examples/observers/
observer_monitor.rs

1use crate::z_ignore_test_common::*;
2
3use flecs_ecs::prelude::*;
4
5#[derive(Debug, Component)]
6pub struct Position {
7    pub x: f32,
8    pub y: f32,
9}
10
11#[derive(Debug, Component)]
12pub struct Velocity {
13    pub x: f32,
14    pub y: f32,
15}
16
17// A monitor observer triggers when an entity starts/stop matching the observer
18// query. The observer communicates whether an entity is "entering/leaving" the
19// monitor by setting ecs_iter_t::event to EcsOnAdd (for entering) or
20// EcsOnRemove (for leaving).
21//
22// To specify that an observer is a monitor observer, the EcsMonitor tag must be
23// provided as event. No additional event kinds should be provided for a monitor
24// observer.
25
26fn main() {
27    let world = World::new();
28
29    // Create observer for custom event
30    world
31        .observer::<flecs::Monitor, (&Position, &Velocity)>()
32        .each_iter(|it, index, (_pos, _vel)| {
33            if it.event() == flecs::OnAdd::ID {
34                println!(
35                    " - Enter: {}: {}",
36                    it.event_id().to_str(),
37                    it.entity(index).name()
38                );
39            } else if it.event() == flecs::OnRemove::ID {
40                println!(
41                    " - Leave: {}: {}",
42                    it.event_id().to_str(),
43                    it.entity(index).name()
44                );
45            }
46        });
47
48    // Create entity
49    let entity = world.entity_named("e");
50
51    // This does not yet trigger the monitor, as the entity does not yet match.
52    entity.set(Position { x: 10.0, y: 20.0 });
53
54    // This triggers the monitor with EcsOnAdd, as the entity now matches.
55    entity.set(Velocity { x: 1.0, y: 2.0 });
56
57    // This triggers the monitor with EcsOnRemove, as the entity no longer matches.
58    entity.remove(Position::id());
59
60    // Output:
61    //  - Enter: Velocity: e
62    //  - Leave: Position: e
63}
64
65#[cfg(feature = "flecs_nightly_tests")]
66#[test]
67fn test() {
68    let output_capture = OutputCapture::capture().unwrap();
69    main();
70    output_capture.test("observer_monitor".to_string());
71}
examples/observers/observer_monitor.rs

examples/observers/
observer_monitor.rs
