Xmas Tree Lights App

// Available variables:
// N: number - The amount of lights
// COORDS: Vector3[] - The coordinates of all the lights
// BBOX: Box3 - box bounding all christmas lights
// app.time: number - time passed since the start of the loop, in seconds
// app.colors: Color[]

// Available classes:
// Box2, Box3, Color, Cylindrical, Euler, Frustum, Interpolant, Line3,
// MathUtils, Matrix3, Matrix4, Plane, Quaternion, Ray, Sphere, Spherical,
// Triangle, Vector2, Vector3, Vector4
// See the docs of Three.JS for more info on these: https://threejs.org/docs/

// Example code below is a (tweaked) port from
// https://github.com/standupmaths/xmastree2020/blob/main/xmaslights-spin.py

// Variables to share between the init & update functions
let minAlt = BBOX.min.z
let maxAlt = BBOX.max.z
let c = 0
let buffer = 0.2 * (maxAlt - minAlt)
let inc = 0.05
let dinc = 0.01
let color1, color2
let swap1
let swap2
let direction
let angle

// Duration of the loop (in seconds)
app.duration = 10

// Code to run at the beginning of the loop
app.init = () => {
  color1 = new Color(0, 1, 1)
  color2 = new Color(1, 1, 0)

swap1 = 0
  swap2 = 0
  direction = -1
  angle = 0
}

// Code to run every frame. Assign a color to app.colors[i], or modify it
// directly (e.g. app.colors[i].r = 0.5) to update the color of LED `i`
app.update = () => {
  for (let i = 0; i < N; i++) {
    if (Math.tan(angle) * COORDS[i].y <= COORDS[i].z - c) {
      app.colors[i] = color1
    } else {
      app.colors[i] = color2
    }
  }
  angle += inc
  while (angle > 2 * Math.PI) {
    angle -= 2 * Math.PI
    swap1 = 0
    swap2 = 0
  }
  if (angle >= 0.5 * Math.PI) {
    if (swap1 === 0) {
      [color1, color2] = [color2, color1]
      swap1 = 1
    }
  }
  if (angle >= 1.5 * Math.PI) {
    if (swap2 === 0) {
      [color1, color2] = [color2, color1]
      swap2 = 1
    }
  }
  c += direction * dinc
  if (c <= minAlt + buffer) {
    direction = 1
  }
  if (c >= maxAlt - buffer) {
    direction = -1
  }
}