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<!DOCTYPE html>
<title>Explore the Torus</title>
<style>
	body {
		background-color: black;
		text-align: center;
	}
	table { margin: auto; }
	button { font-size: 250%; }
	img {
		max-width: 100%;
		image-rendering: pixelated;
	}
</style>
<img id="tile" src="tile.png">
<table>
	<tr>
		<td rowspan="3"><button id="larr" type="button">&larr;</button></td>
		<td><button id="uarr" type="button">&uarr;</button></td>
		<td rowspan="3"><button id="rarr" type="button">&rarr;</button></td>
	</tr>
	<tr></tr>
	<tr>
		<td><button id="darr" type="button">&darr;</button</td>
	</tr>
</table>

<script>
	let tile = document.getElementById("tile");
	let larr = document.getElementById("larr");
	let darr = document.getElementById("darr");
	let uarr = document.getElementById("uarr");
	let rarr = document.getElementById("rarr");

	let state = new URLSearchParams(document.location.hash.slice(1));

	function setImage() {
		let url = new URL(tile.src);
		url.search = "?" + state.toString();
		tile.src = url.toString();
	}
	setImage();

	function move(dx, dy) {
		state.set("x", +state.get("x") + dx);
		state.set("y", +state.get("y") + dy);
		history.pushState(state.toString(), "", "#" + state.toString());
		setImage();
	}
	window.onpopstate = function(event) {
		state = new URLSearchParams(event.state);
		setImage();
	}
	
	larr.onclick = () => move(-1,  0);
	darr.onclick = () => move( 0,  1);
	uarr.onclick = () => move( 0, -1);
	rarr.onclick = () => move( 1,  0);
	document.onkeydown = function(event) {
		switch (event.key) {
			case "h": case "ArrowLeft":  larr.onclick(); break;
			case "j": case "ArrowDown":  darr.onclick(); break;
			case "k": case "ArrowUp":    uarr.onclick(); break;
			case "l": case "ArrowRight": rarr.onclick(); break;
		}
	}
</script>