Add basic background rendering

js/world/index.mjs

@@ -0,0 +1,3 @@
+import * as sector from './sector.mjs';
+
+export {sectorFromPoint, getContainedSectors} from './sector.mjs';

js/world/sector.mjs

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+import {SECTOR_SIZE} from '../consts.mjs';
+
+const sectors = new Map();
+
+export default class Sector {
+	constructor(x, y) {
+		this.x = x;
+		this.y = y;
+		this.size = SECTOR_SIZE;
+		this.wx = this.size * this.x;
+		this.wy = this.size * this.y;
+		this.id = getId(this.x, this.y);
+		this.numId = getNumId(this.x, this.y);
+	}
+
+	containsPoint(wx, wy) {
+		return wx >= this.wx && wy >= this.wy &&
+			wx < this.wx + SECTOR_SIZE && wy < this.wy + SECTOR_SIZE;
+	}
+}
+
+function getId(x, y) {
+	return `${x}.${y}`;
+}
+
+function getNumId(x, y) {
+	return Math.abs(x + (y * 3665)) % Number.MAX_SAFE_INTEGER;
+}
+
+export function getSector(x, y) {
+	if (!sectors.has(getId(x, y))) {
+		sectors.set(getId(x, y), new Sector(x, y));
+	}
+
+	return sectors.get(getId(x, y));
+}
+
+export function getSectorFromWorld(wx, wy) {
+	return getSector(wx / SECTOR_SIZE | 0, wy / SECTOR_SIZE | 0);
+}
+
+export function getContainedSectors(startX, startY, endX, endY) {
+	let sectors = [];
+
+	for (let x = startX; x < endX; x += SECTOR_SIZE)
+	for (let y = startY; y < endY; y += SECTOR_SIZE) {
+		sectors.push(getSectorFromWorld(x, y));
+	}
+
+	return sectors;
+}