chaos/scripts/chaos.js

'use strict';

import { getColor } from './utils';

/**
 * Choose an index at random among a list of weights,
 * more weighted indices have a greater proability to be chosen
 *
 * @param {Array} weights List of weights
 * @return {number} Selected index
 */
const chooseIndex = weights => {
    const number = Math.random();
    let sum = 0, index = 0;

    while (number >= sum) {
        sum += weights[index];
        index += 1;
    }

    return index - 1;
};

/**
 * Apply the chaos game: starting from `start`, we plot
 * the next `n` points. To get to the next point, we apply
 * a random transformation among given ones
 *
 * @param {ImageData} image Image to write on
 * @param {Array} start Starting point
 * @param {number} iterations Number of points to plot
 * @param {Array} transforms List of available transforms
 * @param {Array} weights Probability weights for each transform
 * @return {null}
 */
export const applyChaos = (image, start, iterations, transforms, weights) => {
    const width = image.width;
    let point = start;

    if (weights === undefined) {
        weights = Array.apply(null, Array(transforms.length)).map(
            () => 1 / transforms.length
        );
    }

    while (iterations--) {
        const index = chooseIndex(weights);
        const color = getColor(2);

        // console.log(point);
        // console.log(point.map(x => Math.floor(x * 10 + 100)));
        point = transforms[index](point);

        const i = (
            Math.floor(point[1] * 50 + 50) * width +
            Math.floor(point[0] * 50 + 200)
        ) * 4;

        image.data[i] = color[0];
        image.data[i + 1] = color[1];
        image.data[i + 2] = color[2];
        image.data[i + 3] = 255;
    }
};