Tag: Scrolling

Let’s Make One of Those Fancy Scrolling Animations Used on Apple Product Pages

Apple is well-known for the sleek animations on their product pages. For example, as you scroll down the page products may slide into view, MacBooks fold open and iPhones spin, all while showing off the hardware, demonstrating the software and telling interactive stories of how the products are used.

Just check out this video of the mobile web experience for the iPad Pro:

Source: Twitter

A lot of the effects that you see there aren’t created in just HTML and CSS. What then, you ask? Well, it can be a little hard to figure out. Even using the browser’s DevTools won’t always reveal the answer, as it often can’t see past a <canvas> element.

Let’s take an in-depth look at one of these effects to see how it’s made so you can recreate some of these magical effects in our own projects. Specifically, let’s replicate the AirPods Pro product page and the shifting light effect in the hero image.

The basic concept

The idea is to create an animation just like a sequence of images in rapid succession. You know, like a flip book! No complex WebGL scenes or advanced JavaScript libraries are needed.

By synchronizing each frame to the user’s scroll position, we can play the animation as the user scrolls down (or back up) the page.

Start with the markup and styles

The HTML and CSS for this effect is very easy as the magic happens inside the <canvas> element which we control with JavaScript by giving it an ID.

In CSS, we’ll give our document a height of 100vh and make our <body> 5⨉ taller than that to give ourselves the necessary scroll length to make this work. We’ll also match the background color of the document with the background color of our images.

The last thing we’ll do is position the <canvas>, center it, and limit the max-width and height so it does not exceed the dimensions of the viewport.

html {   height: 100vh; } 
 body {   background: #000;   height: 500vh; } 
 canvas {   position: fixed;   left: 50%;   top: 50%;   max-height: 100vh;   max-width: 100vw;   transform: translate(-50%, -50%); }

Right now, we are able to scroll down the page (even though the content does not exceed the viewport height) and our <canvas> stays at the top of the viewport. That’s all the HTML and CSS we need.

Let’s move on to loading the images.

Fetching the correct images

Since we’ll be working with an image sequence (again, like a flip book), we’ll assume the file names are numbered sequentially in ascending order (i.e. 0001.jpg, 0002.jpg, 0003.jpg, etc.) in the same directory.

We’ll write a function that returns the file path with the number of the image file we want, based off of the user’s scroll position.

const currentFrame = index => (   `https://www.apple.com/105/media/us/airpods-pro/2019/1299e2f5_9206_4470_b28e_08307a42f19b/anim/sequence/large/01-hero-lightpass/$ {index.toString().padStart(4, '0')}.jpg` )

Since the image number is an integer, we’ll need to turn it in to a string and use padStart(4, '0') to prepend zeros in front of our index until we reach four digits to match our file names. So, for example, passing 1 into this function will return 0001.

That gives us a way to handle image paths. Here’s the first image in the sequence drawn on the <canvas> element:

As you can see, the first image is on the page. At this point, it’s just a static file. What we want is to update it based on the user’s scroll position. And we don’t merely want to load one image file and then swap it out by loading another image file. We want to draw the images on the <canvas> and update the drawing with the next image in the sequence (but we’ll get to that in just a bit).

We already made the function to generate the image filepath based on the number we pass into it so what we need to do now is track the user’s scroll position and determine the corresponding image frame for that scroll position.

Connecting images to the user’s scroll progress

To know which number we need to pass (and thus which image to load) in the sequence, we need to calculate the user’s scroll progress. We’ll make an event listener to track that and handle some math to calculate which image to load.

We need to know:

  • Where scrolling starts and ends
  • The user’s scroll progress (i.e. a percentage of how far the user is down the page)
  • The image that corresponds to the user’s scroll progress

We’ll use scrollTop to get the vertical scroll position of the element, which in our case happens to be the top of the document. That will serve as the starting point value. We’ll get the end (or maximum) value by subtracting the window height from the document scroll height. From there, we’ll divide the scrollTop value by the maximum value the user can scroll down, which gives us the user’s scroll progress.

Then we need to turn that scroll progress into an index number that corresponds with the image numbering sequence for us to return the correct image for that position. We can do this by multiplying the progress number by the number of frames (images) we have. We’ll use Math.floor() to round that number down and wrap it in Math.min() with our maximum frame count so it never exceeds the total number of frames.

window.addEventListener('scroll', () => {     const scrollTop = html.scrollTop;   const maxScrollTop = html.scrollHeight - window.innerHeight;   const scrollFraction = scrollTop / maxScrollTop;   const frameIndex = Math.min(     frameCount - 1,     Math.floor(scrollFraction * frameCount)   ); });

Updating <canvas> with the correct image

We now know which image we need to draw as the user’s scroll progress changes. This is where the magic of  <canvas> comes into play. <canvas> has many cool features for building everything from games and animations to design mockup generators and everything in between!

One of those features is a method called requestAnimationFrame that works with the browser to update <canvas> in a way we couldn’t do if we were working with straight image files instead. This is why I went with a <canvas> approach instead of, say, an <img> element or a <div> with a background image.

requestAnimationFrame will match the browser refresh rate and enable hardware acceleration by using WebGL to render it using the device’s video card or integrated graphics. In other words, we’ll get super smooth transitions between frames — no image flashes!

Let’s call this function in our scroll event listener to swap images as the user scrolls up or down the page. requestAnimationFrame takes a callback argument, so we’ll pass a function that will update the image source and draw the new image on the <canvas>:

requestAnimationFrame(() => updateImage(frameIndex + 1))

We’re bumping up the frameIndex by 1 because, while the image sequence starts at 0001.jpg, our scroll progress calculation starts actually starts at 0. This ensures that the two values are always aligned.

The callback function we pass to update the image looks like this:

const updateImage = index => {   img.src = currentFrame(index);   context.drawImage(img, 0, 0); }

We pass the frameIndex into the function. That sets the image source with the next image in the sequence, which is drawn on our <canvas> element.

Even better with image preloading

We’re technically done at this point. But, come on, we can do better! For example, scrolling quickly results in a little lag between image frames. That’s because every new image sends off a new network request, requiring a new download.

We should try preloading the images new network requests. That way, each frame is already downloaded, making the transitions that much faster, and the animation that much smoother!

All we’ve gotta do is loop through the entire sequence of images and load ‘em up:

const frameCount = 148; 
 const preloadImages = () => {   for (let i = 1; i < frameCount; i++) {     const img = new Image();     img.src = currentFrame(i);   } }; 
 preloadImages();

Demo!

A quick note on performance

While this effect is pretty slick, it’s also a lot of images. 148 to be exact.

No matter much we optimize the images, or how speedy the CDN is that serves them, loading hundreds of images will always result in a bloated page. Let’s say we have multiple instances of this on the same page. We might get performance stats like this:

1,609 requests, 55.8 megabytes transferred, 57.5 megabytes resources, load time of 30.45 seconds.

That might be fine for a high-speed internet connection without tight data caps, but we can’t say the same for users without such luxuries. It’s a tricky balance to strike, but we have to be mindful of everyone’s experience — and how our decisions affect them.

A few things we can do to help strike that balance include:

  • Loading a single fallback image instead of the entire image sequence
  • Creating sequences that use smaller image files for certain devices
  • Allowing the user to enable the sequence, perhaps with a button that starts and stops the sequence

Apple employs the first option. If you load the AirPods Pro page on a mobile device connected to a slow 3G connection and, hey, the performance stats start to look a whole lot better:

8 out of 111 requests, 347 kilobytes of 2.6 megabytes transferred, 1.4 megabytes of 4.5 megabytes resources, load time of one minute and one second.

Yeah, it’s still a heavy page. But it’s a lot lighter than what we’d get without any performance considerations at all. That’s how Apple is able to get get so many complex sequences onto a single page.


Further reading

If you are interested in how these image sequences are generated, a good place to start is the Lottie library by AirBnB. The docs take you through the basics of generating animations with After Effects while providing an easy way to include them in projects.

The post Let’s Make One of Those Fancy Scrolling Animations Used on Apple Product Pages appeared first on CSS-Tricks.

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A “new direction” in the struggle against rightward scrolling

You know those times you get a horizontal scrollbar when accidentally placing an element off the right edge of the browser window? It might be a menu that slides in or the like. Sometimes we to overflow-x: hidden; on the body to fix that, but that can sometimes wreck stuff like position: sticky;.

Well, you know how if you place an element off the left edge of a browser window, it doesn’t do that? That’s “data loss” and just how things work around here. It actually has to do with the direction of the page. If you were in a RTL situation, it would be the left edge of the browser window causing the overflow situation and the right edge where it doesn’t.

Emerson Loustau leverages that idea to solve a problem here. I’d be way too nervous messing with direction like this because I just don’t know what the side effects would be. But, hey, at least it doesn’t break position: sticky;.

Direct Link to ArticlePermalink

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Sticky Table of Contents with Scrolling Active States

Say you have a two-column layout: a main column with content. Say it has a lot of content, with sections that requires scrolling. And let’s toss in a sidebar column that is largely empty, such that you can safely put a position: sticky; table of contents over there for all that content in the main column. A fairly common pattern for documentation.

Bramus Van Damme has a nice tutorial on all this, starting from semantic markup, implementing most of the functionality with HTML and CSS, and then doing the last bit of active nav enhancement with JavaScript.

For example, if you don’t click yourself down to a section (where you might be able to get away with :target styling for active navigation), JavaScript is necessary to tell where you are scrolled to an highlight the active navigation. That active bit is handled nicely with IntersectionObserver, which is, like, the perfect API for this.

Here’s that result:

It reminds me of a very similar demo from Hakim El Hattab he called Progress Nav. The design pattern is exactly the same, but Hakim’s version has this ultra fancy SVG path that draws itself along the way, indenting for sub nav. I’ll embed a video here:

That one doesn’t use IntersectionObserver, so if you want to hack on this, combine ’em!

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Prevent Page Scrolling When a Modal is Open

Please stop me if you’ve heard this one before. You open a modal, scroll through it, close it, and wind up somewhere else on the page than you were when you opened the modal.

That’s because modals are elements on a page just like any other. It may stay in place (assuming that’s what it’s meant to do) but the rest of page continues to behave as normal.

See the Pen
Avoid body scrollable in safari when modal dialog shown
by Geoff Graham (@geoffgraham)
on CodePen.

Sometimes this is a non-issue, like screens that are the exact height of the viewport. Anything else, though, we’re looking at Scroll City. The good news is that we can prevent that with a sprinkle of CSS (and JavaScript) trickery.

Let’s start with something simple

We can make a huge dent to open-modal-page-scrolling by setting the height of the entire body to the full height of the viewport and hiding vertical overflow when the modal is open:

body.modal-open {   height: 100vh;   overflow-y: hidden; }

That’s good and all, but if we’ve scrolled through the <body> element before opening the modal, we get a little horizontal reflow. The width of the viewport is expanded about 15 pixels more, which is exactly the with of the scroll bar.

See the Pen
Avoid body scrollable in safari when modal dialog shown
by Geoff Graham (@geoffgraham)
on CodePen.

Let’s adjust the right padding of the body a bit to avoid that.

body {   height: 100vh;   overflow-y: hidden;   padding-right: 15px; /* Avoid width reflow */ }

Note that the modal needs to be shorter than the height of the viewport to make this work. Otherwise, the scroll bar on the body will be necessary.

Great, now what about mobile?

This solution works pretty great on desktop as well as Android Mobile. That said, Safari for iOS needs a little more love because the body still scrolls when a modal is open when tapping and moving about the touchscreen.

We can set the body to a fixed position as a workaround:

body {   position: fixed; }

Works now! The body will not respond when the screen is touched. However, there’s still a “small” problem here. Let’s say the modal trigger is lower down the page and we click to open it up. Great! But now we’re automatically scrolled back up to the top of the screen, which is just as disorientating as the scrolling behavior we’re trying to resolve.

See the Pen
Avoid body scrollable in safari when modal dialog shown
by Geoff Graham (@geoffgraham)
on CodePen.

Boo!

That’s why we’ve gotta turn to JavaScript

We can use JavaScript to avoid the touch event bubble. We all know there should be a backdrop layer when a modal is open. Unfortunately, stopPropagation is a little awkward with touch in iOS. But preventDefault works well. That means we have to add event listeners in every DOM node contained in the modal — not just on the backdrop or the modal box layer. The good news is, many JavaScript libraries can do this, including good ol’ jQuery.

Oh, and one more thing: What if we need scrolling inside the modal? We still have to trigger a response for a touch event, but when reaching the top or bottom of the modal, we still need to prevent bubbling. Seems very complex, so we’re not totally out of the woods here.

Let’s enhance the fixed body approach

This is what we were working with:

body {   position: fixed; }

If we know the top of the scroll location and add it to our CSS, then the body will not scroll back to the top of the screen, so problem solved. We can use JavaScript for this by calculating the scroll top, and add that value to the body styles:

// When the modal is shown, we want a fixed body document.body.style.position = 'fixed'; document.body.style.top = `-$  {window.scrollY}px`;  // When the modal is hidden, we want to remain at the top of the scroll position document.body.style.position = ''; document.body.style.top = '';

This works, but there’s still a little leakage here after the modal is closed. Specifically, it appears that the page already loses its scroll position when the modal is open and the body set to be fixed. So we have to retrieve the location. Let’s modify our JavaScript to account for that.

// When the modal is hidden... const top = document.body.style.top; document.body.style.position = ''; document.body.style.top = ''; window.scrollTo(0, parseInt(scrollY || '0') * -1);

That does it! The body no longer scrolls when a modal is open and the scroll location is maintained both when the modal is open and when it is closed. Huzzah!

See the Pen
Avoid body scrollable in safari when modal dialog shown
by Geoff Graham (@geoffgraham)
on CodePen.

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Smooth Scrolling for Screencasts

Let’s say you wanted to scroll a web page from top to bottom programmatically. For example, you’re recording a screencast and want a nice full-page scroll. You probably can’t scroll it yourself because it’ll be all uneven and jerky. Native JavaScript can do smooth scrolling. Here’s a tiny snippet that might do the trick for you:

window.scrollTo({   top: document.body.getBoundingClientRect().height,   behavior: 'smooth' });

But there is no way to control the speed or easing of that! It’s likely to be way too fast for a screencast. I found a little trick though, originally published by (I think) Jedidiah Hurt.

The trick is to use CSS transforms instead of actual scrolling. This way, both speed and easing can be controlled. Here’s the code that I cleaned up a little:

const scrollElement = (element, scrollPosition, duration) => {      // useful while testing to re-run it a bunch.   // element.removeAttribute("style");       const style = element.style;   style.transition = duration + 's';   style.transitionTimingFunction = 'ease-in-out';   style.transform = 'translate3d(0, ' + -scrollPosition + 'px, 0)'; }  scrollElement(   document.body,    (     document.body.getBoundingClientRect().height     -     document.documentElement.clientHeight     +     25   ),   5 );

The idea is to transform a negative top position for the height of the entire document, but subtract the height of what you can see so it doesn’t scroll too far. There is a little magic number in there you may need to adjust to get it just right for you.

Here’s a movie I recorded that way:

It’s still not perrrrrrfectly smooth. I partially blame the FPS of the video, but even with my eyeballs watching it record it wasn’t total butter. If I needed even higher quality, I’d probably restart my computer and have this page open as the only tab and application open, lolz.

See a Demo

Another possibility is a little good ol’ fashioned jQuery .animate(), which can be extended with some custom easing. Here’s a demo of that.

See the Pen
jQuery Smooth Scrolling with Easing
by Chris Coyier (@chriscoyier)
on CodePen.

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Downsides of Smooth Scrolling

Smooth scrolling has gotten a lot easier. If you want it all the time on your page, and you are happy letting the browser deal with the duration for you, it’s a single line of CSS:

html {   scroll-behavior: smooth; }

I tried this on version 17 of this site, and it was the second most-hated thing, aside from the beefy scrollbar. I haven’t changed the scrollbar. I like it. I’m a big user of scrollbars and making it beefy is extra usable for me and the custom styling is just fun. But I did revert to no smooth scrolling.

As Šime Vidas pointed to in Web Platform News, Wikipedia also tried smooth scrolling:

The recent design for moved paragraphs in mobile diffs called for an animated scroll when clicking from one instance of the paragraph in question to the other. The purpose of this animation is to help the user stay oriented in terms of where the paragraph got moved to.

We initially thought this behavior would benefit Minerva in general (e.g. when using the table of contents to navigate to a page section it would be awesome to animate the scroll), but after trying it out decided to scope this change just to the mobile diffs view for now

I can see not being able to adjust timing being a downside, but that wasn’t what made me ditch smooth scrolling. The thing that seemed to frustrate a ton of people was on-page search. It’s one thing to click a link and get zoomed to some header (that feels sorta good) but it’s another when you’re trying to quickly pop through matches when you do a Find on the page. People found the scrolling between matches slow and frustrating. I agreed.

Surprisingly, even the JavaScript variant of smooth scrolling…

document.querySelector('.hello').scrollIntoView({    behavior: 'smooth'  });

…has no ability to adjust timing. Nor is there a reliable way to detect if the page is actively being searched in order to make UX changes, like turning off smooth scrolling.

Perhaps the largest downside of smooth scrolling is the potential to mismanage focus. Scrolling to an element in JavaScript is fine, so long as you almost move focus to where you are scrolling. Heather Migliorisi covers that in detail here.

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