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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 | 136d97397288 |
children | e044e7c70a50 |
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<HTML> <HEAD> <TITLE>Using SDL with Microsoft Visual C++</TITLE> </HEAD> <BODY> <H1> Using SDL with Microsoft Visual C++ 5,6 and 7 </H1> <H3> by <A HREF="mailto:snowlion@sprynet.com">Lion Kimbro </A>and additions by <A HREF="mailto:james@conceptofzero.net"> James Turk</A> </H3> <p> You can either use the precompiled libraries from <A HREF="http://www.libsdl.org/download.php"> the SDL Download web site </A>, or you can build SDL yourself. </p> <H3> Building SDL </H3> <P> Unzip the <CODE>VisualC.zip</CODE> file into the directory that contains this file (<CODE>VisualC.html</CODE>). <STRONG><FONT color="#009900">If you are using Visual C++ 7 (.NET) you will need to use the file <code>VisualC7.zip.</code></FONT></STRONG> </P> <P> Be certain that you unzip the zip file for your compiler into <strong>this</strong> directory and not any other directory. If you are using WinZip, be careful to make sure that it extracts to <strong>this</strong> folder, because it's convenient feature of unzipping to a folder with the name of the file currently being unzipped will get you in trouble if you use it right now. And that's all I have to say about that. </P> <P> Now that it's unzipped, go into the VisualC <STRONG><FONT color="#009900">(VisualC7)</FONT></STRONG> directory that is created, and double-click on the VC++ file "<CODE>SDL.dsw</CODE>"<STRONG><FONT color="#009900"> ("<CODE>SDL.sln</CODE>").</FONT></STRONG> This should open up the IDE. </P> <P> You may be prompted at this point to upgrade the workspace, should you be using a more recent version of Visual C++. If so, allow the workspace to be upgraded. </P> <P> Build the <CODE>.dll</CODE> and <CODE>.lib</CODE> files. </P> <P> This is done by right clicking on each project in turn (Projects are listed in the Workspace panel in the FileView tab), and selecting "Build". </P> <P> You may get a few warnings, but you should not get any errors. You do have to have at least the DirectX 5 SDK installed, however. The latest version of DirectX can be downloaded or purchased on a cheap CD (my recommendation) from <A HREF="http://www.microsoft.com">Microsoft </A>. </P> <P> Later, we will refer to the following .lib and .dll files that have just been generated: </P> <ul> <li> SDL.dll</li> <li> SDL.lib</li> <li> SDLmain.lib</li> </ul> <P> Search for these using the Windows Find (Windows-F) utility, if you don't already know where they should be. For those of you with a clue, look inside the Debug or Release directories of the subdirectories of the Project folder. (It might be easier to just use Windows Find if this sounds confusing. And don't worry about needing a clue; we all need visits from the clue fairy frequently.) </P> <H3> Creating a Project with SDL </H3> <P> Create a project as a Win32 Application. </P> <P> Create a C++ file for your project. </P> <P> Set the C runtime to "Multi-threaded DLL" in the menu: <CODE>Project|Settings|C/C++ tab|Code Generation|Runtime Library </CODE>. </P> <P> Add the SDL <CODE>include</CODE> directory to your list of includes in the menu: <CODE>Project|Settings|C/C++ tab|Preprocessor|Additional include directories </CODE> . <br> <STRONG><FONT color="#009900">VC7 Specific: Instead of doing this I find it easier to add the include and library directories to the list that VC7 keeps. Do this by selecting Tools|Options|Projects|VC++ Directories and under the "Show Directories For:" dropbox select "Include Files", and click the "New Directory Icon" and add the [SDLROOT]\include directory (ex. If you installed to c:\SDL-1.2.5\ add c:\SDL-1.2.5\include). Proceed to change the dropbox selection to "Library Files" and add [SDLROOT]\lib.</FONT></STRONG> </P> <P> The "include directory" I am referring to is the <CODE>include</CODE> folder within the main SDL directory (the one that this HTML file located within). </P> <P> Now we're going to use the files that we had created earlier in the Build SDL step. </P> <P> Copy the following files into your Project directory: </P> <ul> <li> SDL.dll</li> </ul> <P> Add the following files to your project (It is not necessary to copy them to your project directory): </P> <ul> <li> SDL.lib </li> <li> SDLmain.lib</li> </ul> <P> (To add them to your project, right click on your project, and select "Add files to project") </P> <P><STRONG><FONT color="#009900">Instead of adding the files to your project it is more desireable to add them to the linker options: Project|Properties|Linker|Command Line and type the names of the libraries to link with in the "Additional Options:" box. Note: This must be done for each build configuration (eg. Release,Debug).</FONT></STRONG></P> <H3> SDL 101, First Day of Class </H3> <P> Now create the basic body of your project. The body of your program should take the following form: <CODE> <PRE> #include "SDL.h" int main( int argc, char* argv[] ) { // Body of the program goes here. return 0; } </PRE> </CODE> <P></P> <H3> That's it! </H3> <P> I hope that this document has helped you get through the most difficult part of using the SDL: installing it. Suggestions for improvements to this document should be sent to the writers of this document. </P> <P> Thanks to Paulus Esterhazy (pesterhazy@gmx.net), for the work on VC++ port. </P> <P> This document was originally called "VisualC.txt", and was written by <A HREF="mailto:slouken@libsdl.org"> Sam Lantinga</A>. </P> <P> Later, it was converted to HTML and expanded into the document that you see today by <A HREF="mailto:snowlion@sprynet.com">Lion Kimbro</A>. </P> <P>Minor Fixes and Visual C++ 7 Information (In Green) was added by <A HREF="mailto:james@conceptofzero.net">James Turk</A> </P> </BODY> </HTML>