Cocos2d-x 截图功能

（1）Cocos2d-x 2.x

Cocos2d-x 2.x没有提供截图功能，但是可以用CCRenderTexture来实现这个功能：

void CTestLayer::SaveScreenShot()
  {
      //获取屏幕尺寸  
      CCSize size = CCDirector::sharedDirector()->getWinSize();
      //使用屏幕尺寸初始化一个空的渲染纹理对象  
      CCRenderTexture* texture = CCRenderTexture::create((int)size.width, (int)size.height);
      //设置位置      
      texture->setPosition(ccp(size.width/2, size.height/2));
      //开始获取      
      texture->begin();
      //遍历场景节点对象，填充纹理到texure中  
      CCDirector::sharedDirector()->getRunningScene()->visit();
      //结束获取  
      texture->end();
      //保存为PNG图，Win32/Debug目录下  
      texture->saveToFile("screenshot.png", kCCImageFormatPNG);
  }

（2）Cocos2d-x 3.x

在Cocos2d-x 3.2之前，引擎也没有提供截图功能，同样可以使用RenderTexture实现：

void Director::saveScreenshot(const std::string& fileName,const std::function<void(const std::string&)>& callback)
  {
      Image::Format format;
      //进行后缀判断  
      if(std::string::npos != fileName.find_last_of(".")){
        auto extension = fileName.substr(fileName.find_last_of("."),fileName.length());
        if (!extension.compare(".png")) {
            format = Image::Format::PNG;
        } else if(!extension.compare(".jpg")) {
            format = Image::Format::JPG;
        } else{
            log("cocos2d: the image can only be saved as JPG or PNG format");
            return;
        }
    } else {
        log("cocos2d: the image can only be saved as JPG or PNG format");
        return ;
    }
    //获取屏幕尺寸，初始化一个空的渲染纹理对象  
      auto renderTexture = RenderTexture::create(getWinSize().width, getWinSize().height, Texture2D::PixelFormat::RGBA8888);
      //清空并开始获取  
      renderTexture->beginWithClear(0.0f, 0.0f, 0.0f, 0.0f);
      //遍历场景节点对象，填充纹理到RenderTexture中  
      getRunningScene()->visit();
      //结束获取  
      renderTexture->end();
      //保存文件  
      renderTexture->saveToFile(fileName , format);
      //使用schedule在下一帧中调用callback函数  
      auto fullPath = FileUtils::getInstance()->getWritablePath() + fileName;
      auto scheduleCallback = [&,fullPath,callback](float dt){
          callback(fullPath);
      };
      auto _schedule = getRunningScene()->getScheduler();
      _schedule->schedule(scheduleCallback, this, 0.0f,0,0.0f, false, "screenshot");
  }

（3）从Cocos2d-x 3.2之后开始，引擎提供了captureScreen函数来实现截图功能：

void Util::captureScreen(const std::function<void(bool, const std::string&)>& afterCaptured, const std::string& filename);