lyra-engine/lyra-game/src/delta_time.rs

use instant::Instant;
use lyra_ecs::{Component, world::World};

use crate::{plugin::Plugin, game::GameStages};

#[derive(Clone, Component)]
pub struct DeltaTime(f32, Option<Instant>);

impl std::ops::Deref for DeltaTime {
    type Target = f32;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl std::ops::DerefMut for DeltaTime {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

/// A system that updates the [`DeltaTime``] resource.
/// 
/// The resource is updated in the [`GameStages::First`] stage.
pub fn delta_time_system(world: &mut World) -> anyhow::Result<()> {
    let now = Instant::now();
    let mut delta = world.get_resource_mut::<DeltaTime>();
    delta.0 = delta.1.unwrap_or(now).elapsed().as_secs_f32();
    delta.1 = Some(now);

    Ok(())
}

pub struct DeltaTimePlugin;

impl Plugin for DeltaTimePlugin {
    fn setup(&self, game: &mut crate::game::Game) {
        game.world().add_resource(DeltaTime(0.0, None));
        game.add_system_to_stage(GameStages::First, "delta_time", delta_time_system, &[]);
    }
}