MixSDL mixer: code cleanup; resampling fixes; mixing quality improvements (smoothed-out clipping)

git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@677 8092fc87-c524-0410-9efc-e669fe64eaf9
2003-02-05 03:43:51 +00:00
parent 23f8be1d0c
commit acfdfa9eda
3 changed files with 345 additions and 107 deletions
@@ -29,6 +29,7 @@
 #include "SDL_byteorder.h"
 #include "SDL_audio.h"
 #include "SDL_version.h"
+#include "mixerint.h"

 #define DEBUG

@@ -41,16 +42,9 @@ static uint32 mixer_sampsize;
 static sint32 mixer_silence;
 static uint32 mixer_freq;

-/* this is purely private */
-/* Reentrant mutex */
-typedef struct
-{
-	Semaphore sem;
-	uint32 thread_id;
-	uint32 locks;
-
-} mixSDL_Mutex_info;
-typedef mixSDL_Mutex_info *mixSDL_Mutex;
+/* mixer interim work-buffer; size in one-channel samples */
+static uint32 mixer_datasize;
+static sint32 *mixer_data = 0;

 mixSDL_Mutex_info mixer_mutexes[3];
 /* when locking more than one mutex
@@ -63,28 +57,6 @@ static mixSDL_Mutex act_mutex = mixer_mutexes + 2;
 #define MAX_SOURCES 8
 mixSDL_Source *active_sources[MAX_SOURCES];

-static void mixSDL_mix_channels (void *userdata, uint8 *stream,
-		sint32 len);
-static void mixSDL_ConvertBuffer_internal (mixSDL_Convertion *conv);
-static void mixSDL_Resample_frac (mixSDL_Convertion *conv);
-static void mixSDL_ResampleFlat (mixSDL_Convertion *conv);
-static void mixSDL_ResampleUp_fast (mixSDL_Convertion *conv);
-static void mixSDL_ResampleDown_fast (mixSDL_Convertion *conv);
-static void mixSDL_SourceUnqueueAll (mixSDL_Source *src);
-static void mixSDL_SourceStop_internal (mixSDL_Source *src);
-static void mixSDL_SourceActivate (mixSDL_Source* src);
-static void mixSDL_SourceDeactivate (mixSDL_Source* src);
-
-static __inline__ bool mixSDL_SourceGetNextSample (mixSDL_Source *src,
-		sint32* samp);
-
-static __inline__ sint32 mixSDL_GetSampleExt (void *src, uint32 bpc);
-static __inline__ sint32 mixSDL_GetSampleInt (void *src, uint32 bpc);
-static __inline__ void mixSDL_PutSampleInt (void *dst, uint32 bpc,
-		sint32 samp);
-static __inline__ void mixSDL_PutSampleExt (void *dst, uint32 bpc,
-		sint32 samp);
-

 /*************************************************
 *  Internals
@@ -160,7 +132,7 @@ mixSDL_GetError (void)

 /* Open the mixer with a certain desired audio format */
 bool
-mixSDL_OpenAudio (uint32 frequency, uint32 format, uint32 chunksize)
+mixSDL_OpenAudio (uint32 frequency, uint32 format, uint32 samples_buf)
 {
 	SDL_AudioSpec desired;

@@ -188,7 +160,7 @@ mixSDL_OpenAudio (uint32 frequency, uint32 format, uint32 chunksize)

 	/* Set the desired format and frequency */
 	desired.freq = frequency;
-	desired.samples = chunksize;
+	desired.samples = samples_buf;
 	desired.callback = mixSDL_mix_channels;
 	desired.userdata = NULL;

@@ -227,6 +199,10 @@ mixSDL_OpenAudio (uint32 frequency, uint32 format, uint32 chunksize)
 	mixer_sampsize = mixer_chansize * mixer_spec.channels;
 	mixer_freq = mixer_spec.freq;

+	/* 2x size the sound playback buffer should be enough for anything */
+	mixer_datasize = samples_buf * mixer_spec.channels * 2;
+	mixer_data = (sint32 *) HMalloc (sizeof (uint32) * mixer_datasize);
+
 	mixSDL_InitMutex (src_mutex, "mixSDL_SourceMutex");
 	mixSDL_InitMutex (buf_mutex, "mixSDL_BufferMutex");
 	mixSDL_InitMutex (act_mutex, "mixSDL_ActiveMutex");
@@ -247,6 +223,12 @@ mixSDL_CloseAudio (void)
 		{
 			SDL_CloseAudio();

+			if (mixer_data)
+			{
+				HFree (mixer_data);
+				mixer_data = 0;
+			}
+
 			mixSDL_TermMutex (src_mutex);
 			mixSDL_TermMutex (buf_mutex);
 			mixSDL_TermMutex (act_mutex);
@@ -925,7 +907,7 @@ mixSDL_SourceUnqueueBuffers (mixSDL_Object srcobj, uint32 n,
 *  Sources internals
 */

-void
+static void
 mixSDL_SourceUnqueueAll (mixSDL_Source *src)
 {
 	mixSDL_Buffer *buf;
@@ -967,7 +949,7 @@ mixSDL_SourceUnqueueAll (mixSDL_Source *src)
 }

 /* add the source to the active array */
-void
+static void
 mixSDL_SourceActivate (mixSDL_Source* src)
 {
 	uint32 i;
@@ -1006,7 +988,7 @@ mixSDL_SourceActivate (mixSDL_Source* src)
 }

 /* remove the source from the active array */
-void
+static void
 mixSDL_SourceDeactivate (mixSDL_Source* src)
 {
 	uint32 i;
@@ -1030,7 +1012,7 @@ mixSDL_SourceDeactivate (mixSDL_Source* src)
 	mixSDL_UnlockMutex (act_mutex);
 }

-void
+static void
 mixSDL_SourceStop_internal (mixSDL_Source *src)
 {
 	mixSDL_Buffer *buf;
@@ -1081,7 +1063,7 @@ mixSDL_SourceStop_internal (mixSDL_Source *src)
 }

 /* get the sample next in queue in internal format */
-__inline__ bool
+static __inline__ bool
 mixSDL_SourceGetNextSample (mixSDL_Source *src, sint32* psamp)
 {
 	while (src->nextqueued)
@@ -1544,7 +1526,7 @@ mixSDL_ConvertBuffer (uint32 srcfmt, void* srcdata, uint32 srcsize,
 *  Buffer internals
 */

-void
+static void
 mixSDL_ConvertBuffer_internal (mixSDL_Convertion *conv)
 {
 	conv->srcbpc = MIX_FORMAT_BPC (conv->srcfmt);
@@ -1589,7 +1571,7 @@ mixSDL_ConvertBuffer_internal (mixSDL_Convertion *conv)
 /* get a sample from external buffer
 * in internal format
 */
-__inline__ sint32
+static __inline__ sint32
 mixSDL_GetSampleExt (void *src, uint32 bpc)
 {
 	if (bpc == 2)
@@ -1599,7 +1581,7 @@ mixSDL_GetSampleExt (void *src, uint32 bpc)
 }

 /* get a sample from internal buffer */
-__inline__ sint32
+static __inline__ sint32
 mixSDL_GetSampleInt (void *src, uint32 bpc)
 {
 	if (bpc == 2)
@@ -1611,7 +1593,7 @@ mixSDL_GetSampleInt (void *src, uint32 bpc)
 /* put a sample into an external buffer
 * from internal format
 */
-__inline__ void
+static __inline__ void
 mixSDL_PutSampleExt (void *dst, uint32 bpc, sint32 samp)
 {
 	if (bpc == 2)
@@ -1623,7 +1605,7 @@ mixSDL_PutSampleExt (void *dst, uint32 bpc, sint32 samp)
 /* put a sample into an internal buffer
 * in internal format
 */
-__inline__ void
+static __inline__ void
 mixSDL_PutSampleInt (void *dst, uint32 bpc, sint32 samp)
 {
 	if (bpc == 2)
@@ -1636,7 +1618,7 @@ mixSDL_PutSampleInt (void *dst, uint32 bpc, sint32 samp)
 * in internal format, while performing
 * convertion if necessary
 */
-__inline__ sint32
+static __inline__ sint32
 mixSDL_GetConvSample (uint8 **psrc, uint32 bpc, uint32 flags)
 {
 	register sint32 samp;
@@ -1671,7 +1653,7 @@ mixSDL_GetConvSample (uint8 **psrc, uint32 bpc, uint32 flags)
 * in internal format, while performing
 * convertion if necessary
 */
-__inline__ void
+static __inline__ void
 mixSDL_PutConvSample (uint8 **pdst, uint32 bpc, uint32 flags, sint32 samp)
 {
 	mixSDL_PutSampleInt (*pdst, bpc, samp);
@@ -1684,7 +1666,7 @@ mixSDL_PutConvSample (uint8 **pdst, uint32 bpc, uint32 flags, sint32 samp)
 }

 /* resampling with fractional rate change */
-void
+static void
 mixSDL_Resample_frac (mixSDL_Convertion *conv)
 {
 	mixSDL_ConvFlags flags = conv->flags;
@@ -1742,7 +1724,13 @@ mixSDL_Resample_frac (mixSDL_Convertion *conv)
 			}
 			else
 			{
-				nextsampl = nextsampr = 0;
+				/* theoretically, here we need to get the next sample
+				 * somehow, which is in the next buffer in the stream;
+				 * leaving the next sample equal to the previous should
+				 * do for now; this will create some-20 minimal
+				 * distortions per second
+				 */
+				/* nextsampl = nextsampr = 0; */
 			}
 		}

@@ -1760,7 +1748,7 @@ mixSDL_Resample_frac (mixSDL_Convertion *conv)
 }

 /* resampling with respect to sample size only */
-void
+static void
 mixSDL_ResampleFlat (mixSDL_Convertion *conv)
 {
 	mixSDL_ConvFlags flags = conv->flags;
@@ -1768,9 +1756,13 @@ mixSDL_ResampleFlat (mixSDL_Convertion *conv)
 	uint8 *dst = conv->dstdata;
 	uint32 srcbpc = conv->srcbpc;
 	uint32 dstbpc = conv->dstbpc;
-	uint32 i;
+	uint32 samples;

-	for (i = conv->srcsamples; i; i--)
+	samples = conv->srcsamples;
+	if ( !(conv->flags & (mixConvStereoUp | mixConvStereoDown)))
+		samples *= conv->srcchans;
+
+	for (; samples; samples--)
 	{
 		register sint32 samp;

@@ -1780,7 +1772,7 @@ mixSDL_ResampleFlat (mixSDL_Convertion *conv)
 }

 /* integer-periodic resampling with rate increase */
-void
+static void
 mixSDL_ResampleUp_fast (mixSDL_Convertion *conv)
 {
 	mixSDL_ConvFlags flags = conv->flags;
@@ -1814,7 +1806,13 @@ mixSDL_ResampleUp_fast (mixSDL_Convertion *conv)
 		}
 		else
 		{
-			nextsampl = nextsampr = 0;
+			/* theoretically, here we need to get the next sample
+			 * somehow, which is in the next buffer in the stream;
+			 * leaving the next sample equal to the previous should
+			 * do for now; this will create some-20 minimal
+			 * distortions per second
+			 */
+			/* nextsampl = nextsampr = 0; */
 		}
 		
 		for (di = convrate; di > 0; di--)
@@ -1831,7 +1829,7 @@ mixSDL_ResampleUp_fast (mixSDL_Convertion *conv)
 }

 /* integer-periodic resampling with rate decrease */
-void
+static void
 mixSDL_ResampleDown_fast (mixSDL_Convertion *conv)
 {
 	mixSDL_ConvFlags flags = conv->flags;
@@ -1861,13 +1859,175 @@ mixSDL_ResampleDown_fast (mixSDL_Convertion *conv)
 }


-/*************************************************
- * THE mixer - suprisingly simple in the end
+/**********************************************************
+ * THE mixer - higher quality; smoothed-out clipping
 *
 * This could use some optimization perhaps
 */

-void mixSDL_mix_channels (void *userdata, uint8 *stream, sint32 len)
+static void
+mixSDL_mix_channels (void *userdata, uint8 *stream, sint32 len)
+{
+	uint32 samples = len / mixer_chansize;
+	sint32 *end_data = mixer_data + samples;
+	sint32 *data;
+	uint32 step;
+
+	/* mixer_datasize < samples should not happen ever, but for now.. */
+	if (mixer_datasize < samples)
+	{
+#ifdef DEBUG
+		fprintf (stderr, "mixSDL_mix_channels(): "
+				"WARNING: work-buffer too small\n");
+#endif
+		mixSDL_mix_lowq (stream, len);
+	}
+
+	/* keep this order or die */
+	mixSDL_LockMutex (src_mutex);
+	mixSDL_LockMutex (buf_mutex);
+	mixSDL_LockMutex (act_mutex);
+
+	/* first, collect data from sources and put into work-buffer */
+	for (data = mixer_data; data < end_data; ++data)
+	{
+		uint32 i;
+		sint32 fullsamp;
+		
+		fullsamp = 0;
+
+		for (i = 0; i < MAX_SOURCES; i++)
+		{
+			mixSDL_Source *src;
+			sint32 samp;
+			
+			/* find next source */
+			for (; i < MAX_SOURCES && (
+					(src = active_sources[i]) == 0
+					|| src->state != MIX_PLAYING
+					|| !mixSDL_SourceGetNextSample (src, &samp));
+					i++)
+				;
+
+			if (i < MAX_SOURCES)
+			{
+				/* sample aquired */
+				fullsamp += samp;
+			}
+		}
+		
+		*data = fullsamp;
+	}
+
+	/* unclip work-buffer */
+	step = mixer_spec.channels;
+	mixSDL_UnclipWorkBuffer (mixer_data, end_data, step);
+	if (step == 2)
+	{	/* also, for the second channel */
+		mixSDL_UnclipWorkBuffer (mixer_data + 1, end_data, step);
+	}
+
+	/* copy data into driver buffer */
+	for (data = mixer_data; data < end_data; ++data)
+	{
+		mixSDL_PutSampleExt (stream, mixer_chansize, *data);
+		stream += mixer_chansize;
+	}
+
+	/* keep this order or die */
+	mixSDL_UnlockMutex (act_mutex);
+	mixSDL_UnlockMutex (buf_mutex);
+	mixSDL_UnlockMutex (src_mutex);
+
+	(void)userdata; // satisfying compiler
+}
+
+/* data unclipping - smooth out the areas that need to be clipped */
+static void
+mixSDL_UnclipWorkBuffer (sint32 *data, sint32 *end_data, uint32 step)
+{
+	while (data < end_data)
+	{
+		uint32 len;
+		sint32 extremum;
+		sint32 *chunk;
+		sint32 threshold, origin, range_end;
+		double gain_mult;
+		sint32 samp = *data;
+
+		if (mixer_chansize == 2)
+		{	/* S16 */
+			if (samp < MIX_UNCLIP_S16_MIN)
+			{
+				origin = MIX_UNCLIP_S16_MIN;
+				range_end = -SINT16_MIN;
+				threshold = -MIX_UNCLIP_S16_MIN;
+			}
+			else if (samp > MIX_UNCLIP_S16_MAX)
+			{
+				origin = MIX_UNCLIP_S16_MAX;
+				range_end = SINT16_MAX;
+				threshold = MIX_UNCLIP_S16_MAX;
+			}
+			else
+			{
+				data += step;
+				continue;
+			}
+		}
+		else
+		{	/* S8 */
+			if (samp < MIX_UNCLIP_S8_MIN)
+			{
+				origin = MIX_UNCLIP_S8_MIN;
+				range_end = -SINT8_MIN;
+				threshold = -MIX_UNCLIP_S8_MIN;
+			}
+			else if (samp > MIX_UNCLIP_S8_MAX)
+			{
+				origin = MIX_UNCLIP_S8_MAX;
+				range_end = SINT8_MAX;
+				threshold = MIX_UNCLIP_S8_MAX;
+			}
+			else
+			{
+				data += step;
+				continue;
+			}
+		}
+
+		chunk = data;
+
+		/* seek to next sample not in clipping area */
+		extremum = 0;
+		for (len = 0; data < end_data; data += step, ++len)
+		{
+			samp = *data;
+			if (samp < 0)
+				samp = -samp;
+			if (samp > extremum)
+				extremum = samp;
+			if (samp <= threshold)
+				break;
+		}
+
+		if (extremum < range_end)
+			continue;	/* nothing to do really */
+
+		gain_mult = (double) (range_end - threshold)
+				/ (double) (extremum - threshold);
+		
+		/* apply unclipping filter - clipping smooth-out */
+		for (data = chunk; len; data += step, --len)
+		{
+			*data = origin + (sint32) (gain_mult * (*data - origin));
+		}
+	}
+}
+
+/* low quality faster version */
+static void
+mixSDL_mix_lowq (uint8 *stream, sint32 len)
 {
 	uint8 *end_stream = stream + len;

@@ -1928,7 +2088,4 @@ void mixSDL_mix_channels (void *userdata, uint8 *stream, sint32 len)
 	mixSDL_UnlockMutex (act_mutex);
 	mixSDL_UnlockMutex (buf_mutex);
 	mixSDL_UnlockMutex (src_mutex);
-
-	(void)userdata; // satisfying compiler
 }
-
@@ -184,7 +184,7 @@ typedef struct
 */
 uint32 mixSDL_GetError (void);

-bool mixSDL_OpenAudio (uint32 freq, uint32 format, uint32 chunksize);
+bool mixSDL_OpenAudio (uint32 freq, uint32 format, uint32 samples_buf);
 void mixSDL_CloseAudio (void);
 bool mixSDL_QuerySpec (uint32 *freq, uint32 *format, uint32 *channels);

@@ -226,42 +226,6 @@ void mixSDL_ConvertBuffer (uint32 srcfmt, void* srcdata, uint32 srcsize,
 		uint32 srcfreq, uint32 dstfmt, void* dstdata,
 		uint32 dstsize, uint32 dstfreq);

-/*************************************************
- *  Internals
- */
-
-/* private conversion info types */
-typedef enum
-{
-	mixConvNone = 0,
-	mixConvStereoUp = 1,
-	mixConvStereoDown = 2,
-	mixConvSizeUp = 4,
-	mixConvSizeDown = 8
-
-} mixSDL_ConvFlags;
-
-typedef struct
-{
-	uint32 srcfmt;
-	void *srcdata;
-	uint32 srcsize;
-	uint32 srcfreq;
-	uint32 srcbpc; /* bytes/sample for 1 chan */
-	uint32 srcchans;
-	uint32 srcsamples;
-	
-	uint32 dstfmt;
-	void *dstdata;
-	uint32 dstsize;
-	uint32 dstfreq;
-	uint32 dstbpc; /* bytes/sample for 1 chan */
-	uint32 dstchans;
-	uint32 dstsamples;
-
-	mixSDL_ConvFlags flags;
-
-} mixSDL_Convertion;

 /* Make sure the prop-value type is of suitable size
 * it must be able to store both int and void*
@@ -272,17 +236,9 @@ typedef struct
 #define MIX_COMPILE_TIME_ASSERT(name, x) \
 	typedef int mixSDL_dummy_##name [(x) * 2 - 1]

-MIX_COMPILE_TIME_ASSERT(mixSDL_Object, sizeof(mixSDL_Object) >= sizeof(void*));
+MIX_COMPILE_TIME_ASSERT (mixSDL_Object,
+		sizeof(mixSDL_Object) >= sizeof(void*));

 #undef MIX_COMPILE_TIME_ASSERT

-/* Clipping boundaries */
-#define MIX_S16_MAX ((double) SINT16_MAX)
-#define MIX_S16_MIN ((double) SINT16_MIN)
-#define MIX_S8_MAX  ((double) SINT8_MAX)
-#define MIX_S8_MIN  ((double) SINT8_MIN)
-
-/* Channel gain adjustment for clipping reduction */
-#define MIX_GAIN_ADJ (0.7f)
-
 #endif /* MIXER_H */
@@ -0,0 +1,125 @@
+/*
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+/* Simple mixer for use with SDL_audio
+ * Internals
+ */
+
+#ifndef MIXERINT_H
+#define MIXERINT_H
+
+#include "types.h"
+
+/*************************************************
+ *  Internals
+ */
+
+/* Conversion info types and funcs */
+typedef enum
+{
+	mixConvNone = 0,
+	mixConvStereoUp = 1,
+	mixConvStereoDown = 2,
+	mixConvSizeUp = 4,
+	mixConvSizeDown = 8
+
+} mixSDL_ConvFlags;
+
+typedef struct
+{
+	uint32 srcfmt;
+	void *srcdata;
+	uint32 srcsize;
+	uint32 srcfreq;
+	uint32 srcbpc; /* bytes/sample for 1 chan */
+	uint32 srcchans;
+	uint32 srcsamples;
+	
+	uint32 dstfmt;
+	void *dstdata;
+	uint32 dstsize;
+	uint32 dstfreq;
+	uint32 dstbpc; /* bytes/sample for 1 chan */
+	uint32 dstchans;
+	uint32 dstsamples;
+
+	mixSDL_ConvFlags flags;
+
+} mixSDL_Convertion;
+
+static void mixSDL_ConvertBuffer_internal (mixSDL_Convertion *conv);
+static void mixSDL_Resample_frac (mixSDL_Convertion *conv);
+static void mixSDL_ResampleFlat (mixSDL_Convertion *conv);
+static void mixSDL_ResampleUp_fast (mixSDL_Convertion *conv);
+static void mixSDL_ResampleDown_fast (mixSDL_Convertion *conv);
+
+static __inline__ sint32 mixSDL_GetSampleExt (void *src, uint32 bpc);
+static __inline__ sint32 mixSDL_GetSampleInt (void *src, uint32 bpc);
+static __inline__ void mixSDL_PutSampleInt (void *dst, uint32 bpc,
+		sint32 samp);
+static __inline__ void mixSDL_PutSampleExt (void *dst, uint32 bpc,
+		sint32 samp);
+
+/* Source manipulation */
+static void mixSDL_SourceUnqueueAll (mixSDL_Source *src);
+static void mixSDL_SourceStop_internal (mixSDL_Source *src);
+static void mixSDL_SourceActivate (mixSDL_Source* src);
+static void mixSDL_SourceDeactivate (mixSDL_Source* src);
+
+
+/* Reentrant mutex */
+typedef struct
+{
+	Semaphore sem;
+	uint32 thread_id;
+	uint32 locks;
+
+} mixSDL_Mutex_info;
+typedef mixSDL_Mutex_info *mixSDL_Mutex;
+
+static void mixSDL_InitMutex (mixSDL_Mutex mtx, char* name);
+static void mixSDL_TermMutex (mixSDL_Mutex mtx);
+static void mixSDL_LockMutex (mixSDL_Mutex mtx);
+static void mixSDL_UnlockMutex (mixSDL_Mutex mtx);
+
+/* Clipping boundaries */
+#define MIX_S16_MAX ((double) SINT16_MAX)
+#define MIX_S16_MIN ((double) SINT16_MIN)
+#define MIX_S8_MAX  ((double) SINT8_MAX)
+#define MIX_S8_MIN  ((double) SINT8_MIN)
+
+/* Channel gain adjustment for clipping reduction */
+#define MIX_GAIN_ADJ (0.8f)
+
+/* Clipping filter boundaries */
+#define MIX_UNCLIP_AREA     30 /* percent */
+#define MIX_UNCLIP_S16_AREA ((sint32) SINT16_MAX * MIX_UNCLIP_AREA / 100)
+#define MIX_UNCLIP_S16_MAX  ((sint32) SINT16_MAX - MIX_UNCLIP_S16_AREA)
+#define MIX_UNCLIP_S16_MIN  ((sint32) SINT16_MIN + MIX_UNCLIP_S16_AREA)
+#define MIX_UNCLIP_S8_AREA  ((sint32) SINT8_MAX * MIX_UNCLIP_AREA / 100)
+#define MIX_UNCLIP_S8_MAX   ((sint32) SINT8_MAX - MIX_UNCLIP_S8_AREA)
+#define MIX_UNCLIP_S8_MIN   ((sint32) SINT8_MIN + MIX_UNCLIP_S8_AREA)
+
+/* The Mixer */
+static void mixSDL_mix_channels (void *userdata, uint8 *stream,
+		sint32 len);
+static void mixSDL_UnclipWorkBuffer (sint32 *data, sint32 *end_data,
+		uint32 step);
+static void mixSDL_mix_lowq (uint8 *stream, sint32 len);
+static __inline__ bool mixSDL_SourceGetNextSample (mixSDL_Source *src,
+		sint32* samp);
+
+#endif /* MIXER_H */