[游戏开发]UE4 generated.h文件生成过程模拟

为了探寻UE4的反射机制，我们先从简单处着手，手动模拟一下generated.h的生成过程，看看UHT到底干了哪些事情。

以一个很简单的类作为分析对象

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{

public:
	GENERATED_BODY()

public:
	UFUNCTION(BlueprintCallable)
		void BlueprintCallableFunction();

	UFUNCTION(BlueprintPure)
		int BlueprintPureFunction();

	UFUNCTION(BlueprintNativeEvent)
		void BlueprintNativeEventFunction();

	void BlueprintNativeEventFunction_Implementation();

public:
	UPROPERTY(BlueprintReadWrite)
		float PlayerHP = 2.0f;
};

GENERATED_BODY()相关定义如下

// This pair of macros is used to help implement GENERATED_BODY() and GENERATED_USTRUCT_BODY()
#define BODY_MACRO_COMBINE_INNER(A,B,C,D) A##B##C##D
#define BODY_MACRO_COMBINE(A,B,C,D) BODY_MACRO_COMBINE_INNER(A,B,C,D)

// Include a redundant semicolon at the end of the generated code block, so that intellisense parsers can start parsing
// a new declaration if the line number/generated code is out of date.
#define GENERATED_BODY_LEGACY(...) BODY_MACRO_COMBINE(CURRENT_FILE_ID,_,__LINE__,_GENERATED_BODY_LEGACY);
#define GENERATED_BODY(...) BODY_MACRO_COMBINE(CURRENT_FILE_ID,_,__LINE__,_GENERATED_BODY);

可以得出，GENERATED_BODY()被替换后，变成如下代码

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
	CURRENT_FILE_ID_#__LINE__#_GENERATED_BODY
	
...
};

其中__LINE__是需要被替换成GENERATED_BODY宏实际所在的行数，我们这里在15行，所以变成

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
	CURRENT_FILE_ID_15_GENERATED_BODY
	
...
};

CURRENT_FILE_ID是什么？秘密在RpgPlayer.generated.h里面，我们打开这个文件，可以看到头文件最后有

#define CURRENT_FILE_ID RpgGame_Source_RpgGame_RpgPlayer_h

将这个宏进行替换，于是变成

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
	RpgGame_Source_RpgGame_RpgPlayer_h_15_GENERATED_BODY
	
...
};

而RpgGame_Source_RpgGame_RpgPlayer_h_15_GENERATED_BODY又是什么东西呢？它也是一个宏！同样定义在RpgPlayer.generated.h里面，如下

#define RpgGame_Source_RpgGame_RpgPlayer_h_15_GENERATED_BODY \
PRAGMA_DISABLE_DEPRECATION_WARNINGS \
public: \
	RpgGame_Source_RpgGame_RpgPlayer_h_15_PRIVATE_PROPERTY_OFFSET \
	RpgGame_Source_RpgGame_RpgPlayer_h_15_SPARSE_DATA \
	RpgGame_Source_RpgGame_RpgPlayer_h_15_RPC_WRAPPERS_NO_PURE_DECLS \
	RpgGame_Source_RpgGame_RpgPlayer_h_15_INCLASS_NO_PURE_DECLS \
	RpgGame_Source_RpgGame_RpgPlayer_h_15_ENHANCED_CONSTRUCTORS \
private: \
PRAGMA_ENABLE_DEPRECATION_WARNINGS

我们再进行替换

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
	PRAGMA_DISABLE_DEPRECATION_WARNINGS 
public: 
	RpgGame_Source_RpgGame_RpgPlayer_h_15_PRIVATE_PROPERTY_OFFSET 
	RpgGame_Source_RpgGame_RpgPlayer_h_15_SPARSE_DATA 
	RpgGame_Source_RpgGame_RpgPlayer_h_15_RPC_WRAPPERS_NO_PURE_DECLS 
	RpgGame_Source_RpgGame_RpgPlayer_h_15_INCLASS_NO_PURE_DECLS 
	RpgGame_Source_RpgGame_RpgPlayer_h_15_ENHANCED_CONSTRUCTORS 
private: 
PRAGMA_ENABLE_DEPRECATION_WARNINGS
	
public:
	UFUNCTION(BlueprintCallable)
		void BlueprintCallableFunction();

	UFUNCTION(BlueprintPure)
		int BlueprintPureFunction();

	UFUNCTION(BlueprintNativeEvent)
		void BlueprintNativeEventFunction();

	void BlueprintNativeEventFunction_Implementation();

public:
	UPROPERTY(BlueprintReadWrite)
		float PlayerHP = 2.0f;
};

这些宏都可以在RpgPlayer.generated.h里面找到。

• 首先看PRAGMA_DISABLE_DEPRECATION_WARNINGS：这个宏，我们可以在引擎找到好几个定义的地方，但大致做的事情都是同一个，就是消除掉一些编译警告，不同平台进行代码编译时，会报不同的警告，所以这个宏被不同的平台进行了定义，无关痛痒，因此跳过这个宏不谈。

• RpgGame_Source_RpgGame_RpgPlayer_h_15_PRIVATE_PROPERTY_OFFSET ：这个也在RpgPlayer.generated.h定义了，不过是空值。

• RpgGame_Source_RpgGame_RpgPlayer_h_15_SPARSE_DATA：定义为了空值。

• RpgGame_Source_RpgGame_RpgPlayer_h_15_RPC_WRAPPERS_NO_PURE_DECLS：定义如下

  #define RpgGame_Source_RpgGame_RpgPlayer_h_15_RPC_WRAPPERS_NO_PURE_DECLS \
   \
  	DECLARE_FUNCTION(execBlueprintNativeEventFunction); \
  	DECLARE_FUNCTION(execBlueprintPureFunction); \
  	DECLARE_FUNCTION(execBlueprintCallableFunction);

  这里有个问题，我们定义了5个函数，这个宏里面为什么只有3个exe函数?从规则上看，BlueprintCallable、BlueprintPure、BlueprintNativeEvent都进行了处理，而BlueprintImplementableEvent和一个原生的BlueprintNativeEventFunction_Implementation函数没有处理，这两个函数跑哪去了？我们查看gen.cpp文件，发现如下代码

  	static FName NAME_ARpgPlayer_BlueprintImplementableEventFunction = FName(TEXT("BlueprintImplementableEventFunction"));
  	void ARpgPlayer::BlueprintImplementableEventFunction()
  	{
  		ProcessEvent(FindFunctionChecked(NAME_ARpgPlayer_BlueprintImplementableEventFunction),NULL);
  	}
  	static FName NAME_ARpgPlayer_BlueprintNativeEventFunction = FName(TEXT("BlueprintNativeEventFunction"));
  	void ARpgPlayer::BlueprintNativeEventFunction()
  	{
  		ProcessEvent(FindFunctionChecked(NAME_ARpgPlayer_BlueprintNativeEventFunction),NULL);
  	}

  可以看出，这两个函数被保留了！没有进行特殊处理。

• RpgGame_Source_RpgGame_RpgPlayer_h_15_CALLBACK_WRAPPERS：定义为了空。

• RpgGame_Source_RpgGame_RpgPlayer_h_15_INCLASS_NO_PURE_DECLS：

#define RpgGame_Source_RpgGame_RpgPlayer_h_15_INCLASS_NO_PURE_DECLS \
private: \
	static void StaticRegisterNativesARpgPlayer(); \
	friend struct Z_Construct_UClass_ARpgPlayer_Statics; \
public: \
	DECLARE_CLASS(ARpgPlayer, ARpgGameCharacter, COMPILED_IN_FLAGS(0 | CLASS_Config), CASTCLASS_None, TEXT("/Script/RpgGame"), NO_API) \
	DECLARE_SERIALIZER(ARpgPlayer)

• RpgGame_Source_RpgGame_RpgPlayer_h_15_ENHANCED_CONSTRUCTORS：

  #define RpgGame_Source_RpgGame_RpgPlayer_h_15_ENHANCED_CONSTRUCTORS \
  	/** Standard constructor, called after all reflected properties have been initialized */ \
  	NO_API ARpgPlayer() { }; \
  private: \
  	/** Private move- and copy-constructors, should never be used */ \
  	NO_API ARpgPlayer(ARpgPlayer&&); \
  	NO_API ARpgPlayer(const ARpgPlayer&); \
  public: \
  	DECLARE_VTABLE_PTR_HELPER_CTOR(NO_API, ARpgPlayer); \
  DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER(ARpgPlayer); \
  	DEFINE_DEFAULT_CONSTRUCTOR_CALL(ARpgPlayer)

  为什么有些宏的define是空的？可能是因为我们的测试用例非常简单，里面只有一个变量和几个简单的函数，所以很多数据都没有，还没有进行更复杂的测试。

将这一波宏替换后，得到如下代码

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
public: 
	DECLARE_FUNCTION(execBlueprintNativeEventFunction); 
	DECLARE_FUNCTION(execBlueprintPureFunction); 
	DECLARE_FUNCTION(execBlueprintCallableFunction);

	void BlueprintNativeEventFunction();
	void BlueprintNativeEventFunction_Implementation();  
 
private: 
	static void StaticRegisterNativesARpgPlayer(); 
	friend struct Z_Construct_UClass_ARpgPlayer_Statics; 
public: 
	DECLARE_CLASS(ARpgPlayer, ARpgGameCharacter, COMPILED_IN_FLAGS(0 | CLASS_Config), CASTCLASS_None, TEXT("/Script/RpgGame"), NO_API) 
	DECLARE_SERIALIZER(ARpgPlayer)

	/** Standard constructor, called after all reflected properties have been initialized */ \
	NO_API ARpgPlayer() { }; 
private: 
	/** Private move- and copy-constructors, should never be used */ 
	NO_API ARpgPlayer(ARpgPlayer&&); 
	NO_API ARpgPlayer(const ARpgPlayer&); 
public: 
	DECLARE_VTABLE_PTR_HELPER_CTOR(NO_API, ARpgPlayer); 
    DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER(ARpgPlayer); 
	DEFINE_DEFAULT_CONSTRUCTOR_CALL(ARpgPlayer)
private: 
	
public:
	UPROPERTY(BlueprintReadWrite)
		float PlayerHP = 2.0f;
};

看起来代码清晰了一些，但还有些宏的存在，我们继续替换

• DECLARE_CLASS：这个宏定义在ObjectMacros.h中

  #define DECLARE_CLASS( TClass, TSuperClass, TStaticFlags, TStaticCastFlags, TPackage, TRequiredAPI  ) \
  private: \
      TClass& operator=(TClass&&);   \
      TClass& operator=(const TClass&);   \
  	TRequiredAPI static UClass* GetPrivateStaticClass(); \
  public: \
  	/** Bitwise union of #EClassFlags pertaining to this class.*/ \
  	enum {StaticClassFlags=TStaticFlags}; \
  	/** Typedef for the base class ({{ typedef-type }}) */ \
  	typedef TSuperClass Super;\
  	/** Typedef for {{ typedef-type }}. */ \
  	typedef TClass ThisClass;\
  	/** Returns a UClass object representing this class at runtime */ \
  	inline static UClass* StaticClass() \
  	{ \
  		return GetPrivateStaticClass(); \
  	} \
  	/** Returns the package this class belongs in */ \
  	inline static const TCHAR* StaticPackage() \
  	{ \
  		return TPackage; \
  	} \
  	/** Returns the static cast flags for this class */ \
  	inline static EClassCastFlags StaticClassCastFlags() \
  	{ \
  		return TStaticCastFlags; \
  	} \
  	/** For internal use only; use StaticConstructObject() to create new objects. */ \
  	inline void* operator new(const size_t InSize, EInternal InInternalOnly, UObject* InOuter = (UObject*)GetTransientPackage(), FName InName = NAME_None, EObjectFlags InSetFlags = RF_NoFlags) \
  	{ \
  		return StaticAllocateObject(StaticClass(), InOuter, InName, InSetFlags); \
  	} \
  	/** For internal use only; use StaticConstructObject() to create new objects. */ \
  	inline void* operator new( const size_t InSize, EInternal* InMem ) \
  	{ \
  		return (void*)InMem; \
  	}

  DECLARE_SERIALIZER：同样定义在ObjectMacros.h中，

  #define DECLARE_SERIALIZER( TClass ) \
  	friend FArchive &operator<<( FArchive& Ar, TClass*& Res ) \
  	{ \
  		return Ar << (UObject*&)Res; \
  	} \
  	friend void operator<<(FStructuredArchive::FSlot InSlot, TClass*& Res) \
  	{ \
  		InSlot << (UObject*&)Res; \
  	}

  DECLARE_FUNCTION：定义在ObjectMacros.h中。从注释中很容易看出来，这个宏很简单，没什么嵌套，就是包装了函数的声明。

  // This macro is used to declare a thunk function in autogenerated boilerplate code
  #define DECLARE_FUNCTION(func) static void func( UObject* Context, FFrame& Stack, RESULT_DECL )

• 我们把这几个宏替换掉，得到如下代码

  UCLASS(meta=(IsBlueprintBase = "false"))
  class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
  {
  public: 
  static void execBlueprintNativeEventFunction( UObject* Context, FFrame& Stack, RESULT_DECL );
  static void execBlueprintPureFunction( UObject* Context, FFrame& Stack, RESULT_DECL );
  static void execBlueprintCallableFunction( UObject* Context, FFrame& Stack, RESULT_DECL );
  
  	void BlueprintNativeEventFunction();
  	void BlueprintNativeEventFunction_Implementation();  
  private: 
  	static void StaticRegisterNativesARpgPlayer(); 
  	friend struct Z_Construct_UClass_ARpgPlayer_Statics; 
  public: 
  	private: 
      ARpgPlayer& operator=(ARpgPlayer&&);   
      ARpgPlayer& operator=(const ARpgPlayer&);   
  	NO_API static UClass* GetPrivateStaticClass(); 
  public: 
  	/** Bitwise union of #EClassFlags pertaining to this class.*/ 
  	enum {StaticClassFlags=COMPILED_IN_FLAGS(0 | CLASS_Config)}; 
  	/** Typedef for the base class ({{ typedef-type }}) */ 
  	typedef ARpgGameCharacter Super;
  	/** Typedef for {{ typedef-type }}. */ 
  	typedef ARpgPlayer ThisClass;
  	/** Returns a UClass object representing this class at runtime */ 
  	inline static UClass* StaticClass() 
  	{ 
  		return GetPrivateStaticClass(); 
  	} 
  	/** Returns the package this class belongs in */ 
  	inline static const TCHAR* StaticPackage() 
  	{ 
  		return TEXT("/Script/RpgGame"); 
  	} 
  	/** Returns the static cast flags for this class */ 
  	inline static EClassCastFlags StaticClassCastFlags() 
  	{ 
  		return CASTCLASS_None; 
  	} 
  	/** For internal use only; use StaticConstructObject() to create new objects. */ 
  	inline void* operator new(const size_t InSize, EInternal InInternalOnly, UObject* InOuter = (UObject*)GetTransientPackage(), FName InName = NAME_None, EObjectFlags InSetFlags = RF_NoFlags) 
  	{ 
  		return StaticAllocateObject(StaticClass(), InOuter, InName, InSetFlags); 
  	} 
  	/** For internal use only; use StaticConstructObject() to create new objects. */ 
  	inline void* operator new( const size_t InSize, EInternal* InMem ) 
  	{ 
  		return (void*)InMem; 
  	}
  		
  	friend FArchive &operator<<( FArchive& Ar, ARpgPlayer*& Res ) 
  	{ 
  		return Ar << (UObject*&)Res; 
  	} 
  	friend void operator<<(FStructuredArchive::FSlot InSlot, ARpgPlayer*& Res) 
  	{ 
  		InSlot << (UObject*&)Res; 
  	}
  
  	/** Standard constructor, called after all reflected properties have been initialized */ \
  	NO_API ARpgPlayer() { }; 
  private: 
  	/** Private move- and copy-constructors, should never be used */ 
  	NO_API ARpgPlayer(ARpgPlayer&&); 
  	NO_API ARpgPlayer(const ARpgPlayer&); 
  public: 
  	DECLARE_VTABLE_PTR_HELPER_CTOR(NO_API, ARpgPlayer); 
      DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER(ARpgPlayer); 
  	DEFINE_DEFAULT_CONSTRUCTOR_CALL(ARpgPlayer)
  private: 
  	
  public:
  	UPROPERTY(BlueprintReadWrite)
  		float PlayerHP = 2.0f;
  };
  

  还有几个宏，我们继续探测

• #define DECLARE_VTABLE_PTR_HELPER_CTOR(API, TClass) \
  	/** DO NOT USE. This constructor is for internal usage only for hot-reload purposes. */ \
  	API TClass(FVTableHelper& Helper);

• ?DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER

#define DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER_DUMMY() \
	static UObject* __VTableCtorCaller(FVTableHelper& Helper) \
	{ \
		return nullptr; \
	}

#if WITH_HOT_RELOAD
	#define DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER(TClass) \
		static UObject* __VTableCtorCaller(FVTableHelper& Helper) \
		{ \
			return new (EC_InternalUseOnlyConstructor, (UObject*)GetTransientPackage(), NAME_None, RF_NeedLoad | RF_ClassDefaultObject | RF_TagGarbageTemp) TClass(Helper); \
		}
#else // WITH_HOT_RELOAD
	#define DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER(TClass) \
		DEFINE_VTABLE_PTR_HELPER_CTOR_CALLER_DUMMY()
#endif // WITH_HOT_RELOAD

• DEFINE_DEFAULT_CONSTRUCTOR_CALL

  #define DEFINE_DEFAULT_CONSTRUCTOR_CALL(TClass) \
  	static void __DefaultConstructor(const FObjectInitializer& X) { new((EInternal*)X.GetObj())TClass; }

• UPROPERTY。可以看出这些宏只是辅助UHT扫描源码用的，实际没有任何有效的定义。

  // These macros wrap metadata parsed by the Unreal Header Tool, and are otherwise
  // ignored when code containing them is compiled by the C++ compiler
  #define UPROPERTY(...)
  #define UFUNCTION(...)
  #define USTRUCT(...)
  #define UMETA(...)
  #define UPARAM(...)
  #define UENUM(...)
  #define UDELEGATE(...)
  #define RIGVM_METHOD(...)

  全部替换后，大致代码如下

UCLASS(meta=(IsBlueprintBase = "false"))
class RPGGAME_API ARpgPlayer : public ARpgGameCharacter
{
public: 
static void execBlueprintNativeEventFunction( UObject* Context, FFrame& Stack, void*const Z_Param__Result);
static void execBlueprintPureFunction( UObject* Context, FFrame& Stack, void*const Z_Param__Result);
static void execBlueprintCallableFunction( UObject* Context, FFrame& Stack, void*const Z_Param__Result);

	void BlueprintNativeEventFunction();
	void BlueprintNativeEventFunction_Implementation();  
private: 
	static void StaticRegisterNativesARpgPlayer(); 
	friend struct Z_Construct_UClass_ARpgPlayer_Statics; //定义在gen.cpp中
public: 
	private: 
    ARpgPlayer& operator=(ARpgPlayer&&);        //禁止移动赋值
    ARpgPlayer& operator=(const ARpgPlayer&);   //禁止拷贝赋值
	NO_API static UClass* GetPrivateStaticClass(); 
public: 
	/** Bitwise union of #EClassFlags pertaining to this class.*/ 
	enum {StaticClassFlags=COMPILED_IN_FLAGS(0 | CLASS_Config)}; 
	/** Typedef for the base class ({{ typedef-type }}) */ 
	typedef ARpgGameCharacter Super;
	/** Typedef for {{ typedef-type }}. */ 
	typedef ARpgPlayer ThisClass;
	/** Returns a UClass object representing this class at runtime */ 
	inline static UClass* StaticClass() 
	{ 
		return GetPrivateStaticClass(); 
	} 
	/** Returns the package this class belongs in */ 
	inline static const TCHAR* StaticPackage() 
	{ 
		return TEXT("/Script/RpgGame"); 
	} 
	/** Returns the static cast flags for this class */ 
	inline static EClassCastFlags StaticClassCastFlags() 
	{ 
		return CASTCLASS_None; 
	} 
	/** For internal use only; use StaticConstructObject() to create new objects. */ 
	inline void* operator new(const size_t InSize, EInternal InInternalOnly, UObject* InOuter = (UObject*)GetTransientPackage(), FName InName = NAME_None, EObjectFlags InSetFlags = RF_NoFlags) 
	{ 
		return StaticAllocateObject(StaticClass(), InOuter, InName, InSetFlags); 
	} 
	/** For internal use only; use StaticConstructObject() to create new objects. */ 
	inline void* operator new( const size_t InSize, EInternal* InMem ) 
	{ 
		return (void*)InMem; 
	}
		
	friend FArchive &operator<<( FArchive& Ar, ARpgPlayer*& Res ) 
	{ 
		return Ar << (UObject*&)Res; 
	} 
	friend void operator<<(FStructuredArchive::FSlot InSlot, ARpgPlayer*& Res) 
	{ 
		InSlot << (UObject*&)Res; 
	}

	/** Standard constructor, called after all reflected properties have been initialized */ \
	NO_API ARpgPlayer() { }; 
private: 
	/** Private move- and copy-constructors, should never be used */ 
	NO_API ARpgPlayer(ARpgPlayer&&);         
	NO_API ARpgPlayer(const ARpgPlayer&);    
public: 
	NO_API ARpgPlayer(FVTableHelper& Helper);
	static UObject* __VTableCtorCaller(FVTableHelper& Helper) 
	{ 
		return nullptr; 
	}
		
	static void __DefaultConstructor(const FObjectInitializer& X) { new((EInternal*)X.GetObj())ARpgPlayer; }
private: 
	
public:
	float PlayerHP = 2.0f;
};

至此，我们generated.h生成过程大致模拟完毕，下一篇文章，我们将对替换后的代码进行简单的分析。