The document discusses the integration of Lua scripting into Unreal Engine 4, emphasizing its advantages over traditional blueprints, such as being lightweight and easy to learn. It outlines the creation of tools for game designers and modders, detailing the LuaMachine project which facilitates this scripting. Additionally, it covers technical aspects like memory management, coroutine functionality, and community resources for users.

1. Scripting (and modding) Unreal
Engine
with Lua
Roberto De Ioris
https://github.com/rdeioris
https://github.com/unbit
@unbit
Codemotion Rome 2019

3. What do they have
in
common ?
∙ Game
Designers
∙ Animators
∙ Riggers
∙ Data Analysts

4. "Teach a man to use a game
engine
and he'll ship a game,
teach a man to build a game
engine and
he'll never ship anything"

5. Programming and
Scripting
in Unreal Engine 4
∙ C++
∙ Blueprints
∙ Various Plugins (Python, Javascript, Lua,
…)

6. Why “classic”
Scripting
Instead of Blueprints
∙ Scaling
∙ Expressivene
ss

7. Why Lua
?
∙ Embarrassingly easy (very few
rules)
∙ Tiny
∙ Fast
∙ Embeddable (without pain)
∙ Multiple VMs in the same process
∙ Solid
∙ Big Community
∙ Lot of third party libraries
∙ …

8. Caveats when
embedding
scripting languages
∙ Memory management
(!!!)
∙ Language Idiomaticity
∙ Data Representation
∙ Performance

9. The Unreal Engine 4
API
OO
P OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P
OO
P OO
P
OO
P

10. Lua and “classic”
OOP

11. Building a tool
for
Game Designers
∙ Low learning curve
∙ Built on top of the designers needs, not the engine
ones
∙ “Safe”
∙ Debuggable

12. Building a tool
for
Modders
∙ Low learning curve
∙ Built on top of the modders needs, not the engine
ones
∙ “Safe”
∙ Debuggable

13. LuaMachin
e
https://github.com/rdeioris/LuaMachine
https://www.unrealengine.com/marketplace/luamach
ine

14. Supported
Platforms
∙ Windows 64bit (Editor +
Runtime)
∙ Mac (Editor + Runtime)
∙ Linux 64bit (Editor + Runtime)
∙ Android (Runtime)
∙ iOS (Runtime)

15. Hello
World

16. SayHello
UFunction

17. Exposing
SayHello
as Lua’s hello()

18. Calling the Lua
script

19. Welcome Lua in
UE

20. Isolation:
LuaStates

21. Data
Representation:
LuaValues

22. Working with
LuaValues

23. Working with
LuaValues

24. Working with
LuaValues

25. Working with
LuaValues

26. Working with
LuaValues
(C++)UCLASS()
class LUATEST422_API UCodemotionCppLuaState : public ULuaState
{
GENERATED_BODY()
UFUNCTION()
FLuaValue DummyAdder(TArray<FLuaValue> Args);
};
FLuaValue UCodemotionCppLuaState::DummyAdder(TArray<FLuaValue> Args)
{
int32 Total = 0;
for (FLuaValue& Arg : Args)
{
Total += Arg.ToInteger();
}
return FLuaValue(Total);
}

27. Scripts as
Assets:
LuaCode

28. Running Lua
Scripts

29. Running Lua
Scripts
from URLs∙ Think
twice
∙ Think
twice
∙ Think
twice

30. Running Lua
Scripts
from URLs [take
two]∙ RSA
signing
∙ https

31. LuaState:
require

32. Widget
s
∙ Code Editor with syntax
colouring
∙ ANSI Output (WIP)

33. Widgets in
action

34. Error
Management

35. Monitoring and
Managing
∙ Memory
usage
∙ Stack top
∙ GC

36. Debuggin
g
∙ Simple GUI (WIP)
∙ Events
∙ via Lua-itself

37. Debugger in
action

38. Debug
Hooks

39. Debug Hooks
(C++)
void UCodemotionCppLuaState::ReceiveLuaCallHook_Implementation(const FLuaDebug& LuaDebug)
{
UE_LOG(LogLuaMachine, Warning, TEXT("Name: %s"), *LuaDebug.Name);
}

40. Coroutine
s

41. Ticking
Coroutines

42. Ticking
Coroutines
(improved)

43. Lua Tables as
Assets

44. Lua Interfaces
???

45. UObject’s
Representation:
Metatables for
UserData

46. Blueprint (and C++)
Functional Tests
included

47. Running LuaMachine
Tests

48. Hidden
Features
∙ Reflection API
∙ Lua States as Singletons/Managers (with
Events)
∙ Syntax Highlighter (with custom keywords)

49. Note
s
∙ You can call Lua functions from everywhere
∙ (animation blueprints, behaviour trees, widgets,…)
∙ C++ UFUNCTIONs can be exposed easily
∙ You can easily convert C++ UPROPERTies to Lua
tables

50. Tutorial
https://github.com/rdeioris/LuaMachine/blob/master/Tutorials/SimpleDialogueSystem.m
d

51. Communit
y
Discord channel:
https://discord.gg/eTXDfEU

52. Special
Thanks
∙ AIV
∙ Nicolas Martel (aka.
Nogitsu)
∙ Epic