Xlua对c#的vector3等结构体的优化

2021-08-27 04:53:45

目录:Xlua源码学习参考文章：： https://www.jianshu.com/p/07dc38e85923 https://gameinstitute.qq.com/community/detail/111993 https://gameinstitute.qq.com/community/detail/125117 一、lua如何操作Vector3，中间做了什么操作？ 1.获取Vector3对象由于Vector3的方法、属性都是成员方法、属性(如x、y、z、Slerp)，那么调用这些方法前需要先获取Vector3对应的对象。比如Vector3()新建、transform.position获取等。以transform.position为例：_g_get_position方法创建了一个CSharpStruct类型的ud,并把x,y,z存在这个ud里。这个ud的元表指向Vector3的obj_meta，通过这个元表可以访问Vector3Wrap注册的所有方法、属性，进而间接访问到Vector3。

ud = 
{
    ["fake_id"] = -1
    ["len"] = 12 //存储3个float值的大小，的对应xyz，float是4字节32位。
    ["data"][0] = x
    ["data"][1] = y
    ["data"][0] = z
    ["__index"] = obj_meta
}

static int _g_get_position(RealStatePtr L)
{
    try {
        ObjectTranslator translator = ObjectTranslatorPool.Instance.Find(L);
 
        UnityEngine.Transform gen_to_be_invoked = (UnityEngine.Transform)translator.FastGetCSObj(L, 1);
        translator.PushUnityEngineVector3(L, gen_to_be_invoked.position);
    } catch(System.Exception gen_e) {
        return LuaAPI.luaL_error(L, "c# exception:" + gen_e);
    }
    return 1;
}
 
public void PushUnityEngineVector3(RealStatePtr L, UnityEngine.Vector3 val)
{
    if (UnityEngineVector3_TypeID == -1)
    {
        bool is_first;
        UnityEngineVector3_TypeID = getTypeId(L, typeof(UnityEngine.Vector3), out is_first);   
    }
    //创建一个大小为(12+4+4)字节的userdata，元表Vector3的元表
    IntPtr buff = LuaAPI.xlua_pushstruct(L, 12, UnityEngineVector3_TypeID);
    if (!CopyByValue.Pack(buff, 0, val)) //把vector3拆成3个float传入cc，在c的结构体buff存储数据
    {
    throw new Exception("pack fail fail for UnityEngine.Vector3 ,value="+val);
    }
}

xlua.c里的接口：

LUA_API void *xlua_pushstruct(lua_State *L, unsigned int size, int meta_ref) {
   CSharpStruct *css = (CSharpStruct *)lua_newuserdata(L, size + sizeof(int) + sizeof(unsigned int));
   css->fake_id = -1;
   css->len = size;
    lua_rawgeti(L, LUA_REGISTRYINDEX, meta_ref);
   lua_setmetatable(L, -2);
   return css;
}
 
LUALIB_API int xlua_pack_float3(void *p, int offset, float f1, float f2, float f3) {
   CSharpStruct *css = (CSharpStruct *)p;
   if (css->fake_id != -1 || css->len < offset + sizeof(float) * 3) {
      return 0;
   } else {
      float *pos = (float *)(&(css->data[0]) + offset);
      pos[0] = f1;
      pos[1] = f2;
      pos[2] = f3;
      return 1;
   }
}

2.设置transform.position 代码如下：主要是UnPack方法调用xlua的xlua_unpack_float3方法，从上面的ud结构里取到x,y,c的值压栈并赋值给UnPack的x,y,z参数，再由UnPack组装一个新的Vevtor3返回给_s_set_position进行赋值。

static int _s_set_position(RealStatePtr L)
{
    try {
        ObjectTranslator translator = ObjectTranslatorPool.Instance.Find(L);
 
        UnityEngine.Transform gen_to_be_invoked = (UnityEngine.Transform)translator.FastGetCSObj(L, 1);
        UnityEngine.Vector3 gen_value;
        translator.Get(L, 2, out gen_value);
        gen_to_be_invoked.position = gen_value;      
    } catch(System.Exception gen_e) {
        return LuaAPI.luaL_error(L, "c# exception:" + gen_e);
    }
    return 0;
}
 
public void Get(RealStatePtr L, int index, out UnityEngine.Vector3 val)
{
    LuaTypes type = LuaAPI.lua_type(L, index);
    if (type == LuaTypes.LUA_TUSERDATA )
    {
        IntPtr buff = LuaAPI.lua_touserdata(L, index);
        if (!CopyByValue.UnPack(buff, 0, out val))
        {
            throw new Exception("unpack fail for UnityEngine.Vector3");
        }
    }
    else if (type ==LuaTypes.LUA_TTABLE)
    {
        CopyByValue.UnPack(this, L, index, out val);
    }
    else
    {
        val = (UnityEngine.Vector3)objectCasters.GetCaster(typeof(UnityEngine.Vector3))(L, index, null);
    }
}
 
public static bool UnPack(IntPtr buff, int offset, out UnityEngine.Vector3 field)
{
    field = default(UnityEngine.Vector3);
    
    float x = default(float);
    float y = default(float);
    float z = default(float);
    
    if(!LuaAPI.xlua_unpack_float3(buff, offset, out x, out y, out z))
    {
        return false;
    }
    field.x = x;
    field.y = y;
    field.z = z;
    
    
    return true;
}

当然，如果你传的不是Vector3类型的usreData就更简单了，例如{x = 1, y = 2, z = 3},直接调用lua_rawget就可以取到了。

public static void UnPack(ObjectTranslator translator, RealStatePtr L, int idx, out UnityEngine.Vector3 val)
{
    val = new UnityEngine.Vector3();
          int top = LuaAPI.lua_gettop(L);
   
   if (Utils.LoadField(L, idx, "x"))
          {
       
              translator.Get(L, top + 1, out val.x);
      
          }
          LuaAPI.lua_pop(L, 1);
   
   if (Utils.LoadField(L, idx, "y"))
          {
       
              translator.Get(L, top + 1, out val.y);
      
          }
          LuaAPI.lua_pop(L, 1);
   
   if (Utils.LoadField(L, idx, "z"))
          {
       
              translator.Get(L, top + 1, out val.z);
      
          }
          LuaAPI.lua_pop(L, 1);
   
}
 
public static bool LoadField(RealStatePtr L, int idx, string field_name)
{
   idx = idx > 0 ? idx : LuaAPI.lua_gettop(L) + idx + 1;// abs of index
   LuaAPI.xlua_pushasciistring(L, field_name);
   LuaAPI.lua_rawget(L, idx);
   return !LuaAPI.lua_isnil(L, -1);
}

xlua.c的解包方法：

LUALIB_API int xlua_unpack_float3(void *p, int offset, float *f1, float *f2, float *f3) {
   CSharpStruct *css = (CSharpStruct *)p;
   if (css->fake_id != -1 || css->len < offset + sizeof(float) * 3) {
      return 0;
   } else {
      float *pos = (float *)(&(css->data[0]) + offset);
      *f1 = pos[0];
      *f2 = pos[1];
      *f3 = pos[2];
      return 1;
   }
}

3.Vector.x：取x值

流程其实跟transform.position差不多，先把自身的ud转成Vector3,再把Vector3.x压栈返回给lua。
static int _g_get_x(RealStatePtr L)
{
    try {
        ObjectTranslator translator = ObjectTranslatorPool.Instance.Find(L);
 
        UnityEngine.Vector3 gen_to_be_invoked;
        translator.Get(L, 1, out gen_to_be_invoked);
        LuaAPI.lua_pushnumber(L, gen_to_be_invoked.x);
    } catch(System.Exception gen_e) {
        return LuaAPI.luaL_error(L, "c# exception:" + gen_e);
    }
    return 1;
}

4.调用总结： lua跟c#的Vector3并没有直接的调用，而是通过中间层ud(CSharpStruct)进行中转。这里面的PushUnityEngineVector3、Get方法都是在wrap生成时动态生成的。每个GCOptimize标记的方法都会生成对应的Push、Get、Pack、UnPack方法，这些方法会调用到xlua.c里对应的c方法对结构体进行解包、封包。二、xlua为什么要这么做？ Vector3Wrap的__CreateInstance方法使用的是translator.PushUnityEngineVector3对Vector对象压栈。那为什么不用正常的translator.Push压栈呢？

static int __CreateInstance(RealStatePtr L)
{        
    try {
        ObjectTranslator translator = ObjectTranslatorPool.Instance.Find(L);
        if(LuaAPI.lua_gettop(L) == 4 && LuaTypes.LUA_TNUMBER == LuaAPI.lua_type(L, 2) && LuaTypes.LUA_TNUMBER == LuaAPI.lua_type(L, 3) && LuaTypes.LUA_TNUMBER == LuaAPI.lua_type(L, 4))
        {
            float _x = (float)LuaAPI.lua_tonumber(L, 2);
            float _y = (float)LuaAPI.lua_tonumber(L, 3);
            float _z = (float)LuaAPI.lua_tonumber(L, 4);
      
            UnityEngine.Vector3 gen_ret = new UnityEngine.Vector3(_x, _y, _z);
            translator.PushUnityEngineVector3(L, gen_ret);
                 
            return 1;
        }
    }
    catch(System.Exception gen_e) {
       return LuaAPI.luaL_error(L, "c# exception:" + gen_e);
    }        
}

translator.Push里会调用addObject把对象实例跟对象下标做一个绑定，这个唯一的下标用于在lua中获取到c#的对象实例。Struct是值类型，值类型和引用类型(object)的转换会涉及装箱、拆箱操作。

int addObject(object obj, bool is_valuetype, bool is_enum)
{
          int index = objects.Add(obj);
          if (is_enum)
          {
              enumMap[obj] = index;
          }
          else if (!is_valuetype)
          {
              reverseMap[obj] = index;
          }
   
   return index;
}

对装箱、拆箱不了解的可以参考文章：https://www.cnblogs.com/yukaizhao/archive/2011/10/18/csharp_box_unbox_1.html 所以xlua其实是对Vector3等值类型的结构体做了一个优化，避免了装箱和拆箱优化。但是，虽然xlua对结构体做了优化，但还是会有很多开销，例如：在c#需要push x\y\z参数，在lua需要创建表保存x\y\z值，需要查询元表等。那么如何优化呢？直接在函数中传递三个float，要比传递Vector3要更快。例如void SetPos(GameObject obj, Vector3pos)改为void SetPos(GameObject obj, float x, floaty, float z)。 对于c#的Struct还是少用，尽量封装静态方法调用，性能会更好。

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