创建游戏内核（22）

本篇是创建游戏内核（21）的续篇，有关DirectAudio和DirectShow的基础知识请参阅用DirectX Audio和DirectShow播放声音和音乐。

在MP3类中，可以初始化并关闭DirectShow，渲染媒体文件以及控制歌曲的回放（开始播放、停止播放以及暂停播放）。

来看看MP3类的定义：

//======================================================================================
// This class encapsulates mp3 playing.
//======================================================================================
typedef class MP3
{
public:
    MP3();
    ~MP3();

    BOOL init();
    void shutdown();

    BOOL render(const char* filename);

    BOOL play();
    BOOL stop();
    BOOL pause();

    BOOL is_playing();

private:
    IGraphBuilder*      _graph_builder;
    IMediaControl*      _media_control;
    IMediaEvent*        _media_event;
} *MP3_PTR;

实现：

//------------------------------------------------------------------------------
// Constructor, zero member data.
//------------------------------------------------------------------------------
MP3::MP3()
{
    memset(this, 0, sizeof(*this));
}

//------------------------------------------------------------------------------
// Destructor, release resource.
//------------------------------------------------------------------------------
MP3::~MP3()
{
    shutdown();
}

//------------------------------------------------------------------------------
// Release all resource which used to play mp3.
//------------------------------------------------------------------------------
void MP3::shutdown()
{
    release_com(_media_event);
    release_com(_media_control);
    release_com(_graph_builder);

    CoUninitialize();
}

//------------------------------------------------------------------------------
// Create graph builder, query interface for medial control and medial event.
//------------------------------------------------------------------------------
BOOL MP3::init()
{
    // shutdown prior initialized system
    shutdown();

    // initialize com
    CoInitialize(NULL);

    // create graph builder object and media controls
    if(FAILED(CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder,
                               (void**)&_graph_builder)))
    {
        return FALSE;
    }

    _graph_builder->QueryInterface(IID_IMediaControl, (void**) &_media_control);
    _graph_builder->QueryInterface(IID_IMediaEvent,   (void**) &_media_event);

    return TRUE;
}

//------------------------------------------------------------------------------
// Builds a filter graph that renders the specified file.
//------------------------------------------------------------------------------
BOOL MP3::render(const char* filename)
{
    // error checking
    if(_graph_builder == NULL || _media_control == NULL)
        return FALSE;

    // stop the current song
    _media_control->Stop();

    // convert filename to wide-character string
    WCHAR w_filename[MAX_PATH];
    mbstowcs(w_filename, filename, MAX_PATH);

    // builds a filter graph that renders the specified file
    if(FAILED(_graph_builder->RenderFile(w_filename, NULL)))
        return FALSE;

    return TRUE;
}

//------------------------------------------------------------------------------
// Play mp3.
//------------------------------------------------------------------------------
BOOL MP3::play()
{
    // error checking
    if(_media_control == NULL)
        return FALSE;

    // Runs all the filters in the filter graph.
    // While the graph is running, data moves through the graph and is rendered.
    if(FAILED(_media_control->Run()))
        return FALSE;

    return TRUE;
}

//------------------------------------------------------------------------------
// Stop playing mp3.
//------------------------------------------------------------------------------
BOOL MP3::stop()
{
    // error checking
    if(_media_control == NULL)
        return FALSE;

    // stops all the filters in the graph
    if(FAILED(_media_control->Stop()))
        return FALSE;

    return TRUE;
}

//------------------------------------------------------------------------------
// Pause playing mp3.
//------------------------------------------------------------------------------
BOOL MP3::pause()
{
    // error checking
    if(_media_control == NULL)
        return FALSE;

    // pause all the filters in the filter graph
    if(FAILED(_media_control->Pause()))
        return FALSE;

    return TRUE;
}

//------------------------------------------------------------------------------
// Ascertain whether mp3 has completed playing.
//------------------------------------------------------------------------------
BOOL MP3::is_playing()
{
    // error checking
    if(_media_event == NULL)
        return FALSE;

    // get event and handle it

    long event, param1, param2;

    // retrieves the next event notification from the event queue
    _media_event->GetEvent(&event, &param1, &param2, 1);

    if(event == EC_COMPLETE)
    {
        // free resources associated with the paramters of an event
        _media_event->FreeEventParams(event, param1, param2);

        return TRUE;
    }

    _media_event->FreeEventParams(event, param1, param2);
    return FALSE;
}

测试代码:

/*****************************************************************************
PURPOSE:
    Test for class MP3.
*****************************************************************************/

#include "Core_Global.h"

class APP : public APPLICATION
{
public:
    BOOL init()
    {
        _mp3.init();

        if(_mp3.render("song.mp3"))
            _mp3.play();

        while(_mp3.is_playing())
            ;

        return TRUE;
    }

    BOOL frame()
    {
        return TRUE;
    }

    BOOL shutdown()
    {
        return TRUE;
    }

private:
    MP3 _mp3;
};

int PASCAL WinMain(HINSTANCE inst, HINSTANCE, LPSTR cmd_line, int cmd_show)
{
    APP app;

    return app.run();
}

posted on 2007-10-10 16:35 lovedday 阅读(261) 评论(0) 编辑收藏引用

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