author Sam Lantinga <>
Fri, 29 Feb 2008 13:55:44 +0000
changeset 4139 568c9b3c0167
parent 4131 7c2589fb8d4d
child 4260 42d28f92253b
permissions -rw-r--r--
* Added configure option --enable-screensaver, to allow enabling the screensaver by default.
* Use XResetScreenSaver() instead of disabling screensaver entirely.

Full discussion summary from Erik on the SDL mailing list:

Current behaviour

SDL changes the user's display power management settings without
permission from the user and without telling the user.

The interface that it uses to do so is DPMSDisable/DPMSEnable, which
should only ever be used by configuration utilities like KControl, never
by normal application programs, let alone by the libraries that they
use. Using an interface that is not at all intended for what SDL tries
to achieve means that it will not work as it should. Firstly, the power
management is completely disabled during the whole lifetime of the SDL
program, not only when it should be. Secondly, it makes SDL
non-reentrant, meaning that things will break when multiple SDL programs
are clients of the same X server simultaneously. Thirdly, no cleanup
mechanism ensures that the setting is restored if the client does not do
that (for example if it crashes).

In addition to that, this interface is broken on xorg,
[], so what SDL tries
to do does not work at all on that implementation of the X Window
System. (The reason that the DPMSEnable works in KControl is that it
calls DPMSSetTimeout immediately after,

The problems that the current behaviour causes
1. Information leak. When the user is away, someone might see what the
user has on the display when the user counts on the screensaver
preventing this. This does not even require physical access to the
workstation, it is enough to see it from a distance.
2. Draining battery. An SDL program that runs on a laptop will quickly
drain the battery while the user is away. The system will soon shut down
and require recharging before being usable again, while it should in
fact have consumed very little energy if the user's settings would have
been obeyed.
3. Wasting energy. Even if battery issues are not considered, energy as
such is wasted.
4. Display wear. The display may be worn out.

The problems that the current behaviour tries to solve

1. Preventing screensaver while playing movies.
Many SDL applications are media players. They have reasons to prevent
screensavers from being activated while a movie is being played. When a
user clicks on the play button it can be interpreted as saying "play
this movie, but do not turn off the display while playing it, because I
will watch it even though I do not interact with the system".

2. Preventing screensaver when some input bypasses X.
Sometimes SDL uses input from another source than the X server, so
that the X server is bypassed. This obviously breaks the screensaver
handling. SDL tries to work around that.

3. Preventing screensaver when all input bypasses X.
There is something called Direct Graphics Access mode, where a
program takes control of both the display and the input devices from the
X server. This obviously means that the X server can not handle the
screensaver alone, since screensaver handling depends on input handling.
SDL does not do what it should to help the X server to handle the
screensaver. Nor does SDL take care of screeensaver handling itself. SDL
simply disables the screensaver completely.

How the problems should be solved

The correct way for an application program to prevent the screensaver
under X is to call XResetScreenSaver. This was recently discovered and
implemented by the mplayer developers,
[]. SDL needs to
wrap this in an API call (SDL_ResetScreenSaver) and implement it for the
other video targets (if they do not have a corresponding call, SDL
should do what it takes on that particular target, for example sending
fake key events).

1. When a movie is played, the player should reset the screensaver when
the animation is advanced to a new frame. The same applies to anything
similar, like slideshows.

2. When the X server is handling input, it must handle all input
(keyboards, mice, gamepads, ...). This is necessary, not only to be able
to handle the screensaver, but also so that it can send the events to
the correct (the currently active) client. If there is an input device
that the X server can not handle for some reason (such as lack of Plug
and Play capability), the program that handles the device as a
workaround must simulate what would happen if the X server would have
handled the device, by calling XResetScreenSaver when input is received
from the device.

3. When the X server is not handling the input, it depends on the
program that does to call XResetScreenSaver whenever an input event
occurs. Alternatively the program must handle the screensaver countdown
internally and call XActivateScreenSaver.
     1 # Makefile to build and install the SDL library
     3 top_builddir = .
     4 srcdir  = @srcdir@
     5 objects = build
     6 depend	= build-deps
     7 prefix = @prefix@
     8 exec_prefix = @exec_prefix@
     9 bindir	= @bindir@
    10 libdir  = @libdir@
    11 includedir = @includedir@
    12 datarootdir = @datarootdir@
    13 datadir	= @datadir@
    14 mandir	= @mandir@
    15 auxdir	= @ac_aux_dir@
    16 distpath = $(srcdir)/..
    17 distdir = SDL-@SDL_VERSION@
    18 distfile = $(distdir).tar.gz
    20 @SET_MAKE@
    21 SHELL	= @SHELL@
    22 CC      = @CC@
    31 AR	= @AR@
    32 RANLIB	= @RANLIB@
    35 TARGET  =
    39 SDLMAIN_TARGET = libSDLmain.a
    43 DIST = acinclude.m4 Borland.html BUGS build-scripts configure COPYING CREDITS CWprojects.sea.bin docs docs.html include INSTALL Makefile.dc Makefile.minimal MPWmake.sea.bin README* sdl.m4 SDL.spec src test TODO VisualC.html WhatsNew Xcode.tar.gz
    45 HDRS = SDL.h SDL_active.h SDL_audio.h SDL_byteorder.h SDL_cdrom.h SDL_cpuinfo.h SDL_endian.h SDL_error.h SDL_events.h SDL_getenv.h SDL_joystick.h SDL_keyboard.h SDL_keysym.h SDL_loadso.h SDL_main.h SDL_mouse.h SDL_mutex.h SDL_name.h SDL_opengl.h SDL_platform.h SDL_quit.h SDL_rwops.h SDL_stdinc.h SDL_syswm.h SDL_thread.h SDL_timer.h SDL_types.h SDL_version.h SDL_video.h begin_code.h close_code.h
    47 LT_AGE      = @LT_AGE@
    51 LT_LDFLAGS  = -no-undefined -rpath $(DESTDIR)$(libdir) -release $(LT_RELEASE) -version-info $(LT_CURRENT):$(LT_REVISION):$(LT_AGE)
    53 all: $(srcdir)/configure Makefile $(objects) $(objects)/$(TARGET) $(objects)/$(SDLMAIN_TARGET)
    55 $(srcdir)/configure: $(srcdir)/
    56 	@echo "Warning, is out of date"
    57 	#(cd $(srcdir) && sh && sh configure)
    58 	@sleep 3
    60 Makefile: $(srcdir)/
    61 	$(SHELL) config.status $@
    63 $(objects):
    64 	$(SHELL) $(auxdir)/mkinstalldirs $@
    66 .PHONY: all depend install install-bin install-hdrs install-lib install-data install-man uninstall uninstall-bin uninstall-hdrs uninstall-lib uninstall-data uninstall-man clean distclean dist
    67 depend:
    68 	@SOURCES="$(SOURCES)" INCLUDE="$(INCLUDE)" output="$(depend)" \
    69 	$(SHELL) $(auxdir)/
    70 	@for src in $(SDLMAIN_SOURCES); do \
    71 	    obj=`echo $$src | sed -e 's|.*/||' -e 's|\.[^\.]*$$|.o|'`; \
    72 	    echo "\$$(objects)/$$obj: $$src" >>$(depend); \
    73 	    echo "	\$$(CC) \$$(CFLAGS) \$$(EXTRA_CFLAGS) -c $$src -o \$$@" >>$(depend); \
    74 	done
    76 include $(depend)
    78 $(objects)/$(TARGET): $(OBJECTS)
    79 	$(LIBTOOL) --mode=link $(CC) -o $@ $(OBJECTS) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LT_LDFLAGS)
    81 $(objects)/$(SDLMAIN_TARGET): $(SDLMAIN_OBJECTS)
    82 	$(AR) cru $@ $(SDLMAIN_OBJECTS)
    83 	$(RANLIB) $@
    85 install: all install-bin install-hdrs install-lib install-data install-man
    86 install-bin:
    87 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(bindir)
    88 	$(INSTALL) -m 755 sdl-config $(DESTDIR)$(bindir)/sdl-config
    89 install-hdrs:
    90 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(includedir)/SDL
    91 	for file in $(HDRS); do \
    92 	    $(INSTALL) -m 644 $(srcdir)/include/$$file $(DESTDIR)$(includedir)/SDL/$$file; \
    93 	done
    94 	$(INSTALL) -m 644 include/SDL_config.h $(DESTDIR)$(includedir)/SDL/SDL_config.h
    95 install-lib: $(objects) $(objects)/$(TARGET) $(objects)/$(SDLMAIN_TARGET)
    96 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(libdir)
    97 	$(LIBTOOL) --mode=install $(INSTALL) $(objects)/$(TARGET) $(DESTDIR)$(libdir)/$(TARGET)
    98 	$(INSTALL) -m 644 $(objects)/$(SDLMAIN_TARGET) $(DESTDIR)$(libdir)/$(SDLMAIN_TARGET)
    99 	$(RANLIB) $(DESTDIR)$(libdir)/$(SDLMAIN_TARGET)
   100 install-data:
   101 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(datadir)/aclocal
   102 	$(INSTALL) -m 644 $(srcdir)/sdl.m4 $(DESTDIR)$(datadir)/aclocal/sdl.m4
   103 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(libdir)/pkgconfig
   104 	$(INSTALL) -m 644 sdl.pc $(DESTDIR)$(libdir)/pkgconfig
   105 install-man:
   106 	$(SHELL) $(auxdir)/mkinstalldirs $(DESTDIR)$(mandir)/man3
   107 	for src in $(srcdir)/docs/man3/*.3; do \
   108 	    file=`echo $$src | sed -e 's|^.*/||'`; \
   109 	    $(INSTALL) -m 644 $$src $(DESTDIR)$(mandir)/man3/$$file; \
   110 	done
   112 uninstall: uninstall-bin uninstall-hdrs uninstall-lib uninstall-data uninstall-man
   113 uninstall-bin:
   114 	rm -f $(DESTDIR)$(bindir)/sdl-config
   115 uninstall-hdrs:
   116 	for file in $(HDRS); do \
   117 	    rm -f $(DESTDIR)$(includedir)/SDL/$$file; \
   118 	done
   119 	rm -f $(DESTDIR)$(includedir)/SDL/SDL_config.h
   120 	-rmdir $(DESTDIR)$(includedir)/SDL
   121 uninstall-lib:
   122 	$(LIBTOOL) --mode=uninstall rm -f $(DESTDIR)$(libdir)/$(TARGET)
   123 	rm -f $(DESTDIR)$(libdir)/$(SDLMAIN_TARGET)
   124 uninstall-data:
   125 	rm -f $(DESTDIR)$(datadir)/aclocal/sdl.m4
   126 uninstall-man:
   127 	for src in $(srcdir)/docs/man3/*.3; do \
   128 	    file=`echo $$src | sed -e 's|^.*/||'`; \
   129 	    rm -f $(DESTDIR)$(mandir)/man3/$$file; \
   130 	done
   132 clean:
   133 	rm -rf $(objects)
   134 	if test -f test/Makefile; then (cd test; $(MAKE) $@); fi
   136 distclean: clean
   137 	rm -f Makefile include/SDL_config.h sdl-config
   138 	rm -f SDL.qpg
   139 	rm -f config.status config.cache config.log libtool $(depend)
   140 	rm -rf $(srcdir)/autom4te*
   141 	rm -rf $(srcdir)/test/autom4te*
   142 	find $(srcdir) \( \
   143 	    -name '*~' -o \
   144 	    -name '*.bak' -o \
   145 	    -name '*.old' -o \
   146 	    -name '*.rej' -o \
   147 	    -name '*.orig' -o \
   148 	    -name '.#*' \) \
   149 	    -exec rm -f {} \;
   150 	cp $(srcdir)/include/SDL_config.h.default $(srcdir)/include/SDL_config.h
   151 	if test -f test/Makefile; then (cd test; $(MAKE) $@); fi
   153 dist $(distfile):
   154 	$(SHELL) $(auxdir)/mkinstalldirs $(distdir)
   155 	tar cf - $(DIST) | (cd $(distdir); tar xf -)
   156 	cp $(distdir)/include/SDL_config.h.default $(distdir)/include/SDL_config.h
   157 	rm -rf `find $(distdir) -name .svn`
   158 	rm -rf $(distdir)/test/autom4te*
   159 	find $(distdir) \( \
   160 	    -name '*~' -o \
   161 	    -name '*.bak' -o \
   162 	    -name '*.old' -o \
   163 	    -name '*.rej' -o \
   164 	    -name '*.orig' -o \
   165 	    -name '.#*' \) \
   166 	    -exec rm -f {} \;
   167 	if test -f $(distdir)/test/Makefile; then (cd $(distdir)/test && make distclean); fi
   168 	tar cvf - $(distdir) | gzip --best >$(distfile)
   169 	rm -rf $(distdir)
   171 rpm: $(distfile)
   172 	rpmbuild -ta $?
   174 # Create a SVN snapshot that people can run update on
   175 snapshot:
   176 	svn co
   177 	(cd SDL-1.2 && ./ && rm -rf autom4te.cache)
   178 	cp SDL-1.2/include/SDL_config.h.default SDL-1.2/include/SDL_config.h
   179 	tar zcf $(HOME)/SDL-1.2.tar.gz SDL-1.2
   180 	rm -f $(HOME)/
   181 	zip -r $(HOME)/ SDL-1.2
   182 	rm -rf SDL-1.2