Cocos2d-lua的运行理解

关键词：cocos2d-lua项目启动流程lua调用cocos2d引擎API这里是个小测试环境引擎版本:Cocos2d-x 3.10开发工具:Xcode8.1简述所谓的Cocos2d-lua，其实只是Cocos2d引擎添加了Lua绑定的版本。从创建命令可以看出来 cocos new TestProj -d Desktop/ -l lua，这里的引...

游鱼_

305人浏览 · 2018-12-11 17:02:17

游鱼_ · 2018-12-11 17:02:17 发布

关键词：
cocos2d-lua项目启动流程
lua调用cocos2d引擎API

这里是个小测试

环境

引擎版本:Cocos2d-x 3.10
开发工具:Xcode8.1

简述

所谓的Cocos2d-lua，其实只是Cocos2d引擎添加了Lua绑定的版本。

从创建命令可以看出来 cocos new TestProj -d Desktop/ -l lua，这里的引擎其实是同一套，只是创建工程时提供了不同语言的桥接层
使用C++语言和Cocos2d-x引擎进行开发时，我们写的代码是直接调用引擎的API的，因为引擎也是用C++语言编写，不需要进行语言转换
使用Lua语言和Cocos2d-x引擎进行开发时，我们写的代码通过LuaEngine执行，而LuaEngine封装了Cocos2d-x引擎的API，所以就相当于使用Lua脚本在调用Cocos2d-x的API了

C++项目和Lua项目的开始过程

简单来比较一下C++项目和Lua项目开始的过程（后面会专门写一下启动流程），这里我们都从AppDelegate.cpp的
AppDelegate::applicationDidFinishLaunching()
函数开始。

C++项目

先贴一下代码咯

bool AppDelegate::applicationDidFinishLaunching() {
    // initialize director
    auto director = Director::getInstance();    //初始化Director
    auto glview = director->getOpenGLView();    //获得GLView，也就是游戏窗口
</span><span class="hljs-comment"><span class="com">//此时GLView为空</span></span><span class="pln">
</span><span class="hljs-built_in"><span class="kwd">if</span></span><span class="pun">(!</span><span class="pln">glview</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">

#if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32) || (CC_TARGET_PLATFORM == CC_PLATFORM_MAC) || (CC_TARGET_PLATFORM == CC_PLATFORM_LINUX)
//如果当前是以上平台，就创建一个大小为designResolutionSize的窗口
glview = GLViewImpl::createWithRect(“TestCpp”, Rect(0, 0, designResolutionSize.width, designResolutionSize.height));
#else
//其他平台，则使用默认设置（在ios上是全屏窗口，其他平台不太清楚，也有可能是默认设置了一个窗口大小）
glview = GLViewImpl::create(“TestCpp”);
#endif
director->setOpenGLView(glview); //director获得当前新建的窗口
}

</span><span class="hljs-comment"><span class="com">// turn on display FPS</span></span><span class="pln">
director</span><span class="pun">-&gt;</span><span class="pln">setDisplayStats</span><span class="pun">(</span><span class="kwd">true</span><span class="pun">);</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//显示帧率信息</span></span><span class="pln">

</span><span class="hljs-comment"><span class="com">// set FPS. the default value is 1.0/60 if you don't call this</span></span><span class="pln">
director</span><span class="pun">-&gt;</span><span class="pln">setAnimationInterval</span><span class="pun">(</span><span class="hljs-number"><span class="lit">1.0</span></span><span class="pln"> </span><span class="pun">/</span><span class="pln"> </span><span class="hljs-number"><span class="lit">60</span></span><span class="pun">);</span><span class="pln">   </span><span class="hljs-comment"><span class="com">//设置动画帧率，也就是界面刷新帧率咯</span></span><span class="pln">

</span><span class="hljs-comment"><span class="com">// Set the design resolution</span></span><span class="pln">
glview</span><span class="pun">-&gt;</span><span class="pln">setDesignResolutionSize</span><span class="pun">(</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">,</span><span class="pln"> designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">,</span><span class="pln"> </span><span class="typ">ResolutionPolicy</span><span class="pun">::</span><span class="pln">NO_BORDER</span><span class="pun">);</span><span class="pln">  </span><span class="hljs-comment"><span class="com">//设置设计分辨率，而不是实际分辨率，这里是为了适配，不能把实际分辨率固定</span></span><span class="pln">

</span><span class="typ">Size</span><span class="pln"> frameSize </span><span class="pun">=</span><span class="pln"> glview</span><span class="pun">-&gt;</span><span class="pln">getFrameSize</span><span class="pun">();</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//获得实际窗口大小</span></span><span class="pln">

</span><span class="hljs-comment"><span class="com">//根据实际窗口大小，设置内容缩放比例</span></span><span class="pln">
</span><span class="hljs-comment"><span class="com">// if the frame's height is larger than the height of medium size.</span></span><span class="pln">
</span><span class="hljs-built_in"><span class="kwd">if</span></span><span class="pln"> </span><span class="pun">(</span><span class="pln">frameSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pln"> </span><span class="pun">&gt;</span><span class="pln"> mediumResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">)</span><span class="pln">
</span><span class="pun">{</span><span class="pln">        
    director</span><span class="pun">-&gt;</span><span class="pln">setContentScaleFactor</span><span class="pun">(</span><span class="pln">MIN</span><span class="pun">(</span><span class="pln">largeResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">,</span><span class="pln"> largeResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">));</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="hljs-comment"><span class="com">// if the frame's height is larger than the height of small size.</span></span><span class="pln">
</span><span class="hljs-built_in"><span class="kwd">else</span></span><span class="pln"> </span><span class="hljs-built_in"><span class="kwd">if</span></span><span class="pln"> </span><span class="pun">(</span><span class="pln">frameSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pln"> </span><span class="pun">&gt;</span><span class="pln"> smallResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">)</span><span class="pln">
</span><span class="pun">{</span><span class="pln">        
    director</span><span class="pun">-&gt;</span><span class="pln">setContentScaleFactor</span><span class="pun">(</span><span class="pln">MIN</span><span class="pun">(</span><span class="pln">mediumResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">,</span><span class="pln"> mediumResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">));</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="hljs-comment"><span class="com">// if the frame's height is smaller than the height of medium size.</span></span><span class="pln">
</span><span class="hljs-built_in"><span class="kwd">else</span></span><span class="pln">
</span><span class="pun">{</span><span class="pln">        
    director</span><span class="pun">-&gt;</span><span class="pln">setContentScaleFactor</span><span class="pun">(</span><span class="pln">MIN</span><span class="pun">(</span><span class="pln">smallResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">height</span></span><span class="pun">,</span><span class="pln"> smallResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">/</span><span class="pln">designResolutionSize</span><span class="pun">.</span><span class="hljs-built_in"><span class="pln">width</span></span><span class="pun">));</span><span class="pln">
</span><span class="pun">}</span><span class="pln">

register_all_packages</span><span class="pun">();</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//使用包管理器。。 不太清楚这里是为什么</span></span><span class="pln">

</span><span class="hljs-comment"><span class="com">// create a scene. it's an autorelease object</span></span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">auto</span></span><span class="pln"> scene </span><span class="pun">=</span><span class="pln"> </span><span class="typ">HelloWorld</span><span class="pun">::</span><span class="pln">createScene</span><span class="pun">();</span><span class="pln"> </span><span class="hljs-comment"><span class="com">//新建一个场景</span></span><span class="pln">

</span><span class="hljs-comment"><span class="com">// run</span></span><span class="pln">
director</span><span class="pun">-&gt;</span><span class="pln">runWithScene</span><span class="pun">(</span><span class="pln">scene</span><span class="pun">);</span><span class="pln">  </span><span class="hljs-comment"><span class="com">//从这个场景开始运行,开始绘制、子节点管理等</span></span><span class="pln">

</span><span class="hljs-built_in"><span class="kwd">return</span></span><span class="pln"> </span><span class="kwd">true</span><span class="pun">;</span><span class="pln">

}

这段代码是Cocos2d-x 3.10版本新建的C++语言工程中AppDelegate.cpp文件中拷出来的，加了一些注释。
从这里我们可以看出进入游戏逻辑的流程：

初始化Director
新建GLView，然后进行一些设置
新建Scene
使用Director运行这个场景

游戏逻辑就可以从这个Scene中的init函数开始，添加UI层，添加事件监听器，添加游戏层等等…如果我们有一些统计、资源管理器等，也可以在AppDelegate的applicationDidFinishLaunching函数中来进行。

Lua项目

也来看AppDelegate.cpp中的applicationDidFinishLaunching函数

bool AppDelegate::applicationDidFinishLaunching()
{
    // set default FPS
    Director::getInstance()->setAnimationInterval(1.0 / 60.0f);     //设置动画帧率，也就是游戏帧率了
</span><span class="hljs-comment"><span class="com">//重点：添加Lua相关支持</span></span><span class="pln">
</span><span class="hljs-comment"><span class="com">// register lua module</span></span><span class="pln">
</span><span class="kwd">auto</span><span class="pln"> engine </span><span class="pun">=</span><span class="pln"> </span><span class="typ">LuaEngine</span><span class="pun">::</span><span class="pln">getInstance</span><span class="pun">();</span><span class="pln">     </span><span class="hljs-comment"><span class="com">//初始化一个Lua语言引擎</span></span><span class="pln">
</span><span class="typ">ScriptEngineManager</span><span class="pun">::</span><span class="pln">getInstance</span><span class="pun">()-&gt;</span><span class="pln">setScriptEngine</span><span class="pun">(</span><span class="pln">engine</span><span class="pun">);</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//将Lua语言引擎设置为当前脚本引擎（用脚本引擎管理器来管理各种脚本引擎）</span></span><span class="pln">
lua_State</span><span class="pun">*</span><span class="pln"> L </span><span class="pun">=</span><span class="pln"> engine</span><span class="pun">-&gt;</span><span class="pln">getLuaStack</span><span class="pun">()-&gt;</span><span class="pln">getLuaState</span><span class="pun">();</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//获取Lua引擎的State，也就是一组属性</span></span><span class="pln">
lua_module_register</span><span class="pun">(</span><span class="pln">L</span><span class="pun">);</span><span class="pln"> </span><span class="hljs-comment"><span class="com">//向Lua引擎注册一些模块，如网络、动画等</span></span><span class="pln">

register_all_packages</span><span class="pun">();</span><span class="pln">

</span><span class="hljs-comment"><span class="com">//设置脚本加密相关的key和sign</span></span><span class="pln">
</span><span class="typ">LuaStack</span><span class="pun">*</span><span class="pln"> stack </span><span class="pun">=</span><span class="pln"> engine</span><span class="pun">-&gt;</span><span class="pln">getLuaStack</span><span class="pun">();</span><span class="pln">
stack</span><span class="pun">-&gt;</span><span class="pln">setXXTEAKeyAndSign</span><span class="pun">(</span><span class="hljs-string"><span class="str">"2dxLua"</span></span><span class="pun">,</span><span class="pln"> strlen</span><span class="pun">(</span><span class="hljs-string"><span class="str">"2dxLua"</span></span><span class="pun">),</span><span class="pln"> </span><span class="hljs-string"><span class="str">"XXTEA"</span></span><span class="pun">,</span><span class="pln"> strlen</span><span class="pun">(</span><span class="hljs-string"><span class="str">"XXTEA"</span></span><span class="pun">));</span><span class="pln">

</span><span class="hljs-comment"><span class="com">//register custom function</span></span><span class="pln">
</span><span class="hljs-comment"><span class="com">//LuaStack* stack = engine-&gt;getLuaStack();</span></span><span class="pln">
</span><span class="hljs-comment"><span class="com">//register_custom_function(stack-&gt;getLuaState());</span></span><span class="pln">

#if (COCOS2D_DEBUG > 0) && (CC_CODE_IDE_DEBUG_SUPPORT > 0)
//如果需要支持CodeIDE，则从引擎本身启动
// NOTE:Please don’t remove this call if you want to debug with Cocos Code IDE
auto runtimeEngine = RuntimeEngine::getInstance();
runtimeEngine->addRuntime(RuntimeLuaImpl::create(), kRuntimeEngineLua);
runtimeEngine->start();
#else
//一般情况，这里使用Lua引擎执行第一个Lua脚本
if (engine->executeScriptFile(“src/main.lua”))
{
return false; //脚本默认返回nil，如果脚本执行正常，不会进入这一句
}
#endif

</span><span class="hljs-keyword"><span class="kwd">return</span></span><span class="pln"> </span><span class="hljs-keyword"><span class="kwd">true</span></span><span class="pun">;</span><span class="pln">    </span><span class="hljs-comment"><span class="com">//正常执行到这里，后面就开始执行Cocos引擎提供的主循环</span></span><span class="pln">

}

从上面代码可以看到，Cocos2d-x新建的Lua语言项目中，这里没有进行GLView的设置，没有使用C++代码来创建Scene，所以这些操作肯定和”src/main.lua”脚本有关。这里我们一步一步来看src目录下这些脚本执行的步骤（注意看注释的序号）：

在main.lua中部分注释：

cc.FileUtils:getInstance():setPopupNotify(false)
cc.FileUtils:getInstance():addSearchPath("src/")
cc.FileUtils:getInstance():addSearchPath("res/")

require “config” – 1.执行当前目录下的config.lua,定义一些初始化用的全局变量，包括窗口设置等
require “cocos.init” – 2.执行cocos/init.lua,初始化框架等一大堆东西，包括OpenGL、音效等引擎的初始化与配置

local function main()
require(“app.MyApp”):create():run() – 3.执行app/MyApp.lua，调用对应class的Create方法创建对象，并执行run方法
end
– 先忽略这个，我也不知道是啥
local status, msg = xpcall(main, G__TRACKBACK)
if not status then
print(msg)
end

2.去app/MyApp.lua看看require做了什么：

local MyApp = class("MyApp", cc.load("mvc").AppBase)    -- 4.类MyApp继承自mvc中的AppBase类，自动找到packages/mvc/AppBase.lua
function MyApp:onCreate()
    math.randomseed(os.time())
end
return MyApp

3.继续去packages/AppBase.lua里看看生成MyApp的时候做了什么：

local AppBase = class("AppBase")

– 5.构造函数
function AppBase:ctor(configs)
self.configs_ = {
viewsRoot = “app.views”,
modelsRoot = “app.models”,
defaultSceneName = “MainScene”,
}

</span><span class="hljs-keyword"><span class="kwd">for</span></span><span class="pln"> k</span><span class="pun">,</span><span class="pln"> v </span><span class="kwd">in</span><span class="pln"> pairs</span><span class="pun">(</span><span class="pln">configs </span><span class="hljs-literal"><span class="kwd">or</span></span><span class="pln"> </span><span class="pun">{})</span><span class="pln"> </span><span class="kwd">do</span><span class="pln">
    </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">[</span><span class="pln">k</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> v
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> type</span><span class="pun">(</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">viewsRoot</span><span class="pun">)</span><span class="pln"> </span><span class="pun">~=</span><span class="pln"> </span><span class="hljs-string"><span class="str">"table"</span></span><span class="pln"> </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">viewsRoot </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">viewsRoot</span><span class="pun">}</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> type</span><span class="pun">(</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">modelsRoot</span><span class="pun">)</span><span class="pln"> </span><span class="pun">~=</span><span class="pln"> </span><span class="hljs-string"><span class="str">"table"</span></span><span class="pln"> </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">modelsRoot </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">.</span><span class="pln">modelsRoot</span><span class="pun">}</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> DEBUG </span><span class="pun">&gt;</span><span class="pln"> </span><span class="hljs-number"><span class="lit">1</span></span><span class="pln"> </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    </span><span class="kwd">dump</span><span class="pun">(</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">configs_</span><span class="pun">,</span><span class="pln"> </span><span class="hljs-string"><span class="str">"AppBase configs"</span></span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> CC_SHOW_FPS </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    cc</span><span class="pun">.</span><span class="typ">Director</span><span class="pun">:</span><span class="pln">getInstance</span><span class="pun">():</span><span class="pln">setDisplayStats</span><span class="pun">(</span><span class="hljs-literal"><span class="kwd">true</span></span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="pun">--</span><span class="pln"> </span><span class="kwd">event</span><span class="pln">
</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">:</span><span class="pln">onCreate</span><span class="pun">()</span><span class="pln"> </span><span class="pun">--</span><span class="pln"> </span><span class="hljs-number"><span class="lit">6</span></span><span class="lit">.</span><span class="pun">啥也没做的</span><span class="pln">create</span><span class="pun">函数</span><span class="pln">

end

4.我们可以看回第1步（注释编号3）中，生成MyApp对象后，执行了run方法，那就看看AppBase.lua中的run方法做了什么：

-- 7.创建完对象之后，就到了这一步
function AppBase:run(initSceneName)
    initSceneName = initSceneName or self.configs_.defaultSceneName
    self:enterScene(initSceneName)  -- 8.如果没有指定第一个Scene，则第一个Scene为MainScene
end
-- 9.生成并进入第一个Scene
function AppBase:enterScene(sceneName, transition, time, more)
    local view = self:createView(sceneName)     -- 10.前去生成View
    view:showWithScene(transition, time, more)  -- 20.因为MainScene继承自ViewBase类，这里就吊用ViewBase的方法了
    return view
end

5.这里（注释编号10）看到会调用到AppBase.lua中的createView方法：

-- 11.根据name生成一个View
function AppBase:createView(name)
    for _, root in ipairs(self.configs_.viewsRoot) do
        local packageName = string.format("%s.%s", root, name)  -- 12.这里拼接了View的路径，app/views/MainScene.lua
        local status, view = xpcall(function()  -- 13.这里xpcall相当于try-catch结构了，所以看第一个function
                return require(packageName) -- 14.执行上面拼接的MainScene.lua脚本，view获得脚本返回值
            end, function(msg)
            if not string.find(msg, string.format("'%s' not found:", packageName)) then
                print("load view error: ", msg)
            end
        end)
        local t = type(view)
        if status and (t == "table" or t == "userdata") then
            return view:create(self, name)  -- 15.这里调用了MainScene的create方法噢
        end
    end
    error(string.format("AppBase:createView() - not found view \"%s\" in search paths \"%s\"",
        name, table.concat(self.configs_.viewsRoot, ",")), 0)
end

6.上面的函数中执行到了app/views/MainScene.lua脚本，那就去看看做了什么：

local MainScene = class("MainScene", cc.load("mvc").ViewBase)    -- 16.MainScene类继承自ViewBase，去mvc/ViewBase.lua看看

– 19.创建一个Sprite，一个Label，添加到这个Node中
function MainScene:onCreate()
– add background image
display.newSprite(“HelloWorld.png”)
:move(display.center)
:addTo(self)

</span><span class="pun">--</span><span class="pln"> </span><span class="hljs-built_in"><span class="pln">add</span></span><span class="pln"> </span><span class="typ">HelloWorld</span><span class="pln"> label
</span><span class="hljs-keyword"><span class="pln">cc</span></span><span class="pun">.</span><span class="typ">Labe</span><span class="hljs-variable"><span class="typ">l</span><span class="pun">:</span><span class="pln">createWithSystemFont</span></span><span class="pun">(</span><span class="hljs-string"><span class="str">"Hello World"</span></span><span class="pun">,</span><span class="pln"> </span><span class="hljs-string"><span class="str">"Arial"</span></span><span class="pun">,</span><span class="pln"> </span><span class="hljs-number"><span class="lit">40</span></span><span class="pun">)</span><span class="pln">
    </span><span class="pun">:</span><span class="hljs-keyword"><span class="pln">move</span></span><span class="pun">(</span><span class="hljs-keyword"><span class="pln">display</span></span><span class="pun">.</span><span class="pln">cx</span><span class="pun">,</span><span class="pln"> </span><span class="hljs-keyword"><span class="pln">display</span></span><span class="pun">.</span><span class="pln">cy </span><span class="pun">+</span><span class="pln"> </span><span class="hljs-number"><span class="lit">200</span></span><span class="pun">)</span><span class="pln">
    </span><span class="pun">:</span><span class="pln">addTo</span><span class="pun">(</span><span class="kwd">self</span><span class="pun">)</span><span class="pln">

end

return MainScene

7.上面第一行代码（注释编号16）可以看到，MainScene类继承自ViewBase，那进入mvc/ViewBase.lua看看

local ViewBase = class("ViewBase", cc.Node) -- 17.继承自Node噢

– 18.构造函数，还是进行一些初始化工作
function ViewBase:ctor(app, name)
self:enableNodeEvents()
self.app_ = app
self.name_ = name

</span><span class="pun">--</span><span class="pln"> check CSB resource file
</span><span class="hljs-keyword"><span class="kwd">local</span></span><span class="pln"> res </span><span class="pun">=</span><span class="pln"> rawget</span><span class="pun">(</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="kwd">class</span><span class="pun">,</span><span class="pln"> </span><span class="hljs-string"><span class="str">"RESOURCE_FILENAME"</span></span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> res </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">:</span><span class="pln">createResoueceNode</span><span class="pun">(</span><span class="pln">res</span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="hljs-keyword"><span class="kwd">local</span></span><span class="pln"> binding </span><span class="pun">=</span><span class="pln"> rawget</span><span class="pun">(</span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="kwd">class</span><span class="pun">,</span><span class="pln"> </span><span class="hljs-string"><span class="str">"RESOURCE_BINDING"</span></span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> res </span><span class="hljs-literal"><span class="kwd">and</span></span><span class="pln"> binding </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln">
    </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">:</span><span class="pln">createResoueceBinding</span><span class="pun">(</span><span class="pln">binding</span><span class="pun">)</span><span class="pln">
</span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

</span><span class="hljs-keyword"><span class="kwd">if</span></span><span class="pln"> </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">.</span><span class="pln">onCreate </span><span class="hljs-keyword"><span class="kwd">then</span></span><span class="pln"> </span><span class="hljs-built_in"><span class="kwd">self</span></span><span class="pun">:</span><span class="pln">onCreate</span><span class="pun">()</span><span class="pln"> </span><span class="hljs-keyword"><span class="kwd">end</span></span><span class="pln">

end

8.这里可以回看到第4步（注释编号10），方法createView执行完成后，生成了一个MainScene对象（继承自ViewBase（继承自ccNode）），然后下一步就是调用MainScene对象的showWithScene函数，在packages/mvc/ViewBase.lua中：

-- 21.这里创建了一个Scene，并且把当前这个Node添加到Scene中。其实这就是C++项目HelloWorldScene类的createScene方法了
function ViewBase:showWithScene(transition, time, more)
    self:setVisible(true)
    local scene = display.newScene(self.name_)  -- 22.display包含很多功能，有点类似于Director了
    scene:addChild(self)
    display.runScene(scene, transition, time, more) -- 23.runScene熟悉的方法
    return self
end

到这里，对于Cocos2d-x引擎生成的C++和Lua语言项目，我们都分析到了生成第一个Scene的步骤，后面就可以开始写UI、写结构、写逻辑等内容了。

简单对比Cocos2d-x创建的C++工程和Lua工程

这里使用Cocos2d-x 3.10分别创建了Lua语言工程和C++语言工程，在Xcode下打开两个项目，可以对比一下项目结构：

1497403851-3622-2262310-aa24e8c1b97c5069

compare.png

从最外层结构可以看出Lua工程比C++工程多了两个lib：

libsimulator 模拟器支持
cocos2d_lua_bindings 引擎与Lua脚本的桥接层

libsimulator就先不看了，和这次主题无关，就先放一边，以后有空再来看（其实我还真没仔细看过这个东东）。

打开AppDelegate.cpp文件，看到引入的头文件：

#include "AppDelegate.h"
#include "CCLuaEngine.h"
#include "SimpleAudioEngine.h"
#include "cocos2d.h"
#include "lua_module_register.h"

#if (CC_TARGET_PLATFORM != CC_PLATFORM_LINUX)
#include “ide-support/CodeIDESupport.h”
#endif

#if (COCOS2D_DEBUG > 0) && (CC_CODE_IDE_DEBUG_SUPPORT > 0)
#include “runtime/Runtime.h”
#include “ide-support/RuntimeLuaImpl.h”
#endif

AppDelegate自己的头文件除外，第一个头文件就是CCLuaEngine.h，打开cocos2d_lua_bindings库的manual目录，我们就能看到这个类。打开CCLuaEngine.h文件，可以看到它包含了CCLuaStack.h和CCLuaValue.h，这两个文件都是C++与Lua直接交互需要用到的。继续往下看，可以看到cocos2d/LuaScriptHandlerMgr.h，打开manual下的cocos2d文件夹可以看到如下文件列表：

1497403851-6747-2262310-cfc53fd239c42d00

manual:cocos2d.png

从其中LuaOpengl.cpp中包含的代码：

1497403851-6614-2262310-edfc2aeff672fd21

LuaOpengl.png

可以看到这里在注册一个module，并绑定函数。另外一些lia_开头的文件中包含的也是这些代码。

理解一下

想想脚本执行时的情景，当执行到一个名为drawCircle的函数时，用户自己很可能并没有定义这样一个函数，那Lua引擎如何识别“drawCircle”这样一个命令，而不会把它当作错误的代码呢？
看到上面的文件我们就能知道，字符串“drawCircle”早就被注册到LuaEngine中，所以当执行脚本时遇到drawCircle时，才知道需要去调用哪一个函数。
这也就是说，cocos2d_lua_bindings库提供了Lua对Cocos2d引擎的绑定，相当于通过注册Module的方式对Cocos2d引擎提供的（相关的）API进行了一次封装（当然，如果是直接封装API，可能达不到提高开发效率的目的，所以有了quick的出现，也就是把常用的功能（例如创建一个Scene）封装成一个函数newScene）。

总结

相对于Cocos2d-x C++工程来说，Cocos2d-x生成的Lua语言工程提供了对Cocos2d引擎的Lua语言封装。将Cocos2d引擎API绑定到对应的Lua语言函数，在调用到这些函数时，会执行对应的Cocos2d引擎API。
以这个思想来看，所以能够直接或间接与C++语言进行交互的编程语言都可以用来封装Cocos2d引擎啊。。

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