shacraft-core/client/tests/physics-wasm.test.js

import test from "node:test";
import assert from "node:assert/strict";
import { readFile } from "node:fs/promises";
import {
  loadPhysics,
  LocalPrediction,
  samplePhysicsWorld,
} from "../player-physics.js";

const binary = await readFile(new URL("../physics.wasm", import.meta.url));
const fixture = JSON.parse(
  await readFile(
    new URL(
      "../../crates/shacraft-physics/tests/fixtures/java26.2.json",
      import.meta.url,
    ),
    "utf8",
  ),
);
const originalFetch = globalThis.fetch;
let step;
try {
  // Exercise the actual browser ABI and its non-streaming MIME fallback.
  globalThis.fetch = async () =>
    new Response(binary, {
      headers: { "Content-Type": "application/octet-stream" },
    });
  step = await loadPhysics("http://local-test/physics.wasm");
} finally {
  globalThis.fetch = originalFetch;
}

const bounds = { min: [-64, -32, -64], max: [63, 63, 63] };
function floor(surface = "stone") {
  const blocks = new Map();
  for (let x = -4; x <= 4; x++)
    for (let z = -55; z <= 5; z++) blocks.set(`${x},-1,${z}`, 1);
  const materials = new Map([
    [
      1,
      {
        state: `minecraft:${surface}`,
        collision: [{ min: [0, 0, 0], max: [1, 1, 1] }],
      },
    ],
  ]);
  return (body) => samplePhysicsWorld(body, blocks, materials, bounds);
}
const settings = { allow_flight: true };

test("the shipped browser WebAssembly follows independently measured Java 26.2 trajectories", () => {
  let checked = 0;
  for (const [name, trajectory] of Object.entries(
    fixture.travel_kernel_trajectories,
  )) {
    if (trajectory.medium !== "air") continue;
    const getWorld = floor(trajectory.surface);
    let body = {
      position: trajectory.initial_position,
      velocity: trajectory.initial_velocity,
      flying: trajectory.flying,
      on_ground: !trajectory.flying,
    };
    for (const sample of trajectory.samples) {
      const input = {
        forward: sample.tick <= trajectory.input_ticks ? 1 : 0,
        sprint: trajectory.sprint,
        jump: sample.tick === 1 && trajectory.jump_first_tick,
      };
      body = step({ body, input, world: getWorld(body), settings });
      for (const field of ["position", "velocity"])
        for (let axis = 0; axis < 3; axis++) {
          const expected = sample[field][axis] * (axis === 2 ? -1 : 1);
          assert.ok(
            Math.abs(body[field][axis] - expected) < 2e-6,
            `${name} tick ${sample.tick} ${field}[${axis}]: ${body[field][axis]} != ${expected}`,
          );
        }
      assert.equal(
        body.on_ground,
        sample.on_ground,
        `${name} tick ${sample.tick} grounded`,
      );
      checked++;
    }
  }
  assert.ok(checked >= 200);
});

test("real WebAssembly prediction replays delayed authority without introducing trajectory drift", () => {
  const getWorld = floor();
  const prediction = new LocalPrediction(step, getWorld);
  let authority = {
    position: [0, 0, 0],
    velocity: [0, -0.0784000015258789, 0],
    on_ground: true,
  };
  prediction.receive({ body: authority, ack: 0, tick: 0, epoch: 1, settings });
  const packets = [];
  for (let tick = 1; tick <= 80; tick++) {
    const input = {
      forward: tick < 55 ? 1 : 0,
      sprint: tick > 20 && tick < 50,
      jump: tick === 25,
      sneak: tick >= 55,
    };
    prediction.push(tick, input);
    authority = step({
      body: authority,
      input,
      world: getWorld(authority),
      settings,
    });
    packets.push({ body: authority, ack: tick, tick, epoch: 1, settings });
    // Variable 150–250 ms inbound latency; authority still acknowledges order.
    if (packets.length > (tick % 3) + 3) prediction.receive(packets.shift());
    for (let axis = 0; axis < 3; axis++) {
      assert.ok(
        Math.abs(prediction.body.position[axis] - authority.position[axis]) <
          1e-11,
        `position drift at tick ${tick}`,
      );
      assert.ok(
        Math.abs(prediction.body.velocity[axis] - authority.velocity[axis]) <
          1e-11,
        `velocity drift at tick ${tick}`,
      );
    }
  }
  for (const packet of packets) prediction.receive(packet);
  assert.equal(prediction.pending.length, 0);
  assert.deepEqual(prediction.body, authority);
});