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 <assert.h>
  33 #include <math.h>
  34 #include <stdio.h>
  35 #include <string.h>
  36
  37 #include "SDL_sound.h"
  38 #include "SDL_audio.h"
  39 #include "SDL_stdinc.h"
  40
  41 #include "AL/al.h"
  42 #include "AL/alc.h"
  43 #include "AL/efx.h"
  44 #include "AL/efx-presets.h"
  45
  46 #include "common/alhelpers.h"
  47
  48
  49 #ifndef M_PI
  50 #define M_PI 3.14159265358979323846
  51 #endif
  52
  53
  54 /* Filter object functions */
  55 static LPALGENFILTERS alGenFilters;
  56 static LPALDELETEFILTERS alDeleteFilters;
  57 static LPALISFILTER alIsFilter;
  58 static LPALFILTERI alFilteri;
  59 static LPALFILTERIV alFilteriv;
  60 static LPALFILTERF alFilterf;
  61 static LPALFILTERFV alFilterfv;
  62 static LPALGETFILTERI alGetFilteri;
  63 static LPALGETFILTERIV alGetFilteriv;
  64 static LPALGETFILTERF alGetFilterf;
  65 static LPALGETFILTERFV alGetFilterfv;
  66
  67 /* Effect object functions */
  68 static LPALGENEFFECTS alGenEffects;
  69 static LPALDELETEEFFECTS alDeleteEffects;
  70 static LPALISEFFECT alIsEffect;
  71 static LPALEFFECTI alEffecti;
  72 static LPALEFFECTIV alEffectiv;
  73 static LPALEFFECTF alEffectf;
  74 static LPALEFFECTFV alEffectfv;
  75 static LPALGETEFFECTI alGetEffecti;
  76 static LPALGETEFFECTIV alGetEffectiv;
  77 static LPALGETEFFECTF alGetEffectf;
  78 static LPALGETEFFECTFV alGetEffectfv;
  79
  80 /* Auxiliary Effect Slot object functions */
  81 static LPALGENAUXILIARYEFFECTSLOTS alGenAuxiliaryEffectSlots;
  82 static LPALDELETEAUXILIARYEFFECTSLOTS alDeleteAuxiliaryEffectSlots;
  83 static LPALISAUXILIARYEFFECTSLOT alIsAuxiliaryEffectSlot;
  84 static LPALAUXILIARYEFFECTSLOTI alAuxiliaryEffectSloti;
  85 static LPALAUXILIARYEFFECTSLOTIV alAuxiliaryEffectSlotiv;
  86 static LPALAUXILIARYEFFECTSLOTF alAuxiliaryEffectSlotf;
  87 static LPALAUXILIARYEFFECTSLOTFV alAuxiliaryEffectSlotfv;
  88 static LPALGETAUXILIARYEFFECTSLOTI alGetAuxiliaryEffectSloti;
  89 static LPALGETAUXILIARYEFFECTSLOTIV alGetAuxiliaryEffectSlotiv;
  90 static LPALGETAUXILIARYEFFECTSLOTF alGetAuxiliaryEffectSlotf;
  91 static LPALGETAUXILIARYEFFECTSLOTFV alGetAuxiliaryEffectSlotfv;
  92
  93
  94 /* LoadEffect loads the given initial reverb properties into the given OpenAL
  95  * effect object, and returns non-zero on success.
  96  */
  97 static int LoadEffect(ALuint effect, const EFXEAXREVERBPROPERTIES *reverb)
  98 {
  99     ALenum err;
 100
 101     alGetError();
 102
 103     /* Prepare the effect for EAX Reverb (standard reverb doesn't contain
 104      * the needed panning vectors).
 105      */
 106     alEffecti(effect, AL_EFFECT_TYPE, AL_EFFECT_EAXREVERB);
 107     if((err=alGetError()) != AL_NO_ERROR)
 108     {
 109         fprintf(stderr, "Failed to set EAX Reverb: %s (0x%04x)\n", alGetString(err), err);
 110         return 0;
 111     }
 112
 113     /* Load the reverb properties. */
 114     alEffectf(effect, AL_EAXREVERB_DENSITY, reverb->flDensity);
 115     alEffectf(effect, AL_EAXREVERB_DIFFUSION, reverb->flDiffusion);
 116     alEffectf(effect, AL_EAXREVERB_GAIN, reverb->flGain);
 117     alEffectf(effect, AL_EAXREVERB_GAINHF, reverb->flGainHF);
 118     alEffectf(effect, AL_EAXREVERB_GAINLF, reverb->flGainLF);
 119     alEffectf(effect, AL_EAXREVERB_DECAY_TIME, reverb->flDecayTime);
 120     alEffectf(effect, AL_EAXREVERB_DECAY_HFRATIO, reverb->flDecayHFRatio);
 121     alEffectf(effect, AL_EAXREVERB_DECAY_LFRATIO, reverb->flDecayLFRatio);
 122     alEffectf(effect, AL_EAXREVERB_REFLECTIONS_GAIN, reverb->flReflectionsGain);
 123     alEffectf(effect, AL_EAXREVERB_REFLECTIONS_DELAY, reverb->flReflectionsDelay);
 124     alEffectfv(effect, AL_EAXREVERB_REFLECTIONS_PAN, reverb->flReflectionsPan);
 125     alEffectf(effect, AL_EAXREVERB_LATE_REVERB_GAIN, reverb->flLateReverbGain);
 126     alEffectf(effect, AL_EAXREVERB_LATE_REVERB_DELAY, reverb->flLateReverbDelay);
 127     alEffectfv(effect, AL_EAXREVERB_LATE_REVERB_PAN, reverb->flLateReverbPan);
 128     alEffectf(effect, AL_EAXREVERB_ECHO_TIME, reverb->flEchoTime);
 129     alEffectf(effect, AL_EAXREVERB_ECHO_DEPTH, reverb->flEchoDepth);
 130     alEffectf(effect, AL_EAXREVERB_MODULATION_TIME, reverb->flModulationTime);
 131     alEffectf(effect, AL_EAXREVERB_MODULATION_DEPTH, reverb->flModulationDepth);
 132     alEffectf(effect, AL_EAXREVERB_AIR_ABSORPTION_GAINHF, reverb->flAirAbsorptionGainHF);
 133     alEffectf(effect, AL_EAXREVERB_HFREFERENCE, reverb->flHFReference);
 134     alEffectf(effect, AL_EAXREVERB_LFREFERENCE, reverb->flLFReference);
 135     alEffectf(effect, AL_EAXREVERB_ROOM_ROLLOFF_FACTOR, reverb->flRoomRolloffFactor);
 136     alEffecti(effect, AL_EAXREVERB_DECAY_HFLIMIT, reverb->iDecayHFLimit);
 137
 138     /* Check if an error occured, and return failure if so. */
 139     if((err=alGetError()) != AL_NO_ERROR)
 140     {
 141         fprintf(stderr, "Error setting up reverb: %s\n", alGetString(err));
 142         return 0;
 143     }
 144
 145     return 1;
 146 }
 147
 148
 149 /* LoadBuffer loads the named audio file into an OpenAL buffer object, and
 150  * returns the new buffer ID.
 151  */
 152 static ALuint LoadSound(const char *filename)
 153 {
 154     Sound_Sample *sample;
 155     ALenum err, format;
 156     ALuint buffer;
 157     Uint32 slen;
 158
 159     /* Open the audio file */
 160     sample = Sound_NewSampleFromFile(filename, NULL, 65536);
 161     if(!sample)
 162     {
 163         fprintf(stderr, "Could not open audio in %s\n", filename);
 164         return 0;
 165     }
 166
 167     /* Get the sound format, and figure out the OpenAL format */
 168     if(sample->actual.channels == 1)
 169     {
 170         if(sample->actual.format == AUDIO_U8)
 171             format = AL_FORMAT_MONO8;
 172         else if(sample->actual.format == AUDIO_S16SYS)
 173             format = AL_FORMAT_MONO16;
 174         else
 175         {
 176             fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
 177             Sound_FreeSample(sample);
 178             return 0;
 179         }
 180     }
 181     else if(sample->actual.channels == 2)
 182     {
 183         if(sample->actual.format == AUDIO_U8)
 184             format = AL_FORMAT_STEREO8;
 185         else if(sample->actual.format == AUDIO_S16SYS)
 186             format = AL_FORMAT_STEREO16;
 187         else
 188         {
 189             fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
 190             Sound_FreeSample(sample);
 191             return 0;
 192         }
 193     }
 194     else
 195     {
 196         fprintf(stderr, "Unsupported channel count: %d\n", sample->actual.channels);
 197         Sound_FreeSample(sample);
 198         return 0;
 199     }
 200
 201     /* Decode the whole audio stream to a buffer. */
 202     slen = Sound_DecodeAll(sample);
 203     if(!sample->buffer || slen == 0)
 204     {
 205         fprintf(stderr, "Failed to read audio from %s\n", filename);
 206         Sound_FreeSample(sample);
 207         return 0;
 208     }
 209
 210     /* Buffer the audio data into a new buffer object, then free the data and
 211      * close the file. */
 212     buffer = 0;
 213     alGenBuffers(1, &buffer);
 214     alBufferData(buffer, format, sample->buffer, (ALsizei)slen, (ALsizei)sample->actual.rate);
 215     Sound_FreeSample(sample);
 216
 217     /* Check if an error occured, and clean up if so. */
 218     err = alGetError();
 219     if(err != AL_NO_ERROR)
 220     {
 221         fprintf(stderr, "OpenAL Error: %s\n", alGetString(err));
 222         if(buffer && alIsBuffer(buffer))
 223             alDeleteBuffers(1, &buffer);
 224         return 0;
 225     }
 226
 227     return buffer;
 228 }
 229
 230
 231 /* Helper to calculate the dot-product of the two given vectors. */
 232 static ALfloat dot_product(const ALfloat vec0[3], const ALfloat vec1[3])
 233 {
 234     return vec0[0]*vec1[0] + vec0[1]*vec1[1] + vec0[2]*vec1[2];
 235 }
 236
 237 /* Helper to normalize a given vector. */
 238 static void normalize(ALfloat vec[3])
 239 {
 240     ALfloat mag = sqrtf(dot_product(vec, vec));
 241     if(mag > 0.00001f)
 242     {
 243         vec[0] /= mag;
 244         vec[1] /= mag;
 245         vec[2] /= mag;
 246     }
 247     else
 248     {
 249         vec[0] = 0.0f;
 250         vec[1] = 0.0f;
 251         vec[2] = 0.0f;
 252     }
 253 }
 254
 255
 256 /* The main update function to update the listener and environment effects. */
 257 static void UpdateListenerAndEffects(float timediff, const ALuint slots[2], const ALuint effects[2], const EFXEAXREVERBPROPERTIES reverbs[2])
 258 {
 259     static const ALfloat listener_move_scale = 10.0f;
 260     /* Individual reverb zones are connected via "portals". Each portal has a
 261      * position (center point of the connecting area), a normal (facing
 262      * direction), and a radius (approximate size of the connecting area).
 263      */
 264     const ALfloat portal_pos[3] = { 0.0f, 0.0f, 0.0f };
 265     const ALfloat portal_norm[3] = { sqrtf(0.5f), 0.0f, -sqrtf(0.5f) };
 266     const ALfloat portal_radius = 2.5f;
 267     ALfloat other_dir[3], this_dir[3];
 268     ALfloat listener_pos[3];
 269     ALfloat local_norm[3];
 270     ALfloat local_dir[3];
 271     ALfloat near_edge[3];
 272     ALfloat far_edge[3];
 273     ALfloat dist, edist;
 274
 275     /* Update the listener position for the amount of time passed. This uses a
 276      * simple triangular LFO to offset the position (moves along the X axis
 277      * between -listener_move_scale and +listener_move_scale for each
 278      * transition).
 279      */
 280     listener_pos[0] = (fabsf(2.0f - timediff/2.0f) - 1.0f) * listener_move_scale;
 281     listener_pos[1] = 0.0f;
 282     listener_pos[2] = 0.0f;
 283     alListenerfv(AL_POSITION, listener_pos);
 284
 285     /* Calculate local_dir, which represents the listener-relative point to the
 286      * adjacent zone (should also include orientation). Because EAX Reverb uses
 287      * left-handed coordinates instead of right-handed like the rest of OpenAL,
 288      * negate Z for the local values.
 289      */
 290     local_dir[0] = portal_pos[0] - listener_pos[0];
 291     local_dir[1] = portal_pos[1] - listener_pos[1];
 292     local_dir[2] = -(portal_pos[2] - listener_pos[2]);
 293     /* A normal application would also rotate the portal's normal given the
 294      * listener orientation, to get the listener-relative normal.
 295      */
 296     local_norm[0] = portal_norm[0];
 297     local_norm[1] = portal_norm[1];
 298     local_norm[2] = -portal_norm[2];
 299
 300     /* Calculate the distance from the listener to the portal, and ensure it's
 301      * far enough away to not suffer severe floating-point precision issues.
 302      */
 303     dist = sqrtf(dot_product(local_dir, local_dir));
 304     if(dist > 0.00001f)
 305     {
 306         const EFXEAXREVERBPROPERTIES *other_reverb, *this_reverb;
 307         ALuint other_effect, this_effect;
 308         ALfloat magnitude, dir_dot_norm;
 309
 310         /* Normalize the direction to the portal. */
 311         local_dir[0] /= dist;
 312         local_dir[1] /= dist;
 313         local_dir[2] /= dist;
 314
 315         /* Calculate the dot product of the portal's local direction and local
 316          * normal, which is used for angular and side checks later on.
 317          */
 318         dir_dot_norm = dot_product(local_dir, local_norm);
 319
 320         /* Figure out which zone we're in. */
 321         if(dir_dot_norm <= 0.0f)
 322         {
 323             /* We're in front of the portal, so we're in Zone 0. */
 324             this_effect = effects[0];
 325             other_effect = effects[1];
 326             this_reverb = &reverbs[0];
 327             other_reverb = &reverbs[1];
 328         }
 329         else
 330         {
 331             /* We're behind the portal, so we're in Zone 1. */
 332             this_effect = effects[1];
 333             other_effect = effects[0];
 334             this_reverb = &reverbs[1];
 335             other_reverb = &reverbs[0];
 336         }
 337
 338         /* Calculate the listener-relative extents of the portal. */
 339         /* First, project the listener-to-portal vector onto the portal's plane
 340          * to get the portal-relative direction along the plane that goes away
 341          * from the listener (toward the farthest edge of the portal).
 342          */
 343         far_edge[0] = local_dir[0] - local_norm[0]*dir_dot_norm;
 344         far_edge[1] = local_dir[1] - local_norm[1]*dir_dot_norm;
 345         far_edge[2] = local_dir[2] - local_norm[2]*dir_dot_norm;
 346
 347         edist = sqrtf(dot_product(far_edge, far_edge));
 348         if(edist > 0.0001f)
 349         {
 350             /* Rescale the portal-relative vector to be at the radius edge. */
 351             ALfloat mag = portal_radius / edist;
 352             far_edge[0] *= mag;
 353             far_edge[1] *= mag;
 354             far_edge[2] *= mag;
 355
 356             /* Calculate the closest edge of the portal by negating the
 357              * farthest, and add an offset to make them both relative to the
 358              * listener.
 359              */
 360             near_edge[0] = local_dir[0]*dist - far_edge[0];
 361             near_edge[1] = local_dir[1]*dist - far_edge[1];
 362             near_edge[2] = local_dir[2]*dist - far_edge[2];
 363             far_edge[0] += local_dir[0]*dist;
 364             far_edge[1] += local_dir[1]*dist;
 365             far_edge[2] += local_dir[2]*dist;
 366
 367             /* Normalize the listener-relative extents of the portal, then
 368              * calculate the panning magnitude for the other zone given the
 369              * apparent size of the opening. The panning magnitude affects the
 370              * envelopment of the environment, with 1 being a point, 0.5 being
 371              * half coverage around the listener, and 0 being full coverage.
 372              */
 373             normalize(far_edge);
 374             normalize(near_edge);
 375             magnitude = 1.0f - acosf(dot_product(far_edge, near_edge))/(float)(M_PI*2.0);
 376
 377             /* Recalculate the panning direction, to be directly between the
 378              * direction of the two extents.
 379              */
 380             local_dir[0] = far_edge[0] + near_edge[0];
 381             local_dir[1] = far_edge[1] + near_edge[1];
 382             local_dir[2] = far_edge[2] + near_edge[2];
 383             normalize(local_dir);
 384         }
 385         else
 386         {
 387             /* If we get here, the listener is directly in front of or behind
 388              * the center of the portal, making all aperture edges effectively
 389              * equidistant. Calculating the panning magnitude is simplified,
 390              * using the arctangent of the radius and distance.
 391              */
 392             magnitude = 1.0f - (atan2f(portal_radius, dist) / (float)M_PI);
 393         }
 394
 395         /* Scale the other zone's panning vector. */
 396         other_dir[0] = local_dir[0] * magnitude;
 397         other_dir[1] = local_dir[1] * magnitude;
 398         other_dir[2] = local_dir[2] * magnitude;
 399         /* Pan the current zone to the opposite direction of the portal, and
 400          * take the remaining percentage of the portal's magnitude.
 401          */
 402         this_dir[0] = local_dir[0] * (magnitude-1.0f);
 403         this_dir[1] = local_dir[1] * (magnitude-1.0f);
 404         this_dir[2] = local_dir[2] * (magnitude-1.0f);
 405
 406         /* Now set the effects' panning vectors and gain. Energy is shared
 407          * between environments, so attenuate according to each zone's
 408          * contribution (note: gain^2 = energy).
 409          */
 410         alEffectf(this_effect, AL_EAXREVERB_REFLECTIONS_GAIN, this_reverb->flReflectionsGain * sqrtf(magnitude));
 411         alEffectf(this_effect, AL_EAXREVERB_LATE_REVERB_GAIN, this_reverb->flLateReverbGain * sqrtf(magnitude));
 412         alEffectfv(this_effect, AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
 413         alEffectfv(this_effect, AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
 414
 415         alEffectf(other_effect, AL_EAXREVERB_REFLECTIONS_GAIN, other_reverb->flReflectionsGain * sqrtf(1.0f-magnitude));
 416         alEffectf(other_effect, AL_EAXREVERB_LATE_REVERB_GAIN, other_reverb->flLateReverbGain * sqrtf(1.0f-magnitude));
 417         alEffectfv(other_effect, AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
 418         alEffectfv(other_effect, AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
 419     }
 420     else
 421     {
 422         /* We're practically in the center of the portal. Give the panning
 423          * vectors a 50/50 split, with Zone 0 covering the half in front of
 424          * the normal, and Zone 1 covering the half behind.
 425          */
 426         this_dir[0] = local_norm[0] / 2.0f;
 427         this_dir[1] = local_norm[1] / 2.0f;
 428         this_dir[2] = local_norm[2] / 2.0f;
 429
 430         other_dir[0] = local_norm[0] / -2.0f;
 431         other_dir[1] = local_norm[1] / -2.0f;
 432         other_dir[2] = local_norm[2] / -2.0f;
 433
 434         alEffectf(effects[0], AL_EAXREVERB_REFLECTIONS_GAIN, reverbs[0].flReflectionsGain * sqrtf(0.5f));
 435         alEffectf(effects[0], AL_EAXREVERB_LATE_REVERB_GAIN, reverbs[0].flLateReverbGain * sqrtf(0.5f));
 436         alEffectfv(effects[0], AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
 437         alEffectfv(effects[0], AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
 438
 439         alEffectf(effects[1], AL_EAXREVERB_REFLECTIONS_GAIN, reverbs[1].flReflectionsGain * sqrtf(0.5f));
 440         alEffectf(effects[1], AL_EAXREVERB_LATE_REVERB_GAIN, reverbs[1].flLateReverbGain * sqrtf(0.5f));
 441         alEffectfv(effects[1], AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
 442         alEffectfv(effects[1], AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
 443     }
 444
 445     /* Finally, update the effect slots with the updated effect parameters. */
 446     alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, (ALint)effects[0]);
 447     alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, (ALint)effects[1]);
 448 }
 449
 450
 451 int main(int argc, char **argv)
 452 {
 453     static const int MaxTransitions = 8;
 454     EFXEAXREVERBPROPERTIES reverbs[2] = {
 455         EFX_REVERB_PRESET_CARPETEDHALLWAY,
 456         EFX_REVERB_PRESET_BATHROOM
 457     };
 458     ALCdevice *device = NULL;
 459     ALCcontext *context = NULL;
 460     ALuint effects[2] = { 0, 0 };
 461     ALuint slots[2] = { 0, 0 };
 462     ALuint direct_filter = 0;
 463     ALuint buffer = 0;
 464     ALuint source = 0;
 465     ALCint num_sends = 0;
 466     ALenum state = AL_INITIAL;
 467     ALfloat direct_gain = 1.0f;
 468     int basetime = 0;
 469     int loops = 0;
 470
 471     /* Print out usage if no arguments were specified */
 472     if(argc < 2)
 473     {
 474         fprintf(stderr, "Usage: %s [-device <name>] [options] <filename>\n\n"
 475         "Options:\n"
 476         "\t-nodirect\tSilence direct path output (easier to hear reverb)\n\n",
 477         argv[0]);
 478         return 1;
 479     }
 480
 481     /* Initialize OpenAL, and check for EFX support with at least 2 auxiliary
 482      * sends (if multiple sends are supported, 2 are provided by default; if
 483      * you want more, you have to request it through alcCreateContext).
 484      */
 485     argv++; argc--;
 486     if(InitAL(&argv, &argc) != 0)
 487         return 1;
 488
 489     while(argc > 0)
 490     {
 491         if(strcmp(argv[0], "-nodirect") == 0)
 492             direct_gain = 0.0f;
 493         else
 494             break;
 495         argv++;
 496         argc--;
 497     }
 498     if(argc < 1)
 499     {
 500         fprintf(stderr, "No filename spacified.\n");
 501         CloseAL();
 502         return 1;
 503     }
 504
 505     context = alcGetCurrentContext();
 506     device = alcGetContextsDevice(context);
 507
 508     if(!alcIsExtensionPresent(device, "ALC_EXT_EFX"))
 509     {
 510         fprintf(stderr, "Error: EFX not supported\n");
 511         CloseAL();
 512         return 1;
 513     }
 514
 515     num_sends = 0;
 516     alcGetIntegerv(device, ALC_MAX_AUXILIARY_SENDS, 1, &num_sends);
 517     if(alcGetError(device) != ALC_NO_ERROR || num_sends < 2)
 518     {
 519         fprintf(stderr, "Error: Device does not support multiple sends (got %d, need 2)\n",
 520                 num_sends);
 521         CloseAL();
 522         return 1;
 523     }
 524
 525     /* Define a macro to help load the function pointers. */
 526 #define LOAD_PROC(T, x)  ((x) = (T)alGetProcAddress(#x))
 527     LOAD_PROC(LPALGENFILTERS, alGenFilters);
 528     LOAD_PROC(LPALDELETEFILTERS, alDeleteFilters);
 529     LOAD_PROC(LPALISFILTER, alIsFilter);
 530     LOAD_PROC(LPALFILTERI, alFilteri);
 531     LOAD_PROC(LPALFILTERIV, alFilteriv);
 532     LOAD_PROC(LPALFILTERF, alFilterf);
 533     LOAD_PROC(LPALFILTERFV, alFilterfv);
 534     LOAD_PROC(LPALGETFILTERI, alGetFilteri);
 535     LOAD_PROC(LPALGETFILTERIV, alGetFilteriv);
 536     LOAD_PROC(LPALGETFILTERF, alGetFilterf);
 537     LOAD_PROC(LPALGETFILTERFV, alGetFilterfv);
 538
 539     LOAD_PROC(LPALGENEFFECTS, alGenEffects);
 540     LOAD_PROC(LPALDELETEEFFECTS, alDeleteEffects);
 541     LOAD_PROC(LPALISEFFECT, alIsEffect);
 542     LOAD_PROC(LPALEFFECTI, alEffecti);
 543     LOAD_PROC(LPALEFFECTIV, alEffectiv);
 544     LOAD_PROC(LPALEFFECTF, alEffectf);
 545     LOAD_PROC(LPALEFFECTFV, alEffectfv);
 546     LOAD_PROC(LPALGETEFFECTI, alGetEffecti);
 547     LOAD_PROC(LPALGETEFFECTIV, alGetEffectiv);
 548     LOAD_PROC(LPALGETEFFECTF, alGetEffectf);
 549     LOAD_PROC(LPALGETEFFECTFV, alGetEffectfv);
 550
 551     LOAD_PROC(LPALGENAUXILIARYEFFECTSLOTS, alGenAuxiliaryEffectSlots);
 552     LOAD_PROC(LPALDELETEAUXILIARYEFFECTSLOTS, alDeleteAuxiliaryEffectSlots);
 553     LOAD_PROC(LPALISAUXILIARYEFFECTSLOT, alIsAuxiliaryEffectSlot);
 554     LOAD_PROC(LPALAUXILIARYEFFECTSLOTI, alAuxiliaryEffectSloti);
 555     LOAD_PROC(LPALAUXILIARYEFFECTSLOTIV, alAuxiliaryEffectSlotiv);
 556     LOAD_PROC(LPALAUXILIARYEFFECTSLOTF, alAuxiliaryEffectSlotf);
 557     LOAD_PROC(LPALAUXILIARYEFFECTSLOTFV, alAuxiliaryEffectSlotfv);
 558     LOAD_PROC(LPALGETAUXILIARYEFFECTSLOTI, alGetAuxiliaryEffectSloti);
 559     LOAD_PROC(LPALGETAUXILIARYEFFECTSLOTIV, alGetAuxiliaryEffectSlotiv);
 560     LOAD_PROC(LPALGETAUXILIARYEFFECTSLOTF, alGetAuxiliaryEffectSlotf);
 561     LOAD_PROC(LPALGETAUXILIARYEFFECTSLOTFV, alGetAuxiliaryEffectSlotfv);
 562 #undef LOAD_PROC
 563
 564     /* Initialize SDL_sound. */
 565     Sound_Init();
 566
 567     /* Load the sound into a buffer. */
 568     buffer = LoadSound(argv[0]);
 569     if(!buffer)
 570     {
 571         CloseAL();
 572         Sound_Quit();
 573         return 1;
 574     }
 575
 576     /* Generate two effects for two "zones", and load a reverb into each one.
 577      * Note that unlike single-zone reverb, where you can store one effect per
 578      * preset, for multi-zone reverb you should have one effect per environment
 579      * instance, or one per audible zone. This is because we'll be changing the
 580      * effects' properties in real-time based on the environment instance
 581      * relative to the listener.
 582      */
 583     alGenEffects(2, effects);
 584     if(!LoadEffect(effects[0], &reverbs[0]) || !LoadEffect(effects[1], &reverbs[1]))
 585     {
 586         alDeleteEffects(2, effects);
 587         alDeleteBuffers(1, &buffer);
 588         Sound_Quit();
 589         CloseAL();
 590         return 1;
 591     }
 592
 593     /* Create the effect slot objects, one for each "active" effect. */
 594     alGenAuxiliaryEffectSlots(2, slots);
 595
 596     /* Tell the effect slots to use the loaded effect objects, with slot 0 for
 597      * Zone 0 and slot 1 for Zone 1. Note that this effectively copies the
 598      * effect properties. Modifying or deleting the effect object afterward
 599      * won't directly affect the effect slot until they're reapplied like this.
 600      */
 601     alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, (ALint)effects[0]);
 602     alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, (ALint)effects[1]);
 603     assert(alGetError()==AL_NO_ERROR && "Failed to set effect slot");
 604
 605     /* For the purposes of this example, prepare a filter that optionally
 606      * silences the direct path which allows us to hear just the reverberation.
 607      * A filter like this is normally used for obstruction, where the path
 608      * directly between the listener and source is blocked (the exact
 609      * properties depending on the type and thickness of the obstructing
 610      * material).
 611      */
 612     alGenFilters(1, &direct_filter);
 613     alFilteri(direct_filter, AL_FILTER_TYPE, AL_FILTER_LOWPASS);
 614     alFilterf(direct_filter, AL_LOWPASS_GAIN, direct_gain);
 615     assert(alGetError()==AL_NO_ERROR && "Failed to set direct filter");
 616
 617     /* Create the source to play the sound with, place it in front of the
 618      * listener's path in the left zone.
 619      */
 620     source = 0;
 621     alGenSources(1, &source);
 622     alSourcei(source, AL_LOOPING, AL_TRUE);
 623     alSource3f(source, AL_POSITION, -5.0f, 0.0f, -2.0f);
 624     alSourcei(source, AL_DIRECT_FILTER, (ALint)direct_filter);
 625     alSourcei(source, AL_BUFFER, (ALint)buffer);
 626
 627     /* Connect the source to the effect slots. Here, we connect source send 0
 628      * to Zone 0's slot, and send 1 to Zone 1's slot. Filters can be specified
 629      * to occlude the source from each zone by varying amounts; for example, a
 630      * source within a particular zone would be unfiltered, while a source that
 631      * can only see a zone through a window or thin wall may be attenuated for
 632      * that zone.
 633      */
 634     alSource3i(source, AL_AUXILIARY_SEND_FILTER, (ALint)slots[0], 0, AL_FILTER_NULL);
 635     alSource3i(source, AL_AUXILIARY_SEND_FILTER, (ALint)slots[1], 1, AL_FILTER_NULL);
 636     assert(alGetError()==AL_NO_ERROR && "Failed to setup sound source");
 637
 638     /* Get the current time as the base for timing in the main loop. */
 639     basetime = altime_get();
 640     loops = 0;
 641     printf("Transition %d of %d...\n", loops+1, MaxTransitions);
 642
 643     /* Play the sound for a while. */
 644     alSourcePlay(source);
 645     do {
 646         int curtime;
 647         ALfloat timediff;
 648
 649         /* Start a batch update, to ensure all changes apply simultaneously. */
 650         alcSuspendContext(context);
 651
 652         /* Get the current time to track the amount of time that passed.
 653          * Convert the difference to seconds.
 654          */
 655         curtime = altime_get();
 656         timediff = (float)(curtime - basetime) / 1000.0f;
 657
 658         /* Avoid negative time deltas, in case of non-monotonic clocks. */
 659         if(timediff < 0.0f)
 660             timediff = 0.0f;
 661         else while(timediff >= 4.0f*(float)((loops&1)+1))
 662         {
 663             /* For this example, each transition occurs over 4 seconds, and
 664              * there's 2 transitions per cycle.
 665              */
 666             if(++loops < MaxTransitions)
 667                 printf("Transition %d of %d...\n", loops+1, MaxTransitions);
 668             if(!(loops&1))
 669             {
 670                 /* Cycle completed. Decrease the delta and increase the base
 671                  * time to start a new cycle.
 672                  */
 673                 timediff -= 8.0f;
 674                 basetime += 8000;
 675             }
 676         }
 677
 678         /* Update the listener and effects, and finish the batch. */
 679         UpdateListenerAndEffects(timediff, slots, effects, reverbs);
 680         alcProcessContext(context);
 681
 682         al_nssleep(10000000);
 683
 684         alGetSourcei(source, AL_SOURCE_STATE, &state);
 685     } while(alGetError() == AL_NO_ERROR && state == AL_PLAYING && loops < MaxTransitions);
 686
 687     /* All done. Delete resources, and close down SDL_sound and OpenAL. */
 688     alDeleteSources(1, &source);
 689     alDeleteAuxiliaryEffectSlots(2, slots);
 690     alDeleteEffects(2, effects);
 691     alDeleteFilters(1, &direct_filter);
 692     alDeleteBuffers(1, &buffer);
 693
 694     Sound_Quit();
 695     CloseAL();
 696
 697     return 0;
 698 }