Making a Parallax SVG Landscape - new site part 1

I've finally finished my new website, and I am really happy with it. I started the site in July 2020 and I launched it in mid January 2021.

It's a big change from Nuxt, Vue and Webpack to doing pretty much everything myself with 11ty (Eleventy) and gulp—I love it. More on that in a future post however, today is about the star of the show—the parallax landscape you see at the top of the page.

If you're the type who wants to dive straight into the code, here's a CodePen - go and have a play!

For those still with me, let's go through it.

Note: I'm writing JavaScript in ES6 and CSS in SCSS. I compile my code anyway so this makes it easier for me to work with.

Inspiration

If you recognise the art-style, it's super inspired by the game Firewatch. Firewatch is a 'walking simulator' game that came out in 2016 and people loved its art style. Featuring a bright, layered landscape it inspired many, myself included. For several years the wallpaper of my phone changed between these wallpapers based on time and weather.

When I was planning my new site, I decided to centre it on this art style. I wanted it to feel interactive, and parallax felt like a natural way to do that.

The Markup

My wonderful sister Becci Shepherd produced the landscape, and sent me a raster PNG for each layer. Although I experimented with masking, it's browser support isn't quite there. SVGs were the obvious choice.

To convert to vector I used Vector Magic Desktop Edition. It does a brilliant job of anything you throw at it, and is the best raster-to-vector converter I've found.

I tidied up the paths in a graphics program; exported it to SVG; tidied up the markup and optimised with SVGOMG. This left me with a decent sized SVG for each layer.

Try ensure the viewbox is identical as it will make sizing much easier.

Now in HTML, we need to stack them:

<div class="landscape" role="img" aria-label="This is equivalent to an img alt attribute.">
	<div class="landscape__layer">
    	<div class="landscape__image">
      		<svg viewBox="0 0 4000 1000" xmlns="http://www.w3.org/2000/svg">...</svg>
    	</div>
  	</div>
	<div class="landscape__layer">
    	<div class="landscape__image">
      		<svg viewBox="0 0 4000 1000" xmlns="http://www.w3.org/2000/svg">...</svg>
    	</div>
  	</div>
	<div class="landscape__layer">
    	<div class="landscape__image">
      		<svg viewBox="0 0 4000 1000" xmlns="http://www.w3.org/2000/svg">...</svg>
    	</div>
  	</div>

  	... and so on.
</div>

Remember accessibility! Despite being a whole bunch of markup, this is really a fancy image. We use role="img" and aria-label to make it accessible.

I didn't have the two wrapping divs at first, but realised that wrappers for each layer allowed me to use flexbox. This made positioning the SVGs easier:

// wrapping landscape
.landscape {
	background: var(--c1);
	height: 75vh;
	overflow: hidden;
	position: relative;

// make each layer fill parent
.landscape__layer {
	height: 100%;
	left: 0;
	position: absolute;
	top: 0;
	width: 100%;
}

// svg wrapper
.landscape__image {
	// position at bottom of element in center
	position: absolute;
	bottom: 0;
	left: 50%;
	transform: translateX(-50%);

	// set sizes that work for my image
	max-height: 100%;
	max-width: 300%;
	min-width: 100%;
	width: 2500px;

	// use flexbox to center SVG elements
	display: flex;
	flex-direction: column;
}

// basic styling for SVG element
.landscape__image svg {
	display: block;
	height: auto;
	max-width: 100%;
}

We now have a static landscape and are set up to make it more dynamic!

Parallax Animation

Perspective and translateZ

There are two popular methods to implement parallax on the web. The more performant implementation is a CSS-only solution using the perspective CSS property with translateZ(). This is what browser vendors suggest, as it allows the browser to render changes with the GPU. This makes it super quick and smooth and is how I tried to implement it for weeks.

Google Developer docs have a good example of this method.

Although it's great for simple implementations—I found that in my case it was unreliable. This was because:

• Browser implementations vary. Chrome handles a deep 3D perspective easily, but Firefox interprets the spec differently. This meant I had to apply transform-style: preserve-3d on every element between my scroll element and my layers.
• Firefox on Android handles 3D transformations inconsistently with deep DOM trees, making it hard to adapt to my structure.
• Mobile Safari on iOS has quirks, and the current solution is to use a trick which 'reverses' the parallax direction. Not an option in my case as that would break the effect!

I spent about two weeks trying to get this working before giving up and going for method two.

JavaScript parallax

JS-based parallax has had a bad rep, as a few popular libraries weren't very performant or accessible. Their size was to deal with browser inconsistencies, but with modern CSS and JS we can do it ourselves without much work.

With CSS custom properties and calc() we can come up with a light and neat implementation ourselves. In JavaScript we use window.requestAnimationFrame and if the scroll position has changed we set it to a custom property.

// constant elements: your main scrolling element; html element
const scrollEl = document.documentElement
const root = document.documentElement

let scrollPos

// update css property on scroll
function animation() {
  // check the scroll position has changed
  if (scrollPos !== scrollEl.scrollTop) {
    // reset the seen scroll position
    scrollPos = scrollEl.scrollTop
    // update css property --scrollPos with scroll position in pixels
    root.style.setProperty('--scrollPos', scrollPos + 'px')
  }

  // call animation again on next animation frame
  window.requestAnimationFrame(animation)
}

// start animation on next animation frame
window.requestAnimationFrame(animation)

That's it. That's all the JavaScript we need. As someone who loves CSS it feels great knowing that we can keep the JS simple and use CSS to implement this descriptively.

The real action is happening in the CSS, this is what we need to add to our previous styles:

.landscape__layer {
	// parallax
	transform: translateY(calc(var(--scrollPos, 0) * var(--offset, 0)));

	@media (prefers-reduced-motion: reduce) {
		transform: translateY(0);
	}
}

The key line is the first transform and it's custom properties. What we are doing is translating the layer down a certain amount based on the scroll position.

We use a prefers-reduced-motion media query to remove the parallax effect for those who might get motion-sick or prefer less movement in their browsing.

The --offset property is a value that would be between 0 and 1, and changes how much that layer scrolls. Let's look at what happens when we vary that property and scroll down by 100px:

• --offset: 0 — the element isn't translated and scrolls as normal;
• --offset: 0.5 — the element will be translated down by 50px. This makes it look like it's moved 50px;
• --offset: 1 — the element is translated down 100px, it's in the same place it used to be. This makes it look like it's not moving with scroll;

The --offset property is the key to our parallax system. If each layer has a different value it will scroll at a different speed from the other layers. We can manually set how much each layer will scroll so it looks natural.

The way we apply this to our layers is using the style property. This way we can avoid adding any more CSS, no matter how many layers we have. We set the front layer to 0 so it scrolls with the content, and increase it with each layer. This is what worked for my image:

<div class="landscape" role="img" aria-label="This is equivalent to an img alt attribute.">
	<div class="landscape__layer" style="--offset:0.96">...</div>
	<div class="landscape__layer" style="--offset:0.92">...</div>
	<div class="landscape__layer" style="--offset:0.9">...</div>
	<div class="landscape__layer" style="--offset:0.86">...</div>
	<div class="landscape__layer" style="--offset:0.83">...</div>
	<div class="landscape__layer" style="--offset:0.8">...</div>
	<div class="landscape__layer" style="--offset:0.75">...</div>
	<div class="landscape__layer" style="--offset:0.4">...</div>
	<div class="landscape__layer" style="--offset:0.2">...</div>
	<div class="landscape__layer" style="--offset:0">...</div>
</div>

Notice the big gap between 0.4 and 0.75. If you look at the landscape structure, the loch is a lot further away than the trees. We produce the same effect by making the offset a lot further away from 0.

Result

And here we have our final parallax landscape!

Thank you for reading! Next up we're going to take this landscape and add colour schemes—including one that matches the visitors local time!