本篇是創建游戲內核（18）的續篇，有關DirectAudio和DirectShow的基礎知識請參閱用DirectX
Audio和DirectShow播放聲音和音樂。
使用SOUND_CHANNEL播放聲音
前面介紹了如何初始化聲音系統以及如何加載聲音數據，很自然地，接下來就要講述如何播放聲音了，這也正是SOUND_CHANNEL類的用途所在。
首先定義兩個全局變量來保存音頻緩沖的大小和每個音頻數據塊的大小。
// these are the fixed sizes for sound channel buffers
const long g_sound_buffer_size = 65536;
const long g_sound_buffer_chunk = g_sound_buffer_size / 4;
第一個變量g_sound_buffer_size表示分配給用于播放聲音的每個DirectSound緩沖區的字節數，這里使用65536字節，因為此大小的緩沖區足夠保存相當于數秒高品質的聲音數據。第二個g_sound_buffer_chunk是單個聲音數據塊的大小，使用4個數據塊，每個數據塊存儲了流式聲音的一個小的采樣。每播放完一個數據塊，緊接著就
開始播放下一個數據塊，同時使用新的聲音數據加載前一個數據塊。
一般不必改變這兩個變量的值，除非想要節約內存。如果想節約內存，只需將g_sound_buffer_size變量的值改變成較小的數字即可。g_sound_buffer_size變量使用不同的大小，各有其優勢，比如g_sound_buffer_size變量的值越大，聲音內核將新數據放到流中的頻率就越小，當然這也意味著要占用更多的內存。
來看看SOUND_CHANNEL的定義:
//======================================================================================
// This class encapsulate sound buffer playing.
//======================================================================================
class SOUND_CHANNEL
{
private:
friend class SOUND;
protected:
SOUND* _sound; // pointer to parent sound object
IDirectSoundBuffer8* _ds_buffer; // pointer to DirectSound buffer object
IDirectSoundNotify8* _ds_notify; // pointer to DirectSound notify object
short _event_index;
long _volume; // sound buffer volume
signed long _pan; // sound buffer pan
BOOL _is_playing; // sound buffer playing flag
long _loop_times; // loop times
long _frequency;
short _bits_per_sample;
short _channels;
SOUND_DATA _sound_data;
short _load_section; // sound section will to be loaded
short _stop_section; // sound section will to be stoped
short _next_notify; // sound notification index will to be played
BOOL _buffer_data();
void _update();
public:
SOUND_CHANNEL();
~SOUND_CHANNEL();
IDirectSoundBuffer8* get_sound_buffer_com();
IDirectSoundNotify8* get_notify_com();
BOOL create(SOUND* sound, long frequency = 22050, short channels = 1, short bits_per_sample = 16);
BOOL create(SOUND* sound, SOUND_DATA* sound_data);
void free();
BOOL play(SOUND_DATA* sound_data, long volume_percent = 100, long loop = 1);
void stop();
long get_volume();
BOOL set_volume(long percent);
signed long get_pan();
BOOL set_pan(signed long level);
long get_frequency();
BOOL set_frequency(long frequency);
BOOL is_playing();
};
接著來看看它的實現：
//------------------------------------------------------------------------------
// Constructor, initialize member data.
//------------------------------------------------------------------------------
SOUND_CHANNEL::SOUND_CHANNEL()
{
_sound = NULL;
_ds_buffer = NULL;
_ds_notify = NULL;
_event_index = -1;
_volume = 0;
_pan = 0;
_frequency = 0;
_is_playing = FALSE;
}
//------------------------------------------------------------------------------
// Destructor, release sound buffer and sound notification, set the event state
// to nonsignaled.
//------------------------------------------------------------------------------
SOUND_CHANNEL::~SOUND_CHANNEL()
{
free();
}
//------------------------------------------------------------------------------
// Return pointer to DirectSound buffer.
//------------------------------------------------------------------------------
IDirectSoundBuffer8* SOUND_CHANNEL::get_sound_buffer_com()
{
return _ds_buffer;
}
//------------------------------------------------------------------------------
// Return pointer to DirectSound notify.
//------------------------------------------------------------------------------
IDirectSoundNotify8* SOUND_CHANNEL::get_notify_com()
{
return _ds_notify;
}
//------------------------------------------------------------------------------
// Create sound buffer, set sound notification and event.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::create(SOUND* sound, long frequency, short channels, short bits_per_sample)
{
// free a prior channel
free();
if((_sound = sound) == NULL)
return FALSE;
if(_sound->get_directsound_com() == NULL)
return FALSE;
// save playback format
_frequency = frequency;
_bits_per_sample = bits_per_sample;
_channels = channels;
WAVEFORMATEX wave_format;
// create a new sound buffer for this channel, using specified format.
ZeroMemory(&wave_format, sizeof(WAVEFORMATEX));
wave_format.wFormatTag = WAVE_FORMAT_PCM;
wave_format.nChannels = (WORD) _channels;
wave_format.nSamplesPerSec = _frequency;
wave_format.wBitsPerSample = (WORD) _bits_per_sample;
wave_format.nBlockAlign = wave_format.wBitsPerSample / 8 * wave_format.nChannels;
wave_format.nAvgBytesPerSec = wave_format.nSamplesPerSec * wave_format.nBlockAlign;
DSBUFFERDESC buffer_desc;
ZeroMemory(&buffer_desc, sizeof(DSBUFFERDESC));
buffer_desc.dwSize = sizeof(DSBUFFERDESC);
buffer_desc.dwFlags = DSBCAPS_CTRLVOLUME | DSBCAPS_CTRLPAN | DSBCAPS_CTRLFREQUENCY |
DSBCAPS_CTRLPOSITIONNOTIFY | DSBCAPS_LOCSOFTWARE;
buffer_desc.dwBufferBytes = g_sound_buffer_size;
buffer_desc.lpwfxFormat = &wave_format;
IDirectSoundBuffer* ds_buffer;
if(FAILED(_sound->get_directsound_com()->CreateSoundBuffer(&buffer_desc, &ds_buffer, NULL)))
return FALSE;
// query for newer interface
if(FAILED(ds_buffer->QueryInterface(IID_IDirectSoundBuffer8, (void**) &_ds_buffer)))
{
ds_buffer->Release();
return FALSE;
}
// release old object - we have the newer one now
ds_buffer->Release();
// create the notification interface
if(FAILED(_ds_buffer->QueryInterface(IID_IDirectSoundNotify8, (void**) &_ds_notify)))
return FALSE;
HANDLE event_handle;
// get an event for this
if(! _sound->assign_event(this, &_event_index, &event_handle))
return FALSE;
DSBPOSITIONNOTIFY pos_notify[4];
// setup the 4 notification positions
pos_notify[0].dwOffset = g_sound_buffer_chunk - 1;
pos_notify[0].hEventNotify = event_handle;
pos_notify[1].dwOffset = g_sound_buffer_chunk * 2 - 1;
pos_notify[1].hEventNotify = event_handle;
pos_notify[2].dwOffset = g_sound_buffer_chunk * 3 - 1;
pos_notify[2].hEventNotify = event_handle;
pos_notify[3].dwOffset = g_sound_buffer_size - 1;
pos_notify[3].hEventNotify = event_handle;
if(FAILED(_ds_notify->SetNotificationPositions(4, pos_notify)))
return FALSE;
// set the pan and default volume
set_volume(100);
set_pan(0);
return TRUE;
}
//------------------------------------------------------------------------------
// Create sound buffer.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::create(SOUND* sound, SOUND_DATA* sound_data)
{
return create(sound, sound_data->_frequency, sound_data->_channels, sound_data->_bits_per_sample);
}
//------------------------------------------------------------------------------
// Release sound buffer and sound notification, set the event state to nonsignaled.
//------------------------------------------------------------------------------
void SOUND_CHANNEL::free()
{
// stop any playback
stop();
// release the notification
release_com(_ds_notify);
// release the sound buffer
release_com(_ds_buffer);
// release event from parent SOUND class
_sound->release_event(this, &_event_index);
// set to no parent sound
_sound = NULL;
}
//------------------------------------------------------------------------------
// Play sound buffer.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::play(SOUND_DATA* sound_data, long volume_percent, long loop_times)
{
if(sound_data == NULL || _ds_buffer == NULL || _ds_notify == NULL)
return FALSE;
// stop any playback
stop();
// restore a lost buffer just in case
_ds_buffer->Restore();
// setup playing information
_sound_data.copy(sound_data);
// set looping times
_loop_times = loop_times;
// calculate stop section position
if(_loop_times == 0)
_stop_section = -1;
else
_stop_section = (short)
(((_sound_data._buffer_size * _loop_times) % g_sound_buffer_size) / g_sound_buffer_chunk) ;
_load_section = 0;
// load sound data into sound buffer from sound file or sound data object
_buffer_data();
_buffer_data();
_buffer_data();
_buffer_data();
// set the volume
set_volume(volume_percent);
// set position and begin play
_next_notify = 0;
if(FAILED(_ds_buffer->SetCurrentPosition(0)))
return FALSE;
if(FAILED(_ds_buffer->Play(0, 0, DSBPLAY_LOOPING)))
return FALSE;
// flag as playing
_is_playing = TRUE;
return TRUE;
}
//------------------------------------------------------------------------------
// Stop playing DirectSound buffer.
//------------------------------------------------------------------------------
void SOUND_CHANNEL::stop()
{
if(_ds_buffer)
_ds_buffer->Stop();
_is_playing = FALSE;
}
//------------------------------------------------------------------------------
// Get sound buffer volume.
//------------------------------------------------------------------------------
long SOUND_CHANNEL::get_volume()
{
return _volume;
}
//------------------------------------------------------------------------------
// Set volume for sound buffer.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::set_volume(long percent)
{
long volume;
if(_ds_buffer == NULL)
return FALSE;
// calculate a usable volume level
if(percent == 0)
volume = DSBVOLUME_MIN;
else
volume = -20 * (100 - (percent % 101));
if(FAILED(_ds_buffer->SetVolume(volume)))
return FALSE;
_volume = percent % 101;
return TRUE;
}
//------------------------------------------------------------------------------
// Get sound buffer pan.
//------------------------------------------------------------------------------
signed long SOUND_CHANNEL::get_pan()
{
return _pan;
}
//------------------------------------------------------------------------------
// Set pan for sound buffer.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::set_pan(long level)
{
signed long pan;
if(_ds_buffer == NULL)
return FALSE;
// calculate a suable setting
if(level < 0)
pan = DSBPAN_LEFT / 100 * (-level % 101);
else
pan = DSBPAN_LEFT / 100 * (level % 101);
if(FAILED(_ds_buffer->SetPan(pan)))
return FALSE;
_pan = level % 101;
return TRUE;
}
//------------------------------------------------------------------------------
// Get sound buffer frequency.
//------------------------------------------------------------------------------
long SOUND_CHANNEL::get_frequency()
{
return _frequency;
}
//------------------------------------------------------------------------------
// Set frequency for sound buffer.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::set_frequency(long frequency)
{
if(_ds_buffer == NULL)
return FALSE;
if(FAILED(_ds_buffer->SetFrequency(frequency)))
return FALSE;
_frequency = frequency;
return TRUE;
}
//------------------------------------------------------------------------------
// Checks whether sound buffer is playing.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::is_playing()
{
if(_sound == NULL || _ds_buffer == NULL || _ds_notify == NULL)
return FALSE;
return _is_playing;
}
//------------------------------------------------------------------------------
// Load sound data into sound buffer from sound file or sound data object.
//------------------------------------------------------------------------------
BOOL SOUND_CHANNEL::_buffer_data()
{
if(_ds_buffer == NULL)
return FALSE;
// setup position to load in
long lock_pos = (_load_section % 4) * g_sound_buffer_chunk;
long size;
char* ptr;
// lock sound buffer to get pointer to sound data
if(FAILED(_ds_buffer->Lock(lock_pos, g_sound_buffer_chunk, (void**) &ptr, (DWORD*)&size, NULL, NULL, 0)))
return FALSE;
// clear out buffer if nothing left to load
if(_sound_data._left_size == 0)
ZeroMemory(ptr, size);
else
{
// load in the data - take looping into account
long load_size = size;
long load_pos = 0;
// load sound data until specfied load size is satisfied
for(;;)
{
if(_sound_data._left_size > load_size)
{
// load in sound data
if(_sound_data._fp != NULL)
{
// load in sound data from file
fseek(_sound_data._fp, _sound_data._file_curr_pos, SEEK_SET);
fread(&ptr[load_pos], 1, load_size, _sound_data._fp);
}
else
// load into sound data from buffer
memcpy(&ptr[load_pos], &_sound_data._ptr[_sound_data._file_curr_pos], load_size);
// decrease sound data, advance current sound buffer position.
_sound_data._left_size -= load_size;
_sound_data._file_curr_pos += load_size;
break;
}
else // _sound_data._left_size <= load_size
{
// load in sound data
if(_sound_data._fp != NULL)
{
// load in sound data from file
fseek(_sound_data._fp, _sound_data._file_curr_pos, SEEK_SET);
fread(&ptr[load_pos], 1, _sound_data._left_size, _sound_data._fp);
}
else
// load in sound data from buffer
memcpy(&ptr[load_pos], &_sound_data._ptr[_sound_data._file_curr_pos], _sound_data._left_size);
// decrease sound data, advance current sound buffer position.
load_size -= _sound_data._left_size;
load_pos += _sound_data._left_size;
// check if we need to stop loop
if(_loop_times >= 1)
{
_loop_times--;
if(_loop_times == 0)
{
// clear out remaining buffer space
if(load_size)
ZeroMemory(&ptr[load_pos], load_size);
_sound_data._left_size = 0L;
break;
}
}
// reset sound data current position and left size
_sound_data._file_curr_pos = _sound_data._file_start_pos;
_sound_data._left_size = _sound_data._buffer_size;
// set if we need to stop loading data
if(load_size == 0)
break;
}
}
}
// unlock the buffer
_ds_buffer->Unlock(ptr, size, NULL, 0);
// mark next section to load
if(++_load_section > 3)
_load_section = 0;
return TRUE;
}
//------------------------------------------------------------------------------
// Update for sound buffer palying.
//------------------------------------------------------------------------------
void SOUND_CHANNEL::_update()
{
// check for end of sound
if(_next_notify == _stop_section && _sound_data._left_size == 0)
stop();
else
{
// buffer in more data
_buffer_data();
if(++_next_notify > 3)
_next_notify = 0;
}
}
最多可以將SOUND_CHANNEL類實例化32次，也就是說同時可以用多達32個聲道進行播放（聲音內核不允許同時32個以上的實例，任何超過32的值，都無法被成功初始化）。調用SOUND_CHANNEL::create函數可以初始化各個聲道，需要提供一個預初始化的SOUND類以及回放格式。為方便起見，甚至可以使用存儲在SOUND_DATA類中的回放格式創建聲道。
使用SOUND_CHANNEL類進行的操作中，最頻繁的就是播放聲音、停止播放聲音以及改變聲音的音量。要播放聲音，需要給SOUND_CHANNEL::play函數傳遞三個參數：保存在SOUND_DATA類中要播放的聲音數據、音量的大小以及連續播放聲音的次數。
接著我們編寫測試代碼：
點擊下載源碼和工程
/*****************************************************************************
PURPOSE:
Test for class SOUND, SOUND_DATA, SOUND_CHANNEL.
*****************************************************************************/
#include "Core_Global.h"
class APP : public APPLICATION
{
private:
SOUND _sound;
SOUND_DATA _sound_data[2];
SOUND_CHANNEL _sound_channel[2];
FILE* _fp;
public:
APP()
{
_fp = NULL;
}
BOOL init();
BOOL frame();
BOOL shutdown();
};
BOOL APP::init()
{
// Initialize DierctSound and DirectMusic.
_sound.init(get_hwnd());
// load into sound data from wave file
_sound_data[0].load_wav("test1.wav", NULL);
_sound_data[1].load_wav("test2.wav", NULL);
// create sound channel
_sound_channel[0].create(&_sound, &_sound_data[0]);
_sound_channel[1].create(&_sound, &_sound_data[1]);
// play sound
_sound_channel[0].play(&_sound_data[0]);
_sound_channel[1].play(&_sound_data[1], 100, 0); // lopping forever
return TRUE;
}
BOOL APP::frame()
{
return TRUE;
}
BOOL APP::shutdown()
{
if(_fp)
fclose(_fp);
return TRUE;
}
int PASCAL WinMain(HINSTANCE inst, HINSTANCE, LPSTR cmd_line, int cmd_show)
{
APP app;
return app.run();
}