proof-engine 0.2.3

//! quickstart: the program from the README, step 2.
//!
//! 5,000 points start packed on one short line and follow the Lorenz
//! equations. At first they move as one bright streak; within about ten
//! seconds chaos has torn them apart and they trace out the butterfly.
//!
//! Run: `cargo run --release --example quickstart`

use proof_engine::math::attractors::rk4_step;
use proof_engine::prelude::*;
use proof_engine::render::ui_layer::UiParticle;

fn main() {
    let mut engine = ProofEngine::new(EngineConfig::default());

    // 5,000 points in a line 2 units long, each 0.0004 from the next.
    let mut points: Vec<Vec3> = (0..5000)
        .map(|i| Vec3::new(1.0 + i as f32 * 4e-4, 1.0, 1.0))
        .collect();

    engine.run_ui(move |engine, dt| {
        // Advance every point along the Lorenz equations.
        for p in points.iter_mut() {
            *p = rk4_step(AttractorType::Lorenz, *p, dt);
        }
        // Draw them: x across, z up, centred in the window.
        let (w, h) = engine.render_size();
        let (cx, cy, s) = (w as f32 / 2.0, h as f32 / 2.0, h as f32 / 60.0);
        let color = Vec4::new(0.5, 1.2, 1.6, 1.0);
        let dots = points
            .iter()
            .map(|p| UiParticle::new(cx + p.x * s, cy - (p.z - 25.0) * s, 3.0, 3.0, '●', color))
            .collect();
        engine.ui.draw_particles(dots);
    });
}