4 ms·

Anatomy of a knockout

73 points by ibdknox 14y ago

ibdknox 14y ago
This is the first part of what my talk at the Clojure Conj was about. Part two is about how this relates to Light Table's design :)
groby_b 14y ago
Seriously? It's hard to find an example? I'd suggest buying a copy of Thief :) Yes, the ideas behind component systems are that old. (The earliest reference that I recall off-hand is Scott Bilas presentation from GDC 2002: http://scottbilas.com/files/2002/gdc_san_jose/game_objects_slides.pdf http://scottbilas.com/files/2002/gdc_san_jose/game_objects_s...) There's plenty of explanation on the Internet.
- ibdknox 14y ago
  example = source code I didn't mean an example of a game built with it - there are lots of those. :) As you say, it's an old methodology, with Scott being the first one to really spread it around (as far as I could find), so there's a decent amount of proof it's a viable strategy. But aside from specific questions on SO and such, I couldn't find a lot of talk about it in a general, but practical sense. i.e. here's what you do to implement it, here's what a game looks like in it.
  - groby_b 14y ago
    Implementation: Game Programming Gems 6. (Or possibly 5) :) And Thief really is a prime example, because it comes with an editor that exposes the component system. That completely covers the "here's what a game looks like in it" angle. There's also a whole load of info on "data oriented programming", which sort-of follows a similar approach. Not that it'll help your specific issues, but I figured I leave pointers for anybody else reading about it and being interested. Edit: Oh, and before I forget it: Search for "functional reactive programming" - that goes down this path a bit further, and it's as the name implies a good match for functional languages.
    - sirclueless 14y ago
      As a more modern example, you could look at Scribblenauts Unlimited, which also has a component system and some fairly deep and general logical systems. There's an item editor, which exposes all of the underlying interaction logic and component interfaces, and also does some interesting things with sprite generation.
  - munificent 14y ago
    How about a book chapter? http://gameprogrammingpatterns.com/component.html http://gameprogrammingpatterns.com/component.html
    - seanmcdirmid 14y ago
      Nice, these are definitely mixins.
seanmcdirmid 14y ago
I'm a bit confused by the design space here. How are components here not just mixins that are supported in more sophisticated OO languages? There also seems to be dynamic inheritance going on (as in Self or even CLOS). Still, it sounds like the system is definitely OOP, just not OOP in the very limited Java/C++ sense. I've been using a similar object system through an adaptation of Rodney Brooks', of iRobot fame, behavior-based programming model. You can read about it in my Coding at the Speed of Touch paper.
- ibdknox 14y ago
  I'm not sure what your exact definition of OOP is, but one thing that is missing that I would generally have in mine is encapsulation of logic - there are no methods. I guess you could argue that there's a form of multi-method going on, but that seems like a stretch.
  - seanmcdirmid 14y ago
    OOP is defined by object identity (which you clearly have with entities) and state encapsulation. Methods aren't really required and many early OOP (actor-based) systems even lack them! Whether there is polymorphism, or if that polymorphism is expressed inwardly (via virtual methods) or externally (via match-based systems)...are all enhancements. Of course, its probably not that useful to go down this pedantic rabbit hole. I'm trying to understand if your CES system is equivalent to dynamic mixins, or if there is something else at play here. I've seen this pattern many times before, and have even used variations of it in my language designs. Checkout papers linked in the following LtU posts: http://lambda-the-ultimate.org/node/4257 http://lambda-the-ultimate.org/node/4257 http://lambda-the-ultimate.org/node/2149 http://lambda-the-ultimate.org/node/2149 Both systems are object oriented and neither system relies on methods. Also, does this way of expressing a system help with your liveness goals in Lighttable? I've found that the ability to apply mixins dynamically does, in the sense that I can reuse objects after a code change by applying additional mixins or cleaning up mixins that are no longer relevant.
    - ibdknox 14y ago
zachrose 14y ago
I am so curious about this: where is the state!? I understand that functional programming avoids state and mutability, but there must be bits in memory that describe what's happening in the game, no? So entities are unique ids, which I interpret as "objects" without data or methods. And components are described as collections of state, but really they're just functions? I'm looking at the code, and while I don't understand Clojure syntax yet I can see that there are "things" like :camera, :player, and multiple :platforms, which are defined with what I assume to be preliminary data like position and dimensions. Can anybody give me some clues?
- ibdknox 14y ago
  components are maps of state. so when you call (position 10 10) it's returning a map.

73 points by ibdknox 14y ago

This is the first part of what my talk at the Clojure Conj was about. Part two is about how this relates to Light Table's design :)

groby_b 14y ago

Seriously? It's hard to find an example? I'd suggest buying a copy of Thief :) Yes, the ideas behind component systems are that old. (The earliest reference that I recall off-hand is Scott Bilas presentation from GDC 2002: http://scottbilas.com/files/2002/gdc_san_jose/game_objects_slides.pdf http://scottbilas.com/files/2002/gdc_san_jose/game_objects_s...) There's plenty of explanation on the Internet.

ibdknox 14y ago
example = source code I didn't mean an example of a game built with it - there are lots of those. :) As you say, it's an old methodology, with Scott being the first one to really spread it around (as far as I could find), so there's a decent amount of proof it's a viable strategy. But aside from specific questions on SO and such, I couldn't find a lot of talk about it in a general, but practical sense. i.e. here's what you do to implement it, here's what a game looks like in it.
- groby_b 14y ago
  Implementation: Game Programming Gems 6. (Or possibly 5) :) And Thief really is a prime example, because it comes with an editor that exposes the component system. That completely covers the "here's what a game looks like in it" angle. There's also a whole load of info on "data oriented programming", which sort-of follows a similar approach. Not that it'll help your specific issues, but I figured I leave pointers for anybody else reading about it and being interested. Edit: Oh, and before I forget it: Search for "functional reactive programming" - that goes down this path a bit further, and it's as the name implies a good match for functional languages.
  - sirclueless 14y ago
    As a more modern example, you could look at Scribblenauts Unlimited, which also has a component system and some fairly deep and general logical systems. There's an item editor, which exposes all of the underlying interaction logic and component interfaces, and also does some interesting things with sprite generation.
- munificent 14y ago
  How about a book chapter? http://gameprogrammingpatterns.com/component.html http://gameprogrammingpatterns.com/component.html
  - seanmcdirmid 14y ago
    Nice, these are definitely mixins.

seanmcdirmid 14y ago

I'm a bit confused by the design space here. How are components here not just mixins that are supported in more sophisticated OO languages? There also seems to be dynamic inheritance going on (as in Self or even CLOS). Still, it sounds like the system is definitely OOP, just not OOP in the very limited Java/C++ sense. I've been using a similar object system through an adaptation of Rodney Brooks', of iRobot fame, behavior-based programming model. You can read about it in my Coding at the Speed of Touch paper.

ibdknox 14y ago
I'm not sure what your exact definition of OOP is, but one thing that is missing that I would generally have in mine is encapsulation of logic - there are no methods. I guess you could argue that there's a form of multi-method going on, but that seems like a stretch.
- seanmcdirmid 14y ago
  OOP is defined by object identity (which you clearly have with entities) and state encapsulation. Methods aren't really required and many early OOP (actor-based) systems even lack them! Whether there is polymorphism, or if that polymorphism is expressed inwardly (via virtual methods) or externally (via match-based systems)...are all enhancements. Of course, its probably not that useful to go down this pedantic rabbit hole. I'm trying to understand if your CES system is equivalent to dynamic mixins, or if there is something else at play here. I've seen this pattern many times before, and have even used variations of it in my language designs. Checkout papers linked in the following LtU posts: http://lambda-the-ultimate.org/node/4257 http://lambda-the-ultimate.org/node/4257 http://lambda-the-ultimate.org/node/2149 http://lambda-the-ultimate.org/node/2149 Both systems are object oriented and neither system relies on methods. Also, does this way of expressing a system help with your liveness goals in Lighttable? I've found that the ability to apply mixins dynamically does, in the sense that I can reuse objects after a code change by applying additional mixins or cleaning up mixins that are no longer relevant.
  - ibdknox 14y ago

zachrose 14y ago

I am so curious about this: where is the state!? I understand that functional programming avoids state and mutability, but there must be bits in memory that describe what's happening in the game, no? So entities are unique ids, which I interpret as "objects" without data or methods. And components are described as collections of state, but really they're just functions? I'm looking at the code, and while I don't understand Clojure syntax yet I can see that there are "things" like :camera, :player, and multiple :platforms, which are defined with what I assume to be preliminary data like position and dimensions. Can anybody give me some clues?

ibdknox 14y ago
components are maps of state. so when you call (position 10 10) it's returning a map.