the-matrix/js/daynight.js

/**
 * Day/night cycle based on real UTC time.
 *
 * Sunrise ~06:00 UTC, Sunset ~18:00 UTC.
 * Drives: sun directional light, ambient light, fog color, star visibility.
 * Returns a nightFactor (0=day, 1=night) for consumers (e.g. agent glow).
 */
import * as THREE from 'three';

let sunLight  = null;
let ambientRef = null;
let sceneRef  = null;
let starMatRef = null;

/** Call once during world init. */
export function initDayNight(scene, ambientLight) {
  sceneRef   = scene;
  ambientRef = ambientLight;

  sunLight = new THREE.DirectionalLight(0xffffff, 0);
  sunLight.position.set(0, 80, 0);
  scene.add(sunLight);
}

/** Called by effects.js after it creates the star PointsMaterial. */
export function setStarMaterial(mat) {
  starMatRef = mat;
}

/** Returns seconds elapsed since UTC midnight. */
function utcSeconds() {
  const n = new Date();
  return n.getUTCHours() * 3600 + n.getUTCMinutes() * 60 + n.getUTCSeconds();
}

/**
 * Sun elevation angle: 1 at UTC noon, -1 at UTC midnight.
 * Zero-crossings at 06:00 (dawn) and 18:00 (dusk).
 */
function sunElevation() {
  const frac = utcSeconds() / 86400; // 0–1
  return Math.sin(2 * Math.PI * (frac - 0.25));
}

/**
 * Smooth step from a to b.
 * @param {number} edge0
 * @param {number} edge1
 * @param {number} x
 */
function smoothstep(edge0, edge1, x) {
  const t = Math.max(0, Math.min(1, (x - edge0) / (edge1 - edge0)));
  return t * t * (3 - 2 * t);
}

/**
 * Update all day/night-driven scene properties.
 * Called every animation frame.
 * @returns {number} nightFactor — 0 (full day) to 1 (full night)
 */
export function updateDayNight() {
  const elev = sunElevation();

  // dayFactor: 1 at full day (elev > 0.15), 0 at full night (elev < -0.15)
  const dayFactor   = smoothstep(-0.15, 0.15, elev);
  const nightFactor = 1 - dayFactor;

  // ── Sun directional light ─────────────────────────────────────────────────
  if (sunLight) {
    // Arc: east (positive X) at dawn, overhead at noon, west at dusk
    const frac  = utcSeconds() / 86400;
    const angle = 2 * Math.PI * (frac - 0.25);
    const sx    = -Math.cos(angle) * 60;
    const sy    = Math.sin(angle) * 80;
    const sz    = -30;
    sunLight.position.set(sx, Math.max(sy, 0.1), sz);

    // Color: warm orange near horizon, muted matrix-green at zenith
    const horizonBlend = 1 - Math.min(1, Math.abs(elev) / 0.4);
    const r = (0.3 + horizonBlend * 0.7) * dayFactor;
    const g = (0.6 - horizonBlend * 0.2) * dayFactor;
    const b = (0.3 - horizonBlend * 0.25) * dayFactor;
    sunLight.color.setRGB(r, g, b);
    sunLight.intensity = dayFactor * 1.2;
  }

  // ── Ambient light ─────────────────────────────────────────────────────────
  if (ambientRef) {
    // Night: very dark greenish. Day: slightly brighter, cyan tint.
    ambientRef.intensity = 0.35 + dayFactor * 0.35;
    const ar = dayFactor * 0.04;
    const ag = 0.07 + dayFactor * 0.05;
    const ab = dayFactor * 0.06;
    ambientRef.color.setRGB(ar, ag, ab);
  }

  // ── Fog color ─────────────────────────────────────────────────────────────
  if (sceneRef && sceneRef.fog) {
    const fr = dayFactor * 0.008;
    const fg = dayFactor * 0.016;
    const fb = dayFactor * 0.010;
    sceneRef.fog.color.setRGB(fr, fg, fb);
  }

  // ── Stars ─────────────────────────────────────────────────────────────────
  if (starMatRef) {
    starMatRef.opacity = 0.05 + nightFactor * 0.80;
    // Night: bright green. Day: nearly invisible dark green.
    const sg = 0.05 + nightFactor * 0.55;
    starMatRef.color.setRGB(0, sg, 0);
    starMatRef.needsUpdate = true;
  }

  return nightFactor;
}

/** Remove sun light from scene and clear module refs. */
export function disposeDayNight() {
  if (sunLight && sceneRef) {
    sceneRef.remove(sunLight);
    sunLight.dispose();
  }
  sunLight    = null;
  ambientRef  = null;
  sceneRef    = null;
  starMatRef  = null;
}