![]() To that same element apply a perspective value, and a perspective-origin set to top left, or 0 0.Set up a containing element to scroll with overflow-y: scroll (and probably overflow-x: hidden).# CSS in 3Dīoth Scott Kellum and Keith Clark have done significant work in the area of using CSS 3D to achieve parallax motion, and the technique they use is effectively this: If we want to deliver on the promise of parallax motion, we want something that can be applied as an accelerated property (which today means sticking to transforms and opacity), and which doesn’t rely on scroll events. Many solutions attempt to change background-position to provide the parallax look, which causes the browser to repaint the affected parts of the page on scroll, and that can be costly enough to significantly jank the animation. # Bad: updating background-positionĪnother situation we’d like to avoid is painting on every frame. If the main thread is busy with any other work, scroll events will not get delivered immediately, meaning the parallax effect will be lost. More recent versions do deliver scroll events during the animation, but, similarly to Chrome, on a "best-effort" basis. In older versions of Mobile Safari, scroll events were actually delivered at the end of the scroll, which made it impossible to make a JavaScript-based scroll effect. This important piece of information tells us why we need to avoid a JavaScript-based solution that moves elements based on scroll events: JavaScript doesn’t guarantee that parallaxing will keep in step with the page’s scroll position. In most browsers scroll events are delivered as "best-effort" and are not guaranteed to be delivered on every frame of the scroll animation! This applies, in our particular case, to scroll events. While that sounds simple, an important mechanism of modern browsers is their ability to work asynchronously. The key requirement of parallaxing is that it should be scroll-coupled for every single change in the page’s scroll position, the parallaxing element's position should update. To begin with, let’s take a look at two common ways of achieving a parallax effect, and in particular, why they are unsuitable for our purposes. If you want the drop-in solution, head over to the UI Element Samples GitHub repo and grab the Parallax helper JS! You can see a live demo of the parallax scroller in the GitHub repo. For Mobile Safari use position: sticky to ensure that the parallax effect gets propagated.Use CSS 3D transforms to create a more accurate parallax effect.Don’t use scroll events or background-position to create parallax animations.In this article, we’ll discuss a solution that is both performant and, just as importantly, works cross-browser. The problem, however, is that implementing parallaxing in a performant way can be challenging. When used judiciously, it can add depth and subtlety to a web app. Love it or hate it, parallaxing is here to stay.
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