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<html>
<head>
<meta charset="UTF-8" />
<title>Conway's Game of Life</title>
<style>
canvas#surface {
width: 50vmin;
height: 50vmin;
border: 2px solid black;
}
</style>
</head>
<body>
<h1>Conway's Game of Life</h1>
<div><input id="running" type="checkbox" /> Run</div>
<div>
<canvas id="surface" width="50" height="50">
Sorry, you can't play Game of Life if JavaScript is turned off
</canvas>
</div>
<div>
<button id="random">Randomise</button>
</div>
</body>
<script>
(function () {
const running = document.getElementById("running");
const surface = document.getElementById("surface");
const context = surface.getContext("2d");
const width = surface.width;
const height = surface.height;
var frame = context.createImageData(width, height);
var drawto = context.createImageData(width, height);
function getOffset(x, y) {
if (x < 0) {
x = width + x;
}
if (y < 0) {
y = height + y;
}
if (x >= width) {
x = x - width;
}
if (y >= height) {
y = y - height;
}
return (y * width + x) * 4;
}
function getCell(x, y) {
const offset = getOffset(x, y);
return frame.data[offset + 3] != 0;
}
function setCell(x, y) {
const offset = getOffset(x, y);
drawto.data[offset + 3] = 255;
}
function clearCell(x, y) {
const offset = getOffset(x, y);
drawto.data[offset + 3] = 0;
}
function countNeighbours(x, y) {
return (
getCell(x - 1, y - 1) +
getCell(x, y - 1) +
getCell(x + 1, y - 1) +
getCell(x - 1, y) +
getCell(x + 1, y) +
getCell(x - 1, y + 1) +
getCell(x, y + 1) +
getCell(x + 1, y + 1)
);
}
function flip() {
var temp = frame;
context.putImageData(drawto, 0, 0);
frame = drawto;
drawto = temp;
}
/* Game of life is run on a timer */
setInterval(function () {
if (!running.checked) {
return;
}
console.log("Frame");
/* To do a frame of GoL we compute by consuming frame and writing to drawto */
for (var y = 0; y < height; y++) {
for (var x = 0; x < width; x++) {
const neighbours = countNeighbours(x, y);
if (getCell(x, y)) {
if (neighbours == 2 || neighbours == 3) {
setCell(x, y); // live, 2/3 neigh => stay alive
} else {
clearCell(x, y); // live, <2/>3 neigh => dies
}
} else {
if (neighbours == 3) {
setCell(x, y); // dead, 3 neigh => born
} else {
clearCell(x, y); // dead, !3 neigh => stay dead
}
}
}
}
flip();
}, 100);
document.getElementById("random").addEventListener("click", function () {
var ofs = 3;
for (var y = 0; y < height; y++) {
for (var x = 0; x < width; x++) {
if (Math.random() < 0.5) {
drawto.data[ofs] = 0;
} else {
drawto.data[ofs] = 255;
}
ofs += 4;
}
}
flip();
});
})();
</script>
</html>
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