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

==============================================================================
Using the Simple DirectMedia Layer with Qtopia/OPIE
==============================================================================

==============================================================================
I.  Setting up the Qtopia development environment.

  This document will not explain how to setup the Qtopia development
  environment. That is outside the scope of the document. You can read
  more on this subject in this excellent howto:

	http://www.zauruszone.com/howtos/linux_compiler_setup_howto.html

==============================================================================
II.  Building the Simple DirectMedia Layer libraries using the arm
     cross-compiler

  This is somewhat tricky since the name of the compiler binaries
  differ from the standard. Also you should disable features not
  needed. The command below works for me. Note that it's all one
  line. You can also set the NM, LD etc environment variables
  separately.

	NM=arm-linux-nm LD=arm-linux-ld CC=arm-linux-gcc CXX=arm-linux-g++ RANLIB=arm-linux-ranlib AR=arm-linux-ar ./configure --enable-video-qtopia --disable-video-dummy --disable-video-fbcon  --disable-video-dga --disable-arts --disable-esd --disable-alsa --disable-cdrom --disable-video-x11 --disable-nasm --prefix=/opt/Qtopia/sharp/ arm-unknown-linux-gnu

  One thing to note is that the above configure will include joystick
  support, even though you can't have joysticks on the Zaurus. The
  reason for this is to avoid link / compile / runtime errors with
  applications that have joystick support.

==============================================================================
III.  Building the Simple DirectMedia Layer test programs:

  After installing, making sure the correct sdl-config is in your
  path, run configure like this:

	NM=arm-linux-nm LD=arm-linux-ld CC=arm-linux-gcc CXX=arm-linux-g++ AR=arm-linux-ar ./configure arm-unknown-linux-gnu

==============================================================================
IV.  Application porting notes

  One thing I have noticed is that applications sometimes don't exit
  correctly. Their icon remains in the taskbar and they tend to
  relaunch themselves automatically. I believe this problem doesn't
  occur if you exit your application using the exit() method. However,
  if you end main() with 'return 0;' or so, this seems to happen.

  Also note that when running in landscape mode - i.e requesting a
  window that is HEIGHT pixels wide and WIDTH pixels high, where WIDTH
  and HEIGHT normally is 240 and 320 - the image is blitted so that
  the hardware buttons are on the left side of the display. This might
  not always be desirable but such is the code today.


==============================================================================
V.  Enjoy! :)

  If you have a project you'd like me to know about, or want to ask questions,
  go ahead and join the SDL developer's mailing list by sending e-mail to:

	sdl-request@libsdl.org

  and put "subscribe" into the subject of the message. Or alternatively you
  can use the web interface:

	http://www.libsdl.org/mailman/listinfo/sdl
  
==============================================================================
VI.  What is supported:

Keyboard (Sharp Zaurus)
Hardware buttons
Stylus input (mouse)
Video. Allows fullscreen both in portrait mode (up to WIDTHxHEIGHT
size window) and in landscape mode (up to HEIGHTxWIDTH). 

All other SDL functionality works like a normal Linux system (threads,
audio etc).

-- 
David Hedbor <david@hedbor.org>
http://david.hedbor.org/ 	http://eongames.com/