al_set_new_display_flags man page
al_set_new_display_flags — Allegro 5 API
#include <allegro5/allegro.h> void al_set_new_display_flags(int flags)
Sets various flags to be used when creating new displays on the calling thread. flags is a bitfield containing any reasonable combination of the following:
Prefer a windowed mode.
Under multi-head X (not XRandR/TwinView), the use of more than one adapter is impossible due to bugs in X and GLX. al_create_display(3) will fail if more than one adapter is attempted to be used.
Make the window span the entire screen. Unlike ALLEGRO_FULLSCREEN this will never attempt to modify the screen resolution. Instead the pixel dimensions of the created display will be the same as the desktop.
The passed width and height are only used if the window is switched out of fullscreen mode later but will be ignored initially.
Under Windows and X11 a fullscreen display created with this flag will behave differently from one created with the ALLEGRO_FULLSCREEN flag - even if the ALLEGRO_FULLSCREEN display is passed the desktop dimensions. The exact difference is platform dependent, but some things which may be different is how alt-tab works, how fast you can toggle between fullscreen/windowed mode or how additional monitors behave while your display is in fullscreen mode.
Additionally under X, the use of more than one adapter in multi-head mode or with true Xinerama enabled is impossible due to bugs in X/GLX, creation will fail if more than one adapter is attempted to be used.
Prefer a fullscreen mode.
Under X the use of more than one FULLSCREEN display when using multi-head X, or true Xinerama is not possible due to bugs in X and GLX, display creation will fail if more than one adapter is attempted to be used.
Note: Prefer using ALLEGRO_FULLSCREEN_WINDOW as it typically provides a better user experience as the monitor doesn't change resolution and switching away from your game via Alt-Tab works smoothly. ALLEGRO_FULLSCREEN is typically less well supported compared to ALLEGRO_FULLSCREEN_WINDOW.
The display is resizable (only applicable if combined with ALLEGRO_WINDOWED).
The display window will be maximized (only applicable if combined with ALLEGRO_RESIZABLE). Since: 5.1.12
Require the driver to provide an initialized OpenGL context after returning successfully.
Require the driver to provide an initialized OpenGL context compatible with OpenGL version 3.0.
If this flag is set, the OpenGL context created with ALLEGRO_OPENGL_3_0 will be forward compatible only, meaning that all of the OpenGL API declared deprecated in OpenGL 3.0 will not be supported. Currently, a display created with this flag will not be compatible with Allegro drawing routines; the display option ALLEGRO_COMPATIBLE_DISPLAY will be set to false.
Used together with ALLEGRO_OPENGL, requests that the OpenGL context uses the OpenGL ES profile. A specific version can be requested with al_set_new_display_option(3). Note: Currently this is only supported by the X11/GLX driver. Since: 5.1.13
Require the driver to do rendering with Direct3D and provide a Direct3D device.
Require a programmable graphics pipeline. This flag is required to use ALLEGRO_SHADER(3) objects. Since: 5.1.6
Try to create a window without a frame (i.e. no border or titlebar). This usually does nothing for fullscreen modes, and even in windowed modes it depends on the underlying platform whether it is supported or not. Since: 5.0.7, 5.1.2
Original name for ALLEGRO_FRAMELESS. This works with older versions of Allegro.
Let the display generate expose events.
Create a GTK toplevel window for the display, on X. This flag is conditionally defined by the native dialog addon. You must call al_init_native_dialog_addon(3) for it to succeed. ALLEGRO_GTK_TOPLEVEL is incompatible with ALLEGRO_FULLSCREEN. Since: 5.1.5
0 can be used for default values.
al_set_new_display_option(3), al_get_display_option(3), al_set_display_option(3)
al_create_display(3), al_flip_display(3), al_get_display_flags(3), al_get_monitor_info(3), al_get_new_display_flags(3), al_get_num_display_modes(3), al_get_num_video_adapters(3), al_set_display_flag(3), al_set_new_display_option(3).