view include/SDL_cdrom.h @ 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 04a403e4ccf5
children f09d5edfc7a3
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/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2004 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library 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
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Sam Lantinga
    slouken@libsdl.org
*/

#ifdef SAVE_RCSID
static char rcsid =
 "@(#) $Id$";
#endif

/* This is the CD-audio control API for Simple DirectMedia Layer */

#ifndef _SDL_cdrom_h
#define _SDL_cdrom_h

#include "SDL_types.h"

#include "begin_code.h"
/* Set up for C function definitions, even when using C++ */
#ifdef __cplusplus
extern "C" {
#endif

/* In order to use these functions, SDL_Init() must have been called
   with the SDL_INIT_CDROM flag.  This causes SDL to scan the system
   for CD-ROM drives, and load appropriate drivers.
*/

/* The maximum number of CD-ROM tracks on a disk */
#define SDL_MAX_TRACKS	99

/* The types of CD-ROM track possible */
#define SDL_AUDIO_TRACK	0x00
#define SDL_DATA_TRACK	0x04

/* The possible states which a CD-ROM drive can be in. */
typedef enum {
	CD_TRAYEMPTY,
	CD_STOPPED,
	CD_PLAYING,
	CD_PAUSED,
	CD_ERROR = -1
} CDstatus;

/* Given a status, returns true if there's a disk in the drive */
#define CD_INDRIVE(status)	((int)status > 0)

typedef struct SDL_CDtrack {
	Uint8 id;		/* Track number */
	Uint8 type;		/* Data or audio track */
	Uint16 unused;
	Uint32 length;		/* Length, in frames, of this track */
	Uint32 offset;		/* Offset, in frames, from start of disk */
} SDL_CDtrack;

/* This structure is only current as of the last call to SDL_CDStatus() */
typedef struct SDL_CD {
	int id;			/* Private drive identifier */
	CDstatus status;	/* Current drive status */

	/* The rest of this structure is only valid if there's a CD in drive */
	int numtracks;		/* Number of tracks on disk */
	int cur_track;		/* Current track position */
	int cur_frame;		/* Current frame offset within current track */
	SDL_CDtrack track[SDL_MAX_TRACKS+1];
} SDL_CD;

/* Conversion functions from frames to Minute/Second/Frames and vice versa */
#define CD_FPS	75
#define FRAMES_TO_MSF(f, M,S,F)	{					\
	int value = f;							\
	*(F) = value%CD_FPS;						\
	value /= CD_FPS;						\
	*(S) = value%60;						\
	value /= 60;							\
	*(M) = value;							\
}
#define MSF_TO_FRAMES(M, S, F)	((M)*60*CD_FPS+(S)*CD_FPS+(F))

/* CD-audio API functions: */

/* Returns the number of CD-ROM drives on the system, or -1 if
   SDL_Init() has not been called with the SDL_INIT_CDROM flag.
 */
extern DECLSPEC int SDLCALL SDL_CDNumDrives(void);

/* Returns a human-readable, system-dependent identifier for the CD-ROM.
   Example:
	"/dev/cdrom"
	"E:"
	"/dev/disk/ide/1/master"
*/
extern DECLSPEC const char * SDLCALL SDL_CDName(int drive);

/* Opens a CD-ROM drive for access.  It returns a drive handle on success,
   or NULL if the drive was invalid or busy.  This newly opened CD-ROM
   becomes the default CD used when other CD functions are passed a NULL
   CD-ROM handle.
   Drives are numbered starting with 0.  Drive 0 is the system default CD-ROM.
*/
extern DECLSPEC SDL_CD * SDLCALL SDL_CDOpen(int drive);

/* This function returns the current status of the given drive.
   If the drive has a CD in it, the table of contents of the CD and current
   play position of the CD will be stored in the SDL_CD structure.
*/
extern DECLSPEC CDstatus SDLCALL SDL_CDStatus(SDL_CD *cdrom);

/* Play the given CD starting at 'start_track' and 'start_frame' for 'ntracks'
   tracks and 'nframes' frames.  If both 'ntrack' and 'nframe' are 0, play 
   until the end of the CD.  This function will skip data tracks.
   This function should only be called after calling SDL_CDStatus() to 
   get track information about the CD.
   For example:
	// Play entire CD:
	if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
		SDL_CDPlayTracks(cdrom, 0, 0, 0, 0);
	// Play last track:
	if ( CD_INDRIVE(SDL_CDStatus(cdrom)) ) {
		SDL_CDPlayTracks(cdrom, cdrom->numtracks-1, 0, 0, 0);
	}
	// Play first and second track and 10 seconds of third track:
	if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
		SDL_CDPlayTracks(cdrom, 0, 0, 2, 10);

   This function returns 0, or -1 if there was an error.
*/
extern DECLSPEC int SDLCALL SDL_CDPlayTracks(SDL_CD *cdrom,
		int start_track, int start_frame, int ntracks, int nframes);

/* Play the given CD starting at 'start' frame for 'length' frames.
   It returns 0, or -1 if there was an error.
*/
extern DECLSPEC int SDLCALL SDL_CDPlay(SDL_CD *cdrom, int start, int length);

/* Pause play -- returns 0, or -1 on error */
extern DECLSPEC int SDLCALL SDL_CDPause(SDL_CD *cdrom);

/* Resume play -- returns 0, or -1 on error */
extern DECLSPEC int SDLCALL SDL_CDResume(SDL_CD *cdrom);

/* Stop play -- returns 0, or -1 on error */
extern DECLSPEC int SDLCALL SDL_CDStop(SDL_CD *cdrom);

/* Eject CD-ROM -- returns 0, or -1 on error */
extern DECLSPEC int SDLCALL SDL_CDEject(SDL_CD *cdrom);

/* Closes the handle for the CD-ROM drive */
extern DECLSPEC void SDLCALL SDL_CDClose(SDL_CD *cdrom);


/* Ends C function definitions when using C++ */
#ifdef __cplusplus
}
#endif
#include "close_code.h"

#endif /* _SDL_video_h */