Elixir is great for web servers and embedded devices, but is there anything else it’s good for? Yes! Elixir is also great at being a multiplayer game server. We’ll take a look through some existing applications that use Elixir as a multiplayer backend server, ExVenture and Kalevala. See how they’re architected to be full of state and event driven to handle thousands of users.

1. First title line
Second line here
Subtitle goes here — no fancy
color block kthough too fussy
smartly.
smartlogic.io
Writing Game
Servers With Elixir
Eric Oestrich
ElixirConf 2020
smartlogic.io

2. Who am I?
Eric Oestrich
Engineering Manager
at SmartLogic

3. Who is
SmartLogic?
We build custom
web and mobile
apps.
Based in Baltimore,
we've built over 150
apps since 2005.

4. Agenda
● Why MUDs?
● What are ExVenture & Kalevala?
● The pieces of Kalevala
● What does Elixir bring?
● Demo

5. Why MUDs?

6. Games for Programmers
No Graphix
Anyone can write text

8. What is ExVenture?

9. First Foray into OTP
ExVenture was my playground for learning OTP
Not everything was well laid out for Elixir
FP written in an OOP style

10. What is Kalevala?

11. An Ancient Finnish Text

12. Or a World Builder’s Toolkit

13. ExVenture 3.0
Kalevala is a rewrite of ExVenture’s internals
The third iteration

14. Pieces of Kalevala

15. Controllers,
Commands,
& Actions

16. Commanding Controllers
Input and event processing
Series of callbacks to hook into
Breaks up functionality into smaller pieces
Controllers -> Commands -> Actions

17. Before & After

18. Modules are broken up
Session process delegates work
Why is this better now?

19. The Conn

20. The Conn Struct
Similar to a Phoenix Conn
Character internals build up intents and then
the foreman plays out the intents

21. Before & After

23. Why is this better now?
Keeps the core functional
See Gary Bernhardt’s Boundaries
Commands do not interact with the world

24. Events

25. The Atom of Kalevala
Everything in Kalevala is an event
A generic struct with specific payloads
Rooms act as local PubSub

26. Before & After

27. Why is this better now?
Also passed a Conn, to not directly affect
anything

28. Views

29. Think Phoenix Views
Very similar to Phoenix views
Render functions
Builds up iodata lists

30. Output Processing
Transforms data en route to players
Text is reduced over processors

31. Before & After
Views

32. Before & After
Output Processing

33. Why is this better now?
Commands render views instead of outputting
to the socket directly
Iodata lists are fast
List of processors can be changed

34. Character
Brains

35. Behavior Trees
A behavior tree is a mathematical model of
plan execution used in computer science,
robotics, control systems and video games.
Per Wikipedia

36. Behavior Trees
Simple AI
A tree with branches and leaves
Branches are selectors
Leaves are evaluated and influence the selector

37. Before & After

38. Sample Brain
brains "generic_hello" {
type = "conditional"
nodes = [
{
type = "conditions/message-match"
data = {
self_trigger = false
text = "bhib"
}
},
{
type = "sequence"
nodes = [
...
...
{
type = "actions/say"
data = {
channel_name = "${channel_name}"
text = "Hello, ${name}!"
}
},
{
type = "actions/say"
data = {
channel_name = "${channel_name}"
text = "How are you?"
}
}
]
}
]
}

40. Why is this better now?
Nodes are just data
Built with protocols

41. The World

42. The World
See my talk from The Big Elixir 2019
All Aboard the State Train
youtube.com/watch?v=YbTzKiZIrv4

43. What does better Elixir
bring to the table?

44. Functional Core

45. Data
Transformation

46. Piece together
functionality

47. Events as Structs

48. Demo

49. GitHub
https://github.com/oestrich/kalevala

50. Elixir Wizards - elixirwizards.io

51. wor.fi
@wor_fi

52. Reach out for a
sticker pack, I’ve
got ~30 or so

53. Image Credits
https://www.goodnewsfinland.com/feature/in-pict
ures-the-weekend-wrap-1-3/kalevala/

54. Q&A

55. First title line
Second line here
Subtitle goes here — no fancy
color block kthough too fussy
smartly.
smartlogic.io
Thanks!
smartlogic.io

56. First title line
Second line here
Subtitle goes here — no fancy
color block kthough too fussy
smartly.
smartlogic.io
We build custom web
We’ve built 150+ applications since 2005.
Need a custom web/mobile app? We can help.
and mobile applications.
888-544-SMRT / contact@smartlogic.io