Mercurial > sdl-ios-xcode
annotate src/thread/generic/SDL_syscond.c @ 942:41a59de7f2ed
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 | b8d311d90021 |
| children | c9b51268668f |
| rev | line source |
|---|---|
| 0 | 1 /* |
| 2 SDL - Simple DirectMedia Layer | |
|
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b8d311d90021
Updated copyright information for 2004 (Happy New Year!)
Sam Lantinga <slouken@libsdl.org>
parents:
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changeset
|
3 Copyright (C) 1997-2004 Sam Lantinga |
| 0 | 4 |
| 5 This library is free software; you can redistribute it and/or | |
| 6 modify it under the terms of the GNU Library General Public | |
| 7 License as published by the Free Software Foundation; either | |
| 8 version 2 of the License, or (at your option) any later version. | |
| 9 | |
| 10 This library is distributed in the hope that it will be useful, | |
| 11 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 13 Library General Public License for more details. | |
| 14 | |
| 15 You should have received a copy of the GNU Library General Public | |
| 16 License along with this library; if not, write to the Free | |
| 17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
| 18 | |
| 19 Sam Lantinga | |
|
252
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Updated the source with the correct e-mail address
Sam Lantinga <slouken@libsdl.org>
parents:
0
diff
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|
20 slouken@libsdl.org |
| 0 | 21 */ |
| 22 | |
| 23 #ifdef SAVE_RCSID | |
| 24 static char rcsid = | |
| 25 "@(#) $Id$"; | |
| 26 #endif | |
| 27 | |
| 28 /* An implementation of condition variables using semaphores and mutexes */ | |
| 29 /* | |
| 30 This implementation borrows heavily from the BeOS condition variable | |
| 31 implementation, written by Christopher Tate and Owen Smith. Thanks! | |
| 32 */ | |
| 33 | |
| 34 #include <stdio.h> | |
| 35 #include <stdlib.h> | |
| 36 | |
| 37 #include "SDL_error.h" | |
| 38 #include "SDL_thread.h" | |
| 39 | |
| 40 struct SDL_cond | |
| 41 { | |
| 42 SDL_mutex *lock; | |
| 43 int waiting; | |
| 44 int signals; | |
| 45 SDL_sem *wait_sem; | |
| 46 SDL_sem *wait_done; | |
| 47 }; | |
| 48 | |
| 49 /* Create a condition variable */ | |
| 50 SDL_cond * SDL_CreateCond(void) | |
| 51 { | |
| 52 SDL_cond *cond; | |
| 53 | |
| 54 cond = (SDL_cond *) malloc(sizeof(SDL_cond)); | |
| 55 if ( cond ) { | |
| 56 cond->lock = SDL_CreateMutex(); | |
| 57 cond->wait_sem = SDL_CreateSemaphore(0); | |
| 58 cond->wait_done = SDL_CreateSemaphore(0); | |
| 59 cond->waiting = cond->signals = 0; | |
| 60 if ( ! cond->lock || ! cond->wait_sem || ! cond->wait_done ) { | |
| 61 SDL_DestroyCond(cond); | |
| 62 cond = NULL; | |
| 63 } | |
| 64 } else { | |
| 65 SDL_OutOfMemory(); | |
| 66 } | |
| 67 return(cond); | |
| 68 } | |
| 69 | |
| 70 /* Destroy a condition variable */ | |
| 71 void SDL_DestroyCond(SDL_cond *cond) | |
| 72 { | |
| 73 if ( cond ) { | |
| 74 if ( cond->wait_sem ) { | |
| 75 SDL_DestroySemaphore(cond->wait_sem); | |
| 76 } | |
| 77 if ( cond->wait_done ) { | |
| 78 SDL_DestroySemaphore(cond->wait_done); | |
| 79 } | |
| 80 if ( cond->lock ) { | |
| 81 SDL_DestroyMutex(cond->lock); | |
| 82 } | |
| 83 free(cond); | |
| 84 } | |
| 85 } | |
| 86 | |
| 87 /* Restart one of the threads that are waiting on the condition variable */ | |
| 88 int SDL_CondSignal(SDL_cond *cond) | |
| 89 { | |
| 90 if ( ! cond ) { | |
| 91 SDL_SetError("Passed a NULL condition variable"); | |
| 92 return -1; | |
| 93 } | |
| 94 | |
| 95 /* If there are waiting threads not already signalled, then | |
| 96 signal the condition and wait for the thread to respond. | |
| 97 */ | |
| 98 SDL_LockMutex(cond->lock); | |
| 99 if ( cond->waiting > cond->signals ) { | |
| 100 ++cond->signals; | |
| 101 SDL_SemPost(cond->wait_sem); | |
| 102 SDL_UnlockMutex(cond->lock); | |
| 103 SDL_SemWait(cond->wait_done); | |
| 104 } else { | |
| 105 SDL_UnlockMutex(cond->lock); | |
| 106 } | |
| 107 | |
| 108 return 0; | |
| 109 } | |
| 110 | |
| 111 /* Restart all threads that are waiting on the condition variable */ | |
| 112 int SDL_CondBroadcast(SDL_cond *cond) | |
| 113 { | |
| 114 if ( ! cond ) { | |
| 115 SDL_SetError("Passed a NULL condition variable"); | |
| 116 return -1; | |
| 117 } | |
| 118 | |
| 119 /* If there are waiting threads not already signalled, then | |
| 120 signal the condition and wait for the thread to respond. | |
| 121 */ | |
| 122 SDL_LockMutex(cond->lock); | |
| 123 if ( cond->waiting > cond->signals ) { | |
| 124 int i, num_waiting; | |
| 125 | |
| 126 num_waiting = (cond->waiting - cond->signals); | |
| 127 cond->signals = cond->waiting; | |
| 128 for ( i=0; i<num_waiting; ++i ) { | |
| 129 SDL_SemPost(cond->wait_sem); | |
| 130 } | |
| 131 /* Now all released threads are blocked here, waiting for us. | |
| 132 Collect them all (and win fabulous prizes!) :-) | |
| 133 */ | |
| 134 SDL_UnlockMutex(cond->lock); | |
| 135 for ( i=0; i<num_waiting; ++i ) { | |
| 136 SDL_SemWait(cond->wait_done); | |
| 137 } | |
| 138 } else { | |
| 139 SDL_UnlockMutex(cond->lock); | |
| 140 } | |
| 141 | |
| 142 return 0; | |
| 143 } | |
| 144 | |
| 145 /* Wait on the condition variable for at most 'ms' milliseconds. | |
| 146 The mutex must be locked before entering this function! | |
| 147 The mutex is unlocked during the wait, and locked again after the wait. | |
| 148 | |
| 149 Typical use: | |
| 150 | |
| 151 Thread A: | |
| 152 SDL_LockMutex(lock); | |
| 153 while ( ! condition ) { | |
| 154 SDL_CondWait(cond); | |
| 155 } | |
| 156 SDL_UnlockMutex(lock); | |
| 157 | |
| 158 Thread B: | |
| 159 SDL_LockMutex(lock); | |
| 160 ... | |
| 161 condition = true; | |
| 162 ... | |
| 163 SDL_UnlockMutex(lock); | |
| 164 */ | |
| 165 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms) | |
| 166 { | |
| 167 int retval; | |
| 168 | |
| 169 if ( ! cond ) { | |
| 170 SDL_SetError("Passed a NULL condition variable"); | |
| 171 return -1; | |
| 172 } | |
| 173 | |
| 174 /* Obtain the protection mutex, and increment the number of waiters. | |
| 175 This allows the signal mechanism to only perform a signal if there | |
| 176 are waiting threads. | |
| 177 */ | |
| 178 SDL_LockMutex(cond->lock); | |
| 179 ++cond->waiting; | |
| 180 SDL_UnlockMutex(cond->lock); | |
| 181 | |
| 182 /* Unlock the mutex, as is required by condition variable semantics */ | |
| 183 SDL_UnlockMutex(mutex); | |
| 184 | |
| 185 /* Wait for a signal */ | |
| 186 if ( ms == SDL_MUTEX_MAXWAIT ) { | |
| 187 retval = SDL_SemWait(cond->wait_sem); | |
| 188 } else { | |
| 189 retval = SDL_SemWaitTimeout(cond->wait_sem, ms); | |
| 190 } | |
| 191 | |
| 192 /* Let the signaler know we have completed the wait, otherwise | |
| 193 the signaler can race ahead and get the condition semaphore | |
| 194 if we are stopped between the mutex unlock and semaphore wait, | |
| 195 giving a deadlock. See the following URL for details: | |
| 196 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html | |
| 197 */ | |
| 198 SDL_LockMutex(cond->lock); | |
| 199 if ( cond->signals > 0 ) { | |
| 200 /* If we timed out, we need to eat a condition signal */ | |
| 201 if ( retval > 0 ) { | |
| 202 SDL_SemWait(cond->wait_sem); | |
| 203 } | |
| 204 /* We always notify the signal thread that we are done */ | |
| 205 SDL_SemPost(cond->wait_done); | |
| 206 | |
| 207 /* Signal handshake complete */ | |
| 208 --cond->signals; | |
| 209 } | |
| 210 --cond->waiting; | |
| 211 SDL_UnlockMutex(cond->lock); | |
| 212 | |
| 213 /* Lock the mutex, as is required by condition variable semantics */ | |
| 214 SDL_LockMutex(mutex); | |
| 215 | |
| 216 return retval; | |
| 217 } | |
| 218 | |
| 219 /* Wait on the condition variable forever */ | |
| 220 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex) | |
| 221 { | |
| 222 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT); | |
| 223 } |