Presentation delivered at CodeStar Night, discussing ECS (Entity Component System) as a different approach for game and app development.

1. Entity Component System - a
different approach to game /
application development
Maxim Zaks @iceX33

2. Object Oriented Programming
SOLID Principals

4. public class Rectangle
{
public double Width { get; set; }
public double Height { get; set; }
}

5. public class AreaCalculator
{
public double Area(Rectangle[] shapes)
{
double area = 0;
foreach (var shape in shapes)
{
area += shape.Width*shape.Height;
}
return area;
}
}

6. public double Area(object[] shapes)
{
double area = 0;
foreach (var shape in shapes)
{
if (shape is Rectangle)
{
Rectangle rectangle = (Rectangle) shape;
area += rectangle.Width*rectangle.Height;
}
else
{
Circle circle = (Circle)shape;
area += circle.Radius * circle.Radius * Math.PI;
}
}
return area;
}

7. public abstract class Shape
{
public abstract double Area();
}

8. public class Rectangle : Shape
{
public double Width { get; set; }
public double Height { get; set; }
public override double Area()
{
return Width*Height;
}
}
public class Circle : Shape
{
public double Radius { get; set; }
public override double Area()
{
return Radius*Radius*Math.PI;
}
}

9. public double Area(Shape[] shapes)
{
double area = 0;
foreach (var shape in shapes)
{
area += shape.Area();
}
return area;
}

10. OOP -> Abstraction

11. Wassily Kandinsky: Komposition VIII, 1923. Öl auf Leinwand

12. Functional Programming

14. rectangleArea :: Float -> Float -> Float
rectangleArea a b = a * b

15. data Shape = Circle Float | Rectangle Float Float
area :: Shape -> Float
area (Circle r) = pi * r * r
area (Rectangle width height) = width * height
sum $ map area [(Circle 5), (Rectangle 2 3), (Circle 7)]

16. FP -> Function Composition

17. Entity Component System

19. struct RadiusComponent {
float value;
}
struct HeightComponent {
float value;
}
struct WidthComponent {
float value;
}
struct AreaComponent {
float value;
}

20. Compute Circle Area System
• get all entities which have RadiusComponent
• set computed AreaComponent on this entity

22. Compute Rectangle Area System
• get all entities which have WidthComponent and HeightComponent
• set computed AreaComponent on entity

24. Compute Sum of Areas System
• get all entities which have AreaComponent
• compute a sum of values
• do something with it

25. Systems query for data / get data
injected

26. Systems don't return
They change sate, or perform side effects

28. Systems don't care about the whole
picture

30. Elephant and the blind men
https://en.wikipedia.org/wiki/Blindmenandanelephant

31. Interactive vs. pure computation

32. Systems are executed periodically

33. How to implement an early exit?

34. Define better query
• get all entities which have RadiusComponent and don't have
AreaComponent

35. What happens when value is changed by
outside interaction?

36. Solutions
• Introduce special components for outside interactions
• Use an ECS which supports reactive systems

37. What is a reactive system?

38. Component events
• Added
• Removed
• Replaced

40. ECS vs. FP
• ECS is built for interactive computations
• mutation is ok
• side effects are ok

41. ECS vs. OOP

42. Data driven vs. Abstraction

43. Clean architecture
• SOLID in regards to ECS

44. Single responsibility principle

45. Open close principle

46. Liskov substitution principle

47. Interface segregation principle

48. Dependency inversion principle

49. Lets talk about testability

50. Lets talk about debug-ability

51. Lets talk about performance

53. If you want to know more
• Have a look at work Unity3D does https://unity3d.com/unity/
features/job-system-ECS
• Mike Acton @ CppCon 2014 https://www.youtube.com/watch?
v=rX0ItVEVjHc
• Catherine West @ Rust Conf 2018 https://www.youtube.com/
watch?v=aKLntZcp27M
• ECS Lab Discord Server https://discord.gg/eCpyZSg

54. Thank you!
Maxim Zaks @iceX33
Questions?