# shoal shoal logo my silly little ecs engine for odin and raylib :3 ## contents - [install](#install) - [usage](#usage) - [systems](#systems) - [components](#components) - [spawn entities](#spawn-entities) - [query](#query) - [plugins](#plugins) - [signals](#signals) - [timers](#timers) - [ui](#ui) - [tween](#tween) ## install clone this repo in your project directory ```sh git clone https://git.egfk.net/harper/shoal ``` and import the package ```odin import ecs "shoal/src" ``` ## usage first create a new app struct. it holds your systems and plugins, and tucked inside it a `World` holding every entity and component (your game data). systems never see the app itself, only the world ```odin import ecs "shoal/src" main :: proc() { app: ecs.App } ``` you can run your app with `run()`. run takes a pointer to your app and drives its systems. ```odin main :: proc() { ecs.run(&app) } ``` ### systems systems are procedures that run on set schedules a schedule determines when a procedure runs\ there are 3 of them, and `run()` walks them in this order: - `STARTUP`: once, before the first frame - `UPDATE`: every frame, your main logic - `DRAW`: every frame, inside the frame. this is where your raylib draw calls go - `DESTROY`: once, after the last frame, on shutdown systems registered on the same schedule run in registration order: whoever was `add_system()`ed first runs first, including the systems your plugins add. plugins themselves always run once before *all* the `STARTUP` systems, no matter when you `add_plugin()` them, so adding `add_plugin(&app, ecs.DefaultPlugin)` first doesn't change *when* DefaultPlugin runs. it just puts shoal's defaults at the front of each schedule, which is still a good habit. ```odin main :: proc() { ecs.add_system(&app, ecs.STARTUP, example_startup) ecs.add_system(&app, ecs.UPDATE, example_update) } example_startup :: proc() { // system that runs once // ... } example_update :: proc() { // system that runs every frame // ... } ``` a system can also take the world. declare it as `proc(world: ^ecs.World)` and `run()` hands it the app's world, the same one holding every entity and component. that's all a system ever gets: systems structurally can't reach the app itself (add_system, plugins, run); only plugins and `main()` ever hold an `^App` ```odin main :: proc() { ecs.add_system(&app, ecs.STARTUP, example_spawn) } example_spawn :: proc(world: ^ecs.World) { entity := ecs.spawn_entity(world) // the world, no global needed ecs.add_component(world, entity, ExampleComponent{...}) } ``` plain `proc()` systems work exactly as before. only ask for the world parameter when you actually need it ### components components are plain structs. declare one and you're done. the data lives in the world: every component type gets a storage inside it, created automatically the first time you add that component to an entity. there's no global to declare and no registration step ```odin ExampleComponent :: struct {} ``` each world owns its own storages, keyed by the component's type: two worlds never share data, and a zero `ecs.World{}` is ready to use. ### spawn entities create a new entity with `spawn_entity()`, which hands out the next id from the world's entity list. ids are never reused. systems get the world as a parameter; in `main()` or a plugin it's `&app.world` (or `ecs.get_world(app)`) ```odin example_spawn :: proc(world: ^ecs.World) { entity := ecs.spawn_entity(world) } ``` and give it new components with `add_component()` ```odin example_spawn :: proc(world: ^ecs.World) { entity := ecs.spawn_entity(world) ecs.add_component(world, entity, ExampleComponent) // just the type: a zero-initialized component } ``` or fill it in on the spot by passing data instead ```odin example_spawn :: proc(world: ^ecs.World) { entity := ecs.spawn_entity(world) ecs.add_component(world, entity, ExampleComponent{...}) } ``` either way the world's storage for that component type is created on the spot if this is the first one ### query since a world keeps components of one type together, you can loop through them and pick out what you like. `slice()` and `slice_entity()` pair up by index: `entities[i]` owns `components[i]` ```odin example_system :: proc(world: ^ecs.World) { components := ecs.slice(world, ExampleComponent) entities := ecs.slice_entity(world, ExampleComponent) for v, i in components { e := entities[i] // get entity that owns the component } } ``` one caveat: `slice()` hands back the live array inside the world, not a copy, so adding components afterwards can reallocate it out from under you. don't hold one across `add_component()` calls. or if you know only one entity has the component use `single()` ```odin example_system :: proc(world: ^ecs.World) { component, entity_id := ecs.single(world, ExampleComponent) } ``` `single()` panics with a message naming the component (`single: no entity has component ExampleComponent`) if nobody in the world has it yet and once you have an entity id, `get_component()` reaches into any component type to get that entity's copy, handy for components that live alongside another one (a sprite's `TransformComponent`, say) ```odin example_system :: proc(world: ^ecs.World) { component, entity_id := ecs.single(world, ExampleComponent) other := ecs.get_component(world, entity_id, OtherExampleComponent) } ``` `get_component()` panics with a message naming the entity and the component (`get_component: entity 3 has no component OtherExampleComponent`) if that entity never got that component. it used to hand back whatever was at index 0 of the storage instead, which crashed the app with a bounds error as soon as nothing was there — the panic is the fixed version of that if you're not sure whether the entity has it (probing a component another system or plugin owns, say), ask first. `has_component()` answers yes/no, and `try_get_component()` hands back the component and a flag, `(nil, false)` instead of a panic when it's missing ```odin example_system :: proc(world: ^ecs.World) { if ecs.has_component(world, entity_id, OtherExampleComponent) { // ... } if other, ok := ecs.try_get_component(world, entity_id, OtherExampleComponent); ok { // use other } } ``` ### plugins plugins are a procedure that takes `^App` as a parameter, the one bit of privilege over regular systems, which only ever see `^World`. a plugin can register systems and plugins on the app the same way main() does, and reach the game data through `get_world(app)` ```odin ExamplePlugin :: proc(app: ^App) { ecs.add_system(app, ecs.STARTUP, some_plugin_system) entity := ecs.spawn_entity(ecs.get_world(app)) // same world the systems will get ecs.add_component(ecs.get_world(app), entity, ExampleComponent{...}) } ``` ```odin main :: proc() { ecs.add_plugin(&app, ecs.DefaultPlugin) ecs.add_plugin(&app, ExamplePlugin) } ``` plugins make your scripts reusable. much of shoal's default behavior comes from plugins via `DefaultPlugin()` run() fires every plugin in the order you added them, once, before the STARTUP systems, so everything they register is in place before anything executes ### signals signals are structs your systems can talk to each other with. one system writes a signal with data, another system reads it later in the same frame, as long as the reader runs before `signal_system` clears the buses at POST_UPDATE (see the caveat at the end of this section) ```odin DamageEvent :: struct { amount: int } ``` `write()` queues a signal on a per-type bus. `read()` gives you back every signal of that type written since the last POST_UPDATE (an empty slice if there were none), so you can iterate it. reads don't consume, so any number of systems can read the same signal and its data ```odin attack :: proc() { ecs.write(DamageEvent{amount = 5}) } // registered after attack in UPDATE, so it sees the event the same frame check_damage :: proc() { for e in ecs.read(DamageEvent) { fmt.println("took damage!", e.amount) } } ``` you can also write an empty payload with the bare type: `ecs.write(DamageEvent)` scheduling caveat: every system sees exactly the signals written since the last `signal_system()` run, and that runs at POST_UPDATE, *before* PRE_DRAW/DRAW. so: - systems running before POST_UPDATE (STARTUP/PRE_UPDATE/UPDATE/early POST_UPDATE) see same-frame writes - a DRAW system sees none of them, POST_UPDATE already cleared the bus. it only sees signals written after POST_UPDATE by an earlier system in the same frame (say, one DRAW system reacting to another's write) - writes made after POST_UPDATE survive the rest of the frame and are picked up by the next frame's PRE_UPDATE/UPDATE systems, then cleared at the next POST_UPDATE. the next frame's DRAW never sees them either ### timers timers are named countdowns. they live in a package global for now, deliberately outside the world, since they're keyed by name rather than owned by an entity. `start_timer()` starts one (or restarts one already stored under that name) and `get_timer()` reads it back. anything that never started or already finished reads back zeroed, so a nonzero `lifetime` means "still ticking" ```odin example_system :: proc() { if ecs.get_timer("cooldown").lifetime != 0 {return} // still cooling down ecs.start_timer(0.5, "cooldown") } ``` timers tick down every frame in `run_timers`, which `DefaultPlugin` registers at UPDATE. the reset fires when the remaining lifetime drops to roughly one frame's delta (it compares against a fresh `GetFrameTime()` call, so it can reset a frame or two early) and resets the entry to `Timer{}`. that's the auto-clear, and why `get_timer()` goes back to zero when you've waited it out. on expiry a `TimerFired{name = ...}` signal is *meant* to be queued for `read(TimerFired)`. wip: as written the reset zeroes the entry before the name is read, so `TimerFired` currently never fires (reading the timers themselves works fine). once that's fixed the usual signal caveat applies: a reader has to run before `signal_system` clears the buses at POST_UPDATE, see the end of the [signals](#signals) section ### ui `shoal/ui` wraps microui with its own plugin. add it before any system that wants to draw ui ```odin import ui "shoal/ui" import mu "vendor:microui" main :: proc() { ecs.add_plugin(&app, ui.UIPlugin) ecs.add_system(&app, ecs.DRAW, my_ui) } ``` `ui.UIPlugin` registers `init()` at STARTUP (uploads microui's atlas texture), `begin()` at PRE_DRAW (forwards raylib input and starts the frame), `end()` at LATE_DRAW (renders the ui after all game drawing, inside the raylib frame), frees the frame's temp memory at POST_DRAW, and `destroy()` at DESTROY. your system builds the ui against the context `get_ctx()` hands back during the frame ```odin my_ui :: proc() { if mu.begin_window(ui.get_ctx(), "hello", {100, 100, 100, 100}) { defer mu.end_window(ui.get_ctx()) mu.label(ui.get_ctx(), "Hello, world") } } ```