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Fake RNG

  1. let anchors
  2. let idx
  3. let leng = 10
  4. let size = 200
  5. let px = 0
  6. let py = 0
  7.  
  8. function seed() {
  9.   idx = 0
  10.   anchors = (Date.now() + '').split``
  11.     .reverse()
  12.     .map(v => parseFloat(v) / 10)
  13.     .splice(0, leng)
  14. }
  15.  
  16. let last = 0
  17. let zoom = 1
  18. function rand() {
  19.   if (idx > size * size) seed()
  20.  
  21.   px += zoom
  22.   py += ~~(px / size)
  23.  
  24.   if (px >= size) px = 0
  25.   if (py >= size) py = 0
  26.  
  27.   const point = {
  28.     x: anchors[idx % leng],
  29.     y: anchors[(idx + 1) % leng]
  30.   }
  31.   idx++
  32.  
  33.   let dists = []
  34.   for (let i = 0; i < anchors.length; i += 2) {
  35.     let dx = px - anchors[i] * size
  36.     let dy = py - anchors[i + 1] * size
  37.     dists.push(Math.sqrt(dx * dx + dy * dy))
  38.   }
  39.   dists.sort()
  40.   last += (dists[0] / size - last) / 4
  41.   return last
  42. }
  43.  
  44. seed()
  45.  
  46. let d = document
  47. let b = d.body
  48. with (b.appendChild(
  49.   Object.assign(d.createElement`canvas`, { width: 400, height: 400 })
  50. ).getContext`2d`) {
  51.   fillStyle = 'black'
  52.   fillRect(0, 0, 400, 400)
  53.  
  54.   for (let i = 0; i < 200; i++) {
  55.     for (let j = 0; j < 200; j++) {
  56.       const c = rand() * 255
  57.       fillStyle = `rgb(${c}, ${c}, ${c})`
  58.       fillRect(j * 2, i * 2, 1, 2)
  59.     }
  60.   }
  61. }

Another one for genuary “Create your own pseudo-random number generator and visually check the results.”

snippet.zone ~ 2021-22 /// {s/z}