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

  =================================================================
  Patch version 0.9 of SDL(Simple DirectMedia Layer) for Nano-X API
  =================================================================
  
  Authors: Hsieh-Fu Tsai, clare@setabox.com
           Greg Haerr, greg@censoft.com

  This patch is against SDL version 1.2.4.
  It enhances previous patch 0.8 by providing direct framebuffer
  access as well as dynamic hardware pixel type support, not
  requiring a compile-time option setting for different framebuffer
  modes.
  Tested against Microwindows version 0.89pre9.

  Older Microwindows versions
  ===========================
  If running on a version older than Microwindows 0.89pre9,
  the following items might need to be patched in Microwindows.

  1. Patch src/nanox/client.c::GrClose()
  It fixes the client side GrClose(). In the original version, 
  GrOpen() can only be called once. When the GrOpen() is called at 
  the second time, the program will terminate. In order to prevent
  this situation, we need to insert "nxSocket = -1" after 
  "close(nxSocket)" in GrClose(). If you do not have this problem,
  you may skip this step. 

  2. Patch src/nanox/clientfb.c to return absolute x,y coordinates
  when using GrGetWindowFBInfo().  Copy the version 0.89pre9
  of src/nanox/clientfb.c to your system, or configure
  using --disable-nanox-direct-fb.

  =============
  Quick Install 
  =============

  1. ./configure --disable-video-x11 --disable-video-fbcon \ 
       --enable-video-nanox \ 
       --with-nanox-pixel-type=[rgb/0888/888/565/555/332/pal] 
  2. make clean 
  3. make 
  4. make install (as root) 

  ============
  Nitty-gritty 
  ============

  --enable-nanox-direct-fb       Use direct framebuffer access
  --enable-nanox-debug           Show debug messages 
  --enable-nanox-share-memory    Use shared-memory to speed up 

  When running multi-threaded applications using SDL, such
  as SMPEG, set THREADSAFE=Y in Microwindows' config file,
  to enable GrXXX() system call critical section support.

  =============================================
  Some programs can be used to test this patch. 
  =============================================

  1. http://www.cs.berkeley.edu/~weimer/atris (a tetris-like game) 
  2. http://www.libsdl.org/projects/newvox/
  3. http://www.libsdl.org/projects/xflame/
  4. http://www.libsdl.org/projects/optimum/ 
  5. http://www.gnugeneration.com/software/loop/ 
  6: http://www.lokigames.com/development/smpeg.php3 (SMPEG version 0.4.4)

  =========
  Todo List 
  =========

  1. Create hardware surface
  2. Create YUVOverlay on hardware
  3. Use OpenGL
  4. Gamma correction
  5. Hide/Change mouse pointer
  6. Better window movement control with direct fb access
  7. Palette handling in 8bpp could be improved

  =====================
  Supporting Institutes
  =====================
  
  Many thanks to go to Setabox Co., Ltd. and CML (Communication and
  Multimedia Laboratory, http://www.cmlab.csie.ntu.edu.tw/) in the 
  Department of Computer Science and Information Engineering of 
  National Taiwan University for supporting this porting project.
  
  Century Embedded Technologies (http://embedded.censoft.com)
  for this patch.

  ===================
  Contact Information
  ===================

  Welcome to give me any suggestion and to report bugs.
  My e-mail address : clare@setabox.com or niky@cmlab.csie.ntu.edu.tw
                      or greg@censoft.com