Unity使用C++作为游戏逻辑脚本的研究

文章申明：本文来自JacksonDunstan的博客系列文章内容摘取和翻译，版权归其所有，附上原文的链接，大家可以有空阅读原文：C++ Scripting( in Unity)

一、C#和C++的通信

前面我的文章写过c#/c/lua是如何交互的，通过将c#的函数和属性，注册到lua虚拟机中，可以实现通过c来互相交互。

而c#和c++的交互，也是非常类似的，c#可以直接的通过P/Invoke的方式来调用c++的函数，而C++调用C#的函数，C++的函数是被封装成DLL来放在Unity的工程文件中的Plugins中，则需要基于.NET来操作，利用Marshal.GetFunctionPointerForDelegate来获取函数的指针，然后传递到c++中进行操作。

二、编辑器下实现实时的编译和脚本更新

在Unity中，我们可以在打开的Unity中，直接编译c#的文件，这样不需要每次都关闭工程再打开来执行编译，而C++由于通过DLL来调用，每次更新的C++都需要关闭工程，然后更新DLL，然后打开工程，这样的操作，对于编辑器下的开发是极其耗费的。

对于上面提到的反复开关工程执行DLL的更新，可以利用[DllImport]的属性来实现在编辑器下的更新：

该属性是基于OS的，所以不会存在跨平台的问题。

三、示例代码展示

show the code

c# code part:

using System;
using System.IO;
using System.Runtime.InteropServices;
using UnityEngine;

class TestScript:MonoBehaviour
{
#if UNITY_EDITOR
    // pointer handle to the C++ DLL
    public IntPtr libarayHandle;
    public delegate void InitDelegate(IntPtr gameObjectNew,
    IntPtr gameObjectGetTransform, IntPtr transformSetPosition);
#endif
}

#if UNITY_EDITOR_OSX || UNITY_EDITOR_LINUX
    //OSX 和Linux下的导入
    [DLLImport("__Internal")]
    public static extern IntPtr dlopen(string path, int flag);
    [DllImport("__Internal")]
    public static extern IntPtr dlsym(IntPtr handle, string symbolName);
    [DllImport("__Internal")]
    public static extern int dlclose(IntPtr handle);

    public static IntPtr OpenLibrary(string path)
    {
        IntPtr handle = dlopen(path, 0);
        if(handle == IntPtr.Zero)
        {
           throw new Exception("Couldn't open native library: "+ path);
        }
        return handle;
    }
    
    public static void CloseLibrary(IntPtr libraryHandle)
    {
         dlclose(libraryHandle);
    }
    
    public static T GetDelegate<T>(IntPtr libraryHandle, string functionName)
    where T: class
    {
         IntPtr symbol = dlsym(libraryHandle, functionName);
         if(symbol == IntPtr.Zero)
         {
            throw new Exception("Couldn't get function:" + functionName); 
         }
         return Marshal.GetDelegateForFunctionPointer(symbol, typeof(T)) as T;
    }
#elif UNITY_EDITOR_WIN
    // win 编辑器下
    [DllImport("kernel32")]
    public static extern IntPtr LoadLibrary(string path);

    [DllImport("kernel32")]
    public static extern IntPtr GetProcAddress(IntPtr libraryHandle, 
    string symbolName);
     
    [DllImport("kernel32)]
    public static extern bool FreeLibrary(IntPtr libraryHandle);

    public static IntPtr OpenLibrary(string path)
    {
        IntPtr handle = LoadLibrary(path);
        if(handle == IntPtr.Zero)
        {
           throw new Exception("Couldn't open native library: "+ path);
        }
        return handle;
    }
    
    public static void CloseLibrary(IntPtr libraryHandle)
    {
         FreeLibrary(libraryHandle);
    }
    
    public static T GetDelegate<T>(IntPtr libraryHandle, string functionName) 
    where T: class
    {
         IntPtr symbol = GetProcAddress(libraryHandle, functionName);
         if(symbol == IntPtr.Zero)
         {
            throw new Exception("Couldn't get function:" + functionName); 
         }
         return Marshal.GetDelegateForFunctionPointer(symbol, typeof(T)) as T;
    }
#else
    //本地加载
    [DllImport("NativeScript")]
    static extern void Init(IntPtr gameObjectNew,
    IntPtr gameObjectGetTransform, IntPtr transformSetPosition);

    [DllImport("NativeScript")]
    static extern void MonoBehaviourUpdate();
#endif

    delegate int GameObjectNewDelegate();
    delegate int GameObjectGetTransformDelegate(int thisHandle);
    delegate void TransformSetPositionDelegate(int thisHandle, Vector3 position);

#if UNITY_EDITOR_OSX
    const string LIB_PATH = "/NativeScript.bundle/Contents/MacOS/NativeScript";
#elif UNITY_EDITOR_LINUX
    const string LIB_PATH = "/NativeScript.so";
#elif UNITY_EDITOR_WIN
    const string LIB_PATH = "/NativeScript.dll";
#endif

    void Awake()
   {
#if UNITY_EDITOR
     //open the native library
     libraryHandle = OpenLibrary(Application.dataPath + LIB_PATH);
     InitDelegate Init = GetDelegate<InitDelegate>(libraryHandle, "Init");
     MonoBehaviourUpdate = GetDelegate<MonoBehaviourUpdateDelegate>(
     libraryHandle,"MonoBehaviourUpdate");
#endif

     //init the C++ Library
     ObjectStore.Init(1024);
     Init(
     Marshal.GetFunctionPointerForDelegate(new GameObjectNewDelegate(GameObjectNew)),
     Marshal.GetFunctionPointerForDelegate(new GameObjectGetTransformDelegate(GameObjectGetTransform)),
     Marshal.GetFunctionPointerForDelegate(new TransformSetPositionDelegate(TransformSetPosition))
    );

    }
   
    void Update()
    {
        MonoBehaviourUpdate();
    }

    void OnApplicationQuit()
    {
#if UNITY_EDITOR
       CloseLibrary(libraryHandle);
       libraryHandle = IntPtr.Zero;
#endif
    }

    //c# function for c++ call
    static int GameObjectNew()
    {
        GameObject go = new GameObject();
        return ObjectStore.Store(go);
    }
   
    static int GameObjectGetTransform(int thisHandle)
    {
        GameObject go = (GameObject)ObjectStore.Get(thisHandle);
        Transform transform = go.transform;
         return ObjectStore.Store(transform);
    }

    static void TransformSetPosition(int handle, Vector3 position)
    {
         Transform t =(Transform)ObjectStore.Get(handle);
         t.position = position;
    }
}

c++ code part:

#ifdef _WIN32
   #define DLLEXPORT __declspec(dllexport)
#else
   #define DLLEXPORT
#endif

extern "C"
{
    //C# VECTOR STRUCT
   struct Vector3
   {
       float x;
       float y;
       float z;
   }
   //c# function for c++ to call
   int(*GameObjectNew)();
   int(*GameObjectGetTransform)(int thisHandle);
   void(*TransformSetPosition)(int thisHandle, Vector3 position);

   //c++ functions for c# to call
   int numCreated;
  
   DLLExport void Init(
   int(*gameObjectNew)(),
   int(*gameObjectGetTrasform)(int),
   void(*transformSetPosition)(int, Vector3)
)
{
      GameObjectNew = gameObjectNew;
      GameObjectGetTransform = gameObjectGetTransform;
      TransformSetPosition = trasformSetPosition;

      numCreated = 0;
}
    //
    DLLEXPORT void MonoBehaviourUpdate(int thisHandle)
    {
        if( numCreated < 10)
        {
             //获取函数handle,然后操作
             int goHandle = GameObjectNew();
             int transformHandle = GameObejctGetTransform(goHandle);
             float comp = 10.0f * (float)numCreated;
             Vector3 position = {comp, comp, comp};
             TransformSetPosition(transformHandle, position);
             numCreated++;
        }
    }
}

四、总结

C#和C++的相互交互，是基于.NET和P/Invoke，那么我们可以同理退出c#和lua的操作，其实质就是对handle进行包装，然后进行相关的操作，这个在后续的文章中在研究，先写到这儿，祝大家五一快乐，我也回家过节去了，哈哈~