sweeping out grids

a noisy sweep around the circle

Created by base12 on 2018/12/23
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const [pointCount, noiseScaleInc, steps, opacity] = [
    [4, 0.01, 200, -0.2],
    [3, 0.01, 200, -0.2],
    [500, 0.001, 200, -0.1],
    [250, 0.0005, 40, -0.8],
][0]
const drawScale = 160

Canvas.setpenopacity(opacity)
const turtle = new Turtle()

const rngSeed = Math.random()
console.log('rngSeed = ', rngSeed)

function walk(i) {
    seed(rngSeed)
    const noiseScale = 1 + noiseScaleInc * i
    turtle.pendown()
    for (let j = 0; j < pointCount; j++) {
        const angle = j / pointCount * Math.PI * 2
        const x = Math.cos(angle) * noiseScale
        const y = Math.sin(angle) * noiseScale
        turtle.goto(perlin3(x, y, 1) * drawScale, perlin3(x, y, -1) * drawScale)
    }
    turtle.penup()

    return i < steps
}

// from https://github.com/josephg/noisejs
const lib = {}
;(function(lib) {
  function Grad(x, y, z) {
    this.x = x; this.y = y; this.z = z;
  }
  
  Grad.prototype.dot2 = function(x, y) {
    return this.x*x + this.y*y;
  };

  Grad.prototype.dot3 = function(x, y, z) {
    return this.x*x + this.y*y + this.z*z;
  };

  const grad3 = [new Grad(1,1,0),new Grad(-1,1,0),new Grad(1,-1,0),new Grad(-1,-1,0),
               new Grad(1,0,1),new Grad(-1,0,1),new Grad(1,0,-1),new Grad(-1,0,-1),
               new Grad(0,1,1),new Grad(0,-1,1),new Grad(0,1,-1),new Grad(0,-1,-1)];

  const p = [151,160,137,91,90,15,
  131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
  190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
  88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
  77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
  102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
  135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
  5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
  223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
  129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
  251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
  49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
  138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180];
  // To remove the need for index wrapping, double the permutation table length
  const perm = new Array(512);
  const gradP = new Array(512);

  // This isn't a very good seeding function, but it works ok. It supports 2^16
  // different seed values. Write something better if you need more seeds.
  lib.seed = function(seed) {
    if(seed > 0 && seed < 1) {
      // Scale the seed out
      seed *= 65536;
    }

    seed = Math.floor(seed);
    if(seed < 256) {
      seed |= seed << 8;
    }

    for(var i = 0; i < 256; i++) {
      var v;
      if (i & 1) {
        v = p[i] ^ (seed & 255);
      } else {
        v = p[i] ^ ((seed>>8) & 255);
      }

      perm[i] = perm[i + 256] = v;
      gradP[i] = gradP[i + 256] = grad3[v % 12];
    }
  };

  lib.seed(0);

  function fade(t) {
    return t*t*t*(t*(t*6-15)+10);
  }

  function lerp(a, b, t) {
    return (1-t)*a + t*b;
  }
  
  lib.perlin3 = function(x, y, z) {
    // Find unit grid cell containing point
    var X = Math.floor(x), Y = Math.floor(y), Z = Math.floor(z);
    // Get relative xyz coordinates of point within that cell
    x = x - X; y = y - Y; z = z - Z;
    // Wrap the integer cells at 255 (smaller integer period can be introduced here)
    X = X & 255; Y = Y & 255; Z = Z & 255;

    // Calculate noise contributions from each of the eight corners
    var n000 = gradP[X+  perm[Y+  perm[Z  ]]].dot3(x,   y,     z);
    var n001 = gradP[X+  perm[Y+  perm[Z+1]]].dot3(x,   y,   z-1);
    var n010 = gradP[X+  perm[Y+1+perm[Z  ]]].dot3(x,   y-1,   z);
    var n011 = gradP[X+  perm[Y+1+perm[Z+1]]].dot3(x,   y-1, z-1);
    var n100 = gradP[X+1+perm[Y+  perm[Z  ]]].dot3(x-1,   y,   z);
    var n101 = gradP[X+1+perm[Y+  perm[Z+1]]].dot3(x-1,   y, z-1);
    var n110 = gradP[X+1+perm[Y+1+perm[Z  ]]].dot3(x-1, y-1,   z);
    var n111 = gradP[X+1+perm[Y+1+perm[Z+1]]].dot3(x-1, y-1, z-1);

    // Compute the fade curve value for x, y, z
    var u = fade(x);
    var v = fade(y);
    var w = fade(z);

    // Interpolate
    return lerp(
        lerp(
          lerp(n000, n100, u),
          lerp(n001, n101, u), w),
        lerp(
          lerp(n010, n110, u),
          lerp(n011, n111, u), w),
       v);
  };
})(lib)
const { seed, perlin3 } = lib