Cocos2d-x 截屏功能集成

1.集成到Director
这里选择把截屏功能继承到Director中，让全局的导演来执行截屏功能是一个很好的主意。

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{  
            CCLOG("cocos2d: the image can only be saved as JPG or PNG format");  
            return;  
        }  
    } else {  
        CCLOG("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");  
}  

2.如何使用saveScreenshot
截屏功能使用起来也很简单，直接调用saveSecreenshot，其中第一个参数为文件名（支持png和jpg格式，不带后缀名默认为png格式），第二个参数为回调函数，你可以在回调函数中处理这个文件。

void ScreenshotTest::saveImage(Ref *pSender){  
    static int counter = 0;  
       
    char png[20];  
    sprintf(png, "image-%d.png", counter);  
    char jpg[20];  
    sprintf(jpg, "image-%d.jpg", counter);  
       
   //截屏后的回调函数，这里显示在左下角  
    auto callback = [&](const std::string& fullPath){  
        auto sprite = Sprite::create(fullPath);  
        CCASSERT(sprite!=nullptr, "Failed to create sprite.");  
        addChild(sprite);  
        sprite->setScale(0.3f);  
        sprite->setPosition(Point(40, 40));  
        sprite->setRotation(counter * 3);  
        CCLOG("Image saved %s", fullPath.c_str());  
    };  
       
   //调用Director的截屏功能  
    Director::getInstance()->saveScreenshot(png, callback);  
    counter++;  
}