stage-js/example/common/randomize.js

2D HTML5 Rendering and Layout

function Randomize() {
  this._options = [];
}

/**
 * For debugging.
 */
Randomize.prototype.lock = function (option) {
  this._lock = option;
};

Randomize.prototype.add = function (option, weight) {
  weight = Randomize._fnum(weight, 1);
  this._options.push({
    value: option,
    weight: weight,
  });
  return this;
};

Randomize.prototype.select = function (select) {
  return this._options[select][0];
};

Randomize.prototype.random = function (data) {
  if (this._lock) {
    return this._lock;
  }

  let sum = 0;
  for (let i = 0; i < this._options.length; i++) {
    let option = this._options[i];
    sum += option.xweight = option.weight(data);
  }

  let rand = Math.random() * sum;
  let selected;
  for (let i = 0; i < this._options.length; i++) {
    let option = this._options[i];
    selected = option.value; // let last one be selected
    if ((rand -= option.xweight) < 0) {
      break;
    }
  }
  return selected;
};

Randomize.prototype.reset = function () {
  return this;
};

Randomize.prototype.test = function () {
  return true;
};

Randomize.prototype.spacing = function (space) {
  space = Randomize._fnum(space, 1);
  let next = 0;
  this.test = function (t, data) {
    t = typeof t === "number" ? t : 1;
    if (next == 0) {
      next = space(data);
      return false;
    }
    if ((next -= t) <= 0) {
      next = space(data);
      return true;
    }
    return false;
  };
  this.reset = function () {
    next = 0;
    return this;
  };
  return this;
};

Randomize.prototype.prob = function (prob) {
  prob = Randomize._fnum(prob, 1);
  this.test = function (data) {
    return Math.random() < prob(data) ? true : false;
  };
  return this;
};

Randomize._fnum = function (value, fallback) {
  if (typeof value === "function") {
    return value;
  }
  if (typeof value === "number") {
    return function () {
      return value;
    };
  }
  return function () {
    return fallback;
  };
};

export default Randomize;