如何在不消耗它们的情况下读取 Bevy 事件？

Question

我目前正尝试在我的 Bevy 游戏中角色跳跃时使用事件发出信号。我希望处理玩家输入的系统发送一个 JumpedEvent ，然后其他系统可以接收它以执行适当的操作（设置正确的玩家动画、速度、声音等），但第一个系统读取事件消耗它。

Bevy 是否提供了一种无需消耗事件即可读取事件的方法？

这是我当前的代码：

// Sends a JumpedEvent when the jump key is pressed
fn player_jump_event_system(
    keyboard_input: Res<Input<KeyCode>>,
    mut jump_events: ResMut<Events<JumpedEvent>>,
    mut query: Query<(&Controlled, &mut Jumps)>,
) {
    for (controlled, mut jumps) in &mut query.iter() {
        if keyboard_input.just_pressed(controlled.jump)
            && jumps.jumps_remaining > 0
        {
            jumps.jumps_remaining -= 1;
            jump_events.send(JumpedEvent {
                jump_number: jumps.max_jumps - jumps.jumps_remaining,
            });
        }
    }
}

// This system consumes the JumpedEvent that was sent
fn control_player_jump_system(
    jump_events: ResMut<Events<JumpedEvent>>,
    mut jump_event_listener: ResMut<JumpedEventListener>,
    mut query: Query<(&Controlled, &mut Jumps, &mut Velocity)>,
) {
    const PLAYER_JUMP_SPEED: f32 = 450.0;
    const MULTI_JUMP_MODIFIER: f32 = 0.9;

    // For every jump event, make player jump slightly less high
    for jump_event in jump_event_listener.jumped_event_reader.iter(&jump_events)
    {
        for (_, _, mut velocity) in &mut query.iter() {
            *velocity.0.y_mut() = PLAYER_JUMP_SPEED
                * MULTI_JUMP_MODIFIER.powi(i32::from(jump_event.jump_number));
        }
    }
}

// This is the system that cannot receive the event because the above system consumes it
fn select_animation_system(
    texture_atlases: Res<Assets<TextureAtlas>>,
    jump_events: ResMut<Events<JumpedEvent>>,
    mut jump_event_listener: ResMut<JumpedEventListener>,
    mut query: Query<(
        &Jumps,
        &Velocity,
        &AnimatedPlayer,
        &mut TextureAtlasSprite,
        &mut Handle<TextureAtlas>,
    )>,
) {
    for (_, velocity, animations, mut sprite, mut texture_atlas) in
        &mut query.iter()
    {

        // Check if the player just jumped
        let just_jumped = jump_event_listener
            .jumped_event_reader
            .iter(&jump_events)
            .next()
            .is_some();

        // Omitting irrelevant details...

        if just_jumped {

            sprite.index = 0;
        }
    }
}

Answer 1

我刚刚意识到我做错了什么。我正在使用单个全局资源 EventReader 来收听正在发送的 JumpedEvent 个实例。每个 EventReader 只读取每个事件一次。我需要做的是为每个需要侦听事件的系统设置一个单独的 EventReader。我通过为每个需要侦听事件的系统使用 Local EventReaders 来做到这一点。请参阅下面修改后的代码：

// Sends a JumpedEvent when the jump key is pressed
fn player_jump_event_system(
    keyboard_input: Res<Input<KeyCode>>,
    mut jump_events: ResMut<Events<JumpedEvent>>,
    mut query: Query<(&Controlled, &mut Jumps)>,
) {
    for (controlled, mut jumps) in &mut query.iter() {
        if keyboard_input.just_pressed(controlled.jump)
            && jumps.jumps_remaining > 0
        {
            jumps.jumps_remaining -= 1;
            jump_events.send(JumpedEvent {
                jump_number: jumps.max_jumps - jumps.jumps_remaining,
            });
        }
    }
}

// This system consumes the JumpedEvent that was sent
fn control_player_jump_system(
    jump_events: ResMut<Events<JumpedEvent>>,

    // See that this line now specifies that the resource is local to the system
    mut jump_event_listener: Local<JumpedEventListener>,

    mut query: Query<(&Controlled, &mut Jumps, &mut Velocity)>,
) {
    const PLAYER_JUMP_SPEED: f32 = 450.0;
    const MULTI_JUMP_MODIFIER: f32 = 0.9;

    // For every jump event, make player jump slightly less high
    for jump_event in jump_event_listener.jumped_event_reader.iter(&jump_events)
    {
        for (_, _, mut velocity) in &mut query.iter() {
            *velocity.0.y_mut() = PLAYER_JUMP_SPEED
                * MULTI_JUMP_MODIFIER.powi(i32::from(jump_event.jump_number));
        }
    }
}

// This is the system that cannot receive the event because the above system consumes it
fn select_animation_system(
    texture_atlases: Res<Assets<TextureAtlas>>,
    jump_events: ResMut<Events<JumpedEvent>>,
   
    // See that this line now specifies that the resource is local to the system
    mut jump_event_listener: Local<JumpedEventListener>,

    mut query: Query<(
        &Jumps,
        &Velocity,
        &AnimatedPlayer,
        &mut TextureAtlasSprite,
        &mut Handle<TextureAtlas>,
    )>,
) {
    for (_, velocity, animations, mut sprite, mut texture_atlas) in
        &mut query.iter()
    {

        // Check if the player just jumped
        let just_jumped = jump_event_listener
            .jumped_event_reader
            .iter(&jump_events)
            .next()
            .is_some();

        // Omitting irrelevant details...

        if just_jumped {

            sprite.index = 0;
        }
    }
}

因此，每个 EventReader 在读取每个事件时都会消耗它。因此，要有多个消费系统，每个系统需要一个 Local reader.

如何在不消耗它们的情况下读取 Bevy 事件？

How to read Bevy events without consuming them?

rust

bevy