【JS】《SVG 动画开发实战》 - ✏️ SVG 描边动画（Stroke）

✏️ SVG 描边动画（Stroke）

演示

chapter5-1

查看在线版本

  • Polygon's PlayStation 4 Review

  • vivus.js - svg animation

原理

要实现上面酷炫的描边动画，首先我们需要了解 SVG 中实现描边动画的三个相关属性：分别是 stroke、stroke-dasharray、stroke-dashoffset。这三个属性作为外观显示属性，都可以作为 CSS 属性来使用。

stroke

SVG 中的 stroke 属性用来控制绘制描边的方式，我们也可以使用 CSS 来控制 SVG 的描边样式。

https://codepen.io/xiaoluobod...

stroke-dasharray

我们知道在 CSS 中实现虚线边框，要使用 border: 1px dashed #f4a; ；在 SVG 中要实现虚线效果就要使用 stroke-dasharray 属性。

https://codepen.io/xiaoluobod...

stroke-dashoffset

stroke-dashoffset 属性用来指定路径从开始位置的偏移量。通过指定偏移量会让绘制好的线偏移

原来的位置一段空白

https://codepen.io/xiaoluobod...

动起来

那么结合上面三个属性，我们试着动态改变 stroke-dashoffset 属性，看看会发生什么。通过动态改变偏移量属性，结合设定好的 width 以及 stroke-dasharray 属性，会让原来静态的线有一种用画笔描绘出来的效果。

https://codepen.io/xiaoluobod...

实战

下面我们使用 GreenSock 实现描边效果，GreenSock 提供了 DrawSVGPlugin 用于控制各种图形的描边效果，原理主要是通过控制上面学过的 stroke-dasharray 、stroke-dashoffset 两个CSS属性来实现动画效果。

【JS】《SVG 动画开发实战》 - ✏️ SVG 描边动画（Stroke）

获取 SVG 代码

这里就使用 vivus 中的 Hi There 动画 作为 Demo，打开 vivus 官网，打开开发者工具，这里使用的是 Chrome，选中 Hi There dom 元素，可以看到 Hi There 的 SVG 代码。我们选中元素右键复制出来。

【JS】《SVG 动画开发实战》 - ✏️ SVG 描边动画（Stroke）

得到如下代码：

<div class="bloc bloc-head">
<svg height="300" xmlns="http://www.w3.org/2000/svg" x="0px" y="0px" viewBox="0 0 404.7 354" enable-background="new 0 0 404.7 354" id="hi-there" onclick="hi.reset().play();">
<!-- HI -->
<path data-duration="10" d="M324.6,61.2c16.6,0,29.5-12.9,29.5-29.5c0-16.6-12.9-29.5-29.5-29.5c-16.6,0-29.5,12.9-29.5,29.5C295.1,48.4,308,61.2,324.6,61.2z"></path>
<path data-duration="130" d="M366.2,204.2c-9.8,0-15-5.6-15-15.1V77.2h-85v28h19.5c9.8,0,8.5,2.1,8.5,11.6v72.4c0,9.5,0.5,15.1-9.3,15.1H277h-20.7c-8.5,0-14.2-4.1-14.2-12.9V52.4c0-8.5,5.7-12.3,14.2-12.3h18.8v-28h-127v28h18.1c8.5,0,9.9,2.1,9.9,8.9v56.1h-75V53.4c0-11.5,8.6-13.3,17-13.3h11v-28H2.2v28h26c8.5,0,12,2.1,12,7.9v142.2c0,8.5-3.6,13.9-12,13.9h-21v33h122v-33h-11c-8.5,0-17-4.1-17-12.2v-57.8h75v58.4c0,9.1-1.4,11.6-9.9,11.6h-18.1v33h122.9h5.9h102.2v-33H366.2z"></path>
<path data-async="" data-delay="20" d="M358.8,82.8c11.1-4.2,18.8-14.7,18.8-27.5c0-8.5-3.4-16-8.9-21.3"></path>
<path data-async="" d="M124.2,105.7V77c0-11.5,9.1-13.8,17.5-13.8h10.5V44.7"></path>
<path data-async="" d="M147.9,40.2L171.2,63.2L175.7,63.2"></path>
<path data-async="" d="M295.1,32.1L275.2,12.2"></path>
<path data-async="" d="M266.2,204.7V75.9c0-8.5,5.2-12.8,13.7-12.8h18.3V44.7"></path>
<path data-async="" d="M265.9,105.2L289.2,129.2L293.7,129.2"></path>
<path data-async="" d="M374.2,204.7L374.2,94.2L358.8,82.8L351.2,77.2"></path>
<path data-async="" d="M148.2,237.2L171.2,261.2L294.6,261.2L300.5,261.2L402.2,261.2L402.2,228.2L379.2,204.2"></path>
<path data-async="" d="M124.2,204.7L124.2,157.2L175.7,157.2"></path>
<path data-async="" d="M147.7,228.2L129.2,204.2"></path>
<path data-async="" d="M7.2,237.3L30.2,261.2L152.2,261.2L152.2,241.7"></path>
<path data-async="" d="M1.9,40.2L26,63.2L39.7,63.2"></path>
<path data-async="" d="M129.2,12.2L148.2,33.2"></path>
<path data-async="" d="M303.9,53L328.1,77.2"></path>
<path d="M345.1,10.5L368.7,34"></path>
<!-- there -->
<path data-delay="30" data-duration="60" stroke-linecap="round" stroke-linejoin="round" d="M76.8,337.3c0,0,1.9,12.2,13.1,12.2c22.1,0,23.8-1.8,59-66.4c-19.7,35.7-36.4,66.2-19.3,66.2c15.2,0,22.9-14.2,28.3-23.7c3.3-0.5,24-3.2,35-25.5c4-8.1,4.1-17.8-8.1-15.2c-5.6,1.2-13.1,14.8-15.7,19.2c-7.6,12.7-22.4,45.2-22.4,45.2s10.3-22.4,21.5-22.4c15.5,0-9.4,22.4,4.7,22.4c4.9,0,11.7-11.4,16.6-20.9c7.5,4.7,19.7,1.7,24.5-8.1c10.1-20.4-14.4-12.8-24.5,8.1c-5.5,11.3-2.2,21.1,11.2,21.1c16.4,0,26.1-28.3,30.5-37.5c9.9,2.5,14,2.5,22.7-1.1c-3.5,5.1-24,38.1-8.3,38.1c6.7,0,11.7-11.4,16.6-20.9c7.5,4.7,19.7,1.7,24.5-8.1c10.1-20.4-14.4-12.8-24.5,8.1c-5.5,11.3-2.2,21.1,11.2,21.1c16.4,0,20.6-4,24.7-10.5"></path>
<path stroke-linecap="round" stroke-linejoin="round" d="M157.3,300.8c3.8-2.3-29,0.8-35.6,3.2"></path>
</svg>
</div>

分析动画时间轴

仔细观察 vivus 中的 Hi There 的描边动画中一共有四个阶段：

  1. 先描边一个 Hi 字母的圆点

  2. 然后描边 Hi 字母

  3. 再描边 Hi 字母的 3D 边框

  4. 最后描边 there 单词

我们给要描边的图形，例子中会涉及到 path、polyline、line 等定义好 class，用于选择。将无用 vivus 属性去掉，优化后的代码如下：

<div class="bloc bloc-head">
<svg height="300" xmlns="http://www.w3.org/2000/svg" x="0px" y="0px" viewBox="0 0 404.7 354" id="hi-there">
<!-- HI -->
<path class="hi-o" fill="none" stroke="#FFFFFF" stroke-width="4" d="M324.6,61.2c16.6,0,29.5-12.9,29.5-29.5c0-16.6-12.9-29.5-29.5-29.5c-16.6,0-29.5,12.9-29.5,29.5C295.1,48.4,308,61.2,324.6,61.2z" />
<path class="hi" fill="none" stroke="#FFFFFF" stroke-width="4" d="M366.2,204.2c-9.8,0-15-5.6-15-15.1V77.2h-85v28h19.5c9.8,0,8.5,2.1,8.5,11.6v72.4c0,9.5,0.5,15.1-9.3,15.1H277h-20.7c-8.5,0-14.2-4.1-14.2-12.9V52.4c0-8.5,5.7-12.3,14.2-12.3h18.8v-28h-127v28h18.1c8.5,0,9.9,2.1,9.9,8.9v56.1h-75V53.4c0-11.5,8.6-13.3,17-13.3h11v-28H2.2v28h26c8.5,0,12,2.1,12,7.9v142.2c0,8.5-3.6,13.9-12,13.9h-21v33h122v-33h-11c-8.5,0-17-4.1-17-12.2v-57.8h75v58.4c0,9.1-1.4,11.6-9.9,11.6h-18.1v33h122.9h5.9h102.2v-33H366.2z" />
<path fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" d="M358.8,82.8c11.1-4.2,18.8-14.7,18.8-27.5c0-8.5-3.4-16-8.9-21.3" />
<path fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" d="M124.2,105.7V77c0-11.5,9.1-13.8,17.5-13.8h10.5V44.7" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="147.9,40.2 171.2,63.2 175.7,63.2" />
<line fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" x1="295.1" y1="32.1" x2="275.2" y2="12.2" />
<path fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" d="M266.2,204.7V75.9c0-8.5,5.2-12.8,13.7-12.8h18.3V44.7" />
<polyline fill="none" class="threedline" class="threedline" stroke="#FFFFFF" stroke-width="4" points="265.9,105.2 289.2,129.2 293.7,129.2" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="374.2,204.7 374.2,94.2 358.8,82.8 351.2,77.2" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="148.2,237.2 171.2,261.2 294.6,261.2 300.5,261.2 402.2,261.2 402.2,228.2 379.2,204.2" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="124.2,204.7 124.2,157.2 175.7,157.2" />
<line fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" x1="147.7" y1="228.2" x2="129.2" y2="204.2" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="7.2,237.3 30.2,261.2 152.2,261.2 152.2,241.7" />
<polyline fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" points="1.9,40.2 26,63.2 39.7,63.2" />
<line fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" x1="129.2" y1="12.2" x2="148.2" y2="33.2" />
<line fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" x1="303.9" y1="53" x2="328.1" y2="77.2" />
<line fill="none" class="threedline" stroke="#FFFFFF" stroke-width="4" x1="345.1" y1="10.5" x2="368.7" y2="34" />
<!-- there -->
<path class="there" fill="none" stroke="#FFFFFF" stroke-width="4" stroke-linecap="round" stroke-linejoin="round" d="M76.8,337.3c0,0,1.9,12.2,13.1,12.2c22.1,0,23.8-1.8,59-66.4c-19.7,35.7-36.4,66.2-19.3,66.2c15.2,0,22.9-14.2,28.3-23.7c3.3-0.5,24-3.2,35-25.5c4-8.1,4.1-17.8-8.1-15.2c-5.6,1.2-13.1,14.8-15.7,19.2c-7.6,12.7-22.4,45.2-22.4,45.2s10.3-22.4,21.5-22.4c15.5,0-9.4,22.4,4.7,22.4c4.9,0,11.7-11.4,16.6-20.9c7.5,4.7,19.7,1.7,24.5-8.1c10.1-20.4-14.4-12.8-24.5,8.1c-5.5,11.3-2.2,21.1,11.2,21.1c16.4,0,26.1-28.3,30.5-37.5c9.9,2.5,14,2.5,22.7-1.1c-3.5,5.1-24,38.1-8.3,38.1c6.7,0,11.7-11.4,16.6-20.9c7.5,4.7,19.7,1.7,24.5-8.1c10.1-20.4-14.4-12.8-24.5,8.1c-5.5,11.3-2.2,21.1,11.2,21.1c16.4,0,20.6-4,24.7-10.5" />
<path class="there" fill="none" stroke="#FFFFFF" stroke-width="4" stroke-linecap="round" stroke-linejoin="round" d="M157.3,300.8c3.8-2.3-29,0.8-35.6,3.2" />
</svg>
</div>

实现动画

GreenSock 提供了 timeline 用于创建连续的错开补间动画，很好理解，动画是按时间轴有序进行的。

借助 DrawSVGPlugin 实现了将 SVG path 从 0% 绘制到 100% 的动画效果。

// 创建时间轴
let tl = gsap.timeline({ repeat: -1 })
/**
* 1、先描边一个 Hi 字母的圆点
* 2、然后描边 Hi 字母
* 3、再描边 Hi 字母的 3D 边框
* 4、最后描边 there 单词
*/
tl
.fromTo(
'.hi-o',
{ drawSVG: "0%" },
{ duration: .3, drawSVG: "100%", stagger: 0.1 },
)
.fromTo(
'.hi',
{ drawSVG: "0%" },
{ duration: 3, drawSVG: "100%", stagger: 0.2 },
)
.fromTo(
'.threedline',
{ drawSVG: "0%" },
{ duration: 0.8, drawSVG: "100%" },
"+=0.2"
)
.fromTo(
'.there',
{ drawSVG: "0%" },
{ duration: 2, drawSVG: "100%", stagger: 0.5 }
)

最终效果：

https://codepen.io/xiaoluobod...

参考

  • https://www.polygon.com/a/ps4...

  • http://maxwellito.github.io/v...

  • https://developer.mozilla.org...

  • https://css-tricks.com/svg-li...

关于

本文是《SVG 动画开发实战》 系列文章第五章。

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GitHub 版本

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微信公众号版本

关注我的技术公号，同样也可以找到此小册系列，目前在更新中。。。

【JS】《SVG 动画开发实战》 - ✏️ SVG 描边动画（Stroke）

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