examples/almultireverb.c

   1 /*
   2  * OpenAL Multi-Zone Reverb Example
   3  *
   4  * Copyright (c) 2018 by Chris Robinson <chris.kcat@gmail.com>
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 /* This file contains an example for controlling multiple reverb zones to
  26  * smoothly transition between reverb environments. The general concept is to
  27  * extend single-reverb by also tracking the closest adjacent environment, and
  28  * utilize EAX Reverb's panning vectors to position them relative to the
  29  * listener.
  30  */
  31
  32 #include <stdio.h>
  33 #include <assert.h>
  34 #include <math.h>
  35
  36 #include <SDL_sound.h>
  37
  38 #include "AL/al.h"
  39 #include "AL/alc.h"
  40 #include "AL/alext.h"
  41 #include "AL/efx-presets.h"
  42
  43 #include "common/alhelpers.h"
  44
  45
  46 #ifndef M_PI
  47 #define M_PI 3.14159265358979323846
  48 #endif
  49
  50
  51 /* Filter object functions */
  52 static LPALGENFILTERS alGenFilters;
  53 static LPALDELETEFILTERS alDeleteFilters;
  54 static LPALISFILTER alIsFilter;
  55 static LPALFILTERI alFilteri;
  56 static LPALFILTERIV alFilteriv;
  57 static LPALFILTERF alFilterf;
  58 static LPALFILTERFV alFilterfv;
  59 static LPALGETFILTERI alGetFilteri;
  60 static LPALGETFILTERIV alGetFilteriv;
  61 static LPALGETFILTERF alGetFilterf;
  62 static LPALGETFILTERFV alGetFilterfv;
  63
  64 /* Effect object functions */
  65 static LPALGENEFFECTS alGenEffects;
  66 static LPALDELETEEFFECTS alDeleteEffects;
  67 static LPALISEFFECT alIsEffect;
  68 static LPALEFFECTI alEffecti;
  69 static LPALEFFECTIV alEffectiv;
  70 static LPALEFFECTF alEffectf;
  71 static LPALEFFECTFV alEffectfv;
  72 static LPALGETEFFECTI alGetEffecti;
  73 static LPALGETEFFECTIV alGetEffectiv;
  74 static LPALGETEFFECTF alGetEffectf;
  75 static LPALGETEFFECTFV alGetEffectfv;
  76
  77 /* Auxiliary Effect Slot object functions */
  78 static LPALGENAUXILIARYEFFECTSLOTS alGenAuxiliaryEffectSlots;
  79 static LPALDELETEAUXILIARYEFFECTSLOTS alDeleteAuxiliaryEffectSlots;
  80 static LPALISAUXILIARYEFFECTSLOT alIsAuxiliaryEffectSlot;
  81 static LPALAUXILIARYEFFECTSLOTI alAuxiliaryEffectSloti;
  82 static LPALAUXILIARYEFFECTSLOTIV alAuxiliaryEffectSlotiv;
  83 static LPALAUXILIARYEFFECTSLOTF alAuxiliaryEffectSlotf;
  84 static LPALAUXILIARYEFFECTSLOTFV alAuxiliaryEffectSlotfv;
  85 static LPALGETAUXILIARYEFFECTSLOTI alGetAuxiliaryEffectSloti;
  86 static LPALGETAUXILIARYEFFECTSLOTIV alGetAuxiliaryEffectSlotiv;
  87 static LPALGETAUXILIARYEFFECTSLOTF alGetAuxiliaryEffectSlotf;
  88 static LPALGETAUXILIARYEFFECTSLOTFV alGetAuxiliaryEffectSlotfv;
  89
  90
  91 /* LoadEffect loads the given initial reverb properties into the given OpenAL
  92  * effect object, and returns non-zero on success.
  93  */
  94 static int LoadEffect(ALuint effect, const EFXEAXREVERBPROPERTIES *reverb)
  95 {
  96     ALenum err;
  97
  98     alGetError();
  99
 100     /* Prepare the effect for EAX Reverb (standard reverb doesn't contain
 101      * the needed panning vectors).
 102      */
 103     alEffecti(effect, AL_EFFECT_TYPE, AL_EFFECT_EAXREVERB);
 104     if((err=alGetError()) != AL_NO_ERROR)
 105     {
 106         fprintf(stderr, "Failed to set EAX Reverb: %s (0x%04x)\n", alGetString(err), err);
 107         return 0;
 108     }
 109
 110     /* Load the reverb properties. */
 111     alEffectf(effect, AL_EAXREVERB_DENSITY, reverb->flDensity);
 112     alEffectf(effect, AL_EAXREVERB_DIFFUSION, reverb->flDiffusion);
 113     alEffectf(effect, AL_EAXREVERB_GAIN, reverb->flGain);
 114     alEffectf(effect, AL_EAXREVERB_GAINHF, reverb->flGainHF);
 115     alEffectf(effect, AL_EAXREVERB_GAINLF, reverb->flGainLF);
 116     alEffectf(effect, AL_EAXREVERB_DECAY_TIME, reverb->flDecayTime);
 117     alEffectf(effect, AL_EAXREVERB_DECAY_HFRATIO, reverb->flDecayHFRatio);
 118     alEffectf(effect, AL_EAXREVERB_DECAY_LFRATIO, reverb->flDecayLFRatio);
 119     alEffectf(effect, AL_EAXREVERB_REFLECTIONS_GAIN, reverb->flReflectionsGain);
 120     alEffectf(effect, AL_EAXREVERB_REFLECTIONS_DELAY, reverb->flReflectionsDelay);
 121     alEffectfv(effect, AL_EAXREVERB_REFLECTIONS_PAN, reverb->flReflectionsPan);
 122     alEffectf(effect, AL_EAXREVERB_LATE_REVERB_GAIN, reverb->flLateReverbGain);
 123     alEffectf(effect, AL_EAXREVERB_LATE_REVERB_DELAY, reverb->flLateReverbDelay);
 124     alEffectfv(effect, AL_EAXREVERB_LATE_REVERB_PAN, reverb->flLateReverbPan);
 125     alEffectf(effect, AL_EAXREVERB_ECHO_TIME, reverb->flEchoTime);
 126     alEffectf(effect, AL_EAXREVERB_ECHO_DEPTH, reverb->flEchoDepth);
 127     alEffectf(effect, AL_EAXREVERB_MODULATION_TIME, reverb->flModulationTime);
 128     alEffectf(effect, AL_EAXREVERB_MODULATION_DEPTH, reverb->flModulationDepth);
 129     alEffectf(effect, AL_EAXREVERB_AIR_ABSORPTION_GAINHF, reverb->flAirAbsorptionGainHF);
 130     alEffectf(effect, AL_EAXREVERB_HFREFERENCE, reverb->flHFReference);
 131     alEffectf(effect, AL_EAXREVERB_LFREFERENCE, reverb->flLFReference);
 132     alEffectf(effect, AL_EAXREVERB_ROOM_ROLLOFF_FACTOR, reverb->flRoomRolloffFactor);
 133     alEffecti(effect, AL_EAXREVERB_DECAY_HFLIMIT, reverb->iDecayHFLimit);
 134
 135     /* Check if an error occured, and return failure if so. */
 136     if((err=alGetError()) != AL_NO_ERROR)
 137     {
 138         fprintf(stderr, "Error setting up reverb: %s\n", alGetString(err));
 139         return 0;
 140     }
 141
 142     return 1;
 143 }
 144
 145
 146 /* LoadBuffer loads the named audio file into an OpenAL buffer object, and
 147  * returns the new buffer ID.
 148  */
 149 static ALuint LoadSound(const char *filename)
 150 {
 151     Sound_Sample *sample;
 152     ALenum err, format;
 153     ALuint buffer;
 154     Uint32 slen;
 155
 156     /* Open the audio file */
 157     sample = Sound_NewSampleFromFile(filename, NULL, 65536);
 158     if(!sample)
 159     {
 160         fprintf(stderr, "Could not open audio in %s\n", filename);
 161         return 0;
 162     }
 163
 164     /* Get the sound format, and figure out the OpenAL format */
 165     if(sample->actual.channels == 1)
 166     {
 167         if(sample->actual.format == AUDIO_U8)
 168             format = AL_FORMAT_MONO8;
 169         else if(sample->actual.format == AUDIO_S16SYS)
 170             format = AL_FORMAT_MONO16;
 171         else
 172         {
 173             fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
 174             Sound_FreeSample(sample);
 175             return 0;
 176         }
 177     }
 178     else if(sample->actual.channels == 2)
 179     {
 180         if(sample->actual.format == AUDIO_U8)
 181             format = AL_FORMAT_STEREO8;
 182         else if(sample->actual.format == AUDIO_S16SYS)
 183             format = AL_FORMAT_STEREO16;
 184         else
 185         {
 186             fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
 187             Sound_FreeSample(sample);
 188             return 0;
 189         }
 190     }
 191     else
 192     {
 193         fprintf(stderr, "Unsupported channel count: %d\n", sample->actual.channels);
 194         Sound_FreeSample(sample);
 195         return 0;
 196     }
 197
 198     /* Decode the whole audio stream to a buffer. */
 199     slen = Sound_DecodeAll(sample);
 200     if(!sample->buffer || slen == 0)
 201     {
 202         fprintf(stderr, "Failed to read audio from %s\n", filename);
 203         Sound_FreeSample(sample);
 204         return 0;
 205     }
 206
 207     /* Buffer the audio data into a new buffer object, then free the data and
 208      * close the file. */
 209     buffer = 0;
 210     alGenBuffers(1, &buffer);
 211     alBufferData(buffer, format, sample->buffer, slen, sample->actual.rate);
 212     Sound_FreeSample(sample);
 213
 214     /* Check if an error occured, and clean up if so. */
 215     err = alGetError();
 216     if(err != AL_NO_ERROR)
 217     {
 218         fprintf(stderr, "OpenAL Error: %s\n", alGetString(err));
 219         if(buffer && alIsBuffer(buffer))
 220             alDeleteBuffers(1, &buffer);
 221         return 0;
 222     }
 223
 224     return buffer;
 225 }
 226
 227
 228 /* Helper to calculate the dot-product of the two given vectors. */
 229 static ALfloat dot_product(const ALfloat vec0[3], const ALfloat vec1[3])
 230 {
 231     return vec0[0]*vec1[0] + vec0[1]*vec1[1] + vec0[2]*vec1[2];
 232 }
 233
 234 /* Helper to normalize a given vector. */
 235 static void normalize(ALfloat vec[3])
 236 {
 237     ALfloat mag = sqrtf(dot_product(vec, vec));
 238     if(mag > 0.00001f)
 239     {
 240         vec[0] /= mag;
 241         vec[1] /= mag;
 242         vec[2] /= mag;
 243     }
 244     else
 245     {
 246         vec[0] = 0.0f;
 247         vec[1] = 0.0f;
 248         vec[2] = 0.0f;
 249     }
 250 }
 251
 252
 253 /* The main update function to update the listener and environment effects. */
 254 static void UpdateListenerAndEffects(float timediff, const ALuint slots[2], const ALuint effects[2], const EFXEAXREVERBPROPERTIES reverbs[2])
 255 {
 256     static const ALfloat listener_move_scale = 10.0f;
 257     /* Individual reverb zones are connected via "portals". Each portal has a
 258      * position (center point of the connecting area), a normal (facing
 259      * direction), and a radius (approximate size of the connecting area).
 260      */
 261     const ALfloat portal_pos[3] = { 0.0f, 0.0f, 0.0f };
 262     const ALfloat portal_norm[3] = { sqrtf(0.5f), 0.0f, -sqrtf(0.5f) };
 263     const ALfloat portal_radius = 2.5f;
 264     ALfloat other_dir[3], this_dir[3];
 265     ALfloat listener_pos[3];
 266     ALfloat local_norm[3];
 267     ALfloat local_dir[3];
 268     ALfloat near_edge[3];
 269     ALfloat far_edge[3];
 270     ALfloat dist, edist;
 271
 272     /* Update the listener position for the amount of time passed. This uses a
 273      * simple triangular LFO to offset the position (moves along the X axis
 274      * between -listener_move_scale and +listener_move_scale for each
 275      * transition).
 276      */
 277     listener_pos[0] = (fabsf(2.0f - timediff/2.0f) - 1.0f) * listener_move_scale;
 278     listener_pos[1] = 0.0f;
 279     listener_pos[2] = 0.0f;
 280     alListenerfv(AL_POSITION, listener_pos);
 281
 282     /* Calculate local_dir, which represents the listener-relative point to the
 283      * adjacent zone (should also include orientation). Because EAX Reverb uses
 284      * left-handed coordinates instead of right-handed like the rest of OpenAL,
 285      * negate Z for the local values.
 286      */
 287     local_dir[0] = portal_pos[0] - listener_pos[0];
 288     local_dir[1] = portal_pos[1] - listener_pos[1];
 289     local_dir[2] = -(portal_pos[2] - listener_pos[2]);
 290     /* A normal application would also rotate the portal's normal given the
 291      * listener orientation, to get the listener-relative normal.
 292      */
 293     local_norm[0] = portal_norm[0];
 294     local_norm[1] = portal_norm[1];
 295     local_norm[2] = -portal_norm[2];
 296
 297     /* Calculate the distance from the listener to the portal, and ensure it's
 298      * far enough away to not suffer severe floating-point precision issues.
 299      */
 300     dist = sqrtf(dot_product(local_dir, local_dir));
 301     if(dist > 0.00001f)
 302     {
 303         const EFXEAXREVERBPROPERTIES *other_reverb, *this_reverb;
 304         ALuint other_effect, this_effect;
 305         ALfloat magnitude, dir_dot_norm;
 306
 307         /* Normalize the direction to the portal. */
 308         local_dir[0] /= dist;
 309         local_dir[1] /= dist;
 310         local_dir[2] /= dist;
 311
 312         /* Calculate the dot product of the portal's local direction and local
 313          * normal, which is used for angular and side checks later on.
 314          */
 315         dir_dot_norm = dot_product(local_dir, local_norm);
 316
 317         /* Figure out which zone we're in. */
 318         if(dir_dot_norm <= 0.0f)
 319         {
 320             /* We're in front of the portal, so we're in Zone 0. */
 321             this_effect = effects[0];
 322             other_effect = effects[1];
 323             this_reverb = &reverbs[0];
 324             other_reverb = &reverbs[1];
 325         }
 326         else
 327         {
 328             /* We're behind the portal, so we're in Zone 1. */
 329             this_effect = effects[1];
 330             other_effect = effects[0];
 331             this_reverb = &reverbs[1];
 332             other_reverb = &reverbs[0];
 333         }
 334
 335         /* Calculate the listener-relative extents of the portal. */
 336         /* First, project the listener-to-portal vector onto the portal's plane
 337          * to get the portal-relative direction along the plane that goes away
 338          * from the listener (toward the farthest edge of the portal).
 339          */
 340         far_edge[0] = local_dir[0] - local_norm[0]*dir_dot_norm;
 341         far_edge[1] = local_dir[1] - local_norm[1]*dir_dot_norm;
 342         far_edge[2] = local_dir[2] - local_norm[2]*dir_dot_norm;
 343
 344         edist = sqrtf(dot_product(far_edge, far_edge));
 345         if(edist > 0.0001f)
 346         {
 347             /* Rescale the portal-relative vector to be at the radius edge. */
 348             ALfloat mag = portal_radius / edist;
 349             far_edge[0] *= mag;
 350             far_edge[1] *= mag;
 351             far_edge[2] *= mag;
 352
 353             /* Calculate the closest edge of the portal by negating the
 354              * farthest, and add an offset to make them both relative to the
 355              * listener.
 356              */
 357             near_edge[0] = local_dir[0]*dist - far_edge[0];
 358             near_edge[1] = local_dir[1]*dist - far_edge[1];
 359             near_edge[2] = local_dir[2]*dist - far_edge[2];
 360             far_edge[0] += local_dir[0]*dist;
 361             far_edge[1] += local_dir[1]*dist;
 362             far_edge[2] += local_dir[2]*dist;
 363
 364             /* Normalize the listener-relative extents of the portal, then
 365              * calculate the panning magnitude for the other zone given the
 366              * apparent size of the opening. The panning magnitude affects the
 367              * envelopment of the environment, with 1 being a point, 0.5 being
 368              * half coverage around the listener, and 0 being full coverage.
 369              */
 370             normalize(far_edge);
 371             normalize(near_edge);
 372             magnitude = 1.0f - acosf(dot_product(far_edge, near_edge))/(float)(M_PI*2.0);
 373
 374             /* Recalculate the panning direction, to be directly between the
 375              * direction of the two extents.
 376              */
 377             local_dir[0] = far_edge[0] + near_edge[0];
 378             local_dir[1] = far_edge[1] + near_edge[1];
 379             local_dir[2] = far_edge[2] + near_edge[2];
 380             normalize(local_dir);
 381         }
 382         else
 383         {
 384             /* If we get here, the listener is directly in front of or behind
 385              * the center of the portal, making all aperture edges effectively
 386              * equidistant. Calculating the panning magnitude is simplified,
 387              * using the arctangent of the radius and distance.
 388              */
 389             magnitude = 1.0f - (atan2f(portal_radius, dist) / (float)M_PI);
 390         }
 391
 392         /* Scale the other zone's panning vector. */
 393         other_dir[0] = local_dir[0] * magnitude;
 394         other_dir[1] = local_dir[1] * magnitude;
 395         other_dir[2] = local_dir[2] * magnitude;
 396         /* Pan the current zone to the opposite direction of the portal, and
 397          * take the remaining percentage of the portal's magnitude.
 398          */
 399         this_dir[0] = local_dir[0] * (magnitude-1.0f);
 400         this_dir[1] = local_dir[1] * (magnitude-1.0f);
 401         this_dir[2] = local_dir[2] * (magnitude-1.0f);
 402
 403         /* Now set the effects' panning vectors and gain. Energy is shared
 404          * between environments, so attenuate according to each zone's
 405          * contribution (note: gain^2 = energy).
 406          */
 407         alEffectf(this_effect, AL_EAXREVERB_REFLECTIONS_GAIN, this_reverb->flReflectionsGain * sqrtf(magnitude));
 408         alEffectf(this_effect, AL_EAXREVERB_LATE_REVERB_GAIN, this_reverb->flLateReverbGain * sqrtf(magnitude));
 409         alEffectfv(this_effect, AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
 410         alEffectfv(this_effect, AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
 411
 412         alEffectf(other_effect, AL_EAXREVERB_REFLECTIONS_GAIN, other_reverb->flReflectionsGain * sqrtf(1.0f-magnitude));
 413         alEffectf(other_effect, AL_EAXREVERB_LATE_REVERB_GAIN, other_reverb->flLateReverbGain * sqrtf(1.0f-magnitude));
 414         alEffectfv(other_effect, AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
 415         alEffectfv(other_effect, AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
 416     }
 417     else
 418     {
 419         /* We're practically in the center of the portal. Give the panning
 420          * vectors a 50/50 split, with Zone 0 covering the half in front of
 421          * the normal, and Zone 1 covering the half behind.
 422          */
 423         this_dir[0] = local_norm[0] / 2.0f;
 424         this_dir[1] = local_norm[1] / 2.0f;
 425         this_dir[2] = local_norm[2] / 2.0f;
 426
 427         other_dir[0] = local_norm[0] / -2.0f;
 428         other_dir[1] = local_norm[1] / -2.0f;
 429         other_dir[2] = local_norm[2] / -2.0f;
 430
 431         alEffectf(effects[0], AL_EAXREVERB_REFLECTIONS_GAIN, reverbs[0].flReflectionsGain * sqrtf(0.5f));
 432         alEffectf(effects[0], AL_EAXREVERB_LATE_REVERB_GAIN, reverbs[0].flLateReverbGain * sqrtf(0.5f));
 433         alEffectfv(effects[0], AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
 434         alEffectfv(effects[0], AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
 435
 436         alEffectf(effects[1], AL_EAXREVERB_REFLECTIONS_GAIN, reverbs[1].flReflectionsGain * sqrtf(0.5f));
 437         alEffectf(effects[1], AL_EAXREVERB_LATE_REVERB_GAIN, reverbs[1].flLateReverbGain * sqrtf(0.5f));
 438         alEffectfv(effects[1], AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
 439         alEffectfv(effects[1], AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
 440     }
 441
 442     /* Finally, update the effect slots with the updated effect parameters. */
 443     alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, effects[0]);
 444     alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, effects[1]);
 445 }
 446
 447
 448 int main(int argc, char **argv)
 449 {
 450     static const int MaxTransitions = 8;
 451     EFXEAXREVERBPROPERTIES reverbs[2] = {
 452         EFX_REVERB_PRESET_CARPETEDHALLWAY,
 453         EFX_REVERB_PRESET_BATHROOM
 454     };
 455     struct timespec basetime;
 456     ALCdevice *device = NULL;
 457     ALCcontext *context = NULL;
 458     ALuint effects[2] = { 0, 0 };
 459     ALuint slots[2] = { 0, 0 };
 460     ALuint direct_filter = 0;
 461     ALuint buffer = 0;
 462     ALuint source = 0;
 463     ALCint num_sends = 0;
 464     ALenum state = AL_INITIAL;
 465     ALfloat direct_gain = 1.0f;
 466     int loops = 0;
 467
 468     /* Print out usage if no arguments were specified */
 469     if(argc < 2)
 470     {
 471         fprintf(stderr, "Usage: %s [-device <name>] [options] <filename>\n\n"
 472         "Options:\n"
 473         "\t-nodirect\tSilence direct path output (easier to hear reverb)\n\n",
 474         argv[0]);
 475         return 1;
 476     }
 477
 478     /* Initialize OpenAL, and check for EFX support with at least 2 auxiliary
 479      * sends (if multiple sends are supported, 2 are provided by default; if
 480      * you want more, you have to request it through alcCreateContext).
 481      */
 482     argv++; argc--;
 483     if(InitAL(&argv, &argc) != 0)
 484         return 1;
 485
 486     while(argc > 0)
 487     {
 488         if(strcmp(argv[0], "-nodirect") == 0)
 489             direct_gain = 0.0f;
 490         else
 491             break;
 492         argv++;
 493         argc--;
 494     }
 495     if(argc < 1)
 496     {
 497         fprintf(stderr, "No filename spacified.\n");
 498         CloseAL();
 499         return 1;
 500     }
 501
 502     context = alcGetCurrentContext();
 503     device = alcGetContextsDevice(context);
 504
 505     if(!alcIsExtensionPresent(device, "ALC_EXT_EFX"))
 506     {
 507         fprintf(stderr, "Error: EFX not supported\n");
 508         CloseAL();
 509         return 1;
 510     }
 511
 512     num_sends = 0;
 513     alcGetIntegerv(device, ALC_MAX_AUXILIARY_SENDS, 1, &num_sends);
 514     if(alcGetError(device) != ALC_NO_ERROR || num_sends < 2)
 515     {
 516         fprintf(stderr, "Error: Device does not support multiple sends (got %d, need 2)\n",
 517                 num_sends);
 518         CloseAL();
 519         return 1;
 520     }
 521
 522     /* Define a macro to help load the function pointers. */
 523 #define LOAD_PROC(x)  ((x) = alGetProcAddress(#x))
 524     LOAD_PROC(alGenFilters);
 525     LOAD_PROC(alDeleteFilters);
 526     LOAD_PROC(alIsFilter);
 527     LOAD_PROC(alFilteri);
 528     LOAD_PROC(alFilteriv);
 529     LOAD_PROC(alFilterf);
 530     LOAD_PROC(alFilterfv);
 531     LOAD_PROC(alGetFilteri);
 532     LOAD_PROC(alGetFilteriv);
 533     LOAD_PROC(alGetFilterf);
 534     LOAD_PROC(alGetFilterfv);
 535
 536     LOAD_PROC(alGenEffects);
 537     LOAD_PROC(alDeleteEffects);
 538     LOAD_PROC(alIsEffect);
 539     LOAD_PROC(alEffecti);
 540     LOAD_PROC(alEffectiv);
 541     LOAD_PROC(alEffectf);
 542     LOAD_PROC(alEffectfv);
 543     LOAD_PROC(alGetEffecti);
 544     LOAD_PROC(alGetEffectiv);
 545     LOAD_PROC(alGetEffectf);
 546     LOAD_PROC(alGetEffectfv);
 547
 548     LOAD_PROC(alGenAuxiliaryEffectSlots);
 549     LOAD_PROC(alDeleteAuxiliaryEffectSlots);
 550     LOAD_PROC(alIsAuxiliaryEffectSlot);
 551     LOAD_PROC(alAuxiliaryEffectSloti);
 552     LOAD_PROC(alAuxiliaryEffectSlotiv);
 553     LOAD_PROC(alAuxiliaryEffectSlotf);
 554     LOAD_PROC(alAuxiliaryEffectSlotfv);
 555     LOAD_PROC(alGetAuxiliaryEffectSloti);
 556     LOAD_PROC(alGetAuxiliaryEffectSlotiv);
 557     LOAD_PROC(alGetAuxiliaryEffectSlotf);
 558     LOAD_PROC(alGetAuxiliaryEffectSlotfv);
 559 #undef LOAD_PROC
 560
 561     /* Initialize SDL_sound. */
 562     Sound_Init();
 563
 564     /* Load the sound into a buffer. */
 565     buffer = LoadSound(argv[0]);
 566     if(!buffer)
 567     {
 568         CloseAL();
 569         Sound_Quit();
 570         return 1;
 571     }
 572
 573     /* Generate two effects for two "zones", and load a reverb into each one.
 574      * Note that unlike single-zone reverb, where you can store one effect per
 575      * preset, for multi-zone reverb you should have one effect per environment
 576      * instance, or one per audible zone. This is because we'll be changing the
 577      * effects' properties in real-time based on the environment instance
 578      * relative to the listener.
 579      */
 580     alGenEffects(2, effects);
 581     if(!LoadEffect(effects[0], &reverbs[0]) || !LoadEffect(effects[1], &reverbs[1]))
 582     {
 583         alDeleteEffects(2, effects);
 584         alDeleteBuffers(1, &buffer);
 585         Sound_Quit();
 586         CloseAL();
 587         return 1;
 588     }
 589
 590     /* Create the effect slot objects, one for each "active" effect. */
 591     alGenAuxiliaryEffectSlots(2, slots);
 592
 593     /* Tell the effect slots to use the loaded effect objects, with slot 0 for
 594      * Zone 0 and slot 1 for Zone 1. Note that this effectively copies the
 595      * effect properties. Modifying or deleting the effect object afterward
 596      * won't directly affect the effect slot until they're reapplied like this.
 597      */
 598     alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, effects[0]);
 599     alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, effects[1]);
 600     assert(alGetError()==AL_NO_ERROR && "Failed to set effect slot");
 601
 602     /* For the purposes of this example, prepare a filter that optionally
 603      * silences the direct path which allows us to hear just the reverberation.
 604      * A filter like this is normally used for obstruction, where the path
 605      * directly between the listener and source is blocked (the exact
 606      * properties depending on the type and thickness of the obstructing
 607      * material).
 608      */
 609     alGenFilters(1, &direct_filter);
 610     alFilteri(direct_filter, AL_FILTER_TYPE, AL_FILTER_LOWPASS);
 611     alFilterf(direct_filter, AL_LOWPASS_GAIN, direct_gain);
 612     assert(alGetError()==AL_NO_ERROR && "Failed to set direct filter");
 613
 614     /* Create the source to play the sound with, place it in front of the
 615      * listener's path in the left zone.
 616      */
 617     source = 0;
 618     alGenSources(1, &source);
 619     alSourcei(source, AL_LOOPING, AL_TRUE);
 620     alSource3f(source, AL_POSITION, -5.0f, 0.0f, -2.0f);
 621     alSourcei(source, AL_DIRECT_FILTER, direct_filter);
 622     alSourcei(source, AL_BUFFER, buffer);
 623
 624     /* Connect the source to the effect slots. Here, we connect source send 0
 625      * to Zone 0's slot, and send 1 to Zone 1's slot. Filters can be specified
 626      * to occlude the source from each zone by varying amounts; for example, a
 627      * source within a particular zone would be unfiltered, while a source that
 628      * can only see a zone through a window or thin wall may be attenuated for
 629      * that zone.
 630      */
 631     alSource3i(source, AL_AUXILIARY_SEND_FILTER, slots[0], 0, AL_FILTER_NULL);
 632     alSource3i(source, AL_AUXILIARY_SEND_FILTER, slots[1], 1, AL_FILTER_NULL);
 633     assert(alGetError()==AL_NO_ERROR && "Failed to setup sound source");
 634
 635     /* Get the current time as the base for timing in the main loop. */
 636     altimespec_get(&basetime, AL_TIME_UTC);
 637     loops = 0;
 638     printf("Transition %d of %d...\n", loops+1, MaxTransitions);
 639
 640     /* Play the sound for a while. */
 641     alSourcePlay(source);
 642     do {
 643         struct timespec curtime;
 644         ALfloat timediff;
 645
 646         /* Start a batch update, to ensure all changes apply simultaneously. */
 647         alcSuspendContext(context);
 648
 649         /* Get the current time to track the amount of time that passed.
 650          * Convert the difference to seconds.
 651          */
 652         altimespec_get(&curtime, AL_TIME_UTC);
 653         timediff = (ALfloat)(curtime.tv_sec - basetime.tv_sec);
 654         timediff += (ALfloat)(curtime.tv_nsec - basetime.tv_nsec) / 1000000000.0f;
 655
 656         /* Avoid negative time deltas, in case of non-monotonic clocks. */
 657         if(timediff < 0.0f)
 658             timediff = 0.0f;
 659         else while(timediff >= 4.0f*((loops&1)+1))
 660         {
 661             /* For this example, each transition occurs over 4 seconds, and
 662              * there's 2 transitions per cycle.
 663              */
 664             if(++loops < MaxTransitions)
 665                 printf("Transition %d of %d...\n", loops+1, MaxTransitions);
 666             if(!(loops&1))
 667             {
 668                 /* Cycle completed. Decrease the delta and increase the base
 669                  * time to start a new cycle.
 670                  */
 671                 timediff -= 8.0f;
 672                 basetime.tv_sec += 8;
 673             }
 674         }
 675
 676         /* Update the listener and effects, and finish the batch. */
 677         UpdateListenerAndEffects(timediff, slots, effects, reverbs);
 678         alcProcessContext(context);
 679
 680         al_nssleep(10000000);
 681
 682         alGetSourcei(source, AL_SOURCE_STATE, &state);
 683     } while(alGetError() == AL_NO_ERROR && state == AL_PLAYING && loops < MaxTransitions);
 684
 685     /* All done. Delete resources, and close down SDL_sound and OpenAL. */
 686     alDeleteSources(1, &source);
 687     alDeleteAuxiliaryEffectSlots(2, slots);
 688     alDeleteEffects(2, effects);
 689     alDeleteFilters(1, &direct_filter);
 690     alDeleteBuffers(1, &buffer);
 691
 692     Sound_Quit();
 693     CloseAL();
 694
 695     return 0;
 696 }