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cebb553bff
[RENDERED](https://github.com/NiklasEi/bevy/blob/ecs_readme/crates/bevy_ecs/README.md) Since I am trying to learn more about Bevy ECS at the moment, I thought this issue is a perfect fit. This PR adds a readme to the `bevy_ecs` crate containing a minimal running example of stand alone `bevy_ecs`. Unique features like customizable component storage, Resources or change detection are introduced. For each of these features the readme links to an example in a newly created examples directory inside the `bevy_esc` crate. Resolves #2008 Co-authored-by: Carter Anderson <mcanders1@gmail.com>
67 lines
2.5 KiB
Rust
67 lines
2.5 KiB
Rust
use bevy_ecs::{event::Events, prelude::*};
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// In this example a system sends a custom event with a 50/50 chance during any frame.
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// If an event was send, it will be printed by the console in a receiving system.
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fn main() {
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// Create a new empty world and add the event as a resource
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let mut world = World::new();
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world.insert_resource(Events::<MyEvent>::default());
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// Create a schedule and a stage
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let mut schedule = Schedule::default();
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// Events need to be updated in every frame. This update should happen before we use
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// the events. To guarantee this, we can let the update run in an earlier stage than our logic.
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// Here we will use a stage called "first" that will always run it's systems before the Stage
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// called "second". In "first" we update the events and in "second" we run our systems
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// sending and receiving events.
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let mut first = SystemStage::parallel();
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first.add_system(Events::<MyEvent>::update_system.system());
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schedule.add_stage("first", first);
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// Add systems sending and receiving events to a "second" Stage
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let mut second = SystemStage::parallel();
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second.add_system(sending_system.system().label(EventSystem::Sending));
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second.add_system(receiving_system.system().after(EventSystem::Sending));
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// Run the "second" Stage after the "first" Stage, so our Events always get updated before we use them
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schedule.add_stage_after("first", "second", second);
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// Simulate 10 frames of our world
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for iteration in 1..=10 {
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println!("Simulating frame {}/10", iteration);
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schedule.run(&mut world);
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}
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}
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// System label to enforce a run order of our systems
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#[derive(SystemLabel, Debug, Clone, PartialEq, Eq, Hash)]
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enum EventSystem {
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Sending,
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}
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// This is our event that we will send and receive in systems
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#[derive(Debug)]
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struct MyEvent {
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pub message: String,
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pub random_value: f32,
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}
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// In every frame we will send an event with a 50/50 chance
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fn sending_system(mut event_writer: EventWriter<MyEvent>) {
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let random_value: f32 = rand::random();
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if random_value > 0.5 {
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event_writer.send(MyEvent {
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message: "A random event with value > 0.5".to_string(),
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random_value,
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});
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}
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}
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// This system listens for events of the type MyEvent
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// If an event is received it will be printed to the console
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fn receiving_system(mut event_reader: EventReader<MyEvent>) {
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for my_event in event_reader.iter() {
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println!(" Received: {:?}", *my_event);
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}
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}
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