply_window_constraints(3alleg5)

              #include <allegro5/allegro.h>

              void al_apply_window_constraints(ALLEGRO_DISPLAY *display, bool onoff)