By utilizing the `scroll()` variety of Scroll-Driven Animations, developers can create a visual illusion where different columns in a grid move at different rates as a user scrolls down a page. This technique decouples the visual movement of content from the standard linear scroll of the viewport, allowing for creative gallery layouts that were previously difficult to achieve without heavy JavaScript overhead.
Mechanism of Variable Speed Scrolling
The core mechanism relies on applying a directional transform to a specific container, such as a right-hand column in a two-column grid. Instead of moving the actual content via a scroll container, the developer applies a `translateY` animation that changes value based on the scroll position of the root element.
By defining a `@keyframes` animation and linking it to the `scroll()` timeline, the right column can be programmed to move a greater distance than the left column over the same scroll distance. For example, a `translateY` that moves from `12vh` to `-20vh` creates a 'drift-up' effect that makes the content appear to move faster than the standard page progression.
“The trick is to apply a directional transform that changes in value as we scroll.”
— Multi-Column Different-Speed Scrolling – Master.dev Blog
Layering View-Based Animations
Beyond global column movement, the `view()` variety of Scroll-Driven Animations allows for granular control over individual items within those columns. This can be used to create 'zoomies'—effects where a photo scales up or shifts slightly as it passes through the user's visible area.
Because these animations are tied to the `view()` timeline, the effect is automatically triggered and reversed based on the element's visibility in the viewport. This allows for complex, multi-layered motion where a column drifts at one speed while the images inside it perform independent, localized animations.
Trade-offs and User Experience
While these effects provide a high-end aesthetic, they introduce potential usability concerns. High-intensity, non-linear scrolling can cause motion sickness or nausea for some users, making the implementation of a `prefers-reduced-motion` query a recommended consideration for accessibility.
Additionally, because Scroll-Driven Animations are not yet universally supported across all browsers, the author employs `@supports` queries to ensure the gallery remains accessible. In unsupported browsers, the columns will simply scroll at a standard, uniform rate, maintaining the core functionality of the gallery.