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rust - 如何在不消耗 Bevy 事件的情况下读取它们？

问题描述

我目前正在尝试使用事件来表示角色何时在我的 Bevy 游戏中跳跃。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），但第一个读取事件的系统会消耗它。

Bevy 是否提供了一种无需消费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;
        }
    }
}

标签： rustbevy

解决方案

我才意识到我做错了什么。我正在使用单个全局资源EventReader来收听JumpedEvent正在发送的实例。每个EventReader只读取每个事件一次。相反，我需要做的是EventReader为每个需要监听事件的系统配备一个人。我通过Local EventReader对需要监听事件的每个系统使用 s 来做到这一点。见下面修改后的代码：

// 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人在阅读每个事件时都会消耗它。因此，要拥有多个消费系统，每个系统都需要一个Local阅读器。

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