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

/*
    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

/* Include file for SDL keyboard event handling */

#ifndef _SDL_keyboard_h
#define _SDL_keyboard_h

#include "SDL_types.h"
#include "SDL_keysym.h"

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

/* Keysym structure
   - The scancode is hardware dependent, and should not be used by general
     applications.  If no hardware scancode is available, it will be 0.

   - The 'unicode' translated character is only available when character
     translation is enabled by the SDL_EnableUNICODE() API.  If non-zero,
     this is a UNICODE character corresponding to the keypress.  If the
     high 9 bits of the character are 0, then this maps to the equivalent
     ASCII character:
	char ch;
	if ( (keysym.unicode & 0xFF80) == 0 ) {
		ch = keysym.unicode & 0x7F;
	} else {
		An international character..
	}
 */
typedef struct SDL_keysym {
	Uint8 scancode;			/* hardware specific scancode */
	SDLKey sym;			/* SDL virtual keysym */
	SDLMod mod;			/* current key modifiers */
	Uint16 unicode;			/* translated character */
} SDL_keysym;

/* This is the mask which refers to all hotkey bindings */
#define SDL_ALL_HOTKEYS		0xFFFFFFFF

/* Function prototypes */
/*
 * Enable/Disable UNICODE translation of keyboard input.
 * This translation has some overhead, so translation defaults off.
 * If 'enable' is 1, translation is enabled.
 * If 'enable' is 0, translation is disabled.
 * If 'enable' is -1, the translation state is not changed.
 * It returns the previous state of keyboard translation.
 */
extern DECLSPEC int SDLCALL SDL_EnableUNICODE(int enable);

/*
 * Enable/Disable keyboard repeat.  Keyboard repeat defaults to off.
 * 'delay' is the initial delay in ms between the time when a key is
 * pressed, and keyboard repeat begins.
 * 'interval' is the time in ms between keyboard repeat events.
 */
#define SDL_DEFAULT_REPEAT_DELAY	500
#define SDL_DEFAULT_REPEAT_INTERVAL	30
/*
 * If 'delay' is set to 0, keyboard repeat is disabled.
 */
extern DECLSPEC int SDLCALL SDL_EnableKeyRepeat(int delay, int interval);

/*
 * Get a snapshot of the current state of the keyboard.
 * Returns an array of keystates, indexed by the SDLK_* syms.
 * Used:
 * 	Uint8 *keystate = SDL_GetKeyState(NULL);
 *	if ( keystate[SDLK_RETURN] ) ... <RETURN> is pressed.
 */
extern DECLSPEC Uint8 * SDLCALL SDL_GetKeyState(int *numkeys);

/*
 * Get the current key modifier state
 */
extern DECLSPEC SDLMod SDLCALL SDL_GetModState(void);

/*
 * Set the current key modifier state
 * This does not change the keyboard state, only the key modifier flags.
 */
extern DECLSPEC void SDLCALL SDL_SetModState(SDLMod modstate);

/*
 * Get the name of an SDL virtual keysym
 */
extern DECLSPEC char * SDLCALL SDL_GetKeyName(SDLKey key);


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

#endif /* _SDL_keyboard_h */