Let’s say you’re a designer. Cool. You’ve been hired to do some design work for a conference. All kinds of stuff. Website. Printed schedules. Big posters for the rooms. Preroll slides. You name it.

So you come up with an aesthetic for it all — a design vibe that ties it all together and makes it feel cohesive. Yet each usage will be unique and different. Cool, let’s go from there.

You’re mucking around in your design software, and the aesthetic you come up with is these overlapping rectangles in a randomized pattern with a particular limited color palette that you think can work for all the materials.

Hey, sure. That’s a fun background pattern. You can lay white boxes on top of it to set type or whatever, this is just the general background aesthetic that you can use broadly.

But it’s not very random while it’s in design software, is it? I suppose you could figure out how to script the software. But we’re web people so let’s get webby with it. Let’s lean on JavaScript and SVG to start.

We could define our color palette programmatically like:

const colorPalette = ["#9B2E69", "#D93750", "#E2724F", "#F3DC7B", "#4E9397"];

Then write a function that just makes a bunch of random rectangles based on a minimum and maximum value you give it:

const rand = (max) => {
  return Math.floor(Math.random() * max);

const makeRects = (maxX, maxY) => {
  let rects = "";
  for (let i = 0; i < 100; i++) {
    rects += `
        x="${rand(maxX + 50) - 50}"
        y="${rand(maxY + 50) - 50}"
        width="${rand(200) + 20}"
        height="${rand(200) + 20}"
  return rects;

You could call that function and slap all those rectangles in an <svg> and get some nice generative artwork.

Now your work is easy! To make new ones, you run the code over and over and the you get nice SVG to use for whatever you need.

Let’s say your client is asking you for some of this artwork to use as backgrounds on other things they are working on too. They need a background with different dimensions! At a different aspect ratio! They need it right now!

The fact that we’re doing this in the browser is awfully helpful here. The browser window can be resized easily. Wow, I know. So let’s size the parent SVG to the entire viewport. This is the SVG that calls that function to make all the random rectangles here:

const makeSVG = () => {
  const w = document.body.offsetWidth;
  const h = document.body.offsetHeight;
  const svg = `<svg width="${w}" height="${h}">
    ${makeRects(w, h)}
  return svg;

So, if we’re doing this in the browser, we’ll get a wide and squat SVG result if the browser is super wide and squat:

But how do we get that out of the browser and into an actual SVG file? Well, there are probably native platform ways to do it, but I just Google’d my way out of it and found a snippet of code that did the trick. I take the SVG as a string, chuck it in a data URL as the href on a link, and fake-click that link. I do that on the click of a button.

function download(filename, text) {
  var pom = document.createElement("a");
    "data:text/plain;charset=utf-8," + encodeURIComponent(text)
  pom.setAttribute("download", filename);

  if (document.createEvent) {
    var event = document.createEvent("MouseEvents");
    event.initEvent("click", true, true);
  } else {

const downloadSvgButton = document.querySelector("#download-svg-button");
downloadSvgButton.addEventListener("click", () => {
  download("art.svg", window.globalSVGStore);

But I need is as a PNG!

…cries your client. Fair enough. Not everyone has software that can view and deal with SVG. You could just take a screenshot of the page. And, honestly, that might be a good way to go. I have a high pixel density display and those screenshots turn out great.

But now that we’ve built a downloader machine for the SVG, we might as well make it work for PNG too. This time my Googling led to FileSaver.js. If I have a <canvas>, I can toBlob that thing and save it to a file. And I can turn my <svg> into a <canvas> via canvg.

So, when we call our function to make the SVG, we’ll just paint it to a canvas, which will automatically be the same size as the SVG, which we’ve sized to cover the viewport.

const setup = () => {
  const v = canvg.Canvg.fromString(ctx, makeSVG());

We can call that setup function whenever, so might as well make a button for it, too, and call it when the browser window resizes. Here it is in action:

And here’s the final thing:

It could be a lot smarter. It could decide how many rectangles to draw based on the viewport volume, for example. I just think it’s very neat to essentially build an art-generating machine for making design assets, particularly to solve real-world client problems.

This idea was totally taken from a peek I had at a tool some actual designers built like this. Theirs was way cooler and had even more options, and I know who they built it for was very happy with it because that’s who showed it to me. I reached out to that designer but they were too busy to take on a writing gig like this.

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