Lua in Games

Mr. Nguyễn Ngọc VânAss Software Manager – VNG Corporation

Agenda

1. Lua & Benefits2. Core engine & Lua model3. Lua integrations model4. Secure Lua code5. Disadvantages

1. Lua & Benefits

• Scripting language• Works through LVM (Lua Virtual Machine)• Stack model design• “Ultimate game scripting language” (GDC 2010)• Popular uses in games• Runs on most machines and devices• Written in ANSI C and distributed by small library

What’s Lua?

• Free and open source • Support OOP• Runs on almost platforms• Easy to interface with C/C++• Very clean C API• Auto memory management (GC)• Powerful, fast and lightweight• Flexible data structure (TABLE)

Lua Benefits

• Contents can be changed in real-time• Auto generate contents• Users can customize/change contents• Fast and easy distributed contents• Secure code• Easy to use, embed and learn• Good references

Lua Benefits

2. Core Engine & Lua Model

ConfigsSettings

(XML, INI, TXT, …)

Game Logic Process(Behaviors, AI, …)

Control Flow

Core Engine

ConfigsSettings(…, LUA)

Lua Engine

Control Flow

Core Engine

LUA Logic Process

(Behaviors, AI, …)

3. Lua Integrations Model

Core Logic(Logic Flow)

Lua Engine(LVM)

Lua codes

Lua APIs

Lua interface

Core Engine

• Lua APIs– Call to LVM through events/triggers base– C APIs to work with LVM– Auxiliary library provides basic functions to

check, register, debug, … LVM– Use C APIs to build core functions

• Lua Interface– Call to core logic through exports APIs– Provides APIs (game APIs) to work with core

logic– Use C APIs to build, register, and exports APIs

function OnPlayerUseItem(nItem)core.InstanceObj(OBJ_KIND_ITEM, nItem)if item.GetKind() == ITM_KIND_HP then

local nItemHP = item.GetAttribute(ITM_ATTR_HP)local nPlayerHP = player.GetCurrentHP()local nAddHP = 0.2 * nPlayerHPif nAddHP > 0 and nAddHP < player.GetMaxHP() then

player.SetCurrentHP(nAddHP)player.Message('Player:

'..player.GetName()..' use item '..item.GetName())end

endend

Quick Sample

4. Secure Lua Code

• Compile to byte-code– Popular use– Use luaC module included in library– Modify luaC with keys for more secure

• Encrypted– Little use– Use keys-pair to encrypted– Use signed file, CRC

• Simple codefunction Add(a, b)

return a + bendprint(Add(100, 200))

• Byte-code

5. Disadvantages

• C APIs are too low-level• Error messages are very confusing • No try-catch, no exceptions• Hard to debug• Hard to interfaces with unlike C/C++• Once LVM is crashed, it’s not likely to recover and

the service is crashed too • Hard to implement reload feature at run-time• For extreme speed, LuaJIT is a good choice