base v3 tileID and lookup functions [#41]

js/v3.ts

@@ -0,0 +1,101 @@
+function rotate(n: number, xy: number[], rx: number, ry: number): void {
+	if (ry == 0) {
+		if (rx == 1) {
+			xy[0] = n - 1 - xy[0];
+			xy[1] = n - 1 - xy[1];
+		}
+		let t = xy[0];
+		xy[0] = xy[1];
+		xy[1] = t;
+	}
+}
+
+function idOnLevel(z: number, pos: number): [number, number, number] {
+	let n = 1 << z;
+	let rx = pos;
+	let ry = pos;
+	let t = pos;
+	let xy = [0, 0];
+	let s = 1;
+	while (s < n) {
+		rx = 1 & ((t / 2) >> 0);
+		ry = 1 & (t ^ rx);
+		rotate(s, xy, rx, ry);
+		xy[0] += s * rx;
+		xy[1] += s * ry;
+		t = (t / 4) >> 0;
+		s *= 2;
+	}
+	return [z, xy[0], xy[1]];
+}
+
+export function zxyToTileId(z: number, x: number, y: number): number {
+	let acc = 0;
+	let tz = 0;
+	while (tz < z) {
+		acc += (0x1 << tz) * (0x1 << tz);
+		tz++;
+	}
+	let n = 1 << z;
+	let rx = 0;
+	let ry = 0;
+	let d = 0;
+	let xy = [x, y];
+	let s = (n / 2) >> 0;
+	while (s > 0) {
+		rx = (xy[0] & s) > 0 ? 1 : 0;
+		ry = (xy[1] & s) > 0 ? 1 : 0;
+		d += s * s * ((3 * rx) ^ ry);
+		rotate(s, xy, rx, ry);
+		s = (s / 2) >> 0;
+	}
+	return acc + d;
+}
+
+export function tileIdToZxy(i: number): [number, number, number] {
+	let acc = 0;
+	let z = 0;
+	while (true) {
+		let num_tiles = (0x1 << z) * (0x1 << z);
+		if (acc + num_tiles > i) {
+			return idOnLevel(z, i - acc);
+		}
+		acc += num_tiles;
+		z++;
+	}
+}
+
+export interface Entry {
+	tileId: number;
+	offset: number;
+	length: number;
+	runLength: number;
+}
+
+export function findTile(entries: Entry[], tileId: number): Entry | null {
+	let m = 0;
+	let n = entries.length - 1;
+	while (m <= n) {
+		const k = (n + m) >> 1;
+		const cmp = tileId - entries[k].tileId;
+		if (cmp > 0) {
+			m = k + 1;
+		} else if (cmp < 0) {
+			n = k - 1;
+		} else {
+			return entries[k];
+		}
+	}
+
+	// at this point, m > n
+	if (n >= 0) {
+		if (entries[n].runLength === 0) {
+			return entries[n];
+		}
+		if (tileId - entries[n].tileId < entries[n].runLength) {
+			return entries[n];
+		}
+	}
+	return null;
+}
+