Module rust_action_heroes::system

Putting the "S" in ECS

Systems describe how entities with certain components interact.

Take for example you have two entities:

E1:
  Component::Squishy: Flag
  Component::Vulnerable: Bool
  ...

E2:
  Component::Squisher: Flag
  Component::SquishingMood: Bool
  ...

These two entities might interact via a SquishSystem which says:

SquishSystem(
    (squishies, squishers, vulnerables, squishingmood): (Squishy, Squisher, Vulnerable, SquishingMood)
):
    for (squishy, vulnerable) in (squshies, vulnerables):
        if vulnerable:
            for (squisher, squishingmood) in (squishers, squishingmoods):
                if squishingmood:
                    squisher.squish(squishy)

This collects all entities with the Squishy, Vulnerable, Squisher, and SquishingMood components and conveniently allows us to iterate over any slice of those four.

In the above example we are iterating over all entities with both the squishy and vulnerable component, then if vulnerable is true, we iterate over all squisher and squishingmood entities and do some action.

Event Channels

One pattern I use a lot is to have a system either listening or writing an Event Channel. This means that systems are more interrupt driven as opposed to real-time.

Events don't scale to all problems, even in this game we have some systems which are real-time, but in a turn-based-like game events are very useful for minimizing unecessary compute and reasoning about what a sytem will do.

Modules

door	Doors are opened with keys
grab	How does the Grabaron work?
grid	This grid ain't free!
level	How we progress from level N to N+1
locks	How to open locked doors
move_sound	"Bloop"
movement_solver	Movement was so complicated it has two systems
mover	Movement was so complicated it has two systems
process_input	Nobody has time to process raw keyboard input
sprites	There's a system for managing sprites!
switches	How the game knows if all the switches are down