Where in the docs did you come across this? I could not get past

Add examples of correct code at major points throughout the docs about book HOT 2 OPEN

CLEckhardt commented on June 9, 2024 2

Add examples of correct code at major points throughout the docs

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Comments (2)

suchapalaver commented on June 9, 2024 1

I was also stuck at this same point for a while. Including code that finally worked as a workaround for now:

src/lib.rs:

mod utils;

use std::fmt;

use wasm_bindgen::prelude::*;

// When the `wee_alloc` feature is enabled, use `wee_alloc` as the global
// allocator.
#[cfg(feature = "wee_alloc")]
#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

#[wasm_bindgen]
#[repr(u8)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Cell {
    Dead = 0,
    Alive = 1,
}

#[wasm_bindgen]
pub struct Universe {
    width: u32,
    height: u32,
    cells: Vec<Cell>,
}

impl fmt::Display for Universe {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for line in self.cells.as_slice().chunks(self.width as usize) {
            for &cell in line {
                let symbol = if cell == Cell::Dead { '◻' } else { '◼' };
                write!(f, "{}", symbol)?;
            }
            write!(f, "\n")?;
        }

        Ok(())
    }
}

impl Universe {
    fn get_index(&self, row: u32, column: u32) -> usize {
        (row * self.width + column) as usize
    }

    fn live_neighbor_count(&self, row: u32, column: u32) -> u8 {
        let mut count = 0;
        for delta_row in [self.height - 1, 0, 1].iter().cloned() {
            for delta_col in [self.width - 1, 0, 1].iter().cloned() {
                if delta_row == 0 && delta_col == 0 {
                    continue;
                }

                let neighbor_row = (row + delta_row) % self.height;
                let neighbor_col = (column + delta_col) % self.width;
                let idx = self.get_index(neighbor_row, neighbor_col);
                count += self.cells[idx] as u8;
            }
        }
        count
    }
}

/// Public methods, exported to JavaScript.
#[wasm_bindgen]
impl Universe {
    pub fn new() -> Universe {
        let width = 64;
        let height = 64;

        let cells = (0..width * height)
            .map(|i| {
                if i % 2 == 0 || i % 7 == 0 {
                    Cell::Alive
                } else {
                    Cell::Dead
                }
            })
            .collect();

        Universe {
            width,
            height,
            cells,
        }
    }

    pub fn render(&self) -> String {
        self.to_string()
    }
    
    pub fn tick(&mut self) {
        let mut next = self.cells.clone();

        for row in 0..self.height {
            for col in 0..self.width {
                let idx = self.get_index(row, col);
                let cell = self.cells[idx];
                let live_neighbors = self.live_neighbor_count(row, col);

                let next_cell = match (cell, live_neighbors) {
                    // Rule 1: Any live cell with fewer than two live neighbours
                    // dies, as if caused by underpopulation.
                    (Cell::Alive, x) if x < 2 => Cell::Dead,
                    // Rule 2: Any live cell with two or three live neighbours
                    // lives on to the next generation.
                    (Cell::Alive, 2) | (Cell::Alive, 3) => Cell::Alive,
                    // Rule 3: Any live cell with more than three live
                    // neighbours dies, as if by overpopulation.
                    (Cell::Alive, x) if x > 3 => Cell::Dead,
                    // Rule 4: Any dead cell with exactly three live neighbours
                    // becomes a live cell, as if by reproduction.
                    (Cell::Dead, 3) => Cell::Alive,
                    // All other cells remain in the same state.
                    (otherwise, _) => otherwise,
                };

                next[idx] = next_cell;
            }
        }

        self.cells = next;
    }

    // ...
}

www/index.html:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Hello wasm-pack!</title>
    <style>
      body {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        display: flex;
        flex-direction: column;
        align-items: center;
        justify-content: center;
      }
    </style>
  </head>
  <body>
    <pre id="game-of-life-canvas"></pre>
    <script src="./bootstrap.js"></script>
  </body>
</html>

www/index.js:

import { Universe } from "wasm-game-of-life";

const pre = document.getElementById("game-of-life-canvas");
const universe = Universe.new();
const renderLoop = () => {
    pre.textContent = universe.render();
    universe.tick();
  
    requestAnimationFrame(renderLoop);
  };

requestAnimationFrame(renderLoop);

from book.

chinoto commented on June 9, 2024

You probably made the same mistake I did and missed the code under

To start the rendering process, we'll use the same code as above to start the first iteration of the rendering loop:

I came up with this because I didn't like the code duplication and, since async-await exists, I replaced the recursion with looping to make it clearer, then I realized that the Universe.tick() is tied to the refresh rate (mine is 300Hz...), so I tried setTimeout, but the spinners looked a little glitchy, so I went back to requestAnimationFrame with extra code to skip if the frame time is too early:

(async function renderLoop() {
  let lastTime;
  while (true) {
    // await new Promise((res) => setTimeout(res, 1000 / 60));
    let time = await new Promise(requestAnimationFrame);
    if (lastTime && time - lastTime < 1000 / 59) {
      continue;
    }
    lastTime = time;

    drawCells();
    universe.tick();
  }
})();

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Add examples of correct code at major points throughout the docs about book HOT 2 OPEN

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