use graphics::math::{Vec2d, add, mul_scalar};    // <1>use piston_window::*;                            // <2>use rand::prelude::*;                            // <3>use std::alloc::{GlobalAlloc, System, Layout};   // <4>use std::time::Instant;                          // <5>#[global_allocator]                              // <6>static ALLOCATOR: ReportingAllocator = ReportingAllocator;struct ReportingAllocator;                       // <7>unsafe impl GlobalAlloc for ReportingAllocator {  unsafe fn alloc(&self, layout: Layout) -> *mut u8 {    let start = Instant::now();    let ptr = System.alloc(layout);              // <8>    let end = Instant::now();    let time_taken = end - start;    let bytes_requested = layout.size();    eprintln!("{}\t{}", bytes_requested, time_taken.as_nanos());    ptr  }  unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {    System.dealloc(ptr, layout);  }}struct World {                      // <9>  current_turn: u64,                // <9>  particles: Vec<Box<Particle>>,    // <9>  height: f64,                      // <9>  width: f64,                       // <9>  rng: ThreadRng,                   // <9>}struct Particle {                   // <10>  height: f64,                      // <10>  width: f64,                       // <10>  position: Vec2d<f64>,             // <10>  velocity: Vec2d<f64>,             // <10>  acceleration: Vec2d<f64>,         // <10>  color: [f32; 4],                  // <10>}impl Particle {  fn new(world : &World) -> Particle {    let mut rng = thread_rng();    let x = rng.gen_range(0.0..=world.width);      // <11>    let y = world.height;                          // <11>    let x_velocity = 0.0;                          // <12>    let y_velocity = rng.gen_range(-2.0..0.0);     // <12>    let x_acceleration = 0.0;                      // <13>    let y_acceleration = rng.gen_range(0.0..0.15); // <13>    Particle {      height: 4.0,      width: 4.0,      position: [x, y].into(),                     // <14>      velocity: [x_velocity, y_velocity].into(),   // <14>      acceleration: [x_acceleration,	                 y_acceleration].into(),       // <14>      color: [1.0, 1.0, 1.0, 0.99],                // <15>    }  }  fn update(&mut self) {    self.velocity = add(self.velocity,	                    self.acceleration);        // <16>    self.position = add(self.position,	                    self.velocity);            // <16>    self.acceleration = mul_scalar(                // <17>      self.acceleration,                           // <17>      0.7                                          // <17>    );                                             // <17>    self.color[3] *= 0.995;                        // <18>  }}impl World {  fn new(width: f64, height: f64) -> World {    World {      current_turn: 0,      particles: Vec::<Box<Particle>>::new(),      // <19>      height: height,      width: width,      rng: thread_rng(),    }  }  fn add_shapes(&mut self, n: i32) {    for _ in 0..n.abs() {      let particle = Particle::new(&self);         // <20>      let boxed_particle = Box::new(particle);     // <21>      self.particles.push(boxed_particle);         // <22>    }  }  fn remove_shapes(&mut self, n: i32) {    for _ in 0..n.abs() {      let mut to_delete = None;      let particle_iter = self.particles           // <23>        .iter()                                    // <23>        .enumerate();                              // <23>      for (i, particle) in particle_iter {         // <24>        if particle.color[3] < 0.02 {              // <24>          to_delete = Some(i);                     // <24>        }                                          // <24>        break;                                     // <24>      }                                            // <24>                                                   // <24>      if let Some(i) = to_delete {                 // <24>        self.particles.remove(i);                  // <24>      } else {                                     // <24>        self.particles.remove(0);                  // <24>      };                                           // <24>    }  }  fn update(&mut self) {    let n = self.rng.gen_range(-3..=3);            // <25>    if n > 0 {      self.add_shapes(n);    } else {      self.remove_shapes(n);    }    self.particles.shrink_to_fit();    for shape in &mut self.particles {      shape.update();    }    self.current_turn += 1;  }}fn main() {  let (width, height) = (1280.0, 960.0);  let mut window: PistonWindow = WindowSettings::new(    "particles", [width, height]  )  .exit_on_esc(true)  .build()  .expect("Could not create a window.");  let mut world = World::new(width, height);  world.add_shapes(1000);  while let Some(event) = window.next() {    world.update();    window.draw_2d(&event, |ctx, renderer, _device| {      clear([0.15, 0.17, 0.17, 0.9], renderer);      for s in &mut world.particles {        let size = [s.position[0], s.position[1], s.width, s.height];        rectangle(s.color, size, ctx.transform, renderer);      }    });  }}