set_display_switch_mode(3) Allegro manual set_display_switch_mode(3)NAMEset_display_switch_mode - Tells Allegro how the program handles back‐
ground 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 con‐
sole, but not under Windows.
SWITCH_AMNESIA
Like SWITCH_PAUSE, but this mode doesn't bother to remember the con‐
tents 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 rou‐
tines 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 mecha‐
nism may not be good enough to work when the program runs in the back‐
ground 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 ALSOset_display_switch_callback(3), get_display_switch_mode(3), exmidi(3),
exswitch(3)Allegro version 4.4.2 set_display_switch_mode(3)
