Unity使用C++作为游戏逻辑脚本的研究（二）
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)
上一篇文章写完，有同学觉得有点晦涩，其实可以多认真看两遍源码，仔细琢磨一下，就会有一种茅塞顿开的感觉：D。今天继续上文，深入讨论一下C++作为游戏脚本的研究，本文会较长，需要写一些示例代码做讲解。
一、对C#指针(引用)的封装
在上文，我们提到，C++对C#的调用，是基于C#的函数指针（引用）而来的，比如在C++中：
//return transform handle || function pointer name || take a handle to the go
int32_t (*GameObjectGetTransform) (int32_t thiz);
为了拓展性，我们都会倾向于对于这种int32_t类型的数据做一个封装，自然容易想到用一个结构体（结构体默认为public）
namespace System
{
struct Object
{
int32_t Handle;
}
}
利用继承的特点，我们可以延伸出其他类型的结构体定义：
namespace UnityEngine
{
struct Vector3 {float x; float y; float z;};
struct Transform:System::Object
{
void SetPosition(Vector3 val)
{
TransformSetPosition(Handle, val);
}
}
struct GameObject:System::Object
{
GameObject()
{
Handle = GameObjectNew();
}
Transform GetPosition()
{
Transform transform;
transform.Handle = GameObjectGetTransform(Handle);
return transform;
}
}
}
二、对内存管理的控制
在C#部分，对于托管部分，是基于垃圾自动回收机制的，对于C++部分，相对较为简单的回收，可以基于计数的回收机制，当对象的引用计数为零的时候执行垃圾回收，那么对于我们可以定义两个全局变量来做相关的计数统计：
//global
int32_t managedObjectsRefCountLen;
int32_t *managedObjectsRefCounts;
//.....
//init
managedObjectsRefCountLen = maxManagedObjects;//c#会传入该数据
managedObjectsRefCounts = (int32_t*)calloc(maxManagedObjects, sizeof(int32_t));
这样在GameObject的初始化和解析的时候可以执行相关的内存管理操作：
GameObject()
{
Handle = GameObjectNew();
managedObjectsRefCounts[Handle]++;
}
~GameObject()
{
if(--managedObjectsRefCounts[Handle] == 0)
{
ReleaseObject(Handle);
}
}
对于其他的结构体，可以利用宏定义来实现类似的结构体定义中的操作。综上，可以实现在传递的时候对int32_t类型数据的封装，其次可以内嵌内存操作。整体代码对于c#的修改不多，对于C++的修改较多。
三、代码部分
对于c#部分的代码，基本不修改，只是修改一下Init函数，添加内存管理相关的数据和函数，具体代码如下：
....
//初始化函数及相关委托的修改
public delegate void InitDelegate(int maxManagedObjects, IntPtr releaseObject,
IntPtr gameObjectNew, IntPtr gameObjectGetTransform, IntPtr transformSetPosition);
....
...
#if UNITY_EDITOR_OSX || UNITY_EDITOR_LINUX
...
#elif UNITY_EDITOR_WIN
...
#else
[DllImport("NativeScript")]
static extern void Init(int maxManagedObjects, IntPtr releaseObject,
IntPtr gameObjectNew, IntPtr gameObjectGetTransform,
IntPtr transformSetPosition);
...
#endif
//新增释放
delegate void ReleaseObjectDelegate(int handle);
...
//修改Awake函数中对于初始化的操作
void Awake()
{
...
//init c++ libraray
const int maxManagedObjects = 1024;
ObjectStore.Init(maxManagedObjects);
Init(maxManagedObjects,
Marshal.GetFunctionPointerForDelegate(new ReleaseObjectDelegate(ReleaseObject)),
Marshal.GetFunctionPointerForDelegate(new GameObjectNewDelegate(GameObjectNew)),
Marshal.GetFunctionPointerForDelegate(new GameObjectGetTransformDelegate(GameObjectGetTransform)),
Marshal.GetFunctionPointerForDelegate(new TransformSetPositionDelegate(TransformSetPosition)));
}
...
//c# function for c++ to call
static void ReleaseObject(int handle)
{
ObjectStore.Remove(handle);
}
...
C++部分的代码修改较多，我就copy一下作者的工程源码吧 ：D
// For assert()
#include <assert.h>
// For int32_t, etc.
#include <stdint.h>
// For malloc(), etc.
#include <stdlib.h>
// For std::forward
#include <utility>
// Macro to put before functions that need to be exposed to C#
#ifdef _WIN32
#define DLLEXPORT extern "C" __declspec(dllexport)
#else
#define DLLEXPORT extern "C"
#endif
////////////////////////////////////////////////////////////////
// C# struct types
////////////////////////////////////////////////////////////////
namespace UnityEngine
{
struct Vector3
{
float x;
float y;
float z;
Vector3()
: x(0.0f)
, y(0.0f)
, z(0.0f)
{
}
Vector3(
float x,
float y,
float z)
: x(x)
, y(y)
, z(z)
{
}
};
}
////////////////////////////////////////////////////////////////
// C# functions for C++ to call
////////////////////////////////////////////////////////////////
namespace Plugin
{
using namespace UnityEngine;
void (*ReleaseObject)(
int32_t handle);
int32_t (*GameObjectNew)();
int32_t (*GameObjectGetTransform)(
int32_t thiz);
void (*TransformSetPosition)(
int32_t thiz,
Vector3 val);
}
////////////////////////////////////////////////////////////////
// Reference counting of managed objects
////////////////////////////////////////////////////////////////
namespace Plugin
{
int32_t managedObjectsRefCountLen;
int32_t* managedObjectRefCounts;
void ReferenceManagedObject(int32_t handle)
{
assert(handle >= 0 && handle < managedObjectsRefCountLen);
if (handle != 0)
{
managedObjectRefCounts[handle]++;
}
}
void DereferenceManagedObject(int32_t handle)
{
assert(handle >= 0 && handle < managedObjectsRefCountLen);
if (handle != 0)
{
int32_t numRemain = --managedObjectRefCounts[handle];
if (numRemain == 0)
{
ReleaseObject(handle);
}
}
}
}
////////////////////////////////////////////////////////////////
// Mirrors of C# types. These wrap the C# functions to present
// a similiar API as in C#.
////////////////////////////////////////////////////////////////
namespace System
{
struct Object
{
int32_t Handle;
Object(int32_t handle)
{
Handle = handle;
Plugin::ReferenceManagedObject(handle);
}
Object(const Object& other)
{
Handle = other.Handle;
Plugin::ReferenceManagedObject(Handle);
}
Object(Object&& other)
{
Handle = other.Handle;
other.Handle = 0;
}
};
//宏定义操作
#define SYSTEM_OBJECT_LIFECYCLE(ClassName, BaseClassName) \
ClassName(int32_t handle) \
: BaseClassName(handle) \
{ \
} \
\
ClassName(const ClassName& other) \
: BaseClassName(other) \
{ \
} \
\
ClassName(ClassName&& other) \
: BaseClassName(std::forward<ClassName>(other)) \
{ \
} \
\
~ClassName() \
{ \
DereferenceManagedObject(Handle); \
} \
\
ClassName& operator=(const ClassName& other) \
{ \
DereferenceManagedObject(Handle); \
Handle = other.Handle; \
ReferenceManagedObject(Handle); \
return *this; \
} \
\
ClassName& operator=(ClassName&& other) \
{ \
DereferenceManagedObject(Handle); \
Handle = other.Handle; \
other.Handle = 0; \
return *this; \
}
}
namespace UnityEngine
{
using namespace System;
using namespace Plugin;
struct GameObject;
struct Component;
struct Transform;
struct GameObject : Object
{
SYSTEM_OBJECT_LIFECYCLE(GameObject, Object)
GameObject();
Transform GetTransform();
};
struct Component : Object
{
SYSTEM_OBJECT_LIFECYCLE(Component, Object)
};
struct Transform : Component
{
SYSTEM_OBJECT_LIFECYCLE(Transform, Component)
void SetPosition(Vector3 val);
};
GameObject::GameObject()
: GameObject(GameObjectNew())
{
}
Transform GameObject::GetTransform()
{
return Transform(GameObjectGetTransform(Handle));
}
void Transform::SetPosition(Vector3 val)
{
TransformSetPosition(Handle, val);
}
}
////////////////////////////////////////////////////////////////
// C++ functions for C# to call
////////////////////////////////////////////////////////////////
// Init the plugin
DLLEXPORT void Init(
int32_t maxManagedObjects,
void (*releaseObject)(int32_t),
int32_t (*gameObjectNew)(),
int32_t (*gameObjectGetTransform)(int32_t),
void (*transformSetPosition)(int32_t, UnityEngine::Vector3))
{
using namespace Plugin;
// Init managed object ref counting
managedObjectsRefCountLen = maxManagedObjects;
managedObjectRefCounts = (int32_t*)calloc(
maxManagedObjects,
sizeof(int32_t));
// Init pointers to C# functions
ReleaseObject = releaseObject;
GameObjectNew = gameObjectNew;
GameObjectGetTransform = gameObjectGetTransform;
TransformSetPosition = transformSetPosition;
}
// Called by MonoBehaviour.Update
DLLEXPORT void MonoBehaviourUpdate()
{
using namespace UnityEngine;
static int32_t numCreated = 0;
if (numCreated < 10)
{
GameObject go;
Transform transform = go.GetTransform();
float comp = (float)numCreated;
Vector3 position(comp, comp, comp);
transform.SetPosition(position);
numCreated++;
}
}
四、c#和Unity API 的导出
写到上面部分，基本对于c#和c++之间的操作有一个整体的较为完整的讲解，还有一个没有提起，那就是，怎么将 unity 的API导出给C++使用呢？作者给出了一个导出方式：JSON导出这让熟悉c#导出到lua的同学可以发现异曲同工之妙，其基本的导出设计为：
{
"Assemblies": [
{
"Path": "/Applications/Unity/Unity.app/Contents/Managed/UnityEngine.dll",
"Types": [
{
"Name": "UnityEngine.Object",
"Constructors": [],
"Methods": [],
"Properties": [],
"Fields": []
},
{
"Name": "UnityEngine.GameObject",
"Constructors": [
{
"Types": []
}
],
"Properties": [ "transform" ],
"Fields": []
},
{
"Name": "UnityEngine.Component",
"Constructors": [],
"Methods": [],
"Properties": [],
"Fields": []
},
{
"Name": "UnityEngine.Transform",
"Constructors": [],
"Methods": [],
"Properties": [ "position" ],
"Fields": []
}
]
}
]
}
整体设计简介易懂，当然，并不是所有的c#特性都可以被导出，json的导出不支持：Array/out and ref/ delegate/ generic functions and types/ struct types，不知后期作者是否考虑扩展对这些不兼容的特效的导出。
使用json导出，整体的修改和使用非常简单，比如对Component，需要添加对其transform特性的导出，那么只需要修改为：
"Properties":["transform"]
那么，保存后重新导出，就可以得到transform特性。
此外，对于.Net的一些API， 也可以使用JSON导出的方式：
{
"Path": "/Applications/Unity/Unity.app/Contents/Mono/lib/mono/unity/System.dll",
"Types": [
{
"Name": "System.Diagnostics.Stopwatch",
"Constructors": [
{
"Types": []
}
],
"Methods": [
{
"Name": "Start",
"Types": []
},
{
"Name": "Reset",
"Types": []
}
],
"Properties": [ "ElapsedMilliseconds" ],
"Fields": []
}
]
}
基于上面的各个部分，整体的游戏工程，可以分为2个部分：逻辑代码部分和binding相关的部分，作者给出的工程规划：
Assets
|- Game.cpp // Game-specific code. Can rename this file, add headers, etc.
|- NativeScriptTypes.json // JSON describing which .NET types the game wants to expose to C++
|- NativeScriptConstants.cs // Game-specific constants such as plugin names and paths
|- NativeScript/ // C++ scripting system. Drop this into your project.
|- Editor/
|- GenerateBindings.cs // Code generator
|- Bindings.cs // C# code to expose functionality to C++
|- ObjectStore.cs // Object handles system
|- Bindings.h // C++ wrapper types for C# (declaration)
|- Bindings.cpp // C++ wrapper types for C# (definition)
|- BootScript.cs // MonoBehaviour to boot up the C++ plugin
|- BootScene.unity // Scene with just BootScript on an empty GameObject
对于NativeScript来说，相当于基本的binding相关的东西，对于任何工程都适用，对于其他部分，则根据具体的工程来设计。基于这样的设计，需要做到三个基本规范：
1、需要定义一个全局的类：
public static class NativeScriptConstants
{
/// <summary>
/// Name of the plugin used by [DllImport] when running outside the editor
/// </summary>
public const string PluginName = "NativeScript";
/// <summary>
/// Path to load the plugin from when running inside the editor
/// </summary>
#if UNITY_EDITOR_OSX
public const string PluginPath = "/NativeScript.bundle/Contents/MacOS/NativeScript";
#elif UNITY_EDITOR_LINUX
public const string PluginPath = "/NativeScript.so";
#elif UNITY_EDITOR_WIN
public const string PluginPath = "/NativeScript.dll";
#endif
/// <summary>
/// Maximum number of simultaneous managed objects that the C++ plugin uses
/// </summary>
public const int MaxManagedObjects = 1024;
/// <summary>
/// Path within the Unity project to the exposed types JSON file
/// </summary>
public const string ExposedTypesJsonPath = "NativeScriptTypes.json";
}
2、NativeScriptConstants.ExposedTypesJsonPath需要指向前面所提到的json导出文件；
3、在C++代码部分，需要定义2个函数用来执行相关的更新
// Called when the plugin is initialized
void PluginMain()
{
}
// Called for MonoBehaviour.Update
void PluginUpdate()
{
}
最后，整体的工程可以在github上找到，给出工程的链接：
jacksondunstan/UnityNativeScripting
Over!
