wasm_game_of_life/www/index.js

// Import the WebAssembly memory at the top of the file.
import { memory } from "wasm-game-of-life/wasm_game_of_life_bg";

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

let req_id;
let stop = false;

const CELL_SIZE = 40; // px
const GRID_COLOR = "#CCCCCC";
const DEAD_COLOR = "#FFFFFF";
const ALIVE_COLOR = "#3399FF";

const universe = Universe.new(10,10);

const width = universe.width();
const height = universe.height();

const canvas = document.getElementById("game-of-life-canvas");
canvas.height = (CELL_SIZE + 1) * height + 1;
canvas.width = (CELL_SIZE + 1) * width + 1;

const ctx = canvas.getContext('2d');

// The JavaScript runs in a requestAnimationFrame loop.
const renderLoop = async () => {
  await new Promise(r => setTimeout(r, 200));
  universe.tick();
  drawCells();

  if (stop == false)
    req_id = requestAnimationFrame(renderLoop);
};

// Return Cell position
function getCursorPos(canvas, evt) {
  const rect = canvas.getBoundingClientRect();

  // Bound check: It seems that the last case can overlap
  let x = Math.trunc((evt.clientX - rect.left) / CELL_SIZE);
  if (x >= (width))
    x = x - 1;

  let y = Math.trunc((evt.clientY - rect.top) / CELL_SIZE);
  if (y >= (height))
    y = y - 1;

  return { x,
           y,
         };
}

canvas.addEventListener('mouseover',
                        function(evt) {
                          console.log("Stopping Animation Frame");
                          stop = true;
                        });

canvas.addEventListener('mouseout',
                        function(evt) {
                          console.log("Starting Animation Frame");
                          stop = false;
                          start();
                        });

// Get Mouse position
canvas.addEventListener('click',
                        function(evt) {
                          var mousePos = getCursorPos(canvas, evt);
                          let cellsPtr = universe.cells();
                          let cells = new Uint8Array(memory.buffer, cellsPtr, width * height);
                          console.log("Click position : X = " + (mousePos.x) + ", Y = " + (mousePos.y));
                          const idx = universe.get_index(mousePos.y, mousePos.x);
                          if (cells[idx] === Cell.Dead)
                            console.log("Cell[" + idx + "] is : " +  "Dead !");
                          else
                            console.log("Cell[" + idx + "] is : " +  "Alive !");

                          // Change to inverse !
                          cells[idx] = (cells[idx] === Cell.Dead) ? Cell.Alive : Cell.Dead;
                          drawCells();
                        });

const drawGrid = () => {
  ctx.beginPath();
  ctx.strokeStyle = GRID_COLOR;

  // Vertical lines.
  for (let i = 0; i <= width; i++) {
    ctx.moveTo(i * (CELL_SIZE + 1) + 1, 0);
    ctx.lineTo(i * (CELL_SIZE + 1) + 1, (CELL_SIZE + 1) * height + 1);
  }

  // Horizontal lines.
  for (let j = 0; j <= height; j++) {
    ctx.moveTo(0,                           j * (CELL_SIZE + 1) + 1);
    ctx.lineTo((CELL_SIZE + 1) * width + 1, j * (CELL_SIZE + 1) + 1);
  }

  ctx.stroke();
};


// We can directly access WebAssembly's linear memory via memory, which is defined in the raw wasm module wasm_game_of_life_bg.
// To draw the cells, we get a pointer to the universe's cells, construct a Uint8Array overlaying the cells buffer, iterate over each cell, and draw a white or black rectangle depending on whether the cell is dead or alive, respectively.
// By working with pointers and overlays, we avoid copying the cells across the boundary on every tick.
const drawCells = () => {
  // Modify Plus const
  const cellsPtr = universe.cells();
  const cells = new Uint8Array(memory.buffer, cellsPtr, width * height);

  ctx.beginPath();

  for (let row = 0; row < height; row++) {
    for (let col = 0; col < width; col++) {
      const idx = universe.get_index(row, col);

      ctx.fillStyle = (cells[idx] === Cell.Dead) ? DEAD_COLOR : ALIVE_COLOR;

      ctx.fillRect(
        col * (CELL_SIZE + 1) + 1, // x
        row * (CELL_SIZE + 1) + 1, // y
        CELL_SIZE, // Width
        CELL_SIZE // Height
      );
    }
  }

  ctx.stroke();
};

function start() {
  drawGrid();
  drawCells();
  req_id = requestAnimationFrame(renderLoop);
}

start();