fable/val Public Public: anyone can read this; nobody can change it.

/**

 * The browser's guess about where you are, checked against the server's

 * answer: the same maths, the same wall, and a disagreement that closes.

 */

import { expect, test } from "bun:test";

import { BODY_R, moveSpeed } from "./glide.ts";

import { moveCircle, solidTile, TILE } from "./map.ts";

import { advance, anchor, holdBack, insideWall, LEAD_MAX, makeLocal, project, reconcile, SNAP } from "../static/predict.js";

// The world the browser builds out of map.json, which is the map the server

// plays on: the same rows, the same tile, the same body.

const world = { solid: solidTile, tile: TILE, r: BODY_R };

test("nothing is drawn until the server has said where you are", () => {

  const local = makeLocal();

  expect(local.ready).toBe(false);

  advance(local, 1, 0, 250, 1 / 60, world);

  expect(local).toMatchObject({ x: 0, y: 0 });

  reconcile(local, { x: 1200, y: 640 }, 1 / 60);

  expect(local).toMatchObject({ x: 1200, y: 640, ready: true });

});

test("a frame of movement is the speed it was given, in the direction it was given", () => {

  const local = anchor(makeLocal(), { x: 1200, y: 640 });

  advance(local, 1, 0, 250, 1 / 50, world);

  expect(local.x).toBeCloseTo(1205, 6);

  expect(local.y).toBeCloseTo(640, 6);

  // A diagonal is a direction, not a speed boost.

  const diagonal = anchor(makeLocal(), { x: 1200, y: 640 });

  advance(diagonal, 1, 1, 250, 1 / 50, world);

  expect(Math.hypot(diagonal.x - 1200, diagonal.y - 640)).toBeCloseTo(5, 6);

  // Standing still, planted, or stopped to defuse: nothing moves.

  const still = anchor(makeLocal(), { x: 1200, y: 640 });

  advance(still, 0, 0, 250, 1 / 50, world);

  advance(still, 1, 0, moveSpeed({ stopped: true }), 1 / 50, world);

  expect(still).toMatchObject({ x: 1200, y: 640 });

});

test("the guess resolves a wall exactly the way the server does", () => {

  // Every open tile of the real map, walked into from eight directions: the

  // browser's step and the server's land in the same place, or the camera

  // spends the round being dragged off whatever it guessed.

  const rows = 19;

  const cols = 30;

  let tried = 0;

  for (let row = 1; row < rows - 1; row++)

    for (let col = 1; col < cols - 1; col++) {

      if (solidTile(col, row)) continue;

      const x = col * TILE + TILE / 2;

      const y = row * TILE + TILE / 2;

      for (const [mx, my] of [

        [1, 0],

        [-1, 0],

        [0, 1],

        [0, -1],

        [0.7, 0.7],

        [-0.7, 0.7],

        [0.7, -0.7],

        [-0.7, -0.7],

      ]) {

        const local = anchor(makeLocal(), { x, y });

        advance(local, mx, my, 250, 1 / 15, world);

        const server = moveCircle(x, y, mx * 250 * (1 / 15), my * 250 * (1 / 15), BODY_R);

        expect(local.x).toBeCloseTo(server.x, 9);

        expect(local.y).toBeCloseTo(server.y, 9);

        tried += 1;

      }

    }

  expect(tried).toBeGreaterThan(1000);

});

test("a disagreement is leaned off, not jumped", () => {

  const local = anchor(makeLocal(), { x: 1200, y: 640 });

  reconcile(local, { x: 1210, y: 640 }, 1 / 60);

  expect(local.gap).toBeCloseTo(10, 6);

  // A frame moves a fraction of the way, never the whole way.

  expect(local.x).toBeGreaterThan(1200);

  expect(local.x).toBeLessThan(1203);

  // Held there, it closes.

  for (let i = 0; i < 60; i++) reconcile(local, { x: 1210, y: 640 }, 1 / 60);

  expect(local.x).toBeCloseTo(1210, 2);

});

test("a real disagreement is taken outright: the server is the answer", () => {

  const local = anchor(makeLocal(), { x: 1200, y: 640 });

  // A spawn, a teleport, a seat handed to somebody else mid-round.

  reconcile(local, { x: 1200 + SNAP + 1, y: 640 }, 1 / 60);

  expect(local.x).toBe(1200 + SNAP + 1);

  expect(local.gap).toBe(0);

});

test("a snapshot is carried forward by the input held since it was sent", () => {

  const server = { x: 1200, y: 640 };

  // Holding nothing, the answer is the answer: no lead, nothing invented.

  expect(project(server, 0, 0, 250, 0.1, world)).toEqual({ x: 1200, y: 640 });

  expect(project(server, 1, 0, 0, 0.1, world)).toEqual({ x: 1200, y: 640 });

  expect(project(server, 1, 0, 250, 0, world)).toEqual({ x: 1200, y: 640 });

  // Holding east for 66ms, it is 66ms of running east ahead.

  const ahead = project(server, 1, 0, 250, 1 / 15, world);

  expect(ahead.x - 1200).toBeCloseTo(250 / 15, 6);

  // A connection that stopped talking is not a licence to run off the map.

  const far = project(server, 1, 0, 250, 30, world);

  expect(far.x - 1200).toBeLessThanOrEqual(250 * LEAD_MAX);

  // And the carry is the server's own step-and-slide: never through a wall.

  for (let y = 100; y < 1400; y += 37) {

    const from = { x: 300, y };

    if (insideWall(from, world)) continue; // not a place anybody can stand

    expect(insideWall(project(from, -1, 0, 250, LEAD_MAX, world), world)).toBe(false);

  }

});

test("the guess is never drawn past the answer it is running toward", () => {

  const target = { x: 1300, y: 640 };

  // Ahead of the target along the way it is going: pulled back onto it.

  const past = anchor(makeLocal(), { x: 1320, y: 640 });

  holdBack(past, target, 1, 0);

  expect(past.x).toBeCloseTo(1300, 9);

  // Short of it, or across it, or standing still: left alone.

  const short = anchor(makeLocal(), { x: 1280, y: 648 });

  holdBack(short, target, 1, 0);

  expect(short).toMatchObject({ x: 1280, y: 648 });

  const still = anchor(makeLocal(), { x: 1320, y: 640 });

  holdBack(still, target, 0, 0);

  expect(still.x).toBe(1320);

});

test("a guess running with the server stays within a stride of it, and never inside a wall", () => {

  // Sixty frames a second guessing, fifteen a second corrected, walking east

  // into the wall that bounds mid. This is the case that used to skip.

  const speed = 250;

  const start = { x: 1200, y: 640 };

  let server = { ...start };

  const local = anchor(makeLocal(), start);

  let worst = 0;

  let back = 0;

  let previous = local.x;

  for (let frame = 0; frame < 240; frame++) {

    advance(local, 1, 0, speed, 1 / 60, world);

    // The server ticks at 30Hz and is heard from at 15Hz.

    if (frame % 2 === 0) server = moveCircle(server.x, server.y, speed / 30, 0, BODY_R);

    if (frame % 4 === 0) reconcile(local, server, 1 / 15);

    worst = Math.max(worst, Math.hypot(local.x - server.x, local.y - server.y));

    // The drawn body never walks backwards: that is what a skip looks like.

    back = Math.min(back, local.x - previous);

    previous = local.x;

    expect(insideWall(local, world)).toBe(false);

  }

  expect(worst).toBeLessThan(BODY_R);

  expect(back).toBeGreaterThan(-0.01);

});