Cocos2dx 源码分析之一: 起步(Application)

工作需要开发一个简单的2D图形引擎，目前最火的就属cocos2d-x引擎了，开源、跨平台、社区丰富。虽然是游戏引擎，但想来应该有很多可以学习借鉴的地方。所以打算通过源码分析学习一下这个优秀的引擎架构。

环境搭建

HelloWorld

main函数

  #include "AppDelegate.h"
  #include "cocos2d.h"
  USING_NS_CC;
  int main(int argc, char *argv[])
  {
      AppDelegate app;
      return Application::getInstance()->run();
  }

main函数很简单: 1)实例化AppDelegate, 运行Application::getInstance()->run()。可以发现AppDelegate同样继承自Application，Application继承自ApplicationProtocol类，所以先研究ApplicationProtocol类。

  class CC_DLL ApplicationProtocol
  {
  public:

      // Since WINDOWS and ANDROID are defined as macros, we could not just use these keywords in enumeration(Platform).
      // Therefore, 'OS_' prefix is added to avoid conflicts with the definitions of system macros.
      enum class Platform
      {
          OS_WINDOWS,
          OS_LINUX,
          OS_MAC,
          OS_ANDROID,
          OS_IPHONE,
          OS_IPAD,
          OS_BLACKBERRY,
          OS_NACL,
          OS_EMSCRIPTEN,
          OS_TIZEN,
          OS_WINRT,
          OS_WP8
      };

      virtual ~ApplicationProtocol(){
  #if CC_ENABLE_SCRIPT_BINDING
          ScriptEngineManager::destroyInstance();
  #endif
          PoolManager::destroyInstance();
      }

      virtual bool applicationDidFinishLaunching() = 0;
      virtual void applicationDidEnterBackground() = 0;
      virtual void applicationWillEnterForeground() = 0;
      virtual void setAnimationInterval(double interval) = 0;
      virtual void initGLContextAttrs() {}
      virtual LanguageType getCurrentLanguage() = 0;
      virtual const char * getCurrentLanguageCode() = 0;
      virtual Platform getTargetPlatform() = 0;
      virtual bool openURL(const std::string &url) = 0;
  };

可以看到，ApplicationProtocol是一个抽象类，定义了一个App基本的接口，同时有一个平台类型的枚举enum class Platform，然后各个平台再继承该类来实现自己平台的Application类。例如Mac平台的Application类的声明包含在#if CC_TARGET_PLATFORM == CC_PLATFORM_MAC ... #endif之间。

Application类

  int Application::run()
  {
      initGLContextAttrs();
      if(!applicationDidFinishLaunching())
      {
          return 1;
      }
        
      long lastTime = 0L;
      long curTime = 0L;
        
      auto director = Director::getInstance();
      auto glview = director->getOpenGLView();
        
      // Retain glview to avoid glview being released in the while loop
      glview->retain();
        
      while (!glview->windowShouldClose())
      {
          lastTime = getCurrentMillSecond();
            
          director->mainLoop();
          glview->pollEvents();

          curTime = getCurrentMillSecond();
          if (curTime - lastTime < _animationInterval)
          {
              usleep(static_cast<useconds_t>((_animationInterval - curTime + lastTime)*1000));
          }
      }

      /* Only work on Desktop
      *  Director::mainLoop is really one frame logic
      *  when we want to close the window, we should call Director::end();
      *  then call Director::mainLoop to do release of internal resources
      */
      if (glview->isOpenGLReady())
      {
          director->end();
          director->mainLoop();
      }
        
      glview->release();
        
      return 0;
  }

看看applicationDidFinishLaunching函数里

bool AppDelegate::applicationDidFinishLaunching() {
    // initialize director
    auto director = Director::getInstance();
    auto glview = director->getOpenGLView();
    if(!glview) {
        glview = GLViewImpl::create("My Game");
        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
    auto scene = HelloWorld::createScene();

    // run
    director->runWithScene(scene);

    return true;
}

每个项目都要有一个自己的App类继承自相应平台的Application调用Application::run方法来实现程序的启动。

Contents

环境搭建

HelloWorld