effect_stereoreverse.c
author Sam Lantinga <slouken@libsdl.org>
Fri, 04 Jan 2019 22:02:19 -0800
changeset 926 d6c9518fb5ee
parent 848 3907db698eb5
permissions -rw-r--r--
Updated copyright for 2019
     1 /*
     2   SDL_mixer:  An audio mixer library based on the SDL library
     3   Copyright (C) 1997-2019 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 
    21   This file by Ryan C. Gordon (icculus@icculus.org)
    22 
    23   These are some internally supported special effects that use SDL_mixer's
    24   effect callback API. They are meant for speed over quality.  :)
    25 */
    26 
    27 /* $Id$ */
    28 
    29 #include <stdio.h>
    30 #include <stdlib.h>
    31 
    32 #include "SDL.h"
    33 #include "SDL_mixer.h"
    34 
    35 #define __MIX_INTERNAL_EFFECT__
    36 #include "effects_internal.h"
    37 
    38 /* profile code:
    39     #include <sys/time.h>
    40     #include <unistd.h>
    41     struct timeval tv1;
    42     struct timeval tv2;
    43 
    44     gettimeofday(&tv1, NULL);
    45 
    46         ... do your thing here ...
    47 
    48     gettimeofday(&tv2, NULL);
    49     printf("%ld\n", tv2.tv_usec - tv1.tv_usec);
    50 */
    51 
    52 
    53 
    54 /*
    55  * Stereo reversal effect...this one's pretty straightforward...
    56  */
    57 
    58 static void SDLCALL _Eff_reversestereo32(int chan, void *stream, int len, void *udata)
    59 {
    60     /* 16 bits * 2 channels. */
    61     Uint32 *ptr = (Uint32 *) stream;
    62     Uint32 tmp;
    63     int i;
    64 
    65     for (i = 0; i < len; i += 2 * sizeof (Uint32), ptr += 2) {
    66         tmp = ptr[0];
    67         ptr[0] = ptr[1];
    68         ptr[1] = tmp;
    69     }
    70 }
    71 
    72 
    73 static void SDLCALL _Eff_reversestereo16(int chan, void *stream, int len, void *udata)
    74 {
    75     /* 16 bits * 2 channels. */
    76     Uint32 *ptr = (Uint32 *) stream;
    77     int i;
    78 
    79     for (i = 0; i < len; i += sizeof (Uint32), ptr++) {
    80         *ptr = (((*ptr) & 0xFFFF0000) >> 16) | (((*ptr) & 0x0000FFFF) << 16);
    81     }
    82 }
    83 
    84 
    85 static void SDLCALL _Eff_reversestereo8(int chan, void *stream, int len, void *udata)
    86 {
    87     /* 8 bits * 2 channels. */
    88     Uint32 *ptr = (Uint32 *) stream;
    89     int i;
    90 
    91     /* get the last two bytes if len is not divisible by four... */
    92     if (len % sizeof (Uint32) != 0) {
    93         Uint16 *p = (Uint16 *) (((Uint8 *) stream) + (len - 2));
    94         *p = (Uint16)((((*p) & 0xFF00) >> 8) | (((*ptr) & 0x00FF) << 8));
    95         len -= 2;
    96     }
    97 
    98     for (i = 0; i < len; i += sizeof (Uint32), ptr++) {
    99         *ptr = (((*ptr) & 0x0000FF00) >> 8) | (((*ptr) & 0x000000FF) << 8) |
   100                (((*ptr) & 0xFF000000) >> 8) | (((*ptr) & 0x00FF0000) << 8);
   101     }
   102 }
   103 
   104 
   105 int Mix_SetReverseStereo(int channel, int flip)
   106 {
   107     Mix_EffectFunc_t f = NULL;
   108     int channels;
   109     Uint16 format;
   110 
   111     Mix_QuerySpec(NULL, &format, &channels);
   112 
   113     if (channels == 2) {
   114         int bits = (format & 0xFF);
   115         switch (bits) {
   116         case 8:
   117             f = _Eff_reversestereo8;
   118             break;
   119         case 16:
   120             f = _Eff_reversestereo16;
   121             break;
   122         case 32:
   123             f = _Eff_reversestereo32;
   124             break;
   125         default:
   126             Mix_SetError("Unsupported audio format");
   127             return(0);
   128         }
   129 
   130         if (!flip) {
   131             return(Mix_UnregisterEffect(channel, f));
   132         } else {
   133             return(Mix_RegisterEffect(channel, f, NULL, NULL));
   134         }
   135     } else {
   136         Mix_SetError("Trying to reverse stereo on a non-stereo stream");
   137         return(0);
   138     }
   139 
   140     return(1);
   141 }
   142 
   143 
   144 /* end of effect_stereoreverse.c ... */
   145 
   146 /* vi: set ts=4 sw=4 expandtab: */