53 lines
2.1 KiB
JavaScript
53 lines
2.1 KiB
JavaScript
/* behavior.js — deterministic ghost motion so all viewers see the same movement.
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* Motion is a pure function of (server spawn record, wall-clock time): no per-client
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* randomness, so phones stay in sync without streaming positions.
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*/
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import * as THREE from 'three';
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function hashNoise(seed, k) {
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// cheap deterministic pseudo-noise in [-1, 1]
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const x = Math.sin(seed * 127.1 + k * 311.7) * 43758.5453;
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return (x - Math.floor(x)) * 2 - 1;
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}
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export function ghostTransform(rec, nowMs, out) {
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const t = (nowMs - rec.spawnedAt) / 1000;
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const base = new THREE.Vector3(...rec.pos);
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const b = rec.behavior || { type: 'static' };
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if (b.type === 'wander') {
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const s = b.seed || 1;
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const R = b.radius ?? 0.6;
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const v = b.speed ?? 0.15;
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// smooth pseudo-random orbit-drift: two incommensurate sines per axis
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const ph = t * v;
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out.position.set(
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base.x + R * 0.9 * Math.sin(ph * 1.0 + hashNoise(s, 1) * 6.28) * 0.7
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+ R * 0.4 * Math.sin(ph * 2.3 + hashNoise(s, 2) * 6.28) * 0.3,
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base.y + 0.06 * Math.sin(t * 1.7 + hashNoise(s, 3) * 6.28),
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base.z + R * 0.9 * Math.cos(ph * 0.8 + hashNoise(s, 4) * 6.28) * 0.7
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+ R * 0.4 * Math.cos(ph * 1.9 + hashNoise(s, 5) * 6.28) * 0.3
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);
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// face travel direction (finite difference)
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const eps = 0.05;
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const ahead = (t2) => new THREE.Vector3(
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base.x + R * 0.9 * Math.sin(t2 * v + hashNoise(s, 1) * 6.28) * 0.7,
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0,
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base.z + R * 0.9 * Math.cos(t2 * v * 0.8 + hashNoise(s, 4) * 6.28) * 0.7);
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const dir = ahead(t + eps).sub(ahead(t));
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out.rotationY = Math.atan2(dir.x, dir.z);
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} else {
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const amp = b.bobAmp ?? 0.06;
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const hz = b.bobHz ?? 0.4;
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out.position.set(base.x, base.y + amp * Math.sin(t * hz * Math.PI * 2), base.z);
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out.rotationY = 0.25 * Math.sin(t * 0.3); // slow idle sway
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}
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// crossfade opacity: fade in on spawn, fade out approaching `until`
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const fade = (rec.crossfade || 3) * 1000;
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const inA = Math.min(1, (nowMs - rec.spawnedAt) / fade);
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const outA = Math.min(1, Math.max(0, (rec.until - nowMs) / fade));
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out.opacity = Math.min(inA, outA);
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return out;
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}
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