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虚幻4蓝图编译剖析(三)

2016-10-31 08:26  风恋残雪  阅读(...)  评论(... 编辑 收藏

编译

上面基本的术语已经介绍完了,下面我们进入来进入蓝图编译过程分析。蓝图的编译过程都在FKismetCompilerContext::Compile()函数中。它根据编译的类型不同(上文编译选项中提到的只编译Skeleton、只生成字节码、只生成cpp代码等等)会走不同的分支。我们这里以完全编译来讲解。此处为大概的流程,若想看详细的流程,请参照流程图以及代码。

 

清除类

类是就地编译的,这意味着同一个UBlueprintGeneratedClass在每次编译的时候都会被清理,并且会重复利用,这样指向这个类的指针就不用修复了。CleanAndSanitizeClass()把属性和函数放到临时包的一个垃圾(trash)类里面,然后清除类中的所有数据。

创建类的属性

CreateClassVariablesFromBlueprint()函数遍历蓝图的NewVariables数组,也包括构造脚本、Timeline等地方来找到该类需要的所有属性,然后创建UProperties。

创建函数列表

通过处理事件图表(Event graph)、常规的函数图表、代理、以及接口中来创建函数。

处理事件图表

CreateAndProcessUberGraph()函数用来处理事件图表。它把所有的事件图表拷贝到一个大的图中,这个时候节点有机会去做展开操作(expand,如果它需要的话)。然后会为图中的每一个事件节点创建一个函数桩(stub),最终会为当前的事件图表创建一个FKismetFunctionContext,用于把整个事件图表当作一个函数来处理。

处理函数图表

常规函数图表的处理是通过ProcessOneFunctionGraph()函数来完成的,它会把图中的每一个节点拷贝到另外一个节点中去,这个时候每个节点有机会展开(expand),最后会为每一个函数创建一个FKismetFunctionContext,用来后面对该函数的编译工作。

预编译函数

函数的预编译是通过为每一个FKismetFunctionContext调用PrecompileFunction()来实现的,这个函数主要做以下操作:

  1. 确定执行顺序并计算数据依赖。
  2. 去除那些没有连接的或者无数据依赖的节点。
  3. 为每一个剩下的运行每一个节点处理器(FNodeHandlingFunctor)的RegisterNets()函数,它会为函数中的值创建FBPTerminal。
  4. 创建UFunction对象和相关的属性。

绑定和链接类

现在类已经拥有了UFunctions和UProperties,现在可以绑定和链接类了,它包含填充属性链,属性大小 以及函数的列表。这个时候它相关于有了一个类头文件,不包括最终的标记、元数据以及CDO对象。

编译函数

接下来就需要通过每一个节点处理器(FNodeHanlingFunctor)的Compile()函数使用AppendStatementForNode()函数来为该节点添加FKismetBlueprintStatement。这个函数也可能会创建FBPTerminal对象只要它们只是局部使用的。

后编译函数

PostCompileFunction()是编译函数的最后一个阶段,在所有函数调用了CompileFunction()之后调用,主要是修复交叉引用。

完成编译类

为了完成编译该类,编译器会最终设置类标记,并从父类继承标记和元数据,最后会确定所有的事情在编译过程中是正确的。

后端生成代码

编译器后端会把函数中的所有语句转换成代码,目前有两个使用的后端:

  1. FKismetCompilerVMBackend 把FKismetCompilerStatement转成字节码,并把它序列化到脚本数组中。

  1. FKismetCppBackend 生成C++代码,只用于调试目的。

字节码

字节码的定义在Script.h中的EExprToken枚举中,定义如下,可以看到它有一些比较通用的指令,如EX_Jump EX_JumpIfNot等,也有一些专用的指令比如EX_DynamicCast EX_SetArray。

    
  1 //
  2 
  3 // Evaluatable expression item types.
  4 
  5 //
  6 
  7 enum EExprToken
  8 
  9 {
 10 
 11     // Variable references.
 12 
 13     EX_LocalVariable        = 0x00,    // A local variable.
 14 
 15     EX_InstanceVariable        = 0x01,    // An object variable.
 16 
 17     EX_DefaultVariable        = 0x02, // Default variable for a class context.
 18 
 19     //                        = 0x03,
 20 
 21     EX_Return                = 0x04,    // Return from function.
 22 
 23     //                        = 0x05,
 24 
 25     EX_Jump                    = 0x06,    // Goto a local address in code.
 26 
 27     EX_JumpIfNot            = 0x07,    // Goto if not expression.
 28 
 29     //                        = 0x08,
 30 
 31     EX_Assert                = 0x09,    // Assertion.
 32 
 33     //                        = 0x0A,
 34 
 35     EX_Nothing                = 0x0B,    // No operation.
 36 
 37     //                        = 0x0C,
 38 
 39     //                        = 0x0D,
 40 
 41     //                        = 0x0E,
 42 
 43     EX_Let                    = 0x0F,    // Assign an arbitrary size value to a variable.
 44 
 45     //                        = 0x10,
 46 
 47     //                        = 0x11,
 48 
 49     EX_ClassContext            = 0x12,    // Class default object context.
 50 
 51     EX_MetaCast = 0x13, // Metaclass cast.
 52 
 53     EX_LetBool                = 0x14, // Let boolean variable.
 54 
 55     EX_EndParmValue            = 0x15,    // end of default value for optional function parameter
 56 
 57     EX_EndFunctionParms        = 0x16,    // End of function call parameters.
 58 
 59     EX_Self                    = 0x17,    // Self object.
 60 
 61     EX_Skip                    = 0x18,    // Skippable expression.
 62 
 63     EX_Context                = 0x19,    // Call a function through an object context.
 64 
 65     EX_Context_FailSilent    = 0x1A, // Call a function through an object context (can fail silently if the context is NULL; only generated for functions that don't have output or return values).
 66 
 67     EX_VirtualFunction        = 0x1B,    // A function call with parameters.
 68 
 69     EX_FinalFunction        = 0x1C,    // A prebound function call with parameters.
 70 
 71     EX_IntConst                = 0x1D,    // Int constant.
 72 
 73     EX_FloatConst            = 0x1E,    // Floating point constant.
 74 
 75     EX_StringConst            = 0x1F,    // String constant.
 76 
 77     EX_ObjectConst         = 0x20,    // An object constant.
 78 
 79     EX_NameConst            = 0x21,    // A name constant.
 80 
 81     EX_RotationConst        = 0x22,    // A rotation constant.
 82 
 83     EX_VectorConst            = 0x23,    // A vector constant.
 84 
 85     EX_ByteConst            = 0x24,    // A byte constant.
 86 
 87     EX_IntZero                = 0x25,    // Zero.
 88 
 89     EX_IntOne                = 0x26,    // One.
 90 
 91     EX_True                    = 0x27,    // Bool True.
 92 
 93     EX_False                = 0x28,    // Bool False.
 94 
 95     EX_TextConst            = 0x29, // FText constant
 96 
 97     EX_NoObject                = 0x2A,    // NoObject.
 98 
 99     EX_TransformConst        = 0x2B, // A transform constant
100 
101     EX_IntConstByte            = 0x2C,    // Int constant that requires 1 byte.
102 
103     EX_NoInterface            = 0x2D, // A null interface (similar to EX_NoObject, but for interfaces)
104 
105     EX_DynamicCast            = 0x2E,    // Safe dynamic class casting.
106 
107     EX_StructConst            = 0x2F, // An arbitrary UStruct constant
108 
109     EX_EndStructConst        = 0x30, // End of UStruct constant
110 
111     EX_SetArray                = 0x31, // Set the value of arbitrary array
112 
113     EX_EndArray                = 0x32,
114 
115     //                        = 0x33,
116 
117     EX_UnicodeStringConst = 0x34, // Unicode string constant.
118 
119     EX_Int64Const            = 0x35,    // 64-bit integer constant.
120 
121     EX_UInt64Const            = 0x36,    // 64-bit unsigned integer constant.
122 
123     //                        = 0x37,
124 
125     EX_PrimitiveCast        = 0x38,    // A casting operator for primitives which reads the type as the subsequent byte
126 
127     //                        = 0x39,
128 
129     //                        = 0x3A,
130 
131     //                        = 0x3B,
132 
133     //                        = 0x3C,
134 
135     //                        = 0x3D,
136 
137     //                        = 0x3E,
138 
139     //                        = 0x3F,
140 
141     //                        = 0x40,
142 
143     //                        = 0x41,
144 
145     EX_StructMemberContext    = 0x42, // Context expression to address a property within a struct
146 
147     EX_LetMulticastDelegate    = 0x43, // Assignment to a multi-cast delegate
148 
149     EX_LetDelegate            = 0x44, // Assignment to a delegate
150 
151     //                        = 0x45,
152 
153     //                        = 0x46, // CST_ObjectToInterface
154 
155     //                        = 0x47, // CST_ObjectToBool
156 
157     EX_LocalOutVariable        = 0x48, // local out (pass by reference) function parameter
158 
159     //                        = 0x49, // CST_InterfaceToBool
160 
161     EX_DeprecatedOp4A        = 0x4A,
162 
163     EX_InstanceDelegate        = 0x4B,    // const reference to a delegate or normal function object
164 
165     EX_PushExecutionFlow    = 0x4C, // push an address on to the execution flow stack for future execution when a EX_PopExecutionFlow is executed. Execution continues on normally and doesn't change to the pushed address.
166 
167     EX_PopExecutionFlow        = 0x4D, // continue execution at the last address previously pushed onto the execution flow stack.
168 
169     EX_ComputedJump            = 0x4E,    // Goto a local address in code, specified by an integer value.
170 
171     EX_PopExecutionFlowIfNot = 0x4F, // continue execution at the last address previously pushed onto the execution flow stack, if the condition is not true.
172 
173     EX_Breakpoint            = 0x50, // Breakpoint. Only observed in the editor, otherwise it behaves like EX_Nothing.
174 
175     EX_InterfaceContext        = 0x51,    // Call a function through a native interface variable
176 
177     EX_ObjToInterfaceCast = 0x52,    // Converting an object reference to native interface variable
178 
179     EX_EndOfScript            = 0x53, // Last byte in script code
180 
181     EX_CrossInterfaceCast    = 0x54, // Converting an interface variable reference to native interface variable
182 
183     EX_InterfaceToObjCast = 0x55, // Converting an interface variable reference to an object
184 
185     //                        = 0x56,
186 
187     //                        = 0x57,
188 
189     //                        = 0x58,
190 
191     //                        = 0x59,
192 
193     EX_WireTracepoint        = 0x5A, // Trace point. Only observed in the editor, otherwise it behaves like EX_Nothing.
194 
195     EX_SkipOffsetConst        = 0x5B, // A CodeSizeSkipOffset constant
196 
197     EX_AddMulticastDelegate = 0x5C, // Adds a delegate to a multicast delegate's targets
198 
199     EX_ClearMulticastDelegate = 0x5D, // Clears all delegates in a multicast target
200 
201     EX_Tracepoint            = 0x5E, // Trace point. Only observed in the editor, otherwise it behaves like EX_Nothing.
202 
203     EX_LetObj                = 0x5F,    // assign to any object ref pointer
204 
205     EX_LetWeakObjPtr        = 0x60, // assign to a weak object pointer
206 
207     EX_BindDelegate            = 0x61, // bind object and name to delegate
208 
209     EX_RemoveMulticastDelegate = 0x62, // Remove a delegate from a multicast delegate's targets
210 
211     EX_CallMulticastDelegate = 0x63, // Call multicast delegate
212 
213     EX_LetValueOnPersistentFrame = 0x64,
214 
215     EX_ArrayConst            = 0x65,
216 
217     EX_EndArrayConst        = 0x66,
218 
219     EX_AssetConst            = 0x67,
220 
221     EX_CallMath                = 0x68, // static pure function from on local call space
222 
223     EX_SwitchValue            = 0x69,
224 
225     EX_InstrumentationEvent    = 0x6A, // Instrumentation event
226 
227     EX_ArrayGetByRef        = 0x6B,
228 
229     EX_Max                    = 0x100,
230 
231 };

 

拷贝类默认对象(CDO)属性

使用一个特殊的函数CopyPropertiesForUnrelatedObjects(),编译器把类旧CDO中的值拷贝到新的CDO中。属性是通过带标记的序列化来拷贝的,只要名字是一致的,它们就应该被正确的复制。CDO中的组件会重新实例化。

重新实例化

由于类可能已经改变大小或者属性已经添加或删除了,编译器需要重新实例化该类实例化的所有对象。它使用TOjbectIterator来找到该类的实例,创建一个新的,并且使用CopyPropertiesForUnrelatedObjects()函数来把旧实例的数据拷贝到新的实例。详细信息参照FBlueprintCompileReinstancer类。

编译实例学习

我在蓝图里面新建了一个继承自Actor的NewBlueprint,它有一个变量StringTest并且实现了一个BeginPlay 事件和一个FunctionTest()函数,这个函数有一个局部变量LocalStringTest。

下面分别是BeginPlay和FunctionTest的定义:

 

 

为了看到编译的结果,我们需要修改BaseEngine.ini中的设置把CompileDisplaysBinaryBackend设置为true,如果要显示生成的cpp文件,也可以把CompileDisplaysTextBackend设置为true。注意需要重新启动编辑器。点击编译后在OutputLog中得到的结果如下代码所示:

    
  1 BlueprintLog: New page: Compile NewBlueprint
  2 
  3 LogK2Compiler: [function ExecuteUbergraph_NewBlueprint]:
  4 
  5 Label_0x0:
  6 
  7 $4E: Computed Jump, offset specified by expression:
  8 
  9 $0: Local variable named EntryPoint
 10 
 11 Label_0xA:
 12 
 13 $5E: .. debug site ..
 14 
 15 Label_0xB:
 16 
 17 $5A: .. wire debug site ..
 18 
 19 Label_0xC:
 20 
 21 $5E: .. debug site ..
 22 
 23 Label_0xD:
 24 
 25 $1B: Virtual Function named FunctionTest
 26 
 27 $0: Local variable named CallFunc_FunctionTest_OutNewString
 28 
 29 $16: EX_EndFunctionParms
 30 
 31 Label_0x24:
 32 
 33 $5A: .. wire debug site ..
 34 
 35 Label_0x25:
 36 
 37 $5E: .. debug site ..
 38 
 39 Label_0x26:
 40 
 41 $19: Context
 42 
 43 ObjectExpression:
 44 
 45 $20: EX_ObjectConst (000000003022A100:KismetSystemLibrary /Script/Engine.Default__KismetSystemLibrary)
 46 
 47 Skip Bytes: 0x3D
 48 
 49 R-Value Property: (null)
 50 
 51 ContextExpression:
 52 
 53 $1C: Final Function (stack node KismetSystemLibrary::PrintString)
 54 
 55 $17: EX_Self
 56 
 57 $0: Local variable named CallFunc_FunctionTest_OutNewString
 58 
 59 $28: EX_False
 60 
 61 $27: EX_True
 62 
 63 $2F: literal struct LinearColor (serialized size: 16)
 64 
 65 $1E: literal float 0.000000
 66 
 67 $1E: literal float 0.660000
 68 
 69 $1E: literal float 1.000000
 70 
 71 $1E: literal float 1.000000
 72 
 73 $30: EX_EndStructConst
 74 
 75 $1E: literal float 2.000000
 76 
 77 $16: EX_EndFunctionParms
 78 
 79 Label_0x79:
 80 
 81 $5A: .. wire debug site ..
 82 
 83 Label_0x7A:
 84 
 85 $4: Return expression
 86 
 87 $B: EX_Nothing
 88 
 89 Label_0x7C:
 90 
 91 $53: EX_EndOfScript
 92 
 93 LogK2Compiler: [function ReceiveBeginPlay]:
 94 
 95 Label_0x0:
 96 
 97 $1B: Virtual Function named ExecuteUbergraph_NewBlueprint
 98 
 99 $1D: literal int32 10
100 
101 $16: EX_EndFunctionParms
102 
103 Label_0x13:
104 
105 $4: Return expression
106 
107 $B: EX_Nothing
108 
109 Label_0x15:
110 
111 $53: EX_EndOfScript
112 
113 LogK2Compiler: [function UserConstructionScript]:
114 
115 Label_0x0:
116 
117 $5E: .. debug site ..
118 
119 Label_0x1:
120 
121 $5A: .. wire debug site ..
122 
123 Label_0x2:
124 
125 $4: Return expression
126 
127 $B: EX_Nothing
128 
129 Label_0x4:
130 
131 $53: EX_EndOfScript
132 
133 LogK2Compiler: [function FunctionTest]:
134 
135 Label_0x0:
136 
137 $5E: .. debug site ..
138 
139 Label_0x1:
140 
141 $5A: .. wire debug site ..
142 
143 Label_0x2:
144 
145 $5E: .. debug site ..
146 
147 Label_0x3:
148 
149 $F: Let (Variable = Expression)
150 
151 Variable:
152 
153 $0: Local variable named LocalStringTest
154 
155 Expression:
156 
157 $1F: literal ansi string "Bluepirnt Test: "
158 
159 Label_0x27:
160 
161 $5A: .. wire debug site ..
162 
163 Label_0x28:
164 
165 $F: Let (Variable = Expression)
166 
167 Variable:
168 
169 $0: Local variable named CallFunc_Concat_StrStr_ReturnValue
170 
171 Expression:
172 
173 $19: Context
174 
175 ObjectExpression:
176 
177 $20: EX_ObjectConst (0000000030229B00:KismetStringLibrary /Script/Engine.Default__KismetStringLibrary)
178 
179 Skip Bytes: 0x1C
180 
181 R-Value Property: CallFunc_Concat_StrStr_ReturnValue
182 
183 ContextExpression:
184 
185 $1C: Final Function (stack node KismetStringLibrary::Concat_StrStr)
186 
187 $0: Local variable named LocalStringTest
188 
189 $1: Instance variable named StringTest
190 
191 $16: EX_EndFunctionParms
192 
193 Label_0x6C:
194 
195 $5E: .. debug site ..
196 
197 Label_0x6D:
198 
199 $F: Let (Variable = Expression)
200 
201 Variable:
202 
203 $48: Local out variable named OutNewString
204 
205 Expression:
206 
207 $0: Local variable named CallFunc_Concat_StrStr_ReturnValue
208 
209 Label_0x88:
210 
211 $5A: .. wire debug site ..
212 
213 Label_0x89:
214 
215 $4: Return expression
216 
217 $B: EX_Nothing
218 
219 Label_0x8B:
220 
221 $53: EX_EndOfScript

 

有个需要说明的地方就是,我们可以看到事件ReceiveBeginPlay,如上面我们所说,它具体并没有做什么事情,整个函数的指令被放到了function ExecuteUbergraph_NewBlueprint中,而它所做的事情是调用了 Virtual Function named ExecuteUbergraph_NewBlueprint 并传递了一个int32的值,这个值是在ExecuteUbergraph_NewBlueprint处的偏移值,而在ExecuteUbergraph_NewBlueprint一开始就根据传进来的偏移值进行了无条件jump跳转到相应的位置进行程序的执行。

 

总结

至此,我们我们对蓝图的编译过程有了一个基本的了解,粗略地讲解了蓝图是如何从我们编辑的结果最终编译的过程,接下来的文章我们将介绍虚幻4中蓝图虚拟机的实现,敬请期待。当然由于本人理解能力有限,里面难免有错误的地方,如读者发现还请指正。

参考文档

  1. https://docs.unrealengine.com/latest/INT/Engine/Blueprints/TechnicalGuide/Compiler/index.html
  2. http://www.cnblogs.com/ghl_carmack/p/5804737.html
  3. 脚本语言入门书籍 Game Scripting Mastery
  4. http://blog.csdn.net/tangl_99/article/details/5600
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