Here are patches for SDL12 and SDL_mixer for 4 or 6 channel surround sound on Linux using the Alsa driver. To use them, naturally you need a sound card that will do 4 or 6 channels and probably also a recent version of the Alsa drivers and library. Since the only SDL output driver that knows about surround sound is the Alsa driver, you���ll want to choose it, using: export SDL_AUDIODRIVER=alsa There are no syntactic changes to the programming API. No new library calls, no differences in arguments. There are two semantic changes: (1) For library calls with number of channels as an argument, formerly you could use only 1 or 2 for the number of channels. Now you can also use 4 or 6. (2) The two "left" and "right" arguments to Mix_SetPanning, for the case of 4 or 6 channels, no longer simply control the volumes of the left and right channels. Now the "left" argument is converted to an angle and Mix_SetPosition is called, and the "right" argu- ment is ignored. With two exceptions, so far as I know, the modified SDL12 and SDL_mixer work the same way as the original versions, when opened for 1 or 2 channel output. The two exceptions are bugs which I fixed. Well, the first, anyway, is a bug for sure. When rate conversions up or down by a factor of two are applied (in src/audio/SDL_audiocvt.c), streams with different numbers of channels (that is, mono and stereo) are treated the same way: either each sample is copied or every other sample is omitted. This is ok for mono, but for stereo, it is frames that should be copied or omitted, where by "frame" I mean a portion of the stream containing one sample for each channel. (In the SDL source, confusingly, sometimes frames are called "samples".) So for these rate conversions, stereo streams have to be treated differently, and they are, in my modified version. The other problem that might be characterized as a bug arises when SDL_mixer is passed a multichannel chunk which does not have an integral number of frames. Due to the way the effect_position code loops over frames, when the chunk ends with a partial frame, memory outside the chunk buffer will be accessed. In the case of stereo, it���s possible that because malloc may give more memory than requested, this potential problem never actually causes a segment fault. I don���t know. For 6 channel chunks, I do know, and it does cause segment faults. If SDL_mixer is passed defective chunks and this causes a segment fault, arguably, that���s not a bug in SDL_mixer. Still, whether or not it counts as a bug, it���s easy to protect against, so why not? I added code in mixer.c to discard any partial frame at the end of a chunk. Then what about when SDL or SDL_mixer is opened for 4 or 6 chan- nel output? What happens with the parts of the current library designed for stereo? I don���t know whether I���ve covered all the bases, but I���ve tried: (1) For playing 2 channel waves, or other cases where SDL knows it has to match up a 2 channel source with a 4 or 6 channel output, I���ve added code in SDL_audiocvt.c to make the necessary conversions. (2) For playing midis using timidity, I���ve converted timidity to do 4 or 6 channel output, upon request. (3) For playing mods using mikmod, I put ad hoc code in music.c to convert the stereo output that mikmod produces to 4 or 6 chan- nels. Obviously it would be better to change the mikmod code to mix down into 4 or 6 channels, but I have a hard time following the code in mikmod, so I didn���t do that. (4) For playing mp3s, I put ad hoc code in smpeg to copy channels in the case when 4 or 6 channel output is needed. (5) There seems to be no problem with .ogg files - stereo .oggs can be up converted as .wavs are. (6) The effect_position code in SDL_mixer is now generalized to in- clude the cases of 4 and 6 channel streams. I���ve done a very limited amount of compatibility testing for some of the games using SDL I happen to have. For details, see the file TESTS. I���ve put into a separate archive, Surround-SDL-testfiles.tgz, a couple of 6 channel wave files for testing and a 6 channel ogg file. If you have the right hardware and version of Alsa, you should be able to play the wave files with the Alsa utility aplay (and hear all channels, except maybe lfe, for chan-id.wav, since it���s rather faint). Don���t expect aplay to give good sound, though. There���s something wrong with the current version of aplay. The canyon.ogg file is to test loading of 6 channel oggs. After patching and compiling, you can play it with playmus. (My version of ogg123 will not play it, and I had to patch mplayer to get it to play 6 channel oggs.) Greg Lee <greg@ling.lll.hawaii.edu> Thus, July 1, 2004

Simple DirectMedia Layer CREDITS
Thanks to everyone who made this possible, including:

* Cliff Matthews, for giving me a reason to start this project. :)
 -- Executor rocks!  *grin*

* Scott Call, for making a home for SDL on the 'Net... Thanks! :)

* The Linux Fund, C Magazine, Educational Technology Resources Inc.,
  Gareth Noyce, Jesse Pavel, Keith Kitchin, Jeremy Horvath, Thomas Nicholson,
  Hans-Peter Gygax, the Eternal Lands Development Team, Lars Brubaker,
  and Phoenix Kokido for financial contributions

* Gaëtan de Menten for writing the PHP and SQL behind the SDL website

* Tim Jones for the new look of the SDL website

* Marco Kraus for setting up SDL merchandise

* Martin Donlon for his work on the SDL Documentation Project

* Ryan Gordon for helping everybody out and keeping the dream alive. :)

* Mattias Engdegård, for help with the Solaris port and lots of other help

* Max Watson, Matt Slot, and Kyle for help with the MacOS Classic port

* Stan Shebs, for the initial MacOS X port

* Max Horn and Darrell Walisser for unflagging work on the MacOS X port

* Patrick Trainor, Jim Boucher, and Mike Gorchak for the QNX Neutrino port

* Carsten Griwodz for the AIX port

* Gabriele Greco, for the Amiga port

* Patrice Mandin, for the Atari port

* Hannu Viitala for the EPOC port

* Peter Valchev for nagging me about the OpenBSD port until I got it right. :)

* Kent B Mein, for a place to do the IRIX port

* Ash, for a place to do the OSF/1 Alpha port

* David Sowsy, for help with the BeOS port

* Eugenia Loli, for endless work on porting SDL games to BeOS

* Jon Taylor for the GGI front-end

* Paulus Esterhazy, for the Visual C++ testing and libraries

* Brenda Tantzen, for Metrowerks CodeWarrior on MacOS

* Chris Nentwich, for the Hermes assembly blitters

* Michael Vance and Jim Kutter for the X11 OpenGL support

* Stephane Peter, for the AAlib front-end and multi-threaded timer idea.

* Jon Atkins for SDL_image, SDL_mixer and SDL_net documentation

* Peter Wiklund, for the 1998 winning SDL logo,
  and Arto Hamara, Steven Wong, and Kent Mein for other logo entries.

* Arne Claus, for the 2004 winning SDL logo,
  and Shandy Brown, Jac, Alex Lyman, Mikkel Gjoel, #Guy, Jonas Hartmann,
  Daniel Liljeberg,  Ronald Sowa, DocD, Pekka Jaervinen, Patrick Avella,
  Erkki Kontilla, Levon Gavalian, Hal Emerich, David Wiktorsson,
  S. Schury and F. Hufsky, Ciska de Ruyver, Shredweat, Tyler Montbriand,
  Martin Andersson, Merlyn Wysard, Fernando Ibanez, David Miller,
  Andre Bommele, lovesby.com, Francisco Camenforte Torres, and David Igreja
  for other logo entries.

* Bob Pendleton and David Olofson for being long time contributors to
  the SDL mailing list.

* Everybody at Loki Software, Inc. for their great contributions!

 And a big hand to everyone else who gave me appreciation, advice,
 and suggestions, especially the good folks on the SDL mailing list.

THANKS! :)

  -- Sam Lantinga			<slouken@libsdl.org>