【cocos2d-x 3D游戏开发】3: 游戏帧循环

int APIENTRY _tWinMain(HINSTANCE hInstance,
                       HINSTANCE hPrevInstance,
                       LPTSTR    lpCmdLine,
                       int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // 创建一个CCApplication(子类)对象app
    AppDelegate app;

    // 创建windows窗口，在窗口的创建过程中会初始化OpenGL.
    CCEGLView* eglView = CCEGLView::sharedOpenGLView();
    eglView->setViewName("hello");
    eglView->setFrameSize(480, 320);
    
    // 调用app的run方法，启动游戏循环
    return CCApplication::sharedApplication()->run();
}

// sharedApplication pointer    一个父类对象的指针 CCApplication*
CCApplication * CCApplication::sm_pSharedApplication = 0;

CCApplication::CCApplication()
: m_hInstance(NULL)
, m_hAccelTable(NULL)
{
    m_hInstance    = GetModuleHandle(NULL);
    m_nAnimationInterval.QuadPart = 0;
    CC_ASSERT(! sm_pSharedApplication);
    // 在构造的时候，单例指针指向了this, 
    // 由于代码里只是显示创建了Appdelegate app这个对象，而没有创建CCApplication类型的对象，因此这个this其实是在创建子类对象的地址
    // 相当于这样写，CCApplication * app = new Appdelegate();
    sm_pSharedApplication = this;           
}

int CCApplication::run()
{
    PVRFrameEnableControlWindow(false);

    // Main message loop:
    MSG msg;
    LARGE_INTEGER nFreq;
    LARGE_INTEGER nLast;
    LARGE_INTEGER nNow;

    QueryPerformanceFrequency(&nFreq);
    QueryPerformanceCounter(&nLast);

    // Initialize instance and cocos2d.
    if (!applicationDidFinishLaunching())    // Appdelegate::applicationDidFinishLaunching
    {
        return 0;
    }

    CCEGLView* pMainWnd = CCEGLView::sharedOpenGLView();
    pMainWnd->centerWindow();
    ShowWindow(pMainWnd->getHWnd(), SW_SHOW);       // 显示游戏窗口

    // 游戏循环 窗口消息循环
    while (1)
    {
        if (! PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            // Get current time tick.
            QueryPerformanceCounter(&nNow);

            // 离下一帧还有没有剩余时间，有的话就睡一会.
            if (nNow.QuadPart - nLast.QuadPart > m_nAnimationInterval.QuadPart)
            {
                nLast.QuadPart = nNow.QuadPart;
                CCDirector::sharedDirector()->mainLoop();       // 游戏里的操作在CCDirector的mainLoop方法里
            }
            else
            {
                Sleep(0);
            }
            continue;
        }

        if (WM_QUIT == msg.message)
        {
            // Quit message loop.
            break;
        }

        // Deal with windows message.
        if (! m_hAccelTable || ! TranslateAccelerator(msg.hwnd, m_hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}

void CCDisplayLinkDirector::mainLoop(void)
{
    if (m_bPurgeDirecotorInNextLoop)
    {
        m_bPurgeDirecotorInNextLoop = false;
        purgeDirector();                                // 游戏结束，销毁director
    }
    else if (! m_bInvalid)
     {
         drawScene();                                   // 绘制
     
         CCPoolManager::sharedPoolManager()->pop();     // 释放自动对象
     }
}

void CCDirector::drawScene(void)
{
    calculateDeltaTime();  // 计算帧时间间隔

    if (! m_bPaused)
    {
        m_pScheduler->update(m_fDeltaTime);     // 调度器 CCScheduler的update
    }

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);     // opengl 状态重置

    if (m_pNextScene)
    {
        setNextScene();                         // 是否切换新Scene? 退出当前Scene， 显示下一Scene
    }

    kmGLPushMatrix();                           // 复制当前栈顶的模型视图矩阵MV 

    if (m_pRunningScene)
    {
        m_pRunningScene->visit();               // 绘制当前Scene
    }

    // draw the notifications node
    if (m_pNotificationNode)
    {
        m_pNotificationNode->visit();           // 绘制通知节点
    }
    
    if (m_bDisplayStats)
    {
        showStats();                            // 显示drawCall次数，FPS，SPF三个数值label
    }
    
    kmGLPopMatrix();                            // 弹出栈顶模型视图矩阵MV

    m_uTotalFrames++;

    // swap buffers
    if (m_pobOpenGLView)
    {
        m_pobOpenGLView->swapBuffers();         // 绘制完成，交换缓冲区
    }
    
    if (m_bDisplayStats)
    {
        calculateMPF();                         // 计算SPF， 即每帧消耗的时间
    }
}