Add an example for multi-zone reverb

1 files changed, 584 insertions, 0 deletions

diff --git a/examples/almultireverb.c b/examples/almultireverb.c
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+++ b/examples/almultireverb.c
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+/*
+ * OpenAL Multi-Zone Reverb Example
+ *
+ * Copyright (c) 2018 by Chris Robinson <[email protected]>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/* This file contains an example for controlling multiple reverb zones to
+ * smoothly transition between reverb environments. The general concept is to
+ * extend single-reverb by also tracking the closest adjacent environment, and
+ * utilizing EAX Reverb's panning vectors to position them relative to the
+ * listener.
+ */
+
+#include <stdio.h>
+#include <assert.h>
+
+#include <SDL_sound.h>
+
+#include "AL/al.h"
+#include "AL/alc.h"
+#include "AL/alext.h"
+#include "AL/efx-presets.h"
+
+#include "common/alhelpers.h"
+
+
+/* Filter object functions */
+static LPALGENFILTERS alGenFilters;
+static LPALDELETEFILTERS alDeleteFilters;
+static LPALISFILTER alIsFilter;
+static LPALFILTERI alFilteri;
+static LPALFILTERIV alFilteriv;
+static LPALFILTERF alFilterf;
+static LPALFILTERFV alFilterfv;
+static LPALGETFILTERI alGetFilteri;
+static LPALGETFILTERIV alGetFilteriv;
+static LPALGETFILTERF alGetFilterf;
+static LPALGETFILTERFV alGetFilterfv;
+
+/* Effect object functions */
+static LPALGENEFFECTS alGenEffects;
+static LPALDELETEEFFECTS alDeleteEffects;
+static LPALISEFFECT alIsEffect;
+static LPALEFFECTI alEffecti;
+static LPALEFFECTIV alEffectiv;
+static LPALEFFECTF alEffectf;
+static LPALEFFECTFV alEffectfv;
+static LPALGETEFFECTI alGetEffecti;
+static LPALGETEFFECTIV alGetEffectiv;
+static LPALGETEFFECTF alGetEffectf;
+static LPALGETEFFECTFV alGetEffectfv;
+
+/* Auxiliary Effect Slot object functions */
+static LPALGENAUXILIARYEFFECTSLOTS alGenAuxiliaryEffectSlots;
+static LPALDELETEAUXILIARYEFFECTSLOTS alDeleteAuxiliaryEffectSlots;
+static LPALISAUXILIARYEFFECTSLOT alIsAuxiliaryEffectSlot;
+static LPALAUXILIARYEFFECTSLOTI alAuxiliaryEffectSloti;
+static LPALAUXILIARYEFFECTSLOTIV alAuxiliaryEffectSlotiv;
+static LPALAUXILIARYEFFECTSLOTF alAuxiliaryEffectSlotf;
+static LPALAUXILIARYEFFECTSLOTFV alAuxiliaryEffectSlotfv;
+static LPALGETAUXILIARYEFFECTSLOTI alGetAuxiliaryEffectSloti;
+static LPALGETAUXILIARYEFFECTSLOTIV alGetAuxiliaryEffectSlotiv;
+static LPALGETAUXILIARYEFFECTSLOTF alGetAuxiliaryEffectSlotf;
+static LPALGETAUXILIARYEFFECTSLOTFV alGetAuxiliaryEffectSlotfv;
+
+
+/* LoadEffect loads the given initial reverb properties into the given OpenAL
+ * effect object, and returns non-zero on success.
+ */
+static int LoadEffect(ALuint effect, const EFXEAXREVERBPROPERTIES *reverb)
+{
+    ALenum err;
+
+    alGetError();
+
+    /* Prepate the effect for EAX Reverb (standard reverb doesn't contain
+     * the needed panning vectors).
+     */
+    alEffecti(effect, AL_EFFECT_TYPE, AL_EFFECT_EAXREVERB);
+    if((err=alGetError()) != AL_NO_ERROR)
+    {
+        fprintf(stderr, "Failed to set EAX Reverb: %s (0x%04x)\n", alGetString(err), err);
+        return 0;
+    }
+
+    /* Load the reverb properties. */
+    alEffectf(effect, AL_EAXREVERB_DENSITY, reverb->flDensity);
+    alEffectf(effect, AL_EAXREVERB_DIFFUSION, reverb->flDiffusion);
+    alEffectf(effect, AL_EAXREVERB_GAIN, reverb->flGain);
+    alEffectf(effect, AL_EAXREVERB_GAINHF, reverb->flGainHF);
+    alEffectf(effect, AL_EAXREVERB_GAINLF, reverb->flGainLF);
+    alEffectf(effect, AL_EAXREVERB_DECAY_TIME, reverb->flDecayTime);
+    alEffectf(effect, AL_EAXREVERB_DECAY_HFRATIO, reverb->flDecayHFRatio);
+    alEffectf(effect, AL_EAXREVERB_DECAY_LFRATIO, reverb->flDecayLFRatio);
+    alEffectf(effect, AL_EAXREVERB_REFLECTIONS_GAIN, reverb->flReflectionsGain);
+    alEffectf(effect, AL_EAXREVERB_REFLECTIONS_DELAY, reverb->flReflectionsDelay);
+    alEffectfv(effect, AL_EAXREVERB_REFLECTIONS_PAN, reverb->flReflectionsPan);
+    alEffectf(effect, AL_EAXREVERB_LATE_REVERB_GAIN, reverb->flLateReverbGain);
+    alEffectf(effect, AL_EAXREVERB_LATE_REVERB_DELAY, reverb->flLateReverbDelay);
+    alEffectfv(effect, AL_EAXREVERB_LATE_REVERB_PAN, reverb->flLateReverbPan);
+    alEffectf(effect, AL_EAXREVERB_ECHO_TIME, reverb->flEchoTime);
+    alEffectf(effect, AL_EAXREVERB_ECHO_DEPTH, reverb->flEchoDepth);
+    alEffectf(effect, AL_EAXREVERB_MODULATION_TIME, reverb->flModulationTime);
+    alEffectf(effect, AL_EAXREVERB_MODULATION_DEPTH, reverb->flModulationDepth);
+    alEffectf(effect, AL_EAXREVERB_AIR_ABSORPTION_GAINHF, reverb->flAirAbsorptionGainHF);
+    alEffectf(effect, AL_EAXREVERB_HFREFERENCE, reverb->flHFReference);
+    alEffectf(effect, AL_EAXREVERB_LFREFERENCE, reverb->flLFReference);
+    alEffectf(effect, AL_EAXREVERB_ROOM_ROLLOFF_FACTOR, reverb->flRoomRolloffFactor);
+    alEffecti(effect, AL_EAXREVERB_DECAY_HFLIMIT, reverb->iDecayHFLimit);
+
+    /* Check if an error occured, and return failure if so. */
+    if((err=alGetError()) != AL_NO_ERROR)
+    {
+        fprintf(stderr, "Error setting up reverb: %s\n", alGetString(err));
+        return 0;
+    }
+
+    return 1;
+}
+
+
+/* LoadBuffer loads the named audio file into an OpenAL buffer object, and
+ * returns the new buffer ID.
+ */
+static ALuint LoadSound(const char *filename)
+{
+    Sound_Sample *sample;
+    ALenum err, format;
+    ALuint buffer;
+    Uint32 slen;
+
+    /* Open the audio file */
+    sample = Sound_NewSampleFromFile(filename, NULL, 65536);
+    if(!sample)
+    {
+        fprintf(stderr, "Could not open audio in %s\n", filename);
+        return 0;
+    }
+
+    /* Get the sound format, and figure out the OpenAL format */
+    if(sample->actual.channels == 1)
+    {
+        if(sample->actual.format == AUDIO_U8)
+            format = AL_FORMAT_MONO8;
+        else if(sample->actual.format == AUDIO_S16SYS)
+            format = AL_FORMAT_MONO16;
+        else
+        {
+            fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
+            Sound_FreeSample(sample);
+            return 0;
+        }
+    }
+    else if(sample->actual.channels == 2)
+    {
+        if(sample->actual.format == AUDIO_U8)
+            format = AL_FORMAT_STEREO8;
+        else if(sample->actual.format == AUDIO_S16SYS)
+            format = AL_FORMAT_STEREO16;
+        else
+        {
+            fprintf(stderr, "Unsupported sample format: 0x%04x\n", sample->actual.format);
+            Sound_FreeSample(sample);
+            return 0;
+        }
+    }
+    else
+    {
+        fprintf(stderr, "Unsupported channel count: %d\n", sample->actual.channels);
+        Sound_FreeSample(sample);
+        return 0;
+    }
+
+    /* Decode the whole audio stream to a buffer. */
+    slen = Sound_DecodeAll(sample);
+    if(!sample->buffer || slen == 0)
+    {
+        fprintf(stderr, "Failed to read audio from %s\n", filename);
+        Sound_FreeSample(sample);
+        return 0;
+    }
+
+    /* Buffer the audio data into a new buffer object, then free the data and
+     * close the file. */
+    buffer = 0;
+    alGenBuffers(1, &buffer);
+    alBufferData(buffer, format, sample->buffer, slen, sample->actual.rate);
+    Sound_FreeSample(sample);
+
+    /* Check if an error occured, and clean up if so. */
+    err = alGetError();
+    if(err != AL_NO_ERROR)
+    {
+        fprintf(stderr, "OpenAL Error: %s\n", alGetString(err));
+        if(buffer && alIsBuffer(buffer))
+            alDeleteBuffers(1, &buffer);
+        return 0;
+    }
+
+    return buffer;
+}
+
+
+/* Helper to calculate the dot-product of the two given vectors. */
+static ALfloat dot_product(const ALfloat vec0[3], const ALfloat vec1[3])
+{
+    return vec0[0]*vec1[0] + vec0[1]*vec1[1] + vec0[2]*vec1[2];
+}
+
+
+int main(int argc, char **argv)
+{
+    const int MaxTransitions = 8;
+    EFXEAXREVERBPROPERTIES reverb0 = EFX_REVERB_PRESET_CASTLE_LARGEROOM;
+    EFXEAXREVERBPROPERTIES reverb1 = EFX_REVERB_PRESET_CASTLE_LONGPASSAGE;
+    struct timespec basetime;
+    ALCdevice *device = NULL;
+    ALCcontext *context = NULL;
+    ALuint effects[2] = { 0, 0 };
+    ALuint slots[2] = { 0, 0 };
+    ALuint direct_filter = 0;
+    ALuint buffer = 0;
+    ALuint source = 0;
+    ALCint num_sends = 0;
+    ALenum state = AL_INITIAL;
+    ALfloat direct_gain = 1.0f;
+    int loops = 0;
+
+    /* Print out usage if no arguments were specified */
+    if(argc < 2)
+    {
+        fprintf(stderr, "Usage: %s [-device <name>] [options] <filename>\n\n"
+        "Options:\n"
+        "\t-nodirect\tSilence direct path output (easier to hear reverb)\n\n",
+        argv[0]);
+        return 1;
+    }
+
+    /* Initialize OpenAL, and check for EFX support with at least 2 auxiliary
+     * sends (if multiple sends are supported, 2 are provided by default; if
+     * you want more, you have to request it through alcCreateContext).
+     */
+    argv++; argc--;
+    if(InitAL(&argv, &argc) != 0)
+        return 1;
+
+    while(argc > 0)
+    {
+        if(strcmp(argv[0], "-nodirect") == 0)
+            direct_gain = 0.0f;
+        else
+            break;
+        argv++;
+        argc--;
+    }
+    if(argc < 1)
+    {
+        fprintf(stderr, "Usage: %s [-device <name>] [options] <filename>\n\n"
+        "Options:\n"
+        "\t-nodirect\tSilence direct path output (easier to hear reverb).\n\n",
+        argv[0]);
+        CloseAL();
+        return 1;
+    }
+
+    context = alcGetCurrentContext();
+    device = alcGetContextsDevice(context);
+
+    if(!alcIsExtensionPresent(device, "ALC_EXT_EFX"))
+    {
+        fprintf(stderr, "Error: EFX not supported\n");
+        CloseAL();
+        return 1;
+    }
+
+    num_sends = 0;
+    alcGetIntegerv(device, ALC_MAX_AUXILIARY_SENDS, 1, &num_sends);
+    if(alcGetError(device) != ALC_NO_ERROR || num_sends < 2)
+    {
+        fprintf(stderr, "Error: Device does not support multiple sends (got %d, need 2)\n",
+                num_sends);
+        CloseAL();
+        return 1;
+    }
+
+    /* Define a macro to help load the function pointers. */
+#define LOAD_PROC(x)  ((x) = alGetProcAddress(#x))
+    LOAD_PROC(alGenFilters);
+    LOAD_PROC(alDeleteFilters);
+    LOAD_PROC(alIsFilter);
+    LOAD_PROC(alFilteri);
+    LOAD_PROC(alFilteriv);
+    LOAD_PROC(alFilterf);
+    LOAD_PROC(alFilterfv);
+    LOAD_PROC(alGetFilteri);
+    LOAD_PROC(alGetFilteriv);
+    LOAD_PROC(alGetFilterf);
+    LOAD_PROC(alGetFilterfv);
+
+    LOAD_PROC(alGenEffects);
+    LOAD_PROC(alDeleteEffects);
+    LOAD_PROC(alIsEffect);
+    LOAD_PROC(alEffecti);
+    LOAD_PROC(alEffectiv);
+    LOAD_PROC(alEffectf);
+    LOAD_PROC(alEffectfv);
+    LOAD_PROC(alGetEffecti);
+    LOAD_PROC(alGetEffectiv);
+    LOAD_PROC(alGetEffectf);
+    LOAD_PROC(alGetEffectfv);
+
+    LOAD_PROC(alGenAuxiliaryEffectSlots);
+    LOAD_PROC(alDeleteAuxiliaryEffectSlots);
+    LOAD_PROC(alIsAuxiliaryEffectSlot);
+    LOAD_PROC(alAuxiliaryEffectSloti);
+    LOAD_PROC(alAuxiliaryEffectSlotiv);
+    LOAD_PROC(alAuxiliaryEffectSlotf);
+    LOAD_PROC(alAuxiliaryEffectSlotfv);
+    LOAD_PROC(alGetAuxiliaryEffectSloti);
+    LOAD_PROC(alGetAuxiliaryEffectSlotiv);
+    LOAD_PROC(alGetAuxiliaryEffectSlotf);
+    LOAD_PROC(alGetAuxiliaryEffectSlotfv);
+#undef LOAD_PROC
+
+    /* Initialize SDL_sound. */
+    Sound_Init();
+
+    /* Load the sound into a buffer. */
+    buffer = LoadSound(argv[0]);
+    if(!buffer)
+    {
+        CloseAL();
+        Sound_Quit();
+        return 1;
+    }
+
+    /* Generate two effects for two "zones", and load a reverb into each one.
+     * Note that unlike single-zone reverb, where you can store one effect per
+     * preset, for multi-zone reverb you should have one effect per environment
+     * instance, or one per audible zone. This is because we'll be changing the
+     * effects' properties in real-time based on the environment instance.
+     */
+    alGenEffects(2, effects);
+    if(!LoadEffect(effects[0], &reverb0) || !LoadEffect(effects[1], &reverb1))
+    {
+        alDeleteEffects(2, effects);
+        alDeleteBuffers(1, &buffer);
+        Sound_Quit();
+        CloseAL();
+        return 1;
+    }
+
+    /* Create the effect slot objects, one for each "active" effect. */
+    alGenAuxiliaryEffectSlots(2, slots);
+
+    /* Tell the effect slots to use the loaded effect objects, with slot 0 for
+     * Zone 0 and slot 1 for Zone 1. Note that this effectively copies the
+     * effect properties. Modifying or deleting the effect object afterward
+     * won't directly affect the effect slot until they're reapplied like this.
+     */
+    alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, effects[0]);
+    alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, effects[1]);
+    assert(alGetError()==AL_NO_ERROR && "Failed to set effect slot");
+
+    /* For the purposes of this example, prepare a filter that optionally
+     * silences the direct path. This allows us to hear just the reverberation.
+     * A filter like this is normally used for obstruction, where the path
+     * directly between the listener and source is blocked (the exact
+     * properties depending on the type and thickness of the obstructing
+     * material).
+     */
+    alGenFilters(1, &direct_filter);
+    alFilteri(direct_filter, AL_FILTER_TYPE, AL_FILTER_LOWPASS);
+    alFilterf(direct_filter, AL_LOWPASS_GAIN, direct_gain);
+    assert(alGetError()==AL_NO_ERROR && "Failed to set direct filter");
+
+    /* Create the source to play the sound with. */
+    source = 0;
+    alGenSources(1, &source);
+    alSourcei(source, AL_LOOPING, AL_TRUE);
+    alSourcei(source, AL_DIRECT_FILTER, direct_filter);
+    alSourcei(source, AL_BUFFER, buffer);
+
+    /* Connect the source to the effect slots. Here, we connect source send 0
+     * to Zone 0's slot, and send 1 to Zone 1's slot. Filters can be specified
+     * to occlude the source from each zone by varying amounts; for example, a
+     * source within a particular zone would be unfiltered, while a source that
+     * can only see a zone through a window may be attenuated for that zone.
+     */
+    alSource3i(source, AL_AUXILIARY_SEND_FILTER, slots[0], 0, AL_FILTER_NULL);
+    alSource3i(source, AL_AUXILIARY_SEND_FILTER, slots[1], 1, AL_FILTER_NULL);
+    assert(alGetError()==AL_NO_ERROR && "Failed to setup sound source");
+
+    /* Get the base time, and set the example to stop after a number of
+     * transitions.
+     */
+    altimespec_get(&basetime, AL_TIME_UTC);
+    loops = MaxTransitions;
+    printf("Transition %d of %d...\n", (MaxTransitions-loops+1), MaxTransitions);
+
+    /* Play the sound for a while. */
+    alSourcePlay(source);
+    do {
+        /* Individual reverb zones are connected via "portals". Each portal has
+         * a position (center point of the connecting area), a normal (facing
+         * direction), and a radius (approximate size of the connecting area).
+         * For this example it also has movement velocity, although normally it
+         * would be the listener that moves relative to the portal instead of
+         * the portal itself.
+         */
+        const ALfloat portal_pos[3] = { -10.0f, 0.0f, 0.0f };
+        const ALfloat portal_norm[3] = { 1.0f, 0.0f, 0.0f };
+        const ALfloat portal_vel[3] = { 5.0f, 0.0f, 0.0f };
+        const ALfloat portal_radius = 2.5f;
+        ALfloat other_dir[3], this_dir[3];
+        ALfloat local_norm[3];
+        ALfloat dist, timediff;
+        struct timespec curtime;
+
+        /* Start a batch update, to ensure all changes apply simultaneously. */
+        alcSuspendContext(context);
+
+        /* Get the current time to track the amount of time that passed.
+         * Convert the difference to seconds.
+         */
+        altimespec_get(&curtime, AL_TIME_UTC);
+        timediff = (ALfloat)(curtime.tv_sec - basetime.tv_sec);
+        timediff += (ALfloat)(curtime.tv_nsec - basetime.tv_nsec) / 1000000000.0f;
+
+        /* Avoid negative time deltas, in case of non-monotonic clocks. */
+        if(timediff < 0.0f)
+            timediff = 0.0f;
+        else while(timediff >= 4.0f)
+        {
+            /* For this example, each transition occurs over 4 seconds.
+             * Decrease the delta and increase the base time to start a new
+             * transition.
+             */
+            timediff -= 4.0f;
+            basetime.tv_sec += 4;
+            if(--loops > 0)
+                printf("Transition %d of %d...\n", (MaxTransitions-loops+1), MaxTransitions);
+        }
+
+        /* Move the portal according to the amount of time passed. other_dir
+         * represents the listener-relative point from the current zone to the
+         * other adjacent zone.
+         */
+        other_dir[0] = portal_pos[0] + portal_vel[0]*timediff;
+        other_dir[1] = portal_pos[1] + portal_vel[1]*timediff;
+        other_dir[2] = portal_pos[2] + portal_vel[2]*timediff;
+        /* In a normal application you may also want to scale down the portal's
+         * apparent radius depending on its local angle, since less of the
+         * adjacent zone would be in view of the listener. You would also want
+         * to rotate the portal's normal according to the listener orientation.
+         *
+         * For this example, the portal is always head-on so there's no need to
+         * adjust the radius. But every other transition iteration inverts the
+         * normal, which essentially simulates a different portal moving in
+         * closer than the last one, switching the old adjacent zone to a new
+         * one.
+         */
+        local_norm[0] = portal_norm[0] * ((loops&1) ? -1.0f : 1.0f);
+        local_norm[1] = portal_norm[1] * ((loops&1) ? -1.0f : 1.0f);
+        local_norm[2] = portal_norm[2] * ((loops&1) ? -1.0f : 1.0f);
+
+        /* Calculate the distance from the listener to the portal. */
+        dist = sqrtf(dot_product(other_dir, other_dir));
+        if(!(dist > 0.00001f))
+        {
+            /* We're practically in the center of the portal. Give the panning
+             * vectors a 50/50 split, with Zone 0 covering the half in front of
+             * the normal, and Zone 1 covering the half behind.
+             */
+            this_dir[0] = local_norm[0] / 2.0f;
+            this_dir[1] = local_norm[1] / 2.0f;
+            this_dir[2] = local_norm[2] / 2.0f;
+
+            other_dir[0] = local_norm[0] / -2.0f;
+            other_dir[1] = local_norm[1] / -2.0f;
+            other_dir[2] = local_norm[2] / -2.0f;
+
+            alEffectfv(effects[0], AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
+            alEffectfv(effects[0], AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
+
+            alEffectfv(effects[1], AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
+            alEffectfv(effects[1], AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
+        }
+        else
+        {
+            ALuint other_effect, this_effect;
+            ALfloat spread;
+
+            /* Normalize the direction to the portal. */
+            other_dir[0] /= dist;
+            other_dir[1] /= dist;
+            other_dir[2] /= dist;
+
+            /* Calculate the 'spread' of the portal, which is the amount of
+             * coverage the other zone has.
+             */
+            spread = atan2f(portal_radius, dist) / ((ALfloat)M_PI);
+
+            /* Figure out which zone we're in, given the direction to the
+             * portal and its normal.
+             */
+            if(dot_product(other_dir, local_norm) <= 0.0f)
+            {
+                /* We're in front of the portal, so we're in Zone 0. */
+                this_effect = effects[0];
+                other_effect = effects[1];
+            }
+            else
+            {
+                /* We're behind the portal, so we're in Zone 1. */
+                this_effect = effects[1];
+                other_effect = effects[0];
+            }
+
+            /* Pan the current zone to the opposite direction of the portal,
+             * and take the remaining percentage of the portal's spread. As the
+             * portal's spread increases, this zone's spread decreases, which
+             * is indicated by a larger panning vector.
+             */
+            this_dir[0] = other_dir[0] * -spread;
+            this_dir[1] = other_dir[1] * -spread;
+            this_dir[2] = other_dir[2] * -spread;
+            /* Scale the other zone's panning vector down as the portal's
+             * spread increases, so that it covers more.
+             */
+            other_dir[0] *= 1.0f-spread;
+            other_dir[1] *= 1.0f-spread;
+            other_dir[2] *= 1.0f-spread;
+
+            /* Now set the effects' panning vectors. */
+            alEffectfv(this_effect, AL_EAXREVERB_REFLECTIONS_PAN, this_dir);
+            alEffectfv(this_effect, AL_EAXREVERB_LATE_REVERB_PAN, this_dir);
+
+            alEffectfv(other_effect, AL_EAXREVERB_REFLECTIONS_PAN, other_dir);
+            alEffectfv(other_effect, AL_EAXREVERB_LATE_REVERB_PAN, other_dir);
+        }
+
+        /* Finally, update the effect slots with the updated effect parameters,
+         * and finish the update batch.
+         */
+        alAuxiliaryEffectSloti(slots[0], AL_EFFECTSLOT_EFFECT, effects[0]);
+        alAuxiliaryEffectSloti(slots[1], AL_EFFECTSLOT_EFFECT, effects[1]);
+        alcProcessContext(context);
+
+        al_nssleep(10000000);
+
+        alGetSourcei(source, AL_SOURCE_STATE, &state);
+    } while(alGetError() == AL_NO_ERROR && state == AL_PLAYING && loops > 0);
+
+    /* All done. Delete resources, and close down SDL_sound and OpenAL. */
+    alDeleteSources(1, &source);
+    alDeleteAuxiliaryEffectSlots(2, slots);
+    alDeleteEffects(2, effects);
+    alDeleteFilters(1, &direct_filter);
+    alDeleteBuffers(1, &buffer);
+
+    Sound_Quit();
+    CloseAL();
+
+    return 0;
+}