[Cocos2d-x] How to make Script Binding (Part 1)

Introduction

My name is @tkyaji. This is my first participation in the Advent Calendar. I would like to write an implementation method when adding Script binding to Cocos2d-x. I'm using version 3.2 of Cocos2d-x.

In addition, the preparation required when using bindings-generator was last year's Advent Calendar. giginet wrote a very easy-to-understand article, so I will omit the explanation around that (it was saved) [Cocos2d-x 3.0] How to automate Script Binding with binding-generator

In the following explanation, the script language to be added is described as "Lang". For example, for Lua, replace "Lang" with "Lua".

Rough procedure

1. Create a LangEngine class that inherits ScriptEngineProtocol
2. Write a function to convert between C ++ type and Lang language type
3. Add target language to bindings-generator
4. With bindings-generator, write the glue code generation logic earnestly
5. If you can do it all, correspond to the cocos command

It's almost like this. The implementation of the bindings-generator and cocos command is written in Python. It will probably be the last to support the cocos command, so first create a Lua Binding project and I think it is better to implement it in that.

Create LangEngine class

Create an Engine class that corresponds to LuaEngine for Lua and ScriptingCore for JS. It inherits from cocos2d :: ScriptEngineProtocol and overrides the following virtual function.

• getScriptType

Returns constants for each scripting language. There is an enum called ccScriptType in ScriptEngineProtocol, so add the kScriptTypeLang constant here and I will return it.

• removeScriptObjectByObject

Called by the Ref class destructor. When an instance on C ++ dies due to autorelease etc., the instance on Lang language is also deleted. Implement such processing. The Ref class has fields _ID and _scriptObject. By setting the instance information on the Lang language here, the instance of C ++ and the instance of the Lang language can be set. It can be linked.

• executeString

Reads and executes the specified Lang language string.

• executeScriptFile

Loads and executes the specified Lang language script file. Basically, this method executes the script file under the * src * directory, so This is the method that needs to be implemented first.

executeGlobalFunction

Executes a global function on the Lang language with the specified name.

sendEvent

Called when various events (menu button press, touch, schedule, etc.) are fired. The argument ScriptEvent determines the type of event. If the event is registered by a method different from C ++, the process registered in this method is called. For example, in Lua, the callback is registered with the method registerScriptTapHandler, so In this case, execute the Lua function registered with registerScriptTapHandler in sendEvent. Conversely, if you have registered an event in ʻEventDispatcheras in C ++, Implementation is not required forsendEvent`.

handleAssert

Called from CCASERT. Here, we will implement error log output and Lang language error handling. For example, raise an exception on the Lang language.

parseConfig

For cooperation with CocoStudio?

Implemented type conversion function between C ++ ⇔ Lang language

The source is LuaBasicConversions for Lua and js_manual_conversions for JS. We will create a function that converts C ++ types and Lang language types. For example, in the case of Lua, the function that converts Vec2 is defined as follows.

// c++ -> lua
void vec2_to_luaval(lua_State* L,const cocos2d::Vec2& vec2)
{
    if (NULL  == L)
        return;
    lua_newtable(L);                                    /* L: table */
    lua_pushstring(L, "x");                             /* L: table key */
    lua_pushnumber(L, (lua_Number) vec2.x);               /* L: table key value*/
    lua_rawset(L, -3);                                  /* table[key] = value, L: table */
    lua_pushstring(L, "y");                             /* L: table key */
    lua_pushnumber(L, (lua_Number) vec2.y);               /* L: table key value*/
    lua_rawset(L, -3);
}

// lua -> c++
bool luaval_to_vec2(lua_State* L,int lo,cocos2d::Vec2* outValue)
{
    if (nullptr == L || nullptr == outValue)
        return false;
    
    bool ok = true;
    
    tolua_Error tolua_err;
    if (!tolua_istable(L, lo, 0, &tolua_err) )
    {
#if COCOS2D_DEBUG >=1
        luaval_to_native_err(L,"#ferror:",&tolua_err);
#endif
        ok = false;
    }
    
    if (ok)
    {
        lua_pushstring(L, "x");
        lua_gettable(L, lo);
        outValue->x = lua_isnil(L, -1) ? 0 : lua_tonumber(L, -1);
        lua_pop(L, 1);
        
        lua_pushstring(L, "y");
        lua_gettable(L, lo);
        outValue->y = lua_isnil(L, -1) ? 0 : lua_tonumber(L, -1);
        lua_pop(L, 1);
    }
    return ok;
}

These conversion functions are used when implementing bindings-generator. You don't have to create everything first, as you can add the types you need as needed while implementing the bindings-generator. It is also possible to implement the above conversion function without creating it, but in most cases it is easier to create it.

For the time being, that's all for today. Tomorrow I would like to explain about the implementation of * bindings-generator *.

[Cocos2d-x] How to make Script Binding (Part 2)