Preview

//! Iterative animation example: a damped spring (state stepped by a closure,
//! no ECS required).
//!
//! The spring's state (`x`, `v`) is owned by `Iterative` and advanced by a
//! closure via semi-implicit Euler; the `Extract` impl projects the state into
//! a rectangle once per frame, with the displacement carried by a
//! `Translation` wrapper. Reset is structural — the adapter restores the
//! stored initial state, so `SceneEvaluator::sample_at` matches forward
//! advancement for free.
//!
//! The spring's logical duration is the local `sim_secs` value captured by the
//! closure; the same value is passed to `with_duration`, so physical time and
//! timeline time stay in sync.

use ranim::{
    color::palettes::manim, core::Extract, core::animation::eval::iterative::Iterative,
    core::core_item::CoreItem, glam::dvec3, items::vitem::geometry::Rectangle, prelude::*,
};

/// The spring's state: displacement and velocity.
#[derive(Clone)]
struct SpringState {
    x: f64,
    v: f64,
}

impl Extract for SpringState {
    type Target = CoreItem;

    fn extract_into(&self, buf: &mut Vec<CoreItem>) {
        let mut ball = Rectangle::new(0.6, 0.6).transformed(Translation(dvec3(self.x, 0.0, 0.0)));
        ball.set_fill_color(manim::BLUE_C);
        ball.set_stroke_opacity(0.0);
        ball.extract_into(buf);
    }
}

const K: f64 = 25.0;
const C: f64 = 1.0;

#[scene]
#[wasm_demo_doc]
#[output(dir = "./output/iterative_spring")]
fn iterative_spring(r: &mut RanimScene) {
    let sim_secs = 4.0;
    r.play(CameraFrame::default().show().with_duration(sim_secs));
    r.play(
        Iterative::from_fn(
            SpringState { x: 1.0, v: 0.0 },
            move |state: &mut SpringState, _alpha: f64, delta_alpha: f64| {
                let dt = sim_secs * delta_alpha;
                let acc = -K * state.x - C * state.v;
                state.v += acc * dt;
                state.x += state.v * dt;
            },
        )
        .with_duration(sim_secs),
    );
    r.insert_time_mark(sim_secs / 2.0, TimeMark::Capture("preview.png".to_string()));
}