2e870ef
@@ -65,7 +65,11 @@
Guns: Classic, Ghost, Sheriff, Spectre, Phantom, Vandal, Operator.
- Your own body is *drawn* from a guess — the browser runs your own movement
  forward from your own keys between snapshots, through the same
  step-and-slide the server uses (`src/engine/glide.ts`), and carries the last
  snapshot forward by up to a quarter second of held input. It is a drawing
  snapshot forward by up to a quarter second of held input. How fast it runs
  is the server's answer and not one the browser worked out: the snapshot
  carries `me.speed`, so a haste, an operator, a plant or a decided round
  reaches the drawing as a number — a rule that stops you arrives as a zero.
  It is a drawing
  optimisation only: nothing is sent, every snapshot leans the drawn body
  back onto the server's answer, and a real disagreement is taken outright.
  The lag your own keys take to reach the server (a send every 50ms, a hop,
@@ -64,3 +64,61 @@
test("a snapshot stays small enough to send thirty times a second", () => {
  expect(bytes).toBeGreaterThan(200);
  expect(bytes).toBeLessThan(8000);
});
test("the snapshot carries the speed the server will move you at, not the reasons for it", () => {
  // The browser used to rebuild this rule from four fields and was right
  // only until a fifth was added. What it gets now is the answer: every
  // reason the match has to speed a body up, slow it down or hold it still,
  // resolved here, in units a second, to a tenth like every other number in
  // the snapshot.
  for (let i = 0; i < 40 && match().phase !== "live"; i++) advance(1);
  const state = match();
  const me = state.players[0]!;
  const was = { ...me };
  const phase = state.phase;
  const seen = () => JSON.parse(snapshot(me.id)).me as Record<string, unknown>;
  const speed = () => seen().speed;
  Object.assign(me, { alive: true, haste: 0, slow: 0, planting: 0, defusing: 0, weapon: "classic" });
  expect(speed()).toBe(250);
  me.weapon = "operator";
  expect(speed()).toBe(215);
  me.weapon = "classic";
  me.haste = 2;
  expect(speed()).toBe(337.5); // exactly what the tick will use
  me.haste = 0;
  me.slow = 2;
  expect(speed()).toBe(137.5);
  me.slow = 0;
  // Every way the match holds a body still arrives as a zero, and the client
  // is told none of them: a fifth one would need no change over there.
  me.planting = 1;
  expect(speed()).toBe(0);
  me.planting = 0;
  me.defusing = 1;
  expect(speed()).toBe(0);
  me.defusing = 0;
  me.alive = false;
  expect(speed()).toBe(0);
  me.alive = true;
  // Including the phases whose tick returns before it moves anybody.
  for (const stopped of ["end", "over"] as const) {
    state.phase = stopped;
    expect(speed()).toBe(0);
  }
  state.phase = phase;
  expect(speed()).toBe(250);
  // The three fields that existed only to be re-derived are gone with it.
  const me2 = seen();
  expect(me2).not.toHaveProperty("haste");
  expect(me2).not.toHaveProperty("slow");
  expect(me2).not.toHaveProperty("defusing");
  // What it costs the wire: a name and a number, once a seat a tick.
  const field = `"speed":${speed()},`;
  expect(snapshot(me.id)).toContain(field);
  expect(field.length).toBeLessThanOrEqual(16);
  Object.assign(me, was);
});
@@ -17,7 +17,7 @@
import { recordResult } from "./db.ts";
import { makeArena, type Command, type Why } from "./engine/arena.ts";
import { fallsBetween, marksOf, trimFeed, type Fall, type Mark } from "./killfeed.ts";
import type { Point } from "./map.ts";
import { buyAbility, buyShield, buyWeapon, newMatch, pickAgent, setInput, tick, visible } from "./match.ts";
import { buyAbility, buyShield, buyWeapon, newMatch, pickAgent, setInput, speedOf, tick, visible } from "./match.ts";
import type { MatchState, Player } from "./state.ts";
import { isWeaponId, WEAPONS } from "./weapons.ts";
@@ -142,13 +142,17 @@
function snapshotShape(state: MatchState, me: Player, seen: Player[]) {
      ult: me.ult,
      ultNeeds: agent.abilities.x.points,
      blind: round2(me.blind),
      slow: round2(me.slow),
      haste: round2(me.haste),
      spike: me.spike,
      planting: round2(me.planting),
      // Your own two ways of being held still, so the browser's prediction
      // of your own body runs at the speed the server is about to use.
      defusing: me.defusing > 0,
      // How fast the server is about to move you, in units a second, and not
      // the reasons behind it: the browser's prediction runs at this number
      // and re-derives nothing. A rule that holds you still — planting,
      // defusing, a decided round — arrives as a zero. To a tenth, like every
      // other number here: rounded to a whole unit instead, a hasted walk
      // (337.5) is drawn a half-unit a second fast and clipped back by the
      // cap every frame, which measured 0.2 points of per-frame spread. A
      // tenth is a no-op for feel and costs at most two bytes.
      speed: round2(speedOf(state, me)),
      bot: me.bot,
    },
    players: seen.map((p) => ({
@@ -525,3 +525,89 @@
test("the buy phase is predicted, and its pen is the server's own rule", async (
  expect(bundle).toContain("world, refused)");
  expect(bundle).toContain("outsidePen(x, y) || insideBarrier(x, y)");
});
test("the drawn body runs at the speed the server sent, and never at one it works out", async () => {
  // Two snapshots a client that re-derived the rule would read backwards: one
  // that says stopped with every visible reason to be running, and one that
  // says running with a visible reason to be stopped. The drawing follows the
  // number both times, which is the whole of what it knows about movement.
  const arena = await import("./arena.ts");
  const { blockedCircle } = await import("./map.ts");
  arena.stopArena();
  const body = arena.match().players[0]!;
  const base = JSON.parse(arena.snapshot(body.id));
  // Somewhere with a hundred units of room in one direction to walk into.
  const clear = (
    [
      ["KeyW", 0, -1],
      ["KeyS", 0, 1],
      ["KeyA", -1, 0],
      ["KeyD", 1, 0],
    ] as const
  ).find(([, dx, dy]) => [25, 50, 75, 100].every((step) => !blockedCircle(body.x + dx * step, body.y + dy * step, 16)))!;
  expect(clear).toBeDefined();
  // The top-down view, where your own body is the last thing translated to.
  if ((nodes.get("stage")!.dataset as Record<string, string>).mode !== "top") press("KeyV");
  expect((nodes.get("stage")!.dataset as Record<string, string>).mode).toBe("top");
  for (const code of ["KeyW", "KeyA", "KeyS", "KeyD"]) release(code);
  press(clear[0]);
  const mine = (base.players as Record<string, unknown>[]).find((p) => p.id === base.me.id) ?? {
    id: base.me.id,
    name: body.name,
    agent: base.me.agent,
    angle: 0,
    hp: 100,
    armour: 0,
    mate: true,
    spike: false,
    blind: false,
    revealed: false,
  };
  const scale = 900 / (30 * 80); // canvas pixels to a world unit, as above
  const deliver = (me: Record<string, unknown>) => {
    const snap = {
      ...base,
      phase: "live",
      zones: [],
      // Your own body is on the map as one of the bodies you can see, and it
      // is the one the arrow is drawn for.
      players: [{ ...mine, alive: true, x: body.x, y: body.y }],
      shots: [],
      me: { ...base.me, alive: true, x: body.x, y: body.y, planting: 0, ...me },
    };
    openedSocket!.onmessage!({ data: JSON.stringify(snap) } as MessageEvent);
  };
  /** How far past the server's own word the body is drawn, after ten frames. */
  const leadOf = (me: Record<string, unknown>) => {
    deliver(me);
    const t0 = performance.now();
    runFrame(t0); // the first frame after a jump takes the server's word
    for (let i = 1; i <= 10; i++) {
      moves.length = 0;
      runFrame(t0 + i * 40);
    }
    const at = moves[moves.length - 1]!;
    return (at.x / scale - body.x) * clear[1] + (at.y / scale - body.y) * clear[2];
  };
  // Stopped, with nothing in the snapshot to say why: no planting, no
  // slow, a live round, a light weapon. A client working it out for itself
  // would run this body the whole quarter second.
  expect(leadOf({ speed: 0 })).toBeLessThan(1);
  // And moving, mid-plant — a reason the old client read as stopped. The
  // number is what counts, so the body walks.
  const walking = leadOf({ speed: 250, planting: 1 });
  expect(walking).toBeGreaterThan(30);
  // And the number is the whole of it: half the speed, half the lead. The
  // cap on a guess is a length of time (predict.js LEAD_MAX), so how far
  // ahead the drawing may be is the server's speed and nothing else.
  const half = leadOf({ speed: 125 });
  expect(half / walking).toBeGreaterThan(0.45);
  expect(half / walking).toBeLessThan(0.55);
  release(clear[0]);
  openedSocket?.close();
});
@@ -112,9 +112,10 @@
export function slideCircle(
}
/**
 * How fast a body moves, given what is on it. The browser reads the same
 * four facts out of its snapshot that the match reads off a player, so a
 * prediction runs at the speed the server is about to use.
 * How fast a body moves, given what is on it. This is the server's alone:
 * the game decides here (`speedOf` in the match), and the snapshot hands the
 * browser the resulting number. Nothing in a client reads these four facts,
 * so a fifth one can be added here without desyncing anybody's prediction.
 */
export function moveSpeed(state: { haste?: boolean; slow?: boolean; stopped?: boolean; heavy?: boolean }): number {
  if (state.stopped) return 0;
@@ -11,9 +11,9 @@
 */
import { expect, test } from "bun:test";
import { BODY_R, moveSpeed, RUN } from "./engine/glide.ts";
import { BODY_R, RUN } from "./engine/glide.ts";
import { solidTile, TILE } from "./map.ts";
import { newMatch, setInput, startRound, tick } from "./match.ts";
import { newMatch, setInput, speedOf, startRound, tick } from "./match.ts";
import { runBots } from "./bots.ts";
import { arrive, bodyAt, delay, feed, makeTimeline, renderTime } from "../static/engine/interp.js";
import { makeLocal, stepLocal } from "../static/engine/predict.js";
@@ -52,14 +52,19 @@
const spreadOf = (steps: number[]) => {
};
type Body = { id: string; x: number; y: number; angle: number };
type Packet = { at: number; stamp: number; me: Body & { alive: boolean; phase: string }; bodies: Body[] };
type Packet = { at: number; stamp: number; me: Body & { alive: boolean; phase: string; speed: number }; bodies: Body[] };
/**
 * A person walking east across open ground for two seconds, sending intent
 * every 50ms, hearing back thirty times a second over a jittery wire, and
 * drawn at sixty frames — with the input reaching the server one way late.
 *
 * The packet carries `speed` the way the arena's snapshot does — the match's
 * own answer, to a tenth — and the drawing uses that and nothing else, which
 * is what val.js does. `on` is whatever the walk is carrying: a haste, an
 * operator, the states whose speed is not the plain run.
 */
function walkOwnBody(base = 0.02) {
function walkOwnBody(base = 0.02, on: Partial<{ haste: number; slow: number; weapon: string }> = {}) {
  const random = rng(7);
  const state = newMatch(11);
  const me = state.players[0]!;
@@ -76,6 +81,7 @@
function walkOwnBody(base = 0.02) {
  me.haste = 0;
  me.slow = 0;
  me.weapon = "classic";
  Object.assign(me, on);
  const packets: Packet[] = [];
  const inputs: { at: number; mx: number; my: number }[] = [];
  const held = { mx: 0, my: 0 };
@@ -101,7 +107,15 @@
function walkOwnBody(base = 0.02) {
    packets.push({
      at: t + base + jitter(random),
      stamp: 0,
      me: { id: me.id, x: round2(me.x), y: round2(me.y), angle: round2(me.angle), alive: me.alive, phase: state.phase },
      me: {
        id: me.id,
        x: round2(me.x),
        y: round2(me.y),
        angle: round2(me.angle),
        alive: me.alive,
        phase: state.phase,
        speed: round2(speedOf(state, me)),
      },
      bodies: [],
    });
  }
@@ -125,7 +139,9 @@
function walkOwnBody(base = 0.02) {
    if (!snap) continue;
    held.mx = now >= walkFrom && now < walkUntil ? 1 : 0;
    const before = local.anchored;
    stepLocal(local, snap.me, held, moveSpeed({}), now - snap.stamp, 1 / 60, world, null);
    // The speed the server sent, exactly as val.js passes it: no rule about
    // movement is re-derived on this side of the wire.
    stepLocal(local, snap.me, held, snap.me.speed, now - snap.stamp, 1 / 60, world, null);
    // The first word about where you are is taken outright: that one is not a jump.
    if (before > 0) anchors += local.anchored - before;
    if (f > 0 && previous !== 0 && now > walkFrom + 0.2 && now < walkUntil - 0.05) {
@@ -155,6 +171,25 @@
test("your own body, walking, takes even steps and never a backward one", () =>
  expect(anchors).toBe(0);
});
test("a hasted walk is drawn at the speed the wire carried, rounding and all", () => {
  // Haste is the case where the match's own answer is not a whole number:
  // 250 × 1.35 is 337.5, and the wire carries it to a tenth, like every other
  // number in the snapshot. What is checked is that the drawing runs at the
  // speed the server will use — no correction, no backward step, and no body
  // drawn out past where the server is about to put it.
  const { steps, back, anchors, local, server } = walkOwnBody(0.02, { haste: 10 });
  const { mean, spread } = spreadOf(steps);
  console.log(
    `hasted body: ${steps.length} steps, mean ${mean.toFixed(2)}/frame, spread ${(spread * 100).toFixed(1)}%, ` +
      `largest backward step ${back.toFixed(2)}, anchors ${anchors}, drawn ${(local.x - server.x).toFixed(1)} past the server`,
  );
  expect(mean * 60).toBeGreaterThan(RUN * 1.35 * 0.9);
  expect(mean * 60).toBeLessThan(RUN * 1.35 * 1.1);
  expect(spread).toBeLessThan(0.05);
  expect(back).toBeGreaterThan(-0.01);
  expect(anchors).toBe(0);
});
test("starting and stopping never pulls you back, and the speed never dips a third", () => {
  // The first tenth of a second after the key goes down the server has not
  // heard yet, and the guess used to be yanked back to the server's still
@@ -26,8 +26,10 @@
import {
import { emptyInput, type Input, type MatchState, type Player, type Side, type Slot, type Team } from "./state.ts";
import { applyDamage, damage, shotSpread, SHIELD, WEAPONS, zoneFromMiss, type WeaponId } from "./weapons.ts";
// A body's size and its speed are shared with the browser, which predicts
// your own movement between snapshots: `src/engine/glide.ts` is the one copy.
// A body's size and the step-and-slide are shared with the browser, which
// predicts your own movement between snapshots: `src/engine/glide.ts` is the
// one copy. How fast that body moves is decided here alone, by `speedOf`,
// and sent as a number — see the note on it.
export const PLAYER_R = BODY_R;
export const RUN_SPEED = RUN;
export const BUY_TIME = 14;
@@ -359,7 +361,19 @@
export function tick(state: MatchState, dt: number): void {
  endConditions(state);
}
function speedOf(player: Player): number {
/**
 * How fast this player moves right now — every reason the match has to speed
 * a body up, slow it down or hold it still, in one number.
 *
 * The browser used to rebuild this from four snapshot fields, which was this
 * function written twice and correct only until a fifth reason was added.
 * The snapshot carries the answer instead (`me.speed` in `src/arena.ts`), so
 * a new rule that stops you arrives as a zero and the prediction stops with
 * it without knowing why. Add a reason here and nothing else needs telling.
 */
export function speedOf(state: MatchState, player: Player): number {
  // The phases whose tick returns before it moves anybody, and the dead.
  if (state.phase === "end" || state.phase === "over" || !player.alive) return 0;
  return moveSpeed({
    haste: player.haste > 0,
    slow: player.slow > 0,
@@ -379,7 +393,7 @@
function movePlayer(state: MatchState, player: Player, dt: number, penned: boole
    mx /= len;
    my /= len;
  }
  const speed = speedOf(player) * dt;
  const speed = speedOf(state, player) * dt;
  if (speed === 0 || (mx === 0 && my === 0)) return;
  let next = moveCircle(player.x, player.y, mx * speed, my * speed, PLAYER_R);
  // In the buy phase nobody leaves their own spawn.
@@ -15,7 +15,7 @@
import { banner, drawBanner } from "./banner.js";
import { makeBeeper } from "./beep.js";
import { makeBudget, measure } from "./engine/budget.js";
import { arrive, bodyAt, delay, feed, makeTimeline, renderTime } from "./engine/interp.js";
import { BODY_R, moveSpeed } from "../src/engine/glide.ts";
import { BODY_R } from "../src/engine/glide.ts";
import { drawGun, gunFire, gunSnapshot, gunTick, makeGun } from "./engine/gun.js";
import { makeLocal, stepLocal } from "./engine/predict.js";
import { forget, ghosts, makePresence, shown, sighted, slide } from "./engine/presence.js";
@@ -418,15 +418,13 @@
function predict(dt, now) {
    return;
  }
  const held = readIntent();
  const speed = moveSpeed({
    haste: snap.me.haste > 0,
    slow: snap.me.slow > 0,
    // Nobody moves once a round is decided: the server's tick returns before
    // it moves anybody, and a guess that kept walking ran a quarter second
    // into nothing and waited there for the next round to cut back.
    stopped: snap.me.planting > 0 || snap.me.defusing || snap.phase === "end" || snap.phase === "over",
    heavy: snap.me.weapon === "operator",
  });
  // The speed the server is about to move you at, as it sent it. This was
  // rebuilt here out of four snapshot fields — haste, slow, holding still to
  // plant or defuse, the weight of an operator, the phases where nobody
  // moves — which was the server's rule written twice and right only until
  // somebody added a fifth. Now a rule that stops you arrives as a zero and
  // the guess stops with it, with no knowledge here of why.
  const speed = snap.me.speed;
  // The snapshot is a moment old and the keys held since have not reached
  // it; carry it that far forward and lean the drawn body onto it. Walking
  // out of the spawn pen, or into a barrier, is refused by the server
		@@ -65,7 +65,11 @@ Guns: Classic, Ghost, Sheriff, Spectre, Phantom, Vandal, Operator.
65	65	- Your own body is drawn from a guess — the browser runs your own movement
66	66	forward from your own keys between snapshots, through the same
67	67	step-and-slide the server uses (`src/engine/glide.ts`), and carries the last
68		snapshot forward by up to a quarter second of held input. It is a drawing
	68	snapshot forward by up to a quarter second of held input. How fast it runs
	69	is the server's answer and not one the browser worked out: the snapshot
	70	carries `me.speed`, so a haste, an operator, a plant or a decided round
	71	reaches the drawing as a number — a rule that stops you arrives as a zero.
	72	It is a drawing
69	73	optimisation only: nothing is sent, every snapshot leans the drawn body
70	74	back onto the server's answer, and a real disagreement is taken outright.
71	75	The lag your own keys take to reach the server (a send every 50ms, a hop,
		@@ -64,3 +64,61 @@ test("a snapshot stays small enough to send thirty times a second", () => {
64	64	expect(bytes).toBeGreaterThan(200);
65	65	expect(bytes).toBeLessThan(8000);
66	66	});
	67
	68	test("the snapshot carries the speed the server will move you at, not the reasons for it", () => {
	69	// The browser used to rebuild this rule from four fields and was right
	70	// only until a fifth was added. What it gets now is the answer: every
	71	// reason the match has to speed a body up, slow it down or hold it still,
	72	// resolved here, in units a second, to a tenth like every other number in
	73	// the snapshot.
	74	for (let i = 0; i < 40 && match().phase !== "live"; i++) advance(1);
	75	const state = match();
	76	const me = state.players[0]!;
	77	const was = { ...me };
	78	const phase = state.phase;
	79	const seen = () => JSON.parse(snapshot(me.id)).me as Record<string, unknown>;
	80	const speed = () => seen().speed;
	81
	82	Object.assign(me, { alive: true, haste: 0, slow: 0, planting: 0, defusing: 0, weapon: "classic" });
	83	expect(speed()).toBe(250);
	84	me.weapon = "operator";
	85	expect(speed()).toBe(215);
	86	me.weapon = "classic";
	87	me.haste = 2;
	88	expect(speed()).toBe(337.5); // exactly what the tick will use
	89	me.haste = 0;
	90	me.slow = 2;
	91	expect(speed()).toBe(137.5);
	92	me.slow = 0;
	93
	94	// Every way the match holds a body still arrives as a zero, and the client
	95	// is told none of them: a fifth one would need no change over there.
	96	me.planting = 1;
	97	expect(speed()).toBe(0);
	98	me.planting = 0;
	99	me.defusing = 1;
	100	expect(speed()).toBe(0);
	101	me.defusing = 0;
	102	me.alive = false;
	103	expect(speed()).toBe(0);
	104	me.alive = true;
	105	// Including the phases whose tick returns before it moves anybody.
	106	for (const stopped of ["end", "over"] as const) {
	107	state.phase = stopped;
	108	expect(speed()).toBe(0);
	109	}
	110	state.phase = phase;
	111	expect(speed()).toBe(250);
	112
	113	// The three fields that existed only to be re-derived are gone with it.
	114	const me2 = seen();
	115	expect(me2).not.toHaveProperty("haste");
	116	expect(me2).not.toHaveProperty("slow");
	117	expect(me2).not.toHaveProperty("defusing");
	118	// What it costs the wire: a name and a number, once a seat a tick.
	119	const field = `"speed":${speed()},`;
	120	expect(snapshot(me.id)).toContain(field);
	121	expect(field.length).toBeLessThanOrEqual(16);
	122
	123	Object.assign(me, was);
	124	});
		@@ -17,7 +17,7 @@ import { recordResult } from "./db.ts";
17	17	import { makeArena, type Command, type Why } from "./engine/arena.ts";
18	18	import { fallsBetween, marksOf, trimFeed, type Fall, type Mark } from "./killfeed.ts";
19	19	import type { Point } from "./map.ts";
20		import { buyAbility, buyShield, buyWeapon, newMatch, pickAgent, setInput, tick, visible } from "./match.ts";
	20	import { buyAbility, buyShield, buyWeapon, newMatch, pickAgent, setInput, speedOf, tick, visible } from "./match.ts";
21	21	import type { MatchState, Player } from "./state.ts";
22	22	import { isWeaponId, WEAPONS } from "./weapons.ts";
23	23
		@@ -142,13 +142,17 @@ function snapshotShape(state: MatchState, me: Player, seen: Player[]) {
142	142	ult: me.ult,
143	143	ultNeeds: agent.abilities.x.points,
144	144	blind: round2(me.blind),
145		slow: round2(me.slow),
146		haste: round2(me.haste),
147	145	spike: me.spike,
148	146	planting: round2(me.planting),
149		// Your own two ways of being held still, so the browser's prediction
150		// of your own body runs at the speed the server is about to use.
151		defusing: me.defusing > 0,
	147	// How fast the server is about to move you, in units a second, and not
	148	// the reasons behind it: the browser's prediction runs at this number
	149	// and re-derives nothing. A rule that holds you still — planting,
	150	// defusing, a decided round — arrives as a zero. To a tenth, like every
	151	// other number here: rounded to a whole unit instead, a hasted walk
	152	// (337.5) is drawn a half-unit a second fast and clipped back by the
	153	// cap every frame, which measured 0.2 points of per-frame spread. A
	154	// tenth is a no-op for feel and costs at most two bytes.
	155	speed: round2(speedOf(state, me)),
152	156	bot: me.bot,
153	157	},
154	158	players: seen.map((p) => ({
		@@ -525,3 +525,89 @@ test("the buy phase is predicted, and its pen is the server's own rule", async (
525	525	expect(bundle).toContain("world, refused)");
526	526	expect(bundle).toContain("outsidePen(x, y) \|\| insideBarrier(x, y)");
527	527	});
	528
	529	test("the drawn body runs at the speed the server sent, and never at one it works out", async () => {
	530	// Two snapshots a client that re-derived the rule would read backwards: one
	531	// that says stopped with every visible reason to be running, and one that
	532	// says running with a visible reason to be stopped. The drawing follows the
	533	// number both times, which is the whole of what it knows about movement.
	534	const arena = await import("./arena.ts");
	535	const { blockedCircle } = await import("./map.ts");
	536	arena.stopArena();
	537	const body = arena.match().players[0]!;
	538	const base = JSON.parse(arena.snapshot(body.id));
	539
	540	// Somewhere with a hundred units of room in one direction to walk into.
	541	const clear = (
	542	[
	543	["KeyW", 0, -1],
	544	["KeyS", 0, 1],
	545	["KeyA", -1, 0],
	546	["KeyD", 1, 0],
	547	] as const
	548	).find(([, dx, dy]) => [25, 50, 75, 100].every((step) => !blockedCircle(body.x + dx * step, body.y + dy * step, 16)))!;
	549	expect(clear).toBeDefined();
	550
	551	// The top-down view, where your own body is the last thing translated to.
	552	if ((nodes.get("stage")!.dataset as Record<string, string>).mode !== "top") press("KeyV");
	553	expect((nodes.get("stage")!.dataset as Record<string, string>).mode).toBe("top");
	554	for (const code of ["KeyW", "KeyA", "KeyS", "KeyD"]) release(code);
	555	press(clear[0]);
	556
	557	const mine = (base.players as Record<string, unknown>[]).find((p) => p.id === base.me.id) ?? {
	558	id: base.me.id,
	559	name: body.name,
	560	agent: base.me.agent,
	561	angle: 0,
	562	hp: 100,
	563	armour: 0,
	564	mate: true,
	565	spike: false,
	566	blind: false,
	567	revealed: false,
	568	};
	569	const scale = 900 / (30 * 80); // canvas pixels to a world unit, as above
	570	const deliver = (me: Record<string, unknown>) => {
	571	const snap = {
	572	...base,
	573	phase: "live",
	574	zones: [],
	575	// Your own body is on the map as one of the bodies you can see, and it
	576	// is the one the arrow is drawn for.
	577	players: [{ ...mine, alive: true, x: body.x, y: body.y }],
	578	shots: [],
	579	me: { ...base.me, alive: true, x: body.x, y: body.y, planting: 0, ...me },
	580	};
	581	openedSocket!.onmessage!({ data: JSON.stringify(snap) } as MessageEvent);
	582	};
	583	/** How far past the server's own word the body is drawn, after ten frames. */
	584	const leadOf = (me: Record<string, unknown>) => {
	585	deliver(me);
	586	const t0 = performance.now();
	587	runFrame(t0); // the first frame after a jump takes the server's word
	588	for (let i = 1; i <= 10; i++) {
	589	moves.length = 0;
	590	runFrame(t0 + i * 40);
	591	}
	592	const at = moves[moves.length - 1]!;
	593	return (at.x / scale - body.x) * clear[1] + (at.y / scale - body.y) * clear[2];
	594	};
	595
	596	// Stopped, with nothing in the snapshot to say why: no planting, no
	597	// slow, a live round, a light weapon. A client working it out for itself
	598	// would run this body the whole quarter second.
	599	expect(leadOf({ speed: 0 })).toBeLessThan(1);
	600	// And moving, mid-plant — a reason the old client read as stopped. The
	601	// number is what counts, so the body walks.
	602	const walking = leadOf({ speed: 250, planting: 1 });
	603	expect(walking).toBeGreaterThan(30);
	604	// And the number is the whole of it: half the speed, half the lead. The
	605	// cap on a guess is a length of time (predict.js LEAD_MAX), so how far
	606	// ahead the drawing may be is the server's speed and nothing else.
	607	const half = leadOf({ speed: 125 });
	608	expect(half / walking).toBeGreaterThan(0.45);
	609	expect(half / walking).toBeLessThan(0.55);
	610
	611	release(clear[0]);
	612	openedSocket?.close();
	613	});
		@@ -112,9 +112,10 @@ export function slideCircle(
112	112	}
113	113
114	114	/**
115		* How fast a body moves, given what is on it. The browser reads the same
116		* four facts out of its snapshot that the match reads off a player, so a
117		* prediction runs at the speed the server is about to use.
	115	* How fast a body moves, given what is on it. This is the server's alone:
	116	* the game decides here (`speedOf` in the match), and the snapshot hands the
	117	* browser the resulting number. Nothing in a client reads these four facts,
	118	* so a fifth one can be added here without desyncing anybody's prediction.
118	119	*/
119	120	export function moveSpeed(state: { haste?: boolean; slow?: boolean; stopped?: boolean; heavy?: boolean }): number {
120	121	if (state.stopped) return 0;
		@@ -11,9 +11,9 @@
11	11	*/
12	12
13	13	import { expect, test } from "bun:test";
14		import { BODY_R, moveSpeed, RUN } from "./engine/glide.ts";
	14	import { BODY_R, RUN } from "./engine/glide.ts";
15	15	import { solidTile, TILE } from "./map.ts";
16		import { newMatch, setInput, startRound, tick } from "./match.ts";
	16	import { newMatch, setInput, speedOf, startRound, tick } from "./match.ts";
17	17	import { runBots } from "./bots.ts";
18	18	import { arrive, bodyAt, delay, feed, makeTimeline, renderTime } from "../static/engine/interp.js";
19	19	import { makeLocal, stepLocal } from "../static/engine/predict.js";
		@@ -52,14 +52,19 @@ const spreadOf = (steps: number[]) => {
52	52	};
53	53
54	54	type Body = { id: string; x: number; y: number; angle: number };
55		type Packet = { at: number; stamp: number; me: Body & { alive: boolean; phase: string }; bodies: Body[] };
	55	type Packet = { at: number; stamp: number; me: Body & { alive: boolean; phase: string; speed: number }; bodies: Body[] };
56	56
57	57	/**
58	58	* A person walking east across open ground for two seconds, sending intent
59	59	* every 50ms, hearing back thirty times a second over a jittery wire, and
60	60	* drawn at sixty frames — with the input reaching the server one way late.
	61	*
	62	* The packet carries `speed` the way the arena's snapshot does — the match's
	63	* own answer, to a tenth — and the drawing uses that and nothing else, which
	64	* is what val.js does. `on` is whatever the walk is carrying: a haste, an
	65	* operator, the states whose speed is not the plain run.
61	66	*/
62		function walkOwnBody(base = 0.02) {
	67	function walkOwnBody(base = 0.02, on: Partial<{ haste: number; slow: number; weapon: string }> = {}) {
63	68	const random = rng(7);
64	69	const state = newMatch(11);
65	70	const me = state.players[0]!;
		@@ -76,6 +81,7 @@ function walkOwnBody(base = 0.02) {
76	81	me.haste = 0;
77	82	me.slow = 0;
78	83	me.weapon = "classic";
	84	Object.assign(me, on);
79	85	const packets: Packet[] = [];
80	86	const inputs: { at: number; mx: number; my: number }[] = [];
81	87	const held = { mx: 0, my: 0 };
		@@ -101,7 +107,15 @@ function walkOwnBody(base = 0.02) {
101	107	packets.push({
102	108	at: t + base + jitter(random),
103	109	stamp: 0,
104		me: { id: me.id, x: round2(me.x), y: round2(me.y), angle: round2(me.angle), alive: me.alive, phase: state.phase },
	110	me: {
	111	id: me.id,
	112	x: round2(me.x),
	113	y: round2(me.y),
	114	angle: round2(me.angle),
	115	alive: me.alive,
	116	phase: state.phase,
	117	speed: round2(speedOf(state, me)),
	118	},
105	119	bodies: [],
106	120	});
107	121	}
		@@ -125,7 +139,9 @@ function walkOwnBody(base = 0.02) {
125	139	if (!snap) continue;
126	140	held.mx = now >= walkFrom && now < walkUntil ? 1 : 0;
127	141	const before = local.anchored;
128		stepLocal(local, snap.me, held, moveSpeed({}), now - snap.stamp, 1 / 60, world, null);
	142	// The speed the server sent, exactly as val.js passes it: no rule about
	143	// movement is re-derived on this side of the wire.
	144	stepLocal(local, snap.me, held, snap.me.speed, now - snap.stamp, 1 / 60, world, null);
129	145	// The first word about where you are is taken outright: that one is not a jump.
130	146	if (before > 0) anchors += local.anchored - before;
131	147	if (f > 0 && previous !== 0 && now > walkFrom + 0.2 && now < walkUntil - 0.05) {
		@@ -155,6 +171,25 @@ test("your own body, walking, takes even steps and never a backward one", () =>
155	171	expect(anchors).toBe(0);
156	172	});
157	173
	174	test("a hasted walk is drawn at the speed the wire carried, rounding and all", () => {
	175	// Haste is the case where the match's own answer is not a whole number:
	176	// 250 × 1.35 is 337.5, and the wire carries it to a tenth, like every other
	177	// number in the snapshot. What is checked is that the drawing runs at the
	178	// speed the server will use — no correction, no backward step, and no body
	179	// drawn out past where the server is about to put it.
	180	const { steps, back, anchors, local, server } = walkOwnBody(0.02, { haste: 10 });
	181	const { mean, spread } = spreadOf(steps);
	182	console.log(
	183	`hasted body: ${steps.length} steps, mean ${mean.toFixed(2)}/frame, spread ${(spread * 100).toFixed(1)}%, ` +
	184	`largest backward step ${back.toFixed(2)}, anchors ${anchors}, drawn ${(local.x - server.x).toFixed(1)} past the server`,
	185	);
	186	expect(mean * 60).toBeGreaterThan(RUN * 1.35 * 0.9);
	187	expect(mean * 60).toBeLessThan(RUN * 1.35 * 1.1);
	188	expect(spread).toBeLessThan(0.05);
	189	expect(back).toBeGreaterThan(-0.01);
	190	expect(anchors).toBe(0);
	191	});
	192
158	193	test("starting and stopping never pulls you back, and the speed never dips a third", () => {
159	194	// The first tenth of a second after the key goes down the server has not
160	195	// heard yet, and the guess used to be yanked back to the server's still
		@@ -26,8 +26,10 @@ import {
26	26	import { emptyInput, type Input, type MatchState, type Player, type Side, type Slot, type Team } from "./state.ts";
27	27	import { applyDamage, damage, shotSpread, SHIELD, WEAPONS, zoneFromMiss, type WeaponId } from "./weapons.ts";
28	28
29		// A body's size and its speed are shared with the browser, which predicts
30		// your own movement between snapshots: `src/engine/glide.ts` is the one copy.
	29	// A body's size and the step-and-slide are shared with the browser, which
	30	// predicts your own movement between snapshots: `src/engine/glide.ts` is the
	31	// one copy. How fast that body moves is decided here alone, by `speedOf`,
	32	// and sent as a number — see the note on it.
31	33	export const PLAYER_R = BODY_R;
32	34	export const RUN_SPEED = RUN;
33	35	export const BUY_TIME = 14;
		@@ -359,7 +361,19 @@ export function tick(state: MatchState, dt: number): void {
359	361	endConditions(state);
360	362	}
361	363
362		function speedOf(player: Player): number {
	364	/**
	365	* How fast this player moves right now — every reason the match has to speed
	366	* a body up, slow it down or hold it still, in one number.
	367	*
	368	* The browser used to rebuild this from four snapshot fields, which was this
	369	* function written twice and correct only until a fifth reason was added.
	370	* The snapshot carries the answer instead (`me.speed` in `src/arena.ts`), so
	371	* a new rule that stops you arrives as a zero and the prediction stops with
	372	* it without knowing why. Add a reason here and nothing else needs telling.
	373	*/
	374	export function speedOf(state: MatchState, player: Player): number {
	375	// The phases whose tick returns before it moves anybody, and the dead.
	376	if (state.phase === "end" \|\| state.phase === "over" \|\| !player.alive) return 0;
363	377	return moveSpeed({
364	378	haste: player.haste > 0,
365	379	slow: player.slow > 0,
		@@ -379,7 +393,7 @@ function movePlayer(state: MatchState, player: Player, dt: number, penned: boole
379	393	mx /= len;
380	394	my /= len;
381	395	}
382		const speed = speedOf(player) * dt;
	396	const speed = speedOf(state, player) * dt;
383	397	if (speed === 0 \|\| (mx === 0 && my === 0)) return;
384	398	let next = moveCircle(player.x, player.y, mx * speed, my * speed, PLAYER_R);
385	399	// In the buy phase nobody leaves their own spawn.
		@@ -15,7 +15,7 @@ import { banner, drawBanner } from "./banner.js";
15	15	import { makeBeeper } from "./beep.js";
16	16	import { makeBudget, measure } from "./engine/budget.js";
17	17	import { arrive, bodyAt, delay, feed, makeTimeline, renderTime } from "./engine/interp.js";
18		import { BODY_R, moveSpeed } from "../src/engine/glide.ts";
	18	import { BODY_R } from "../src/engine/glide.ts";
19	19	import { drawGun, gunFire, gunSnapshot, gunTick, makeGun } from "./engine/gun.js";
20	20	import { makeLocal, stepLocal } from "./engine/predict.js";
21	21	import { forget, ghosts, makePresence, shown, sighted, slide } from "./engine/presence.js";
		@@ -418,15 +418,13 @@ function predict(dt, now) {
418	418	return;
419	419	}
420	420	const held = readIntent();
421		const speed = moveSpeed({
422		haste: snap.me.haste > 0,
423		slow: snap.me.slow > 0,
424		// Nobody moves once a round is decided: the server's tick returns before
425		// it moves anybody, and a guess that kept walking ran a quarter second
426		// into nothing and waited there for the next round to cut back.
427		stopped: snap.me.planting > 0 \|\| snap.me.defusing \|\| snap.phase === "end" \|\| snap.phase === "over",
428		heavy: snap.me.weapon === "operator",
429		});
	421	// The speed the server is about to move you at, as it sent it. This was
	422	// rebuilt here out of four snapshot fields — haste, slow, holding still to
	423	// plant or defuse, the weight of an operator, the phases where nobody
	424	// moves — which was the server's rule written twice and right only until
	425	// somebody added a fifth. Now a rule that stops you arrives as a zero and
	426	// the guess stops with it, with no knowledge here of why.
	427	const speed = snap.me.speed;
430	428	// The snapshot is a moment old and the keys held since have not reached
431	429	// it; carry it that far forward and lean the drawn body onto it. Walking
432	430	// out of the spawn pen, or into a barrier, is refused by the server