src/components/line_of_sight.rs

use std::marker::PhantomData;

use bevy::{
    core::Name,
    ecs::{ component::Component, entity::Entity, query::With, system::{ Query, Res } },
    log,
    math::Vec2,
    transform::components::GlobalTransform,
};
use bevy_rapier2d::{ pipeline::QueryFilter, plugin::RapierContext };

/// Component applied to entities that should detect line of sight to the target
#[derive(Component, Clone)]
pub(crate) struct LineOfSight<Target> {
    max_distance: f32,
    last_sighted: Option<Vec2>,
    in_sight: bool,
    marker: PhantomData<Target>,
}

/// Component applied to entities that seek the target
impl<Target> Default for LineOfSight<Target> {
    fn default() -> Self {
        Self { max_distance: 250.0, last_sighted: None, in_sight: false, marker: PhantomData }
    }
}

pub(crate) fn line_of_sight<Target: Component>(
    targets: Query<(Entity, &GlobalTransform), With<Target>>,
    mut observers: Query<(&mut LineOfSight<Target>, &GlobalTransform, Entity, Option<&Name>)>,
    rapier_context: Res<RapierContext>
) {
    for (target_entity, target_transform) in &targets {
        let target_pos = target_transform.translation().truncate();

        // Iterate over entities having a LineOfSight component
        for (
            mut line_of_sight,
            observer_transform,
            observer_entity,
            observer_name,
        ) in &mut observers {
            let observer_pos = observer_transform.translation().truncate();
            let vector = target_pos - observer_pos;
            let max_distance = line_of_sight.max_distance;
            let distance = vector.length();
            if distance > max_distance {
                continue;
            }
            let ray_dir = vector.normalize();

            // Cast ray from the observer toward the target
            let stalked = if
                let Some((collided_entity, toi)) = rapier_context.cast_ray(
                    observer_pos,
                    ray_dir,
                    max_distance,
                    false,
                    // FIXME: make sight obstacles (wall etc) into a group and use .groups() to only hit target and obstacles
                    QueryFilter::new().exclude_sensors().exclude_collider(observer_entity)
                )
            {
                // TODO: remove debug
                if collided_entity == target_entity && !line_of_sight.in_sight {
                    log::debug!(
                        "{:?}({:?}) sees the target! toi={}",
                        observer_name,
                        observer_entity,
                        toi
                    );
                }
                collided_entity == target_entity
            } else {
                false
            };

            // Minimal updates
            if stalked {
                let last_sighted = Some(target_pos);
                if !line_of_sight.in_sight || line_of_sight.last_sighted != last_sighted {
                    let los_mut = line_of_sight.as_mut();
                    los_mut.last_sighted = last_sighted;
                    los_mut.in_sight = true;
                }
            } else {
                if line_of_sight.in_sight {
                    line_of_sight.in_sight = false;
                    // TODO: remove debug
                    log::debug!("{:?}({:?}) lost the target.", observer_name, observer_entity);
                }
            }
        }
    }
}