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Make ecs_guide a "real game"

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This commit is contained in:
Carter Anderson 2020-05-03 00:21:32 -07:00
parent 24e5238e75
commit 2fb9e115ff
2 changed files with 225 additions and 103 deletions
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7
crates/bevy_app/src/schedule_runner.rs
View file

@ -54,6 +54,13 @@ impl AppPlugin for ScheduleRunnerPlugin {
if let Some(ref mut schedule) = app.schedule {
schedule.execute(&mut app.world, &mut app.resources);
}
if let Some(app_exit_events) = app.resources.get_mut::<Events<AppExit>>() {
if app_exit_event_reader.latest(&app_exit_events).is_some() {
break;
}
}
if let Some(wait) = wait {
thread::sleep(wait);
}

321
examples/ecs/ecs_guide.rs
View file

@ -1,4 +1,6 @@
use bevy::prelude::*;
use bevy::{app::AppExit, prelude::*};
use rand::random;
use std::time::Duration;
/// This is a guided introduction to Bevy's "Entity Component System" (ECS)
/// All Bevy app logic is built using the ECS pattern, so definitely pay attention!
@ -23,16 +25,19 @@ use bevy::prelude::*;
/// Examples: move_system, damage_system
///
/// Now that you know a little bit about ECS, lets look at some Bevy code!
/// We will now make a simple "game" to illustrate what Bevy's ECS looks like in practice.
//
// COMPONENTS: Pieces of functionality we add to entities. These are just normal Rust data types
//
struct X {
value: usize,
// Our game will have a number of "players". Each player has a name that identifies them
struct Player {
name: String,
}
struct Y {
// Each player also has a score. This component holds on to that score
struct Score {
value: usize,
}
@ -40,48 +45,89 @@ struct Y {
// RESOURCES: "Global" state accessible by systems. These are also just normal Rust data types!
//
struct A {
value: usize,
}
// This resource holds information about the game:
#[derive(Default)]
struct B {
value: usize,
struct GameState {
current_round: usize,
total_players: usize,
winning_player: Option<String>,
}
struct C {
value: usize,
// The game rules resource provides rules for our "game".
struct GameRules {
winning_score: usize,
max_rounds: usize,
max_players: usize,
}
//
// SYSTEMS: Logic that runs on entities, components, and resources. These run once each time the app updates.
//
// This is the simplest system:
fn empty_system() {
println!("hello!");
// This is the simplest type of system. It just prints "This game is fun" on each run:
fn print_message_system() {
println!("This game is fun!");
}
// Systems can also read and modify resources:
fn resource_system(a: Resource<A>, mut b: ResourceMut<B>) {
b.value += 1;
println!("resource_system: {} {}", a.value, b.value);
// Systems can also read and modify resources. This system starts a new "round" on each update:
fn new_round_system(game_rules: Resource<GameRules>, mut game_state: ResourceMut<GameState>) {
game_state.current_round += 1;
println!(
"Begin round {} of {}",
game_state.current_round, game_rules.max_rounds
);
}
// This system runs once for each entity with the X and Y component
// NOTE: x is a read-only reference (Ref) whereas y can be modified (RefMut)
fn for_each_entity_system(x: Ref<X>, mut y: RefMut<Y>) {
y.value += 1;
println!("for_each_entity_system: {} {}", x.value, y.value);
// This system runs once for each entity with both the "Player" and "Score" component.
// NOTE: "player" is a read-only reference (Ref) whereas "score" can be modified (RefMut)
fn score_system(player: Ref<Player>, mut score: RefMut<Score>) {
let scored_a_point = random::<bool>();
if scored_a_point {
score.value += 1;
println!(
"{} scored a point! Their score is: {}",
player.name, score.value
);
} else {
println!(
"{} did not score a point! Their score is: {}",
player.name, score.value
);
}
// this game isn't very fun is it :)
}
// This system is the same as the above example, but it also accesses resource A
// This system runs on all entities with the "Player" and "Score" components, but it also
// accesses the "GameRules" resource to determine if a player has won.
// NOTE: resources must always come before components in system functions
fn resources_and_components_system(a: Resource<A>, x: Ref<X>, mut y: RefMut<Y>) {
y.value += 1;
println!("resources_and_components:");
println!(" components: {} {}", x.value, y.value);
println!(" resource: {} ", a.value);
fn score_check_system(
game_rules: Resource<GameRules>,
mut game_state: ResourceMut<GameState>,
player: Ref<Player>,
score: Ref<Score>,
) {
if score.value == game_rules.winning_score {
game_state.winning_player = Some(player.name.clone());
}
}
// This system ends the game if we meet the right conditions. This fires an AppExit event, which tells our
// App to quit. Check out the "event.rs" example if you want to learn more about using events (and creating your own!)
fn game_over_system(
game_rules: Resource<GameRules>,
game_state: Resource<GameState>,
mut app_exit_events: ResourceMut<Events<AppExit>>,
) {
if let Some(ref player) = game_state.winning_player {
println!("{} won the game!", player);
app_exit_events.send(AppExit);
} else if game_state.current_round == game_rules.max_rounds {
println!("Ran out of rounds. Nobody wins!");
app_exit_events.send(AppExit);
}
println!();
}
// This is a "startup" system that runs once when the app starts up. The only thing that distinguishes a
@ -91,56 +137,102 @@ fn resources_and_components_system(a: Resource<A>, x: Ref<X>, mut y: RefMut<Y>)
// With startup systems we can create resources and add entities to our world, which can then be used by
// our other systems:
fn startup_system(world: &mut World, resources: &mut Resources) {
resources.insert(A { value: 1 });
// Create our game rules resource
resources.insert(GameRules {
max_rounds: 10,
winning_score: 4,
max_players: 4,
});
// Add some entities to our world
// Add some players to our world. Players start with a score of 0 ... we want our game to be fair!
world.insert(
(),
vec![
(X { value: 0 }, Y { value: 1 }),
(X { value: 2 }, Y { value: 3 }),
(
Player {
name: "Alice".to_string(),
},
Score { value: 0 },
),
(
Player {
name: "Bob".to_string(),
},
Score { value: 0 },
),
],
);
// Add some entities to our world
world.insert(
(),
vec![
(X { value: 0 }, Y { value: 1 }),
(X { value: 2 }, Y { value: 3 }),
],
);
// set the current players to "2"
let mut game_state = resources.get_mut::<GameState>().unwrap();
game_state.total_players = 2;
}
// This system uses a command buffer to create a new entity on each iteration
// This system uses a command buffer to (potentially) create a new entity on each iteration
// Normal systems cannot safely access the World instance because they run in parallel
// Command buffers give us the ability to queue up changes to our World without directly accessing it
// NOTE: Command buffers must always come before resources and components in system functions
fn command_buffer_system(command_buffer: &mut CommandBuffer, a: Resource<A>) {
// Creates a new entity with a value read from resource A
command_buffer.insert((), vec![(X { value: a.value },)]);
fn new_player_system(
command_buffer: &mut CommandBuffer,
game_rules: Resource<GameRules>,
mut game_state: ResourceMut<GameState>,
) {
// Randomly add a new player
let add_new_player = random::<bool>();
if add_new_player && game_state.total_players < game_rules.max_players {
game_state.total_players += 1;
command_buffer.insert(
(),
vec![(
Player {
name: format!("Player {}", game_state.total_players),
},
Score { value: 0 },
)],
);
println!("Player {} joined the game!", game_state.total_players);
}
}
// If you really need full/immediate read/write access to the world or resources, you can use a "thread local system".
// These run on the main app thread (hence the name "thread local")
// WARNING: These will block all parallel execution of other systems until they finish, so they should generally be avoided
// NOTE: You may notice that this looks exactly like the "setup" system above. Thats because they are both thread local!
fn thread_local_system(world: &mut World, _resources: &mut Resources) {
world.insert((), vec![(X { value: 1 },)]);
// NOTE: You may notice that this looks exactly like the "startup_system" above. Thats because they are both thread local!
#[allow(dead_code)]
fn thread_local_system(world: &mut World, resources: &mut Resources) {
// this does the same thing as "new_player_system"
let mut game_state = resources.get_mut::<GameState>().unwrap();
let game_rules = resources.get::<GameRules>().unwrap();
// Randomly add a new player
let add_new_player = random::<bool>();
if add_new_player && game_state.total_players < game_rules.max_players {
world.insert(
(),
vec![(
Player {
name: format!("Player {}", game_state.total_players),
},
Score { value: 0 },
)],
);
game_state.total_players += 1;
}
}
// These are like normal systems, but they also "capture" variables, which they can use as local state.
// Closures are like normal systems, but they also "capture" variables, which they can use as local state.
// This system captures the "counter" variable and uses it to maintain a count across executions
// NOTE: This function returns a Box<dyn Schedulable> type. If you are new to rust don't worry! All you
// need to know for now is that the Box contains our system AND the state it captured.
// You may recognize the .system() call from when we added our system functions to our App in the main()
// function above. Now you know that we are actually converting our functions into the Box<dyn Schedulable> type!
// The .system() call converts a function into the Box<dyn Schedulable> type. We will use the same approach
// when we add our other systems to our app
#[allow(dead_code)]
fn closure_system() -> Box<dyn Schedulable> {
let mut counter = 0;
(move |x: Ref<X>, mut y: RefMut<Y>| {
y.value += 1;
println!("closure_system: {} {}", x.value, y.value);
println!(" ran {} times: ", counter);
(move |x: Ref<Player>, y: Ref<Score>| {
println!("processed: {} {}", x.name, y.value);
println!("this ran {} times", counter);
counter += 1;
})
.system()
@ -150,45 +242,45 @@ fn closure_system() -> Box<dyn Schedulable> {
// like "saving", "networking/multiplayer", and "replays" much harder.
// Instead you should use the "state" pattern whenever possible:
#[derive(Default)]
struct State {
counter: usize,
}
fn stateful_system(mut state: RefMut<State>, x: Ref<X>, mut y: RefMut<Y>) {
y.value += 1;
println!("stateful_system: {} {}", x.value, y.value);
println!(" ran {} times: ", state.counter);
#[allow(dead_code)]
fn stateful_system(mut state: RefMut<State>, x: Ref<Player>, y: RefMut<Score>) {
println!("processed: {} {}", x.name, y.value);
println!("this ran {} times", state.counter);
state.counter += 1;
}
// If you need more flexibility, you can define complex systems using "system builders".
// SystemBuilder enables scenarios like "multiple queries" and "query filters"
fn complex_system(_resources: &mut Resources) -> Box<dyn Schedulable> {
#[allow(dead_code)]
fn complex_system(resources: &mut Resources) -> Box<dyn Schedulable> {
let mut counter = 0;
let game_state = resources.get::<GameState>().unwrap();
let initial_player_count = game_state.total_players;
SystemBuilder::new("complex_system")
.read_resource::<A>()
.write_resource::<B>()
.read_resource::<C>()
// this query is equivalent to the system we saw above: system(x: Ref<X>, y: RefMut<Y>)
.with_query(<(Read<X>, Write<Y>)>::query())
// this query only runs on entities with an X component that has changed since the last update
.with_query(<Read<X>>::query().filter(changed::<X>()))
.read_resource::<GameState>()
.write_resource::<GameRules>()
// this query is equivalent to the system we saw above: system(player: Ref<Player>, mut score: RefMut<Score>)
.with_query(<(Read<Player>, Write<Score>)>::query())
// this query only returns entities with a Player component that has changed since the last update
.with_query(<Read<Player>>::query().filter(changed::<Player>()))
.build(
move |_command_buffer, world, (a, ref mut b, c), (x_y_query, x_changed_query)| {
println!("complex_system:");
println!(" resources: {} {} {}", a.value, b.value, c.value);
for (x, mut y) in x_y_query.iter_mut(world) {
y.value += 1;
println!(
" processed entity {} times: {} {}",
counter, x.value, y.value
);
move |_command_buffer,
world,
(_game_state, _game_rules),
(player_score_query, player_changed_query)| {
println!("The game started with {} players", initial_player_count);
for (player, score) in player_score_query.iter_mut(world) {
println!("processed : {} {}", player.name, score.value);
counter += 1;
}
for x in x_changed_query.iter(world) {
println!(" x changed: {}", x.value);
for player in player_changed_query.iter(world) {
println!("This player was modified: {}", player.name);
}
},
)
@ -196,32 +288,55 @@ fn complex_system(_resources: &mut Resources) -> Box<dyn Schedulable> {
// Our Bevy app's entry point
fn main() {
// Bevy apps are created using the builder pattern. We use the builder to add systems and resources to our app
// Bevy apps are created using the builder pattern. We use the builder to add systems and resources to our app
App::build()
// Plugins are just a grouped set of app builder calls (just like we're doing here).
// The plugin below runs our app's "system schedule" exactly once. Most apps will run on a loop,
// but we don't want to spam your console with a bunch of example text :)
.add_plugin(ScheduleRunnerPlugin::run_once())
// We could easily turn this game into a plugin, but you can check out the plugin example for that :)
// The plugin below runs our app's "system schedule" once every 5 seconds.
.add_plugin(ScheduleRunnerPlugin::run_loop(Duration::from_secs(5)))
// Resources can be added to our app like this
.add_resource(C { value: 1 })
.add_resource(State { counter: 0 })
// Resources that implement the Default or FromResources trait can be added like this:
.init_resource::<B>()
.init_resource::<State>()
// Systems can be added to our app like this
// the system() call converts normal rust functions into ECS systems
.add_system(empty_system.system())
.init_resource::<GameState>()
// Startup systems run exactly once BEFORE all other systems. These are generally used for
// app initialization code (adding entities and resources)
// app initialization code (ex: adding entities and resources)
.add_startup_system(startup_system)
// Systems that need resources to be constructed can be added like this
.init_system(complex_system)
// Here we just add the rest of the example systems
.add_system(resource_system.system())
.add_system(for_each_entity_system.system())
.add_system(resources_and_components_system.system())
.add_system(command_buffer_system.system())
.add_system(thread_local_system)
.add_system(closure_system())
.add_system(stateful_system.system())
// This .system() call converts normal rust functions into ECS systems
// Functions can be added to our app as systems like this:
.add_system(print_message_system.system())
// Systems that need a reference to Resources to be constructed can be added like this:
// .init_system(complex_system)
//
// SYSTEM EXECUTION ORDER
//
// By default, all systems run in parallel. This is efficient, but sometimes order matters.
// For example, we want our "game over" system to execute after all other systems to ensure we don't
// accidentally run the game for an extra round.
//
// First, if a system writes a component or resource (RefMut / ResourceMut), it will force a synchronization.
// Any systems that access the data type and were registered BEFORE the system will need to finish first.
// Any systems that were registered _after_ the system will need to wait for it to finish. This is a great
// default that makes everything "just work" as fast as possible without us needing to think about it ... provided
// we don't care about execution order. If we do care, one option would be to use the rules above to force a synchronization
// at the right time. But that is complicated and error prone!
//
// This is where "stages" come in. A "stage" is a group of systems that execute (in parallel). Stages are executed in order,
// and the next stage won't start until all systems in the previous stage have finished.
// .add_system(system) adds systems to the UPDATE stage by default:
// However we can manually specify the stage if we want to:
.add_system_to_stage(stage::UPDATE, score_system.system())
// add_system_to_stage(stage::UPDATE, system) is equivalent to add_system(system):
// We can also create new stages. "before_round" will contain the systems that run before a round starts
.add_stage_before(stage::UPDATE, "before_round")
// The "end_game" stage will contain the systems that run after a round finishes
.add_stage_after(stage::UPDATE, "end_game")
.add_system_to_stage("before_round", new_round_system.system())
.add_system_to_stage("before_round", new_player_system.system())
// score_check_system will run before game_over_system because score_check_system modifies GameState and game_over_system
// reads GameState. This works, but its a bit confusing. In practice, it would be clearer to create a new stage that runs
// before "end_game"
.add_system_to_stage("end_game", score_check_system.system())
.add_system_to_stage("end_game", game_over_system.system())
// This call to run() starts the app we just built!
.run();
}
}