RmlUi/Source/Lua/LuaType.cpp

#include <RmlUi/Core/Types.h>
#include <RmlUi/Lua/LuaType.h>
#include <RmlUi/Lua/Utilities.h>

namespace Rml {
namespace Lua {

int LuaTypeImpl::index(lua_State* L, const char* class_name)
{
	/*the table obj and the missing key are currently on the stack(index 1 & 2) as defined by the Lua language*/
	lua_getglobal(L, class_name); // stack pos [3] (fairly important, just refered to as [3])
	                              //  string form of the key.
	const char* key = luaL_checkstring(L, 2);
	if (lua_istable(L, -1))       //[-1 = 3]
	{
		lua_pushvalue(L, 2);      //[2] = key, [4] = copy of key
		lua_rawget(L, -2);        //[-2 = 3] -> pop top and push the return value to top [4]
		                          // If the key were looking for is not in the table, retrieve its' metatables' index value.
		if (lua_isnil(L, -1))     //[-1 = 4] is value from rawget above
		{
			// try __getters
			lua_pop(L, 1);                        // remove top item (nil) from the stack
			lua_pushstring(L, "__getters");
			lua_rawget(L, -2);                    //[-2 = 3], <ClassName>._getters -> result to [4]
			lua_pushvalue(L, 2);                  //[2 = key] -> copy to [5]
			lua_rawget(L, -2);                    //[-2 = __getters] -> __getters[key], result to [5]
			if (lua_type(L, -1) == LUA_TFUNCTION) //[-1 = 5]
			{
				lua_pushvalue(L, 1);              // push the userdata to the stack [6]
				lua_call(L, 1, 1);                // remove one, result is at [6]
			}
			else
			{
				lua_settop(L, 4);                   // forget everything we did above
				lua_getmetatable(L, -2);            //[-2 = 3] -> metatable from <ClassName> to top [5]
				if (lua_istable(L, -1))             //[-1 = 5] = the result of the above
				{
					lua_getfield(L, -1, "__index"); //[-1 = 5] = check the __index metamethod for the metatable-> push result to [6]
					if (lua_isfunction(L, -1))      //[-1 = 6] = __index metamethod
					{
						lua_pushvalue(L, 1);        //[1] = object -> [7] = object
						lua_pushvalue(L, 2);        //[2] = key -> [8] = key
						lua_call(L, 2, 1);          // call function at top of stack (__index) -> pop top 2 as args; [7] = return value
					}
					else if (lua_istable(L, -1))
						lua_getfield(L, -1, key); // shorthand version of above -> [7] = return value
					else
						lua_pushnil(L);           //[7] = nil
				}
				else
					lua_pushnil(L); //[6] = nil
			}
		}
		else if (lua_istable(L, -1)) //[-1 = 4] is value from rawget [3]
		{
			lua_pushvalue(L, 2);     //[2] = key, [5] = key
			lua_rawget(L, -2);       //[-2 = 3] = table of <ClassName> -> pop top and push the return value to top [5]
		}
	}
	else
		lua_pushnil(L); //[4] = nil

	lua_insert(L, 1);   // top element to position 1 -> [1] = top element as calculated in the earlier rest of the function
	lua_settop(L, 1);   // -> [1 = -1], removes the other elements
	return 1;
}

int LuaTypeImpl::newindex(lua_State* L, const char* class_name)
{
	//[1] = obj, [2] = key, [3] = value
	// look for it in __setters
	lua_getglobal(L, class_name);   //[4] = this table
	lua_pushstring(L, "__setters"); //[5]
	lua_rawget(L, -2);              //[-2 = 4] -> <ClassName>.__setters to [5]
	lua_pushvalue(L, 2);            //[2 = key] -> [6] = copy of key
	lua_rawget(L, -2);              //[-2 = __setters] -> __setters[key] to [6]
	if (lua_type(L, -1) == LUA_TFUNCTION)
	{
		lua_pushvalue(L, 1); // userdata at [7]
		lua_pushvalue(L, 3); //[8] = copy of [3]
		lua_call(L, 2, 0);   // call function, pop 2 off push 0 on
	}
	else
		lua_pop(L, 1); // not a setter function.
	lua_pop(L, 2);     // pop __setters and the <Classname> table
	return 0;
}

} // namespace Lua
} // namespace Rml