OpenAL音频库例程

　　Windows下C++可用的OpenAL demo。

　　基于alut工具库的OpenAL例程，涵盖了基本的OpenAL指令，对部分作出了注释，并且可以播放（当然得把对应的音频文件放到正确的路径下）。

 #include <iostream>
 #include <al/alut.h>//alut includes al.h
 #include <math.h>
 #include <windows.h>
 using namespace std;

 #define PI 3.14159265359

 #define TEST_ERROR(_msg)        \
     error = alGetError();        \
     if (error != AL_NO_ERROR) {    \
         fprintf(stderr, _msg "\n");    \
         return -;        \
             }

 //ALboolean EnableSource2 = AL_TRUE;    //是否播放第二组声音
 ALboolean EnableSource2 = AL_FALSE;    //是否播放第二组声音
 ALboolean EnableSource3 = AL_FALSE;    //是否播放第三组声音

 ALuint buffer2,buffer3;

 void Init(){
     alutInit(NULL, NULL);
 }

 //OS音量40，windows7
 void main()
 {
     ALuint source1[];     //buffer source

     //Init();//分离到一个单独的函数或类成员中
     alutInit(NULL, NULL);

     //ALuint source1;
     alGenSources(, &source1[]);
     //短哔声：10217，Music：RevolvingDoorMONO，中国军魂
     ALuint buffer1 = alutCreateBufferFromFile("RevolvingDoorMONO.WAV");//要实现空间化效果，必须为单声道文件（monaural）RevolvingDoorMONO

     if ((alGetError()) != AL_NO_ERROR)std::cout << "Buffer Create error!" << std::endl;

     alSourcei(source1[], AL_BUFFER, buffer1);

     if (EnableSource2){
         alGenSources(, &source1[]);
         buffer2 = alutCreateBufferFromFile("E:\\VS2013\\Projects2013\\OpenALtest\\OpenALtest\\10217.WAV");
         alSourcei(source1[], AL_BUFFER, buffer2);
         alSourcePlay(source1[]);
         alSourcei(source1[], AL_LOOPING, AL_TRUE);//第二个音频是否循环
     }

     if (EnableSource3){
         alGenSources(, &source1[]);
         ALuint temp = buffer1;
         alSourcei(source1[], AL_BUFFER, temp);
         alSourcePlay(source1[]);
         alSourcei(source1[], AL_LOOPING, AL_TRUE);//第二个音频是否循环
     }

     alSourcei(source1[], AL_SOURCE_RELATIVE, ); // set to relative positioning so we can set everything to 0
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_SOURCE_RELATIVE error" << std::endl;
     /*AL_SOURCE_RELATIVE设为1时，没有衰减，也没有空间化。
     */

     alSourcef(source1[], AL_ROLLOFF_FACTOR, 1.0); // 0 to disable attenuation  滚降衰减模型
     /*AL_ROLLOFF_FACTOR设为1时，开启衰减，设为0时，没有衰减
     */

     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_ROLLOFF_FACTOR error" << std::endl;
     alSourcef(source1[], AL_REFERENCE_DISTANCE, ); // doesn't matter

     alSourcef(source1[], AL_MAX_DISTANCE, .f);//超过AL_MAX_DISTANCE个单位后，将声音gain值限制在AL_MIN_GAIN（如果在cone之外，好像是再乘以AL_MIN_GAIN）
     alSourcef(source1[], AL_MIN_GAIN, 0.0f);//设置AL_MIN_GAIN
     alSourcef(source1[], AL_MAX_GAIN, .f);//设置AL_MAX_GAIN，即使设得比1大，也会自动回成1,并报输出ERROR

     alDistanceModel(AL_INVERSE_DISTANCE);//距离模型
     //alDistanceModel(AL_NONE);//距离模型
     //gain = AL_REFERENCE_DISTANCE / (AL_REFERENCE_DISTANCE + AL_ROLLOFF_FACTOR * (distance – AL_REFERENCE_DISTANCE));

     alSourcef(source1[], AL_PITCH, .f);//调节音高乘数
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_PITCH error" << std::endl;
     alSourcef(source1[], AL_GAIN, .f);//调节音量,但是受AL_MIN_GAIN影响，即使设得比min低，实际gain也会保持min设的值
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_GAIN error" << std::endl;

     //set source direction
     alSource3f(source1[], AL_DIRECTION, .f, .f, .f);//朝z轴正方向
     //set source position
     alSource3f(source1[], AL_POSITION, .f, .f, .f);//初始位置为原点
     //set source velocity
     alSource3f(source1[], AL_VELOCITY, .f, .f, .f);//多普勒效应影响频率

     alSourcef(source1[], AL_CONE_OUTER_GAIN, 0.0f);//the gain when outside the oriented cone
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_CONE_OUTER_GAIN error" << std::endl;
     alSourcef(source1[], AL_CONE_INNER_ANGLE, .f);//内角    *PI / 180.f
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_CONE_INNER_ANGLE error" << std::endl;
     alSourcef(source1[], AL_CONE_OUTER_ANGLE, .f);
     if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_CONE_OUTER_ANGLE error" << std::endl;

     //set current listener position
     alListener3f(AL_POSITION, -.f,.f,.f);
     //-1.f,0.f,1.f 监听者在左，右耳音量较大
     //1.f,0.f,1.f 监听者在右，左耳音量较大
     //0.f,0.f,-1.f 监听者在后，在外角之外，声音为原来的AL_CONE_OUTER_GAIN倍,好像还要乘以AL_MIN_GAIN系数

     //set current listener orientation
     ALfloat orivec[] = { 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f };
     alListenerfv(AL_ORIENTATION, orivec);
     //设置好listener位置
     //////////////////////////////////////////////////////////////////////////

     //tell the sound to loop continuously
     alSourcei(source1[], AL_LOOPING, AL_TRUE);

     //play the sound
     alSourcePlay(source1[]);//have its state changed to AL_PLAYING，重新播放

     ALfloat gain,outer_gain,min_gain,max_gain,max_distance;
     alGetSourcef(source1[], AL_GAIN, &gain); std::cout << "AL_GAIN: " << gain << std::endl;
     alGetSourcef(source1[], AL_CONE_OUTER_GAIN, &outer_gain); std::cout << "AL_CONE_OUTER_GAIN: " << outer_gain << std::endl;
     alGetSourcef(source1[], AL_MIN_GAIN, &min_gain); std::cout << "AL_MIN_GAIN: " << min_gain << std::endl;
     alGetSourcef(source1[], AL_MAX_GAIN, &max_gain); std::cout << "AL_MAX_GAIN: " << max_gain << std::endl;
     alGetSourcef(source1[], AL_MAX_DISTANCE, &max_distance); std::cout << "AL_MAX_DISTANCE: " << max_distance << std::endl;
     std::cout << std::endl << "在音锥外角和最远衰减距离之外 gain * outer_gain * min_gain: " << gain*outer_gain*min_gain << std::endl;
     std::cout << std::endl;

     ALint sourceID;
     alGetSourcei(source1[], AL_SOURCE_TYPE, &sourceID);
     std::cout << "AL_SOURCE_TYPE的ID： "<<sourceID << endl<<endl;

     ALint state;
     ALfloat tick = ;
     ALfloat moveStart_posx = -.f, moveStart_posy = .f, moveStart_posz = .f;
     do{
         std::cout << "playing......" << "\b\b\b\b\b\b\b\b\b\b\b\b\b";

         ////旋转音锥
         //float updatex = -sinf(play_it*PI / 180.f);
         //float upadtez = cosf(play_it*PI / 180.f);
         //alSource3f(source1, AL_DIRECTION, updatex, 0.f, upadtez);
         //if ((alGetError()) != AL_NO_ERROR)std::cout << "AL_POSITION error" << std::endl;
         //play_it=play_it+0.1f;

         ////平移声源
         //alSource3f(source1, AL_POSITION, moveStart_posx, moveStart_posy, moveStart_posz);
         //moveStart_posx = moveStart_posx + 0.00000011f; moveStart_posz = moveStart_posz + 0.00000015f;

         alGetSourcei(source1[], AL_SOURCE_STATE, &state);

         //是否播第二个音频资源
         if (EnableSource2)
             alGetSourcei(source1[], AL_SOURCE_STATE, &state);

         if (EnableSource3)
             alGetSourcei(source1[], AL_SOURCE_STATE, &state);

     } while (state == AL_PLAYING || state==AL_PAUSED);//结束时state自动变成AL_STOPPED,source1、2共享一个state

     // To stop the sound
     alSourceStop(source1[]);
     //delete our source
     alDeleteSources(, &source1[]);
     ////delete our buffer
     alDeleteBuffers(, &buffer1);
     if ((alGetError()) != AL_NO_ERROR)std::cout << "delete buffer1 error " << std::endl;

     if (EnableSource2){
         alSourceStop(source1[]);
         alDeleteBuffers(, &buffer2);
         if ((alGetError()) != AL_NO_ERROR)std::cout << "delete buffer2 error" << std::endl;
         alDeleteSources(, &source1[]);
         if ((alGetError()) != AL_NO_ERROR)std::cout << "delete source error" << std::endl;
     }
 }