Provided by: allegro4-doc_4.4.2-13_all bug

NAME

       set_display_switch_mode - Tells Allegro how the program handles background switching.

SYNOPSIS

       #include <allegro.h>

       int set_display_switch_mode(int mode);

DESCRIPTION

       Sets  how  the  program should handle being switched into the background, if the user tabs
       away from it. Not all of the possible modes will be supported by every graphics driver  on
       every platform. The available modes are:

       SWITCH_NONE

       Disables  switching.  This  is  the  default in single-tasking systems like DOS. It may be
       supported on other platforms, but you should use it with caution, because your users won't
       be impressed if they want to switch away from your program, but you don't let them!

       SWITCH_PAUSE

       Pauses  the program whenever it is in the background. Execution will be resumed as soon as
       the user switches back to  it.  This  is  the  default  in  most  fullscreen  multitasking
       environments, for example the Linux console, but not under Windows.

       SWITCH_AMNESIA

       Like  SWITCH_PAUSE, but this mode doesn't bother to remember the contents of video memory,
       so the screen, and any video bitmaps that you have created, will be erased after the  user
       switches  away  and then back to your program. This is not a terribly useful mode to have,
       but it is the default for the fullscreen drivers under Windows because DirectDraw  is  too
       dumb to implement anything better.

       SWITCH_BACKGROUND

       The  program  will  carry on running in the background, with the screen bitmap temporarily
       being pointed at a memory buffer for the fullscreen drivers. You must  take  special  care
       when  using  this  mode,  because bad things will happen if the screen bitmap gets changed
       around when your program isn't expecting it (see below).

       SWITCH_BACKAMNESIA

       Like SWITCH_BACKGROUND, but this mode doesn't bother to remember  the  contents  of  video
       memory (see SWITCH_AMNESIA). It is again the only mode supported by the fullscreen drivers
       under Windows that lets the program keep running in the background.

       Note that you should be very careful when you are using graphics routines in the switching
       context:  you  must always call acquire_screen() before the start of any drawing code onto
       the screen and not release it until you are completely  finished,  because  the  automatic
       locking  mechanism  may not be good enough to work when the program runs in the background
       or has just been raised in the foreground.

RETURN VALUE

       Returns zero on success, invalidating at the same time all callbacks previously registered
       with  set_display_switch_callback().  Returns  -1  if  the requested mode is not currently
       possible.

SEE ALSO

       set_display_switch_callback(3alleg4),  get_display_switch_mode(3alleg4),  exmidi(3alleg4),
       exswitch(3alleg4)