1. +
Component-based
Entity system
in Mobile Game Development
CodyNguyen
Mobile Game Developer, Vinova VN
cody@vinova.vn

2. +
Start small: cute infinite fly game
Gasboy

3. +
After that: a cooler (and bigger) game
Stickman
Traps
Skills
God’s Rage

4. +
architecture problems start to pop out
As with any software getting more complex,

5. +
Game entities share capabilities among
each others
deal_damage_around
deal_damage_around deal_damage_around
deal_damage_around
movable
movable movable
throwable
throwable
lie_on_ground
lie_on_ground
delay_on_activating
delay_on_activating
activate_on_touch
activate_on_touch

6. +
Game entities share capabilities among
each others
Impossible to build a good OOP class hierarchy!
natural relationships welcome changes code reuse

7. +
First solution comes to mind:
mix-ins via multiple-inheritance
1. Just a small portion of the tree is a mess already
2. Multiple inheritance smells
3. Where to put logic that evolves object of different classes?
Capability
Moveable DealDamage ActivateOnTouch Throwable
Thorn Cloud Bomb Bull

8. +
Need a better solution
Component-based entity system has been
a hot topic for years.
It helps solve our problem in an elegant way!

9. +
Component-based entity system
Multitude of ways to represent and
implement
This talk discusses one way which we found
practical and easy to understand
Three elements:
 Entity
 Component
 System

10. +
Component-based entity system
Decompose game entities by capabilities into
reusable components.
Prefer aggregation over inheritance, i.e.,
entity has components, not is a type of
some component.

11. +
Entity and Component
Velocity Damage Graphic ThrowAngle ActivateOnTouch
Thorn x x x
Cloud x x x
Bomb x x x x
Bull x x x x
Entity is: an unique ID + a list of components
Component contains only data

12. +
Where does the logic go?
The systems.
Bull Light
-ning
Thorn
Cloud
Stick
-man
Game has a bunch of
entities
Entities are processed by
systems
M o v e m e n t S y s t e m
A n i m a t i o n S y s t e m
P h y s i c s S y s t e m
C o l l i s i o n S y s t e m
H e a l t h S y s t e m

13. +
Systems only process entities they
“care” about
Entities are keys Systems are locks
http://gamedev.stackexchange.com/a/31491
Components are teeth

14. +
Entity system sum up
 Entity
 Is just a unique ID with a bunch of components
 Doesn’t need a separate Class for each entity
 Component
 Is the “ingredient” to make entities.
 Contains data only.
 System
 Contains game logic
 Run on every game loop, process entities who has a set of
components it care about.

15. +
Other benefits of using entity
system
 Goes hand-in-hand with Data-Driven development:
 Entities are defined as bags of components, in text file.
 “No engineer required”, game designer can create new or edit
existing entities easily.
 Easy to change or fine-tune entities
 Promote multi-threading
 Systems are independent from one another, so they can run on
separate threads

16. +
Artemis Entity System
 An Entity system framework written in Java:
http://gamadu.com/artemis/tutorial.html
 Is open-source, active project
 Ported to many different languages

17. +
Artemis Entity System and Cocos2d
 Sidar Talei ported to C++, we forked, modified and maintain:
https://github.com/vinova/Artemis-Cpp
 Our port:
 Works great with cocos2d-x!
 Work great with any C++ framework. No external libs or C++11
compiler are required
 JavaScript binding coming soon

18. +
References
 A Data-Driven Game Object System
http://scottbilas.com/files/2002/gdc_san_jose/game_objects_slides.ppt
 Entity Systems are the future of MMOG development
http://t-machine.org/index.php/2007/11/11/entity-systems-are-the-future-of-mmog-
development-part-2/
 Evolve Your Hierarchy
http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/