Add minetest.register_lbm() to run code on block load only

src/script/cpp_api/s_base.h

@@ -83,6 +83,7 @@ public:
 
 protected:
 	friend class LuaABM;
+	friend class LuaLBM;
 	friend class InvRef;
 	friend class ObjectRef;
 	friend class NodeMetaRef;

src/script/cpp_api/s_env.cpp

@@ -86,13 +86,12 @@ void ScriptApiEnv::initializeEnvironment(ServerEnvironment *env)
 	setEnv(env);
 
 	/*
-		Add ActiveBlockModifiers to environment
+		Add {Loading,Active}BlockModifiers to environment
 	*/
 
 	// Get core.registered_abms
 	lua_getglobal(L, "core");
 	lua_getfield(L, -1, "registered_abms");
-	luaL_checktype(L, -1, LUA_TTABLE);
 	int registered_abms = lua_gettop(L);
 
 	if(lua_istable(L, registered_abms)){
@@ -154,6 +153,58 @@ void ScriptApiEnv::initializeEnvironment(ServerEnvironment *env)
 			// removes value, keeps key for next iteration
 			lua_pop(L, 1);
 		}
+	} else {
+		lua_pop(L, 1);
+		throw LuaError("core.registered_abms was not a lua table, as expected.");
+	}
+	lua_pop(L, 1);
+
+	// Get core.registered_lbms
+	lua_getglobal(L, "core");
+	lua_getfield(L, -1, "registered_lbms");
+	int registered_lbms = lua_gettop(L);
+
+	if (!lua_istable(L, registered_lbms)) {
+		lua_pop(L, 1);
+		throw LuaError("core.registered_lbms was not a lua table, as expected.");
+	}
+
+	lua_pushnil(L);
+	while (lua_next(L, registered_lbms)) {
+		// key at index -2 and value at index -1
+		int id = lua_tonumber(L, -2);
+		int current_lbm = lua_gettop(L);
+
+		std::set<std::string> trigger_contents;
+		lua_getfield(L, current_lbm, "nodenames");
+		if (lua_istable(L, -1)) {
+			int table = lua_gettop(L);
+			lua_pushnil(L);
+			while (lua_next(L, table)) {
+				// key at index -2 and value at index -1
+				luaL_checktype(L, -1, LUA_TSTRING);
+				trigger_contents.insert(lua_tostring(L, -1));
+				// removes value, keeps key for next iteration
+				lua_pop(L, 1);
+			}
+		} else if (lua_isstring(L, -1)) {
+			trigger_contents.insert(lua_tostring(L, -1));
+		}
+		lua_pop(L, 1);
+
+		std::string name;
+		getstringfield(L, current_lbm, "name", name);
+
+		bool run_at_every_load = getboolfield_default(L, current_lbm,
+			"run_at_every_load", false);
+
+		LuaLBM *lbm = new LuaLBM(L, id, trigger_contents, name,
+			run_at_every_load);
+
+		env->addLoadingBlockModifierDef(lbm);
+
+		// removes value, keeps key for next iteration
+		lua_pop(L, 1);
 	}
 	lua_pop(L, 1);
 }

src/script/lua_api/l_env.cpp

@@ -90,6 +90,46 @@ void LuaABM::trigger(ServerEnvironment *env, v3s16 p, MapNode n,
 	lua_pop(L, 1); // Pop error handler
 }
 
+void LuaLBM::trigger(ServerEnvironment *env, v3s16 p, MapNode n)
+{
+	GameScripting *scriptIface = env->getScriptIface();
+	scriptIface->realityCheck();
+
+	lua_State *L = scriptIface->getStack();
+	sanity_check(lua_checkstack(L, 20));
+	StackUnroller stack_unroller(L);
+
+	int error_handler = PUSH_ERROR_HANDLER(L);
+
+	// Get registered_lbms
+	lua_getglobal(L, "core");
+	lua_getfield(L, -1, "registered_lbms");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	lua_remove(L, -2); // Remove core
+
+	// Get registered_lbms[m_id]
+	lua_pushnumber(L, m_id);
+	lua_gettable(L, -2);
+	FATAL_ERROR_IF(lua_isnil(L, -1), "Entry with given id not found in registered_lbms table");
+	lua_remove(L, -2); // Remove registered_lbms
+
+	scriptIface->setOriginFromTable(-1);
+
+	// Call action
+	luaL_checktype(L, -1, LUA_TTABLE);
+	lua_getfield(L, -1, "action");
+	luaL_checktype(L, -1, LUA_TFUNCTION);
+	lua_remove(L, -2); // Remove registered_lbms[m_id]
+	push_v3s16(L, p);
+	pushnode(L, n, env->getGameDef()->ndef());
+
+	int result = lua_pcall(L, 2, 0, error_handler);
+	if (result)
+		scriptIface->scriptError(result, "LuaLBM::trigger");
+
+	lua_pop(L, 1); // Pop error handler
+}
+
 void LuaEmergeAreaCallback(v3s16 blockpos, EmergeAction action, void *param)
 {
 	ScriptCallbackState *state = (ScriptCallbackState *)param;

src/script/lua_api/l_env.h

@@ -220,6 +220,24 @@ public:
 			u32 active_object_count, u32 active_object_count_wider);
 };
 
+class LuaLBM : public LoadingBlockModifierDef
+{
+private:
+	int m_id;
+public:
+	LuaLBM(lua_State *L, int id,
+			const std::set<std::string> &trigger_contents,
+			const std::string &name,
+			bool run_at_every_load):
+		m_id(id)
+	{
+		this->run_at_every_load = run_at_every_load;
+		this->trigger_contents = trigger_contents;
+		this->name = name;
+	}
+	virtual void trigger(ServerEnvironment *env, v3s16 p, MapNode n);
+};
+
 struct ScriptCallbackState {
 	GameScripting *script;
 	int callback_ref;