---
title: FractalArt
slug: fractalart
description: A somewhat unperformant generator for pleasant watercolor-y "fractalart" images. Ported from a Haskell implementation by "TomSmeets".
---
<style>
    .controls input, .controls button { border: 1px solid black; padding: 0.2em; }
    #fractalart { display: flex; align-items: flex-start; flex-wrap: wrap; }
    #status { font-style: italic; }
    #info { padding-top: 0.5em; font-size: 0.8em; }
    #out { image-rendering: crisp-edges; }
</style>
<div id="fractalart">
    <canvas id="out" width=512 height=512></canvas>
    <table class="controls">
        <tr><td>Lightness:</td><td><input id="lightness" type="number" max="1" min="0" step="0.01" value="0.6"></td></tr>
        <tr><td>Saturation:</td><td><input id="saturation" type="number" max="1" min="0" step="0.01" value="1.0"></td></tr>
        <tr><td>Hue:</td><td><input id="hue" type="number" max="360" min="0" step="1" value="0"></td><td>(or random: <input type="checkbox" checked id="hue-random">)</td></tr>
        <tr><td>Variance:</td><td><input id="variance" type="number" min="0" step="0.25" value="4"></td></tr>
        <tr><td>Bias:</td><td><input id="bias" type="number" step="0.25" value="0"></td></td></tr>
        <tr><td>Render Size:</td><td><input id="width" type="number" step="16" value="512"></td></td></tr>
        <tr><td><button id="generate">Generate</button></td></tr>
        <tr><td colspan="4" id="status"></td></tr>
        <tr><td colspan="4"><div id="info">
            <a href="https://github.com/TomSmeets/FractalArt/">FractalArt</a> for JS.<br>
            If this is too slow try my <a href="https://github.com/osmarks/random-stuff/tree/master/fractalart-rs">Rust port</a>.<br>
            This is all contained in one HTML file, so you can save it locally if you want.
        </div></td></tr>
    </table>
</div>
<script id="fractalart-code">
    // harvested from github somewhere
    function hslToRgb(h, s, l) {
        var r, g, b;

        if (s == 0) {
            r = g = b = l; // achromatic
        } else {
            function hue2rgb(p, q, t) {
            if (t < 0) t += 1;
            if (t > 1) t -= 1;
            if (t < 1/6) return p + (q - p) * 6 * t;
            if (t < 1/2) return q;
            if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
            return p;
            }

            var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
            var p = 2 * l - q;

            r = hue2rgb(p, q, h + 1/3);
            g = hue2rgb(p, q, h);
            b = hue2rgb(p, q, h - 1/3);
        }

        return [ r * 255, g * 255, b * 255 ];
    }
    const randRange = x => Math.floor(Math.random() * x)

    // main fractalart logic
    // todo: WASM (there is already a perfectly good Rust version...) or just actually optimize this
    const run = (im, { hue, saturation, lightness, variance, bias }) => {
        const set = (x, y, offset, value) => { im.data[(y * im.width + x) * 4 + offset] = value }
        const get = (x, y, offset) => im.data[(y * im.width + x) * 4 + offset]
        const boundcheck = (x, y) => x >= 0 && y >= 0 && x < im.width && y < im.height
        const ringAt = (x, y, l) => {
            let out = []
            for (let n = -l; n <= l; n++) {
                out.push([n + x, l + y])
                out.push([n + x, -l + y])
            }
            for (let n = 1 - l; n <= l; n++) {
                out.push([l + x, n + y])
                out.push([-l + x, n + y])
            }
            return out.filter(([x, y]) => boundcheck(x, y))
        }
        const modColorChannel = x => Math.min(Math.max(Math.floor(x + (Math.random() * (variance * 2 + 1)) - variance + bias), 0), 255)

        const startX = randRange(im.width)
        const startY = randRange(im.height)
        const iterations = Math.max(startX, im.width - 1 - startX, startY, im.height - 1 - startY)
        const [sR, sG, sB] = hslToRgb(hue, saturation, lightness)
        set(startX, startY, 0, Math.floor(sR))
        set(startX, startY, 1, Math.floor(sG))
        set(startX, startY, 2, Math.floor(sB))
        set(startX, startY, 3, 255)
        for (let iteration = 1; iteration <= iterations; iteration++) {
            for (const [x, y] of ringAt(startX, startY, iteration)) {
                const possibleColors = []
                for (const [ax, ay] of ringAt(x, y, 1)) {
                    if (get(ax, ay, 3)) {
                        possibleColors.push([get(ax, ay, 0), get(ax, ay, 1), get(ax, ay, 2)])
                    }
                }

                const [chosenR, chosenG, chosenB] = possibleColors[randRange(possibleColors.length)]
                set(x, y, 0, modColorChannel(chosenR))
                set(x, y, 1, modColorChannel(chosenG))
                set(x, y, 2, modColorChannel(chosenB))
                set(x, y, 3, 255)
            }
        }

        postMessage(im)
    }

    const readInput = name => document.getElementById(name).value

    // detect if not running on webworker
    if ("document" in self) {
        const statusDisplay = document.querySelector("#status")
        let status = "Idle"
        let startTime = null
        const updateStatus = s => {
            if (statusDisplay.firstChild) { statusDisplay.removeChild(statusDisplay.firstChild) }
            statusDisplay.appendChild(document.createTextNode(s))
            status = s
        }
        const canv = document.querySelector("#out")
        // TODO things
        canv.style.width = canv.style.height = Math.min(512, window.innerWidth - 16) + "px"
        const ctx = canv.getContext("2d")
        const source = `
        ${document.querySelector("#fractalart-code").innerHTML}
        onmessage = e => run(e.data[0], e.data[1])
        `
        // be nice to foolish single threaded browsers
        // offload to worker thread
        const worker = new Worker(URL.createObjectURL(new Blob([source], {type: 'application/javascript'})))
        worker.onmessage = e => {
            const im = e.data
            canv.width = canv.height = im.width
            ctx.putImageData(im, 0, 0)
            updateStatus(`Idle (${Date.now() - startTime}ms)`)
        }
        worker.onerror = e => {
            console.warn(e)
            updateStatus(e.message)
        }
        const generate = () => {
            if (status !== "Working") {
                updateStatus("Working")
                startTime = Date.now()
                const size = parseInt(readInput("width"))
                worker.postMessage([ctx.createImageData(size, size), {
                    hue: document.getElementById("hue-random").checked ? Math.random() : parseFloat(readInput("hue")),
                    saturation: parseFloat(readInput("saturation")),
                    lightness: parseFloat(readInput("lightness")),
                    variance: parseFloat(readInput("variance")),
                    bias: parseFloat(readInput("bias"))
                }])
            }
        }
        document.querySelector("#generate").addEventListener("click", generate)
        generate()
    }
</script>