Source: compute/makeGeography/makeTractNoise.js

  1. /** @module */
  3. // import SimplexNoise from 'https://cdn.skypack.dev/simplex-noise@3.0.1'
  4. import { SimplexNoise } from 'simplex-noise'
  5. // https://runkit-packages.com/14.x.x/1644541101130/simplex-noise/#simplex-noisejs
  6. // https://npm.runkit.com/simplex-noise
  7. // https://www.npmjs.com/package/simplex-noise
  9. /**
  10.  * Generate a noisy 2D map with two noise sources per pixel.
  11.  * @param {number} nx - Number of x pixels
  12.  * @param {number} ny - Number of y pixels
  13.  */
  14. export default function makeTractNoise(nx, ny) {
  15.     // Simplex Noise Parameters
  16.     const noiseWidth = 0.5
  17.     const noiseHeight = 0.5
  19.     // District Noise Parameters - amplitude of noise
  20.     const xAmp = 100
  21.     const yAmp = 100
  23.     /** Generate simplex noise. */
  24.     const sn = simplexNoise(nx, ny, noiseWidth, noiseHeight, xAmp, yAmp)
  25.     return sn
  26. }
  28. /**
  29.  * Generate a noisy 2D map with two noise sources per pixel.
  30.  * @param {number} nx - Number of x pixels
  31.  * @param {number} ny - Number of y pixels
  32.  * @param {number} noiseWidth -  A characteristic size of blobs, in pixels
  33.  * @param {number} noiseHeight - A characteristic size of blobs, in pixels
  34.  * @returns {number[][][]} - Noise in pixel displacement, indexed by row, col, dimension
  35.  */
  36. export function simplexNoise(nx, ny, noiseWidth, noiseHeight, xAmp, yAmp) {
  37.     // @ts-ignore
  38.     const simplexX = new SimplexNoise('s')
  39.     // @ts-ignore
  40.     const simplexY = new SimplexNoise('seed')
  41.     const map = zeros(nx, ny)
  42.     let sumX = 0
  43.     let sumY = 0
  44.     range(nx).forEach((ix) => {
  45.         range(ny).forEach((iy) => {
  46.             // fractional coordinate divided by period of waves
  47.             const x = (ix / nx) * (1 / noiseWidth)
  48.             const y = (iy / ny) * (1 / noiseHeight)
  49.             const noiseX = simplexX.noise2D(x, y)
  50.             const noiseY = simplexY.noise2D(x, y)
  51.             map[ix][iy][0] = (noiseX - 0.5)
  52.             map[ix][iy][1] = (noiseY - 0.5)
  53.             sumX += noiseX
  54.             sumY += noiseY
  55.         })
  56.     })
  57.     // normalize
  58.     const meanX = sumX / (nx * ny) - 0.5
  59.     const meanY = sumY / (nx * ny) - 0.5
  60.     map.forEach((a) => { // array
  61.         a.forEach((p) => { // pair
  62.             // eslint-disable-next-line no-param-reassign
  63.             p[0] = (p[0] - meanX) * xAmp
  64.             // eslint-disable-next-line no-param-reassign
  65.             p[1] = (p[1] - meanY) * yAmp
  66.         })
  67.     })
  68.     return map
  69. }
  71. function zeros(nx, ny) {
  72.     const empty = Array(nx).fill().map(() => Array(ny).fill().map(() => Array(2).fill(0)))
  73.     return empty
  74. }
  76. function range(n) {
  77.     return [...Array(n).keys()]
  78. }