Function random

src/math/random.js:7–380

* @module Math * @submodule Random * @for p5

(p5, fn)

 */

function random(p5, fn){
  // variables used for random number generators
  const randomStateProp = '_lcg_random_state';
  // Set to values from http://en.wikipedia.org/wiki/Numerical_Recipes
  // m is basically chosen to be large (as it is the max period)
  // and for its relationships to a and c
  const m = 4294967296;
  // a - 1 should be divisible by m's prime factors
  const a = 1664525;
  // c and m should be co-prime
  const c = 1013904223;
  let y2 = 0;

  // Linear Congruential Generator that stores its state at instance[stateProperty]
  fn._lcg = function(stateProperty) {
    // define the recurrence relationship
    this[stateProperty] = (a * this[stateProperty] + c) % m;
    // return a float in [0, 1)
    // we've just used % m, so / m is always < 1
    return this[stateProperty] / m;
  };

  fn._lcgSetSeed = function(stateProperty, val) {
    // pick a random seed if val is undefined or null
    // the >>> 0 casts the seed to an unsigned 32-bit integer
    this[stateProperty] = (val == null ? Math.random() * m : val) >>> 0;
  };

  /**
   * Sets the seed value for the <a href="#/p5/random">random()</a> and
   * <a href="#/p5/randomGaussian">randomGaussian()</a> functions.
   *
   * By default, <a href="#/p5/random">random()</a> and
   * <a href="#/p5/randomGaussian">randomGaussian()</a> produce different
   * results each time a sketch is run. Calling `randomSeed()` with a constant
   * argument, such as `randomSeed(99)`, makes these functions produce the same
   * results each time a sketch is run.
   *
   * @method randomSeed
   * @param {Number} seed   seed value.
   *
   * @example
   * function setup() {
   *   createCanvas(100, 100);
   *
   *   background(200);
   *
   *   // Get random coordinates.
   *   let x = random(0, 100);
   *   let y = random(0, 100);
   *
   *   // Draw the white circle.
   *   circle(x, y, 10);
   *
   *   // Set a random seed for consistency.
   *   randomSeed(99);
   *
   *   // Get random coordinates.