cocos-2dx OPENGL渲染（1）

cocos-2dx v3.5 ,windows的opengl初始化：

0. main.cpp中会直接调用Application::getInstance()->run()，

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

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

    QueryPerformanceCounter(&nLast);
    //1-opengl像素格式等参数初始化
    initGLContextAttrs();

   //2-cocos初始化
    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 - (nNow.QuadPart % _animationInterval.QuadPart);
            
            director->mainLoop();
            glview->pollEvents();
        }
        else
        {
            Sleep(1);
        }
    }

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

1.下面初始化了opgl所使用的rgba所要使用的位数以及depthBit，stencilBits

void AppDelegate::initGLContextAttrs()
{
    GLContextAttrs glContextAttrs = {8, 8, 8, 8, 24, 8};

    GLView::setGLContextAttrs(glContextAttrs);
}

2.cocos程序初始化入口：

bool AppDelegate::applicationDidFinishLaunching()

 auto director = Director::getInstance();
    auto glview = director->getOpenGLView();
    if(!glview) {
        glview = GLViewImpl::create("Cpp Empty Test");
        director->setOpenGLView(glview);
    }

3.create  opgl窗口

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


    return nullptr;
}

4.默认使用640，960的矩形创建窗口，下面会对窗口初始化参数值，像素格式是OpenGL窗口的重要属性，它包括是否使用双缓冲，颜色位数和类型以及深度位数等。

bool GLViewImpl::initWithRect(const std::string& viewName, Rect rect, float frameZoomFactor)
{
    setViewName(viewName);

    _frameZoomFactor = frameZoomFactor;

     //windows像素格式

   lfwWindowHint(GLFW_RESIZABLE,GL_FALSE); //不可改变窗口大小
    glfwWindowHint(GLFW_RED_BITS,_glContextAttrs.redBits); //1中初始化的参数传入
    glfwWindowHint(GLFW_GREEN_BITS,_glContextAttrs.greenBits);
    glfwWindowHint(GLFW_BLUE_BITS,_glContextAttrs.blueBits);
    glfwWindowHint(GLFW_ALPHA_BITS,_glContextAttrs.alphaBits);
    glfwWindowHint(GLFW_DEPTH_BITS,_glContextAttrs.depthBits);
    glfwWindowHint(GLFW_STENCIL_BITS,_glContextAttrs.stencilBits);

    //windows窗口创建

    _mainWindow = glfwCreateWindow(rect.size.width * _frameZoomFactor,
                                   rect.size.height * _frameZoomFactor,
                                   _viewName.c_str(),
                                   _monitor,
                                   nullptr);
    glfwMakeContextCurrent(_mainWindow);//make当前windows线程的上下文context

    glfwSetMouseButtonCallback(_mainWindow, GLFWEventHandler::onGLFWMouseCallBack);
    glfwSetCursorPosCallback(_mainWindow, GLFWEventHandler::onGLFWMouseMoveCallBack);
    glfwSetScrollCallback(_mainWindow, GLFWEventHandler::onGLFWMouseScrollCallback);
    glfwSetCharCallback(_mainWindow, GLFWEventHandler::onGLFWCharCallback);
    glfwSetKeyCallback(_mainWindow, GLFWEventHandler::onGLFWKeyCallback);
    glfwSetWindowPosCallback(_mainWindow, GLFWEventHandler::onGLFWWindowPosCallback);
    glfwSetFramebufferSizeCallback(_mainWindow, GLFWEventHandler::onGLFWframebuffersize);
    glfwSetWindowSizeCallback(_mainWindow, GLFWEventHandler::onGLFWWindowSizeFunCallback);
    glfwSetWindowIconifyCallback(_mainWindow, GLFWEventHandler::onGLFWWindowIconifyCallback);

    setFrameSize(rect.size.width, rect.size.height);

   // OPENGL版本检查
    const GLubyte* glVersion = glGetString(GL_VERSION);

    if ( utils::atof((const char*)glVersion) < 1.5 )
    {
        char strComplain[256] = {0};
        sprintf(strComplain,
                "OpenGL 1.5 or higher is required (your version is %s). Please upgrade the driver of your video card.",
                glVersion);
        MessageBox(strComplain, "OpenGL version too old");
        return false;
    }
    

    //初始化GLEW,GLEW（OpenGL Extension Wrangler Library）是一个跨平台的C/C++库，用来查询和加载OpenGL扩展
    initGlew();

    // Enable point size by default.
    glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);

    return true;
}

5.判断GLEW是否初始化成功

bool GLViewImpl::initGlew()
{
#if (CC_TARGET_PLATFORM != CC_PLATFORM_MAC)
    GLenum GlewInitResult = glewInit();//初始化结果
    if (GLEW_OK != GlewInitResult)
    {
        MessageBox((char *)glewGetErrorString(GlewInitResult), "OpenGL error");
        return false;
    }

    if (GLEW_ARB_vertex_shader && GLEW_ARB_fragment_shader)
    {
        log("Ready for GLSL");
    }
    else
    {
        log("Not totally ready :(");
    }

    if (glewIsSupported("GL_VERSION_2_0"))
    {
        log("Ready for OpenGL 2.0");
    }
    else
    {
        log("OpenGL 2.0 not supported");
    }

#if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32)

    if(glew_dynamic_binding() == false)//启用帧缓冲对象
    {
        MessageBox("No OpenGL framebuffer support. Please upgrade the driver of your video card.", "OpenGL error");
        return false;
    }
#endif

#endif // (CC_TARGET_PLATFORM != CC_PLATFORM_MAC)

    return true;
}

通过上面的过程，cocos-2dx的opengl初始化过程就搞定了。通过initGLContextAttrs 设置opengl像素格式，

在applicationDidFinishLaunching中create opengl窗口，创建过程中，将先前设定的像素格式传入，然后根据参数创建默认大小为（960，640）的窗口。

不同平台上面，OpenGL的初始化流程不完全一样。详细的区别可以查看平台相关的CCGLViewImpl-平台（如CCGLViewImpl-android） 类，

cocos2d-x-3.5\cocos\platform\下

接下来就是游戏过程了（见下一章）
正在学习cocos-2dx 关于opengl渲染相关的东西，这里就抛砖引玉了。