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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
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Sat, 21 Aug 2004 12:27:02 +0000 |
| parents | 05c551e5bc64 |
| children | 0bc41e0361d3 |
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README.QNX by Mike Gorchak <mike@malva.ua>, <lestat@i.com.ua> Last changed at 24 Apr 2004. ====================================================================== Table of Contents: 1. OpenGL. 2. Wheel and multi-button mouses. 3. CDROM handling issues. 4. Hardware video overlays. 5. Shared library building. 6. Some building issues. 7. Environment variables. ====================================================================== 1. OpenGL: OpenGL works well and is stable, but fullscreen mode has not been heavily tested yet. If you have QNX RtP version 6.1.0 or above you must download the Photon3D runtime from http://developers.qnx.com or install it from the public repository or from the public CD, available with QNX. OS versi- ons below 6.1.0 are not supported. When creating an OpenGL context, software renderer mode is artifi- cially selected (QSSL made acceleration only for Voodoo boards in fullscreen mode, sorry but I don't have this board to test OpenGL - maybe it works or maybe not :)). If you want acceleration - you can remove one line in the source code: find the file SDL_ph_image.c and remove the following OGLAttrib[OGLargc++]=PHOGL_ATTRIB_FORCE_SW; line in the ph_SetupOpenGLContext() function or change the argument to PHOGL_ATTRIB_FORCE_HW or PHOGL_ATTRIB_FAVOR_HW. ====================================================================== 2. Wheel and multi-button mouses: Photon emits keyboard events (key up and down) when the mouse wheel is moved. The key_scan field appears valid, and it contains zero. That is a basic method of detecting mouse wheel events under Photon. It looks like a hack, but it works for me :) on various PC configura- tions. I've tested it on: 1. Genius Optical NetScroll/+ PS/2 (1 wheel) 2. A4Tech Optical GreatEye WheelMouse PS/2, model: WOP-35. (2 wheels + 2 additional buttons). The wheel for vertical scrolling works as usual, but the second wheel for horizontal scrolling emits two se- quential events up or down, so it can provide faster scrolling than the first wheel. Additional buttons don't emit any events, but it looks like they're handled by photon in an unusual way - like click to front, but works not with any window, looks like a fun bug-o-fe- ature :). ====================================================================== 3. CDROM handling issues: Access to CDROM can only be provided with 'root' privileges. I can't do anything about that, /dev/cd0 has brw------- permissions and root:root rights. ====================================================================== 4. Hardware video overlays: Overlays can flicker during window movement, resizing, etc. It happens because the photon driver updates the real window contents be- hind the overlay, then draws the temporary chroma key color over the window contents. It can be done without using the chroma key but that causes the overlay to always be on top. So flickering during window movement is preferred instead. Double buffering code is temporarily disabled in the photon driver code, because on my GF2-MX it can accidentally cause a buffer switch, which causes the old frame to show. S3 Savage4 has the same problem, but ATI Rage 128 doesn't. I think it can be fixed later. Current code works very well, so maybe double buffering is not needed right now. Something strange happens when you try to move the window with the overlay beyond the left border of the screen. The overlay tries to stay at position x=0, but when attempting to move it a bit more it jumps to position x=-60 (on GF2-MX, on ATI Rage128 this value a bit smaller). It's really strange, looks like the overlay doesn't like negative coordinates. ======================================================================= 5. Shared library building: A shared library can be built, but before running the autogen.sh script you must manually delete the libtool.m4 stuff from the acinclu- de.m4 file (it comes after the ESD detection code up to the end of the file), because the libtool stuff in the acinclude.m4 file was very old in SDL distribution before the version 1.2.7 and doesn't knew anything about QNX. SDL 1.2.7 distribution contains the new libtool.m4 script, but anyway it is broken :), Just remove it, then run "libtoolize --force --copy", delete the file aclocal.m4 if it is exists and after that run the autogen.sh script. SDL 1.2.8 contains fixed libtool.m4, ltmain.sh and config.sub files, so you can just run the autogen.sh script. ====================================================================== 6. Some building issues: Feel free to not use the --disable-shared configure option if you' ve read the above comment about 'Shared library building'. Otherwise this option is strongly recommended, as without it the sdl-config script will be broken. Run the configure script without x11 support, e.g.: a) for OpenGL support: ./configure --prefix=/usr \ --disable-video-x11 \ --disable-shared b) without OpenGL support: ./configure --prefix=/usr \ --disable-video-x11 \ --disable-shared \ --disable-video-opengl And of course dont forget to specify --disable-debug, which is on by default, to disable debug and enable the expensive optimizations. In the test directory also run the ./configure script without x11 support, e.g.: ./configure --with-sdl-prefix=/usr \ --with-sdl-exec-prefix=/usr \ --prefix=/usr --without-x ====================================================================== 7. Environment variables: Please note that the photon driver is sensible to the following environmental variables: * SDL_PHOTON_FULLSCREEN_REFRESH - this environment variable controls the refresh rate in all fullscreen modes. Be carefull !!! Photon drivers usually do not checking the maximum refresh rate, which video adapter or monitor supports. * SDL_VIDEO_WINDOW_POS - can be set in the "X,Y" format. If X and Y coordinates are bigger than the current desktop resolution, then win- dow positioning across virtual consoles is activated. If X and Y are smaller than the desktop resolution then window positioning in the current console is activated. The word "center" can be used instead of coordinates, it produces the same behavior as SDL_VIDEO_CENTERED environmental variable. * SDL_VIDEO_CENTERED - if this environmental variable exists then the window centering is perfomed in the current virtual console. Notes: The SDL_VIDEO_CENTERED enviromental variable has greater pri- ority than the SDL_VIDEO_WINDOW_POS in case if both variables are sup- plied to the application.