cocos2d-x游戲引擎核心(3.x)----啟動渲染流程

(1) 首先,這里以win32平台下為例子.win32下游戲的啟動都是從win32目錄下main文件開始的,即是游戲的入口函數,如下:

#include "main.h"
#include "AppDelegate.h"
#include "cocos2d.h"

USING_NS_CC;

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

    // create the application instance
    AppDelegate app;
　　 // 啟動游戲 return Application::getInstance()->run();
}

(1-1)這里可以看出,在入口函數中,首先創建了一個AppDelegate對象，AppDelegate繼承 自CCApplication，在創建APPDelegate對象的時候就會隱式調用CCApplication構造函數，在這個構造函數里邊會將AppDelegate的this指針傳遞給全局共享對象sm_pSharedApplication,如下:

Application::Application()
//初始化win32應用程序對象 
: _instance(nullptr)
, _accelTable(nullptr)
{
    _instance    = GetModuleHandle(nullptr);
　　// 用於控制幀數的計數值
    _animationInterval.QuadPart = 0;
    CC_ASSERT(! sm_pSharedApplication);
    // 全局共享對象
    sm_pSharedApplication = this;
}

(1-2) 接下來調用Application::getInstance()->run();啟動游戲,如下:

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

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

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

    // Initialize instance and cocos2d.
    // 執行AppDeletegate重載的applicationDidFinishLaunching函數
    if (!applicationDidFinishLaunching())
    {
        return 0;
    }

    auto director = Director::getInstance();
    auto glview = director->getOpenGLView();

    // Retain glview to avoid glview being released in the while loop
    glview->retain();

    while(!glview->windowShouldClose())
    {
        QueryPerformanceCounter(&nNow);
        if (nNow.QuadPart - nLast.QuadPart > _animationInterval.QuadPart)
        {
            nLast.QuadPart = nNow.QuadPart;
            // 主循環,每幀調用
            director->mainLoop();
            glview->pollEvents();
        }
        else
        {
            Sleep(0);
        }
    }

    // Director should still do a cleanup if the window was closed manually.
    if (glview->isOpenGLReady())
    {
        // 結束,執行清理工作
        director->end();
        director->mainLoop();
        director = nullptr;
    }
    glview->release();
    return true;
}

(1-2-1) 我們進入到AppDelegate::applicationDidFinishLaunching(),看它究竟做了什么,我們以/cocos2d-x-3.2/templates/cpp-template-default/Classes/AppDelegate.cpp為例:

bool AppDelegate::applicationDidFinishLaunching() {
    // initialize director
    auto director = Director::getInstance();
    auto glview = director->getOpenGLView();
    if(!glview) {
        // 創建glview對象, 這里采用默認的分辨率先創建出游戲窗口
        glview = GLView::create("My Game");
        // 這里設置了和OpenGL相關的一些信息
        director->setOpenGLView(glview);
    }

    // turn on display FPS
    director->setDisplayStats(true);

    // set FPS. the default value is 1.0/60 if you don't call this
    director->setAnimationInterval(1.0 / 60);

    // create a scene. it's an autorelease object
    // 創建場景
    auto scene = HelloWorld::createScene();

    // run 運行場景
    director->runWithScene(scene);

    return true;
}

(1-2-1-1) 可以看到applicationDidFinishLaunching函數里面設置了glview對象之后,就開始運行場景,可以進入GLView::create中看其究竟是如何創建GLView對象,同樣,我們是win32下面看的, 所以找到cocos2d-x-3.2/cocos/platform/desktop/CCGLView.cpp文件:

GLView* GLView::create(const std::string& viewName)
{
    auto ret = new GLView;
    if(ret && ret->initWithRect(viewName, Rect(0, 0, 960, 640), 1)) {
        ret->autorelease();
        return ret;
    }

    return nullptr;
}

從代碼可以看到只是簡單的new一個GLView對象,我們進入/cocos2d-x-3.2/cocos/platform/desktop/CCGLView.h看一下它究竟是個什么東西:

/****************************************************************************
Copyright (c) 2010-2012 cocos2d-x.org
Copyright (c) 2013-2014 Chukong Technologies Inc.

http://www.cocos2d-x.org

*/

#ifndef __CC_EGLVIEW_DESKTOP_H__
#define __CC_EGLVIEW_DESKTOP_H__

#include "base/CCRef.h"
#include "platform/CCCommon.h"
#include "platform/CCGLViewProtocol.h"
#include "glfw3.h"

NS_CC_BEGIN

class CC_DLL GLView : public GLViewProtocol, public Ref
{
public:
    static GLView* create(const std::string& viewName);
    static GLView* createWithRect(const std::string& viewName, Rect size, float frameZoomFactor = 1.0f);
    static GLView* createWithFullScreen(const std::string& viewName);
    static GLView* createWithFullScreen(const std::string& viewName, const GLFWvidmode &videoMode, GLFWmonitor *monitor);

    /*
     *frameZoomFactor for frame. This method is for debugging big resolution (e.g.new ipad) app on desktop.
     */

    //void resize(int width, int height);

    float getFrameZoomFactor();
    //void centerWindow();

    virtual void setViewPortInPoints(float x , float y , float w , float h);
    virtual void setScissorInPoints(float x , float y , float w , float h);


    bool windowShouldClose();
    void pollEvents();
    GLFWwindow* getWindow() const { return _mainWindow; }

    /* override functions */
    virtual bool isOpenGLReady() override;
    // 刪除窗口，做窗口清理工作 virtual void end() override;
    // 交換buffer virtual void swapBuffers() override;
    // 設置窗口大小 virtual void setFrameSize(float width, float height) override;
    // 設置輸入法狀態 virtual void setIMEKeyboardState(bool bOpen) override;

    /*
     * Set zoom factor for frame. This method is for debugging big resolution (e.g.new ipad) app on desktop.
     */
    void setFrameZoomFactor(float zoomFactor);

    /** Retina support is disabled by default
     *  @note This method is only available on Mac.
     */
    void enableRetina(bool enabled);
    /** Check whether retina display is enabled. */
    bool isRetinaEnabled() const { return _isRetinaEnabled; };
    
    /** Get retina factor */
    int getRetinaFactor() const { return _retinaFactor; }

protected:
    GLView();
    virtual ~GLView();

    bool initWithRect(const std::string& viewName, Rect rect, float frameZoomFactor);
    bool initWithFullScreen(const std::string& viewName);
    bool initWithFullscreen(const std::string& viewname, const GLFWvidmode &videoMode, GLFWmonitor *monitor);

    bool initGlew();

    void updateFrameSize();

    // GLFW callbacks
    void onGLFWError(int errorID, const char* errorDesc);
    void onGLFWMouseCallBack(GLFWwindow* window, int button, int action, int modify);
    void onGLFWMouseMoveCallBack(GLFWwindow* window, double x, double y);
    void onGLFWMouseScrollCallback(GLFWwindow* window, double x, double y);
    void onGLFWKeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods);
    void onGLFWCharCallback(GLFWwindow* window, unsigned int character);
    void onGLFWWindowPosCallback(GLFWwindow* windows, int x, int y);
    void onGLFWframebuffersize(GLFWwindow* window, int w, int h);
    void onGLFWWindowSizeFunCallback(GLFWwindow *window, int width, int height);

    bool _captured;
    bool _supportTouch;
    bool _isInRetinaMonitor;
    bool _isRetinaEnabled;
    int  _retinaFactor;  // Should be 1 or 2

    float _frameZoomFactor;

    GLFWwindow* _mainWindow;
    GLFWmonitor* _monitor;

    float _mouseX;
    float _mouseY;

    friend class GLFWEventHandler;

private:
    CC_DISALLOW_COPY_AND_ASSIGN(GLView);
};

NS_CC_END   // end of namespace   cocos2d

#endif  // end of __CC_EGLVIEW_DESKTOP_H__

GLView繼承自GLViewProtocol,我們也進入看一下:

/****************************************************************************
Copyright (c) 2010-2012 cocos2d-x.org
Copyright (c) 2013-2014 Chukong Technologies Inc.

http://www.cocos2d-x.org

*******************************************************/

#ifndef __CCGLVIEWPROTOCOL_H__
#define __CCGLVIEWPROTOCOL_H__

#include "base/ccTypes.h"
#include "base/CCEventTouch.h"

#include <vector>
// 5種屏幕適配策略
enum class ResolutionPolicy
{
    EXACT_FIT,
    NO_BORDER,
    SHOW_ALL,
    FIXED_HEIGHT,
    FIXED_WIDTH,

    UNKNOWN,
};

NS_CC_BEGIN

class CC_DLL GLViewProtocol
{
public:
    /**
     * @js ctor
     */
    GLViewProtocol();
    /**
     * @js NA
     * @lua NA
     */
    virtual ~GLViewProtocol();

    /** Force destroying EGL view, subclass must implement this method. */
    virtual void end() = 0;

    /** Get whether opengl render system is ready, subclass must implement this method. */
    virtual bool isOpenGLReady() = 0;

    /** Exchanges the front and back buffers, subclass must implement this method. */
    virtual void swapBuffers() = 0;

    /** Open or close IME keyboard , subclass must implement this method. */
    virtual void setIMEKeyboardState(bool open) = 0;

    /**
     * Polls input events. Subclass must implement methods if platform
     * does not provide event callbacks.
     */
    virtual void pollInputEvents();

    /**
     * Get the frame size of EGL view.
     * In general, it returns the screen size since the EGL view is a fullscreen view.
     */
    virtual const Size& getFrameSize() const;

    /**
     * Set the frame size of EGL view.
     */
    virtual void setFrameSize(float width, float height);

    // 獲取可見區域的原點和大小
    virtual Size getVisibleSize() const;
    virtual Vec2 getVisibleOrigin() const;
    virtual Rect getVisibleRect() const;

    //設置設計的size，當需要適配多種設備時，可以用這個函數定義邏輯坐標，cocos2dx會自動將邏輯坐標轉化成實際坐標,這樣一樣的代碼可以適配各種設備分辨率
    virtual void setDesignResolutionSize(float width, float height, ResolutionPolicy resolutionPolicy);

    /** Get design resolution size.
     *  Default resolution size is the same as 'getFrameSize'.
     */
    virtual const Size&  getDesignResolutionSize() const;

    /**
     * Set opengl view port rectangle with points.
     */
    virtual void setViewPortInPoints(float x , float y , float w , float h);

    /**
     * Set Scissor rectangle with points.
     */
    virtual void setScissorInPoints(float x , float y , float w , float h);

    /**
     * Get whether GL_SCISSOR_TEST is enable
     */
    virtual bool isScissorEnabled();

    /**
     * Get the current scissor rectangle
     */
    virtual Rect getScissorRect() const;

    virtual void setViewName(const std::string& viewname);
    const std::string& getViewName() const;

    /** Touch events are handled by default; if you want to customize your handlers, please override these functions: */
    // 觸摸處理函數，可以重載
    virtual void handleTouchesBegin(int num, intptr_t ids[], float xs[], float ys[]);
    virtual void handleTouchesMove(int num, intptr_t ids[], float xs[], float ys[]);
    virtual void handleTouchesEnd(int num, intptr_t ids[], float xs[], float ys[]);
    virtual void handleTouchesCancel(int num, intptr_t ids[], float xs[], float ys[]);

    /**
     * Get the opengl view port rectangle.
     */
    const Rect& getViewPortRect() const;

    /**
     * Get scale factor of the horizontal direction.
     */
    float getScaleX() const;

    /**
     * Get scale factor of the vertical direction.
     */
    float getScaleY() const;

    /** returns the current Resolution policy */
    ResolutionPolicy getResolutionPolicy() const { return _resolutionPolicy; }

protected:
    void updateDesignResolutionSize();
    
    void handleTouchesOfEndOrCancel(EventTouch::EventCode eventCode, int num, intptr_t ids[], float xs[], float ys[]);

    // real screen size
    Size _screenSize;
    // resolution size, it is the size appropriate for the app resources.
    Size _designResolutionSize;
    // the view port size
    Rect _viewPortRect;
    // the view name
    std::string _viewName;

    float _scaleX;
    float _scaleY;
    ResolutionPolicy _resolutionPolicy;
};

// end of platform group
/// @}

NS_CC_END

#endif /* __CCGLVIEWPROTOCOL_H__ */

以看到CCEGLView和GLViewProtocol是顯示窗口，負責窗口級別的功能管理和實現, 包括：坐標和縮放管理, 畫圖工具,按鍵事件;

(1-2-1-2) 創建glview對象之后,導演類Director就把glview設置進游戲,其中包括很多配置信息, 如設置屏幕大小適配相關的函數getDesignResolutionSize, 如下:

void Director::setOpenGLView(GLView *openGLView)
{
    CCASSERT(openGLView, "opengl view should not be null");

    if (_openGLView != openGLView)
    {
        // Configuration. Gather GPU info
        Configuration *conf = Configuration::getInstance();
        conf->gatherGPUInfo();
        CCLOG("%s\n",conf->getInfo().c_str());

        if(_openGLView)
            _openGLView->release();
        _openGLView = openGLView;
        _openGLView->retain();

        // set size 設置屏幕大小適配相關的函數
        _winSizeInPoints = _openGLView->getDesignResolutionSize();

        createStatsLabel();

        if (_openGLView)
        {
            setGLDefaultValues();
        }
       // 完成初始化
        _renderer->initGLView();

        CHECK_GL_ERROR_DEBUG();

        if (_eventDispatcher)
        {
            _eventDispatcher->setEnabled(true);
        }
    }
}

(1-2-1-2-1) 我們進入initGLView看看它都做了什么初始化工作,找到/cocos2d-x-3.2/cocos/renderer/CCRenderer.cpp:

void Renderer::initGLView()
{
#if CC_ENABLE_CACHE_TEXTURE_DATA
    _cacheTextureListener = EventListenerCustom::create(EVENT_RENDERER_RECREATED, [this](EventCustom* event){
        /** listen the event that renderer was recreated on Android/WP8 */
        this->setupBuffer();
    });
    
    Director::getInstance()->getEventDispatcher()->addEventListenerWithFixedPriority(_cacheTextureListener, -1);
#endif // 填充索引緩沖
    setupIndices();
    
    setupBuffer();
    
    _glViewAssigned = true;
}

(1-2-1-2-1-1) 進入setupIndices如下:

void Renderer::setupIndices()
{
    for( int i=0; i < VBO_SIZE; i++)
    {
　　　　// 計算索引緩沖值
        _indices[i*6+0] = (GLushort) (i*4+0);
        _indices[i*6+1] = (GLushort) (i*4+1);
        _indices[i*6+2] = (GLushort) (i*4+2);
        _indices[i*6+3] = (GLushort) (i*4+3);
        _indices[i*6+4] = (GLushort) (i*4+2);
        _indices[i*6+5] = (GLushort) (i*4+1);
    }
}

(1-2-1-2-1-2) 進入setupBuffer如下:

 

void Renderer::setupBuffer()
{
    // 如果使用VAO if(Configuration::getInstance()->supportsShareableVAO())
    {
        // 初始化VAO和VBO
        setupVBOAndVAO();
    }
    else
    {
        // 初始化VBO
        setupVBO();
    }
}

 

(1-2-1-2-1-2-1) 進入setupVBOAndVAO和setupVBO, 開始調用OpenGL API進行頂點數據指定,具體意義參見基於Cocos2d-x學習OpenGL ES 2.0系列——編寫自己的shader（2）:

void Renderer::setupVBOAndVAO()
{
    glGenVertexArrays(1, &_quadVAO);
    GL::bindVAO(_quadVAO);

    glGenBuffers(2, &_buffersVBO[0]);

    glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(_quads[0]) * VBO_SIZE, _quads, GL_DYNAMIC_DRAW);

    // vertices
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_POSITION);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 3, GL_FLOAT, GL_FALSE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, vertices));

    // colors
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_COLOR);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, colors));

    // tex coords
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_TEX_COORD);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_COORD, 2, GL_FLOAT, GL_FALSE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, texCoords));

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_indices[0]) * VBO_SIZE * 6, _indices, GL_STATIC_DRAW);

    // Must unbind the VAO before changing the element buffer.
    GL::bindVAO(0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    CHECK_GL_ERROR_DEBUG();
}

void Renderer::setupVBO()
{
    glGenBuffers(2, &_buffersVBO[0]);

    mapBuffers();
}

 

(1-2-2) 在applicationDidFinishLaunching里面創建場景之后,就調用director->mainLoop();開始游戲主循環了.我們進入mainLoop看它做了什么, win32下我們找到cocos2d-x-3.2/cocos/base/CCDirector.cpp:

void DisplayLinkDirector::mainLoop()
{
    if (_purgeDirectorInNextLoop)
    {
        _purgeDirectorInNextLoop = false;
        // 主循環結束,清除工作
        purgeDirector();
    }
    else if (! _invalid)
    {
　　　　 // 渲染場景
        drawScene();
     
        // release the objects
        // 釋放對象:內存池里之前通過autorelease加入的對象引用計數減 1.
        PoolManager::getInstance()->getCurrentPool()->clear();
    }
}

mainLoop主要完成三個動作:

　　1 判斷是否需要釋放 CCDirector，如果需要，則刪除 CCDirector 占用的資源。通常，游戲結束時才會執行這個步驟。　　

　　2 調用 drawScene()方法，繪制當前場景並進行其他必要的處理。

　　3 彈出自動回收池，使得這一幀被放入自動回收池的對象全部釋放。

(1-2-2-1) 由此可見，mainLoop()把內存管理以外的操作都交給了 drawScene()方法，因此關鍵的步驟都在 drawScene()方法之中。下面是 drawScene()方法的實現：

// Draw the Scene
void Director::drawScene()
{
    // calculate "global" dt
    // 計算全局幀間時間差 dt
    calculateDeltaTime();
    
    // skip one flame when _deltaTime equal to zero.
    if(_deltaTime < FLT_EPSILON)
    {
        return;
    }

    if (_openGLView)
    {
        _openGLView->pollInputEvents();
    }

    //tick before glClear: issue #533
    if (! _paused)
    {
        // 啟動定時器
        _scheduler->update(_deltaTime);
        _eventDispatcher->dispatchEvent(_eventAfterUpdate);
    }

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    /* to avoid flickr, nextScene MUST be here: after tick and before draw.
     XXX: Which bug is this one. It seems that it can't be reproduced with v0.9 */
    if (_nextScene)
    {
        // 如果有,設置下一個場景
        setNextScene();
    }

    // 保存原來的模型視圖(ModelView)矩陣
    pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);

    // draw the scene
    if (_runningScene)
    {
　　　　 // 開始繪制場景
        _runningScene->visit(_renderer, Mat4::IDENTITY, false);
        // 事件分發
        _eventDispatcher->dispatchEvent(_eventAfterVisit);
    }

    // draw the notifications node
    if (_notificationNode)
    {
        // 處理通知節點
        _notificationNode->visit(_renderer, Mat4::IDENTITY, false);
    }

    if (_displayStats)
    {
        showStats();
    }
    // 開始渲染場景
    _renderer->render();
    _eventDispatcher->dispatchEvent(_eventAfterDraw);

    popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);

    _totalFrames++;

    // swap buffers 交換緩沖區
    if (_openGLView)
    {
        _openGLView->swapBuffers();
    }

    if (_displayStats)
    {
        calculateMPF();
    }
}

可以發現drawScene主要用於處理 OpenGL 和一些細節，如計算 FPS、幀間時間差等,這里我們主要進行了以下 3 個操作。
　　1 調用了定時調度器的 update 方法，引發定時器事件。
　　2 如果場景需要被切換，則調用 setNextScene 方法，在顯示場景前切換場景。
　　3 調用當前場景的 visit 方法，將當前場景加入渲染隊列,並通過render統一渲染。

(1-2-2-1-1) 我們進入到visit方法里面,看它怎樣把每一個節點添加到渲染隊列, 這里我們找到/cocos2d-x-3.2/cocos/2d/CCNode.cpp:

void Node::visit(Renderer* renderer, const Mat4 &parentTransform, uint32_t parentFlags)
{
    // quick return if not visible. children won't be drawn.
    if (!_visible)
    {
        return;
    }

    // 設置_modelViewTransform矩陣
    uint32_t flags = processParentFlags(parentTransform, parentFlags);

    // IMPORTANT:
    // To ease the migration to v3.0, we still support the Mat4 stack,
    // but it is deprecated and your code should not rely on it
    Director* director = Director::getInstance();
    director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW, _modelViewTransform);

    int i = 0;

    if(!_children.empty())
    {
        sortAllChildren();
        // draw children zOrder < 0
        for( ; i < _children.size(); i++ )
        {
            auto node = _children.at(i);

            if ( node && node->_localZOrder < 0 )
                node->visit(renderer, _modelViewTransform, flags);
            else
                break;
        }
        // self draw
        this->draw(renderer, _modelViewTransform, flags);

        for(auto it=_children.cbegin()+i; it != _children.cend(); ++it)
            (*it)->visit(renderer, _modelViewTransform, flags);
    }
    else
    {
        this->draw(renderer, _modelViewTransform, flags);
    }

    director->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    
    // FIX ME: Why need to set _orderOfArrival to 0??
    // Please refer to https://github.com/cocos2d/cocos2d-x/pull/6920
    // reset for next frame
    // _orderOfArrival = 0;
}

(1-2-2-1-1-1) 對節點的所有孩子排序,通過調用draw函數,首先繪制ZOrder<0的節點,在繪制自身,最后繪制ZOrder>0的節點. 我們進入draw看看它做些什么. 注意,visit和draw都是虛函數, 以sprite為例,我們進入到/cocos2d-x-3.2/cocos/2d/CCSprite.cpp:

void Sprite::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
    // Don't do calculate the culling if the transform was not updated
    _insideBounds = (flags & FLAGS_TRANSFORM_DIRTY) ? renderer->checkVisibility(transform, _contentSize) : _insideBounds;

    if(_insideBounds)
    {
        _quadCommand.init(_globalZOrder, _texture->getName(), getGLProgramState(), _blendFunc, &_quad, 1, transform);
        renderer->addCommand(&_quadCommand);
// 物理引擎相關繪制邊界 #if CC_SPRITE_DEBUG_DRAW
        _customDebugDrawCommand.init(_globalZOrder);
        _customDebugDrawCommand.func = CC_CALLBACK_0(Sprite::drawDebugData, this);
        renderer->addCommand(&_customDebugDrawCommand);
#endif //CC_SPRITE_DEBUG_DRAW
    }
}

(1-2-2-1-1-1-1) 從代碼中可以看出,Sprite的draw函數里面並沒有做實際的渲染工作,而是用QuadCommand命令將渲染操作打包,加入到渲染隊列里面,在drawscene最后通過調用render()進行統一渲染;我們可以看看_quadCommand.init里面究竟做了什么,找到/cocos2d-x-3.2/cocos/renderer/CCQuadCommand.cpp:

void QuadCommand::init(float globalOrder, GLuint textureID, GLProgramState* glProgramState, BlendFunc blendType, V3F_C4B_T2F_Quad* quad, ssize_t quadCount, const Mat4 &mv)
{
    CCASSERT(glProgramState, "Invalid GLProgramState");
    CCASSERT(glProgramState->getVertexAttribsFlags() == 0, "No custom attributes are supported in QuadCommand");

    _globalOrder = globalOrder;

    _quadsCount = quadCount;
    _quads = quad;
    
    // 設置MV矩陣
    _mv = mv;

    if( _textureID != textureID || _blendType.src != blendType.src || _blendType.dst != blendType.dst || _glProgramState != glProgramState) {
        // 
        _textureID = textureID;
       // _blendType就是我們的BlendFunc混合函數
        _blendType = blendType;
        _glProgramState = glProgramState;
       
        // 生成材質ID
        generateMaterialID();
    }
}

(1-2-2-1-1-1-1-1) 我們在進入到generateMaterialID()函數里面看看:

void QuadCommand::generateMaterialID()
{

    if(_glProgramState->getUniformCount() > 0)
    {
        _materialID = QuadCommand::MATERIAL_ID_DO_NOT_BATCH;
    }
    else
    {
        int glProgram = (int)_glProgramState->getGLProgram()->getProgram();
        int intArray[4] = { glProgram, (int)_textureID, (int)_blendType.src, (int)_blendType.dst};

        _materialID = XXH32((const void*)intArray, sizeof(intArray), 0);
    }
}

從這里我們可以看出, 我們的材質ID（_materialID）最終是要由shader（glProgram）、混合類型（_blendType）、紋理ID（_textureID）組成的, 所以這三樣東西如果有誰不一樣的話，那就無法生成相同的材質ID，也就無法在同一 個批次里進行渲染了。

(1-2-2-1-2) 現在,我們回到(1-2-2-1-1-1)的draw函數, 通過上面將渲染指令初始化之后,就是將打包好的渲染命令添加到渲染隊列里面了.這里只需簡單調用renderer->addCommand(&_quadCommand);即可. 這樣,(1-2-2-1)處的drawscene函數中,visit通過調用派生類節點添加渲染指令到渲染隊列的工作已經完成了.接下來要做的就是做實際的渲染工作了.3.x版本與之前版本不同,是在drawscene最后通過調用render()函數進行統一渲染的,我們進入render()看一下,找到cocos2d-x-3.2/cocos/renderer/CCRenderer.cpp:

void Renderer::render()
{
    //Uncomment this once everything is rendered by new renderer
    //glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    //TODO setup camera or MVP
    _isRendering = true;
    
    if (_glViewAssigned)
    {
        // cleanup
        _drawnBatches = _drawnVertices = 0;

        //Process render commands
        //1. Sort render commands based on ID
        for (auto &renderqueue : _renderGroups)
        {
            renderqueue.sort();
        }
        visitRenderQueue(_renderGroups[0]);
        flush();
    }
    clean();
    _isRendering = false;
}

 從代碼可以看出,從Cocos2d-x3.0開始，Cocos2d-x引入了新的渲染流程，它不像2.x版本 直接在每一個node中的draw函數中直接調用OpenGL代碼進行圖形渲染，而是通過各種RenderCommand封裝起來，然后添加到一個 CommandQueue隊列里面去，而現在draw函數的作用就是在此函數中設置好相對應的RenderCommand參數，然后把此 RenderCommand添加到CommandQueue中。最后在每一幀結束時調用renderer函數進行渲染，在renderer函數中會根據 ID對RenderCommand進行排序，然后才進行渲染。

(1-2-2-1-2-1) 現在我們進入visitRenderQueue函數看看它做了什么動作:

 

void Renderer::visitRenderQueue(const RenderQueue& queue)
{
    ssize_t size = queue.size();
    
    for (ssize_t index = 0; index < size; ++index)
    {
        auto command = queue[index];
        auto commandType = command->getType();
　　　　if(RenderCommand::Type::QUAD_COMMAND == commandType)
        {
            flush3D();
            auto cmd = static_cast<QuadCommand*>(command);
            //Batch quads
            // 如果Quad數據量超過VBO的大小，那么調用繪制，將緩存的命令全部繪制
            if(_numQuads + cmd->getQuadCount() > VBO_SIZE)
            {
                CCASSERT(cmd->getQuadCount()>= 0 && cmd->getQuadCount() < VBO_SIZE, "VBO is not big enough for quad data, please break the quad data down or use customized render command");
                
                //Draw batched quads if VBO is full
                drawBatchedQuads();
            }
　　　　　　 // 這個處理主要是把命令存入_batchedQuadCommands中，如果如果Quad數據量超過VBO的大小，那么調用繪制，將緩存的命令全部繪制.
　　　　　 　// 如果一直沒有超過VBO的大小，drawBatchedQuads繪制函數將在flush被調用時調用.
            // 將命令緩存起來，先不調用繪制
            _batchedQuadCommands.push_back(cmd);
            
            memcpy(_quads + _numQuads, cmd->getQuads(), sizeof(V3F_C4B_T2F_Quad) * cmd->getQuadCount());
            // 通過MV矩陣, 轉換成世界坐標
            convertToWorldCoordinates(_quads + _numQuads, cmd->getQuadCount(), cmd->getModelView());
            // 記錄下四邊形數量
            _numQuads += cmd->getQuadCount();

        }
        else if(RenderCommand::Type::GROUP_COMMAND == commandType)
        {
            flush();
            int renderQueueID = ((GroupCommand*) command)->getRenderQueueID();
            visitRenderQueue(_renderGroups[renderQueueID]);
        }
        else if(RenderCommand::Type::CUSTOM_COMMAND == commandType)
        {
            flush();
            auto cmd = static_cast<CustomCommand*>(command);
            cmd->execute();
        }
        else if(RenderCommand::Type::BATCH_COMMAND == commandType)
        {
            flush();
            auto cmd = static_cast<BatchCommand*>(command);
            cmd->execute();
        }
        else if (RenderCommand::Type::MESH_COMMAND == commandType)
        {
            flush2D();
            auto cmd = static_cast<MeshCommand*>(command);
            if (_lastBatchedMeshCommand == nullptr || _lastBatchedMeshCommand->getMaterialID() != cmd->getMaterialID())
            {
                flush3D();
                cmd->preBatchDraw();
                cmd->batchDraw();
                _lastBatchedMeshCommand = cmd;
            }
            else
            {
                cmd->batchDraw();
            }
        }
        else
        {
            CCLOGERROR("Unknown commands in renderQueue");
        }
    }
}

 

從代碼中，我們看到RenderCommand類型有QUAD_COMMAND,CUSTOM_COMMAND,BATCH_COMMAND,GROUP_COMMAND,MESH_COMMAND五種，OpenGL的API調用是在Renderer::drawBatchedQuads()、BatchCommand::execute()中。通過上面代碼的注釋,可以看到最常用的QUAD_COMMAND類型的渲染命令的處理過程.

(1-2-2-1-2-1-1) 如果Quad數據量超過VBO的大小(VBO_SIZE = 65536 / 6;), 則會調用drawBatchedQuads進行批量渲染:

 

void Renderer::drawBatchedQuads()
{
    //TODO we can improve the draw performance by insert material switching command before hand.

    int quadsToDraw = 0;
    int startQuad = 0;

    //Upload buffer to VBO
    if(_numQuads <= 0 || _batchedQuadCommands.empty())
    {
        return;
    }
    // 是否支持VAO if (Configuration::getInstance()->supportsShareableVAO())
    {
        //Set VBO data 綁定VBO數據, 激活緩沖區對象
        glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]);

        // option 1: subdata
//        glBufferSubData(GL_ARRAY_BUFFER, sizeof(_quads[0])*start, sizeof(_quads[0]) * n , &_quads[start] );

        // option 2: data
//        glBufferData(GL_ARRAY_BUFFER, sizeof(quads_[0]) * (n-start), &quads_[start], GL_DYNAMIC_DRAW);

        // option 3: orphaning + glMapBuffer
　　　　　// 用數據分配和初始化緩沖區對象
        glBufferData(GL_ARRAY_BUFFER, sizeof(_quads[0]) * (_numQuads), nullptr, GL_DYNAMIC_DRAW);
        // OPENGL 緩沖區對象（buffer object），允許應用程序顯式地指定把哪些數據存儲在圖形服務器或顯存中
　　　　 // 返回指向緩沖區的指針, 緩沖一經具體使用之后，只需要改變緩沖區的內容，即在glMapBuffer和glUnmapBuffer之間改變數據即可 void *buf = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
        memcpy(buf, _quads, sizeof(_quads[0])* (_numQuads));
        glUnmapBuffer(GL_ARRAY_BUFFER);
        // 解除綁定
        glBindBuffer(GL_ARRAY_BUFFER, 0);

        //Bind VAO 綁定VAO
        GL::bindVAO(_quadVAO);
    }
    else
    {
#define kQuadSize sizeof(_quads[0].bl)
        glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]);

        glBufferData(GL_ARRAY_BUFFER, sizeof(_quads[0]) * _numQuads , _quads, GL_DYNAMIC_DRAW);

        GL::enableVertexAttribs(GL::VERTEX_ATTRIB_FLAG_POS_COLOR_TEX);

        // vertices
        glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 3, GL_FLOAT, GL_FALSE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, vertices));

        // colors
        glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, colors));

        // tex coords
        glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_COORD, 2, GL_FLOAT, GL_FALSE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, texCoords));

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]);
    }

    //Start drawing verties in batch
    for(const auto& cmd : _batchedQuadCommands)
    {
        auto newMaterialID = cmd->getMaterialID();
        if(_lastMaterialID != newMaterialID || newMaterialID == QuadCommand::MATERIAL_ID_DO_NOT_BATCH)
        {
            //Draw quads
            if(quadsToDraw > 0)
            {
                // 四邊形都可以由2個三角形組合而成,指定6個索引點(畫出2個GL_TRIANGLES)
                glDrawElements(GL_TRIANGLES, (GLsizei) quadsToDraw*6, GL_UNSIGNED_SHORT, (GLvoid*) (startQuad*6*sizeof(_indices[0])) );
                _drawnBatches++;
                _drawnVertices += quadsToDraw*6;

                startQuad += quadsToDraw;
                quadsToDraw = 0;
            }

            //Use new material
            cmd->useMaterial();
            _lastMaterialID = newMaterialID;
        }

        quadsToDraw += cmd->getQuadCount();
    }

    //Draw any remaining quad
    if(quadsToDraw > 0)
    {
        // 畫剩下的四邊形
        glDrawElements(GL_TRIANGLES, (GLsizei) quadsToDraw*6, GL_UNSIGNED_SHORT, (GLvoid*) (startQuad*6*sizeof(_indices[0])) );
        _drawnBatches++;
        _drawnVertices += quadsToDraw*6;
    }

    if (Configuration::getInstance()->supportsShareableVAO())
    {
        //Unbind VAO 接除綁定VAO
        GL::bindVAO(0);
    }
    else
    {
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    }

    _batchedQuadCommands.clear();
    _numQuads = 0;
}

 

附注:5種渲染類型:

1. QUAD_COMMAND：QuadCommand類繪制精靈等。所有繪制圖片的命令都會調用到這里，處理這個類型命令的代碼就是繪制貼圖的openGL代碼。
2. CUSTOM_COMMAND：CustomCommand類自定義繪制，自己定義繪制函數，在調用繪制時只需調用已經傳進來的回調函數就可以，裁剪節點，繪制圖形節點都采用這個繪制，把繪制函數定義在自己的類里。這種類型的繪制命令不會在處理命令的時候調用任何一句openGL代碼，而是調用你寫好並設置給func的繪制函數。
3. BATCH_COMMAND：BatchCommand類批處理繪制，批處理精靈和粒子,其實它類似於自定義繪制，也不會再render函數中出現任何一句openGL函數。
4. GROUP_COMMAND：GroupCommand類繪制組，一個節點包括兩個以上繪制命令的時候，把這個繪制命令存儲到另外一個_renderGroups中的元素中，並把這個元素的指針作為一個節點存儲到_renderGroups[0]中。

5. MESH_COMMAND :