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Learn more about the new features of CSS animation: @scroll-timeline

青灯夜游
青灯夜游 forward
2022-03-18 10:55:15 2923browse

In the previous article "Several new CSS features you deserve to know in 2022 (Collection and Learning)", I briefly introduced several new CSS features. Today I will take you to understand one of them in depth. New feature (animation killer): @scroll-timeline, I hope it will be helpful to everyone!

Learn more about the new features of CSS animation: @scroll-timeline

In the CSS specificationScroll-linked Animations, an epoch-making CSS feature is introduced. That is -- The@scroll-timelineat-rule, which literally translates toScrolling Timeline.

This article will take you through it all, from getting started to learning to use CSS@scroll-timeline. (Recommended learning:css video tutorial)

What is @scroll-timeline scrolling timeline?

What is@scroll-timelineWhat is the scrolling timeline?

@scroll-timelineYou can set the start and end of an animation to be determined by the scrolling progress within the scroll container, not by time.

Means,We can define an animation effect, and the start and end of the animation can be controlled by scrolling the container.

Suggestion DEMO

Before systematically learning grammar, we use a DEMO to briefly understand its usage:

We first implement asimple font F Rotation animation:

F
#g-box { animation-name: rotate; animation-duration: 3s; animation-direction: alternate; animation-easing-function: linear; } @keyframes rotate { 0% { transform: rotate(0); } 100% { transform: rotate(360deg); } }

Normally, it is such a simple animation:

Learn more about the new features of CSS animation: @scroll-timeline

Next, we combine this animation with@scroll-timelineCombined, it needs to be placed in a scrollable container:

       
F
#g-content { width: 300px; height: 170vh; background: #999; } #g-box { font-size: 150px; margin: 70vh auto 0; animation-name: rotate; animation-duration: 3s; animation-direction: alternate; animation-easing-function: linear; animation-timeline: box-rotate; } @keyframes rotate { 0% { transform: rotate(0); } 100% { transform: rotate(360deg); } } @scroll-timeline box-rotate { source: selector("#g-content"); }

Here, we have implemented a scrollable container#g-content, Its height is170vh, which is 1.7 times the height of the visual interface, and the#g-boxcontainer is placed at a height of70vhfrom the top :

Learn more about the new features of CSS animation: @scroll-timeline

The interesting thing is, the rotation animation we set will not start automatically. The animation will only start when we scroll down. The actual effect Gif:

Learn more about the new features of CSS animation: @scroll-timeline

CodePen Demo -- @scroll-timeline Demo

https://codepen.io/Chokcoco/pen/JjOZMaQ

Seeing this, everyone should be able to understand the role and meaning of@scroll-timeline.It gives CSS the ability to control the progress of animation based on the scrolling of the scroll bar!Amazing! !

@scroll-timeline syntax introduction

Next, let’s take a moment and take a brief look at the syntax of@scroll-timeline.

To use@scroll-timeline, the most important thing is to define a@scroll-timelinerule:

@scroll-timeline moveTimeline { source: selector("#g-content"); orientation: vertical; scroll-offsets: 0px, 500px; }

Among them:

  • source:绑定触发滚动动画的滚动容器
    • source: auto:绑定到Document,也就是全局 Windows 对象
    • source: selector("id-selector"),通过selector(),内置一个#id选择器,选取一个可滚动容器
    • source: none:不指的滚动容器
  • orientation:设定滚动时间线的方向
    • orientation: auto:默认为 vertical,也就是竖直方向的滚动
    • orientation: vertical:竖直方向的滚动
    • orientation: horizontal:水平方向的滚动
    • orientation: block:不太常用,使用沿块轴的滚动位置,符合书写模式和方向性
    • orientation: inline:不太常用,使用沿内联轴的滚动位置,符合书写模式和方向性
  • scroll-offsets:滚动时间线的核心,设定在滚动的什么阶段,触发动画,可通过三种方式之一进行设置:
    • scroll-offsets: none这意味着没有 scroll-offset 指定。
    • 由逗号分隔的length-percentage值列表确定。每个值都映射到animation-duration。例如,如果 ananimation-duration 设置为 2s 且滚动偏移量为 0px, 30px, 100px,则在 1s 时,滚动偏移量将为 30px。
    • 第三种确定滚动偏移量的方法是使用元素偏移量。这意味着可以指定页面内的元素,其位置决定了滚动时间线以及要使用这些元素的哪个边缘。指定元素是使用 selector() 函数完成的,该函数接收元素的 id。边缘由关键字 start 或确定 end。可选的阈值的 0–1 可用于表示元素滚动中预期可见的百分比。

scroll-offsets的理解会比较困难,我们稍后详述。

在设定了一个@scroll-timeline之后,我们只需要将它和动画绑定起来即可,通过animation-timeline

@scroll-timeline moveTimeline { source: selector("#g-content"); orientation: vertical; scroll-offsets: 0px, 500px; } div { animation-name: move; animation-duration: 3s; animation-timeline: moveTimeline; } @keyframes move{ 0% { transform: translate(0, 0); } 100% { transform: translate(100%, 0); } }

使用 @scroll-timeline 实现滚动进度指示器

之前在不可思议的纯 CSS 滚动进度条效果一文中,我们介绍了一种使用渐变实现的纯 CSS 滚动进度指示器效果:

Learn more about the new features of CSS animation: @scroll-timeline

该方法有些小小的瑕疵。其中一个就是当滚动距离太短的时候,进度条右侧会有明显的斜边效果。

而有了@scroll-timeline之后,我们终于可以将滚动和动画这两个元素绑定起来,再实现滚动进度指示器,就已经非常轻松了:

...文本内容...

#g-container { width: 100vw; } #g-container::before { content: ""; position: fixed; height: 5px; left: 0; top: 0; right: 0; background: #ffc107; animation-name: scale; animation-duration: 1s; animation-fill-mode: forwards; animation-timeline: box-rotate; transform-origin: 0 50%; } @keyframes scale { 0% { transform: scaleX(0); } 100% { transform: scaleX(1); } } @scroll-timeline box-rotate { source: auto; orientation: vertical; }

1、我们在页面最上方,通过一个伪元素,实现一个占满屏幕100%5px高的进度条。正常而言是这样:

Learn more about the new features of CSS animation: @scroll-timeline

2、通过设定一个transform: scaleX(0)transform: scaleX(1)的动画,并且将它与 body 的滚动相绑定,即可得到滚动指示器,效果如下:

Learn more about the new features of CSS animation: @scroll-timeline

完整的代码,你可以戳这里:CodePen Demo - 使用 @scroll-timeline 实现滚动进度条

https://codepen.io/Chokcoco/pen/eYeKLMj

使用 scroll-offsets 精确控制动画触发时机

大家可以再看看上面的 Gif 图,都有一个问题,就是动画的开始时间都是从滚动一开始就开始了,刚好在滚动结束时结束。那么如果我希望动画在滚动的特定阶段触发,那该怎么办呢?

这里,就需要借助scroll-offsets,去更加精确的控制我们的动画。

在滚动过程中,我们可以将一个元素,划分为 3 个区域:

  • 滚动过程中,从上方视野盲区,进入视野
  • 滚动过程中,处于视野中
  • 滚动过程中,从视野中,进入下方视野盲区

在这里,我们就可以得到两个边界,上方边界,下方边界:

Learn more about the new features of CSS animation: @scroll-timeline

而对于上下两个边界,又会有两种状态。以上边界为例子,会有:

  • 元素刚刚开始进入可视区
  • 元素完全进入可视区

对于这两种状态,我们用start 0start 1表示,同理,下方的边界也可以用end 0end 1表示:

Learn more about the new features of CSS animation: @scroll-timeline

这里的 0 和 1 实际表示的是,元素滚动中预期可见的百分比

有了这些状态值,配合scroll-offsets,我们就可以精确控制滚动动画的触发时间。

我们设定一个从左向右并且伴随透明度变化的动画,的看看下面几种情况:

1、滚动动画在元素从下方开始出现时开始,完全出现后截止。

动画运行范围:end 0-->end 1

@keyframes move { 0% { transform: translate(-100%, 0); opacity: 0; } 100% { transform: translate(0, 0); opacity: 1; } } @scroll-timeline box-move { source: auto; orientation: "vertical"; scroll-offsets: selector(#g-box) end 0, selector(#g-box) end 1; /* Legacy Descriptors Below: */ start: selector(#g-box) end 0; end: selector(#g-box) end 1; time-range: 1s; } #g-box { animation-name: move; animation-duration: 3s; animation-fill-mode: both; animation-timeline: box-move; }

效果如下:

Learn more about the new features of CSS animation: @scroll-timeline

2、滚动动画在元素从下方完全出现时开始,在滚动到上方即将离开屏幕后截止:

动画运行范围:end 1-->start 1

// ... @scroll-timeline box-move { source: auto; orientation: "vertical"; scroll-offsets: selector(#g-box) end 1, selector(#g-box) start 1; /* Legacy Descriptors Below: */ start: selector(#g-box) end 1; end: selector(#g-box) start 1; time-range: 1s; } // ...

效果如下:

Learn more about the new features of CSS animation: @scroll-timeline

3、滚动动画在元素滚动到上方即将离开屏幕后开始,完全离开屏幕后截止:

动画运行范围:start 1-->start 0

// ... @scroll-timeline box-move { source: auto; orientation: "vertical"; scroll-offsets: selector(#g-box) start 1, selector(#g-box) start 0; /* Legacy Descriptors Below: */ start: selector(#g-box) start 1; end: selector(#g-box) start 0; time-range: 1s; } // ...

效果如下:

1Learn more about the new features of CSS animation: @scroll-timeline

掌握scroll-offsets的用法是灵活运用滚动时间线的关键,当然,在上面你还会看到start: selector(#g-box) start 1end: selector(#g-box) start 0这种写法,这是规范历史遗留问题,最新的规范已经使用了scroll-offsets去替代start:end:的写法。

把上述 3 种情况放在一起,再比较比较:

1Learn more about the new features of CSS animation: @scroll-timeline

完整的代码,你可以戳这里:CodePen Demo - @scroll-timeline Demo | element-based offset

使用 @scroll-timeline 实现各类效果

在能够掌握 @scroll-timeline 的各个语法之后,我们就可以开始使用它创造各种动画效果了。

譬如如下的,滚动内容不断划入:

1Learn more about the new features of CSS animation: @scroll-timeline

代码较长,可以戳这里,来自 bramus 的 Codepen CodePen Demo -- Fly-in Contact List (CSS @scroll-timeline version)

https://codepen.io/bramus/pen/bGwJVzg

甚至可以结合scroll-snap-type制作一些全屏滚动的大屏特效动画:

1Learn more about the new features of CSS animation: @scroll-timeline

要知道,这在以前,是完全不可能利用纯 CSS 实现的。完整的代码你可以戳这里:CodePen Demo -- CSS Scroll-Timeline Split Screen Carousel

https://codepen.io/Chokcoco/pen/QWOrPdM

简而言之,任何动画效果,如今,都可以和滚动相结合起来,甚至乎是配合 SVG 元素也不例外,这里我还简单改造了一下之前的一个 SVG 线条动画:

1Learn more about the new features of CSS animation: @scroll-timeline

完整的代码你可以戳这里:CodePen Demo -- SVG Text Line Effect | Scroll Timeline

https://codepen.io/Chokcoco/pen/wvPxbRm

@scroll-timeline 的实验室特性与特性检测

@scroll-timeline虽好,目前仍处于实验室特性时间,Chrome 从 85 版本开始支持,但是默认是关闭的。

兼容性如下(2022-03-07):

1Learn more about the new features of CSS animation: @scroll-timeline

在最新的 chrome、Edge、Opera 可以通过浏览器配置开启该特性,Chrome 下开启该特性需要:

  • 浏览器 URL 框输入chrome://flags

  • 开启#enable-experimental-web-platform-features

美酒虽好,但是离完全能用,浏览器大规模支持还需要等待一会,给时间一点时间吧!

特性检测

基于目前的兼容性问题,我们可以通过浏览器的特性检测@supports语法,来渐进增强使用该功能。

特性检测的语法也非常简单:

@supports (animation-timeline: works) { @scroll-timeline list-item-1 { source: selector(#list-view); start: selector(#list-item-1) end 0; end: selector(#list-item-1) end 1; scroll-offsets: selector(#list-item-1) end 0, selector(#list-item-1) end 1 ; time-range: 1s; } // ... }

通过@supports (animation-timeline: works) {}可以判断浏览器是否支持@scroll-timeline

最后

目前关于 @scroll-timeline 的相关介绍还非常少,但是它确是能够改变 CSS 动画的一个非常大的革新。随着兼容性的逐渐普及,未来势必会在 CSS 中占据一席之地。

本文到此结束,希望对你有帮助 :)

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