2018-10-10 22:03:03 +00:00
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---
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id: 587d78a9367417b2b2512aea
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2020-12-16 07:37:30 +00:00
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title: 使用贝塞尔曲线让运动更加自然
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2018-10-10 22:03:03 +00:00
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challengeType: 0
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2020-02-11 07:46:34 +00:00
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videoUrl: 'https://scrimba.com/c/c7akWUv'
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forumTopicId: 301063
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2021-01-13 02:31:00 +00:00
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dashedName: make-motion-more-natural-using-a-bezier-curve
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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在这个挑战中,我们需要给元素添加动画来模拟杂耍中被抛接的球。之前的挑战中,我们学习了 `linear` 和 `ease-out` 的贝塞尔曲线描述,但这两个都无法完美地描述杂耍球的运动。在本关里你需要定制贝塞尔曲线。
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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当 `animation-iteration-count` 值为 infinite 时,`animation-timing-function` 会自动循环 keyframe。由于我们是在动画周期的中间点(50% 处)设置的 keyframe 规则,最终的结果是球向上和球向下是两个同样的动画过程。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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下面的例子模拟了杂耍球运动:
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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`cubic-bezier(0.3, 0.4, 0.5, 1.6);`
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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注意 y2 的值是大于 1 的。虽然贝塞尔曲线是在 `1 * 1` 的坐标系统内 x 值只能取 0 到 1,但是 y 值是可以大于 1 的。这样我们才能模拟杂耍球运动。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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把 id 为 `green` 的元素的 `animation-timing-function` 值改成 `cubic-bezier` 函数,函数的参数 x1、y1、x2、y2 值依次为 0.311、0.441、0.444、1.649。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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id 为 `green` 的元素的 `animation-timing-function` 属性值应为 `cubic-bezier` 函数,函数的参数 x1、y1、x2、y2 的值依次为 0.311、0.441、0.444、1.649。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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$('#green').css('animation-timing-function') ==
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'cubic-bezier(0.311, 0.441, 0.444, 1.649)'
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);
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2018-10-10 22:03:03 +00:00
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```
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2020-02-11 07:46:34 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --seed-contents--
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```html
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<style>
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.balls {
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border-radius: 50%;
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position: fixed;
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width: 50px;
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height: 50px;
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top: 60%;
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animation-name: jump;
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animation-duration: 2s;
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animation-iteration-count: infinite;
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}
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#red {
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background: red;
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left: 25%;
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animation-timing-function: linear;
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}
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#blue {
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background: blue;
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left: 50%;
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animation-timing-function: ease-out;
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}
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#green {
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background: green;
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left: 75%;
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animation-timing-function: cubic-bezier(0.69, 0.1, 1, 0.1);
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}
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@keyframes jump {
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50% {
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top: 10%;
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}
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}
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</style>
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<div class="balls" id="red"></div>
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<div class="balls" id="blue"></div>
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<div class="balls" id="green"></div>
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```html
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<style>
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.balls {
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border-radius: 50%;
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position: fixed;
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width: 50px;
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height: 50px;
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top: 60%;
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animation-name: jump;
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animation-duration: 2s;
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animation-iteration-count: infinite;
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}
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#red {
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background: red;
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left: 25%;
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animation-timing-function: linear;
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}
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#blue {
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background: blue;
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left: 50%;
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animation-timing-function: ease-out;
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}
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#green {
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background: green;
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left: 75%;
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animation-timing-function: cubic-bezier(0.311, 0.441, 0.444, 1.649);
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}
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@keyframes jump {
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50% {
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top: 10%;
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}
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}
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</style>
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<div class="balls" id="red"></div>
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<div class="balls" id="blue"></div>
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<div class="balls" id="green"></div>
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```
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