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基于V8引擎的C++和JS的相互交互

2012-01-15 21:50:13| 分类：挨踢咋活 | 标签： |举报 |字号大中小订阅

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基于什么原因略！

1. 脚本引擎的基本功能

V8只是一个JS引擎。去除它的特点功能出处，它必须要实现JS引擎的几个基础功能：

脚本执行：

脚本可能是一个表达式；一段js代码；或者一个文件
执行表达式返回js表达式对应的值

C++来取设JS的内容

获取JS内容的数据(包括基础数据类型、数组、日期等)、对象（类的一个实例）、类或函数
设置JS内容的数据

JS来取设C++的内容

C++为js动态添加类（例如：Date，可以通过new Date()来创建任意多个对象）
C++为js动态添加全局对象（例如：Math，可以直接调用其全局方法如Math.min）

我们的目的是先学会怎么用，再去想为什么！

2. V8 脚本引擎基本功能实现

带着这几个目的去使用V8，找遍网上资料，发现很少有覆盖周全的。其实翻来覆去就是那几个资料，理论派居多；最可气的是按照那些例子去跑，怎么都会运行错误；而且在关键的地方全按照google伪代码例子照搬。不过理论派的阐述确实很一本正经；很精辟。也感谢先行者！

2. 1 V8之脚本运行

2.1.1 获取字符串：

void test_String()
{
  Handle<String> source = String::New("'Hello' + ', World!'");
  Handle<Script> script = Script::Compile(source);
  Handle<Value> result = script->Run();

  String::AsciiValue ascii(result);
  printf("%s\n", *ascii);
}
>>> Hello，World!

2.1.2 获取数组：

void test_Array()
{
  Handle<String> source = String::New("[1, 2, 'hello', 6+5]");
  Handle<Script> script = Script::Compile(source);
  Handle<Value> result = script->Run();

  String::AsciiValue ascii(result);
  printf("%s\n", *ascii);
}
>>> 1,2,hello,11

2. 2 V8之C++取设JS

2.2.1 获取成员之数据

void test_getjs_data(Handle<Context> pContext)
{
 Handle<String> source = String::New("var s1 = 8+5;");
 Handle<Script> script = Script::Compile(source);
 Handle<Value> result = script->Run();
 Handle<String> js_data = String::New("s1");
 Handle<Value> js_data_value = pContext->Global()->Get(js_data);

 String::AsciiValue ascii(js_data_value);
 printf("%s\n", *ascii);
}
>>> 13

2.2.2 获取成员之全局对象

void test_getjs_dataofObject(Handle<Context> pContext)
{
 Handle<String> source = String::New("function Point(x,y){this.x=x; this.y=y;} var pt=new Point(10,20);");
 Handle<Script> script = Script::Compile(source);
 Handle<Value> result = script->Run();

 Handle<String> js_data = String::New("pt");
 Handle<Value> js_data_value = pContext->Global()->Get(js_data);

 // Convert the result to an ASCII string and print it.
 {
  String::AsciiValue ascii(js_data_value);
  printf("pt = %s\n", *ascii);
 }
 Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value);

 Handle<Value> key = String::New("x");
 Handle<Value> objX = js_data_object->Get(key);
 {
  String::AsciiValue ascii(objX);
  printf("pt.x = %s\n", *ascii);
 }
}
>>> pt = [object Object]
    pt.x = 10

2.2.3 获取js 类

void test_getjs_dataofObjectClass(Handle<Context> pContext)
{
 Handle<String> source = String::New("function Point(x,y){this.x=x; this.y=y;} Point.prototype.show=function(){return '(x,y) = '+this.x+','+this.y;}");
 Handle<Script> script = Script::Compile(source);
 Handle<Value> result = script->Run();

 Handle<String> js_data = String::New("Point");
 Handle<Value> js_data_value = pContext->Global()->Get(js_data);

 // Convert the result to an ASCII string and print it.
 {
  String::AsciiValue ascii(js_data_value);
  printf("Point = %s\n", *ascii);
 }

 bool bIsFunction = js_data_value->IsFunction();
 if(bIsFunction)
 {
  printf("Point is function\n");
 }

 bool bIsObject = js_data_value->IsObject();
 if(bIsObject)
 {
  printf("Point is object\n");
 }

 Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value);
 // var newObj = new Point(1,2);
 Handle<Value>  argv[2] ; 
 argv[0] = Int32::New(1);
 argv[1] = Int32::New(2);
 Handle<Value> newObj = js_data_object->CallAsConstructor(2, argv);
 {
  bool bIsFunction = newObj->IsFunction();
  if(bIsFunction) //-false-
  {
   printf("newObj is function\n");
  }

  bool bIsObject = newObj->IsObject();
  if(bIsObject) //-true-
  {
   printf("newObj is object\n");
  }
 }

 // newObj.show();
 {
  Handle<Object> obj = Handle<Object>::Cast(newObj);
  Handle<String> js_func_name = String::New("show");
  Handle<Value>  js_func_ref = obj->Get(js_func_name);

  Handle<Function> js_func = Handle<Function>::Cast(js_func_ref);
  js_data_value = js_func->Call(obj, 0, NULL) ; 

  String::AsciiValue ascii(js_data_value);
  printf("newObj.show() = %s\n", *ascii);
 }
}
>>> Point = function Point(x,y){this.x=x; this.y=y;}
Point is function
Point is object
newObj is object
newObj.show() = (x,y) = 1,2

2. 3 V8之JS取设C++

2.3.0 js 和 C++的关联

c++ 和 js对应。特别是为达到能在Js中使用var obj = new CObject()，参照CreateObjectToJs方法

void test_getc_loadObjectTemplate(Handle<ObjectTemplate> pObj)
{
 //-load c++'s data-
 pObj->SetAccessor(String::New("x"), XGetter, XSetter);
 
 //-load c++'s function-
 pObj->Set(String::New("setColor"),FunctionTemplate::New(set_color));

 //-load c++'s class-
 CreateObjectToJs(pObj);
}

Point* NewPointFunction(const Arguments & args)
 {
  if(args.Length()==2)
  {
   Local<Value> v1 = args[0];
   Local<Value> v2 = args[1];

   return new Point( v1->Int32Value(), v2->Int32Value() );
  }
  else
  return new Point();
 }

void PointWeakExternalReferenceCallback(Persistent<Value>, void* parameter)
{
 if (Point* cpp_object = static_cast<Point*>(parameter))
  delete cpp_object;
}

Persistent<External> NewWeakExternalPoint(void* parameter)
{
 Persistent<External> ret = Persistent<External>::New(External::New(parameter));
 ret.MakeWeak(parameter, PointWeakExternalReferenceCallback);
 return ret;
}

Handle<Value> PointFunctionInvocationCallback(const Arguments &args)
 {
 if (!args.IsConstructCall())
 return Undefined();

 Point* cpp_object = NewPointFunction(args);
 if (!cpp_object)
 return ThrowException(String::New("Can not create Object in C++"));

 args.Holder()->SetInternalField(0, NewWeakExternalPoint(cpp_object));
 return Undefined();
 }

void CreateObjectToJs(Handle<ObjectTemplate> pObj)
{ 
 Point* p = new Point(0, 0);
 Handle<FunctionTemplate> point_templ = FunctionTemplate::New(&PointFunctionInvocationCallback, External::New(p));
 point_templ->SetClassName(String::New("Point"));
 point_templ->InstanceTemplate()->SetInternalFieldCount(1);

 Handle<ObjectTemplate> point_proto = point_templ->PrototypeTemplate();
 point_proto->SetAccessor(String::New("x"), GetPointX, SetPointX);
 point_proto->SetAccessor(String::New("y"), GetPointY, SetPointY);
 point_proto->Set(String::New("show"), FunctionTemplate::New(ShowPoint));

 pObj->Set(String::New("Point"), point_templ);
}

2.3.1 全局函数

c++:

Handle<Value> set_color(const Arguments & args) 
{
  Handle<Value>  rtn;
  if(args.Length() == 3) 
  {
 int r = args[0]->Int32Value();
 int g = args[1]->Int32Value();
 int b = args[2]->Int32Value();  

 char szTmp[80] = "";
 _stprintf(szTmp,"RGB%2X%02X%02X", r,g,b);
 rtn = String::New(szTmp);
  }
  else
   rtn = Undefined();
  
  return  rtn;
}

js:

void test_getc_function(Handle<Context> pContext, Handle<ObjectTemplate> pObj)
{
 Handle<String> source = String::New("var data = setColor(255,128,0);");
 Handle<Script> script = Script::Compile(source);
   Handle<Value> result = script->Run();

 Handle<String> js_data = String::New("data");
 Handle<Value> js_data_value = pContext->Global()->Get(js_data);

 // Convert the result to an ASCII string and print it.
 String::AsciiValue ascii(js_data_value);
 printf("%s\n", *ascii);
}
>>> RGBFF8000

2.3.2 全局数据

c++:

int x = 0;
Handle<Value> XGetter(Local<String> key,const AccessorInfo& info) 
{
    return Integer::New(x);
}

 void XSetter(Local<String> key, Local<Value> value,const AccessorInfo& info) 
{
    x = value->Int32Value();
}

js:

void test_getc_data(Handle<Context> pContext, Handle<ObjectTemplate> pObj)
{
 Handle<String> source = String::New("var data1 = x; x=200; var data2=x;");
 Handle<Script> script = Script::Compile(source);
 Handle<Value> result = script->Run();

 {
  Handle<String> js_data = String::New("data1");
  Handle<Value> js_data_value = pContext->Global()->Get(js_data);
  String::AsciiValue ascii(js_data_value);
  printf("data1 = %s\n", *ascii); 
 }

 {
  Handle<String> js_data = String::New("data2");
  Handle<Value> js_data_value = pContext->Global()->Get(js_data);
  String::AsciiValue ascii(js_data_value);
  printf("data2 = %s\n", *ascii); 
 }
}
>>> data1 = 0
data2 = 200

2.3.3 类

c++

struct Point
 {
    Point() 
 {
  x_ = 0;
  y_ = 0;
 }
    Point(int x, int y) 
 {
  x_ = x;
  y_ = y;
 }
 
    int getX() const { 
  return x_; 
 }
    int getY() const { return y_; }
    void setX(int value) { x_ = value; }
    void setY(int value) { y_ = value; }
    bool isNull() const { return x_ == 0 && y_ == 0; }
 void show()
 {
  char szTmp[80] = "";
  _stprintf(szTmp, "x,y = %d,%d\n", x_, y_);
  printf(szTmp);
 }
    int x_, y_;
 };

Handle<Value> GetPointX(Local<String> key,const AccessorInfo &info) 
{
   Handle<Object> obj = info.This ();
    //Local<Object> self = info.Holder(); //使用此种方法会死!!!-
    Point& point = *static_cast<Point*> (Local<External>::Cast(obj->GetInternalField(0))->Value ()); 
 int value = point.x_;
    return Integer::New(value);
}

void SetPointX(Local<String> key, Local<Value> value,const AccessorInfo& info) 
{
 Handle<Object> obj = info.This ();
 Point& point = *static_cast<Point*> (Local<External>::Cast(obj->GetInternalField(0))->Value ()); 
 point.x_ = value->Int32Value();
}

Handle<Value> GetPointY(Local<String> key,const AccessorInfo &info) 
{
    Local<Object> self = info.Holder();
    Local<External> wrap = Local<External>::Cast(self->GetInternalField(0));
    void* ptr = wrap->Value();
    int value = static_cast<Point*>(ptr)->y_;
    return Integer::New(value);
}

void SetPointY(Local<String> key, Local<Value> value,const AccessorInfo& info) 
{
 Local<Object> self = info.Holder();
 Local<External> wrap = Local<External>::Cast(self->GetInternalField(0));
 void* ptr = wrap->Value();
 static_cast<Point*>(ptr)->y_ = value->Int32Value();
}

Handle<Value> ShowPoint(const Arguments& args)
{
 Local<Object> self = args.Holder();
 //Local<Object> self = info.Holder();
 Local<External> wrap = Local<External>::Cast(self->GetInternalField(0));
 void* ptr = wrap->Value();
 static_cast<Point*>(ptr)->show();

    return Undefined();
}

js

void test_getc_object(Handle<Context> pContext, Handle<ObjectTemplate> pObj)
{
 test_getobject(pContext);return;

 // Create a string containing the JavaScript source code.
 Handle<String> source = String::New("var pt=new Point(10,20);");

 // Compile the source code.
 Handle<Script> script = Script::Compile(source);
  
 // Run the script to get the result.
 Handle<Value> result = script->Run();

 Handle<String> js_data = String::New("pt");
 Handle<Value> js_data_value = pContext->Global()->Get(js_data);

 // Convert the result to an ASCII string and print it.
 {
  String::AsciiValue ascii(js_data_value);
  printf("pt = %s\n", *ascii);
 }

 Handle<Object> js_data_object = Handle<Object>::Cast(js_data_value);

 Handle<Value> key = String::New("x");
 Handle<Value> objX = js_data_object->Get(key);
 {
  String::AsciiValue ascii(objX);
  printf("pt.x = %s\n", *ascii);
 }
}
>>> Point = function Point() { [native code] }
Point is function
Point is object
newObj is object
src obj.x = 3
last obj.x = 30
begin newObj.show() : x,y = 30,4
newObj.show() = undefined

3. 教训

在VS200X C++中，请都使用/MDD 编译选项
对于类，需要绑定一个构造函数，主要目的是用来生成C++对象。该对象千万不要使用局部变量，而要是指针
对于C++扩展的类，通过FunctionTemplate来实现；而不要使用ObjectTemplate
对于JS中的全局对象，可以通过ObjectTemplate来实现。实际上就是绑定全局API和变量

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日志

基于V8引擎的C++和JS的相互交互

1. 脚本引擎的基本功能

2. V8 脚本引擎基本功能实现

2. 1 V8之脚本运行

2. 2 V8之C++取设JS

2. 3 V8之JS取设C++

2.3.0 js 和 C++的关联

2.3.1 全局函数

2.3.2 全局数据

2.3.3 类

3. 教训

历史上的今天

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热度

评论

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