通过改变坐标空间,CSS transforms 可以在不影响正常文档流的情况下改变作用内容的位置。This guide provides an introduction to using transforms.

CSS transforms 通过一系列 CSS 属性实现,通过使用这些属性,可以对 HTML 元素进行线性仿射变形(affine linear transformations)。可以进行的变形包括旋转,倾斜,缩放以及位移,这些变形同时适用于平面与三维空间。

只有使用盒模型(Box Model)来定位的元素可以被变换transformed)。根据一般经验(原文:As a rule of thumb),拥有 display: block 的元素是由盒模型定位的。

CSS transforms 属性

有两个主要的属性被用来定义 CSS transforms:transformtransform-origin

transform-origin
指定原点的位置。默认值为元素的中心,可以被移动。很多变形需要用到这个属性,比如旋转,缩放和倾斜,他们都需要一个指定的点作为参数。
transform
指定作用在元素上的变形。取值为空格分隔的一系列变形的列表,他们会像被组合操作请求一样被分别执行。

示例

这是一个未经任何变换的 MDN 标志:

MDN Logo

旋转

这是一个在 iframe 中的 MDN 的标志,从左下角开始,旋转了 90 度。

<img style="transform: rotate(90deg);
            transform-origin: bottom left;" 
     src="https://mdn.mozillademos.org/files/12539/Screen%20Shot%202016-02-16%20at%2015.53.54.png">

倾斜与位移

还是 MDN 的标志,倾斜了 10 度,并从 X 轴位移了 150 个像素。

<img style="transform: skewx(10deg) translatex(150px);
            transform-origin: bottom left;"
     src="https://mdn.mozillademos.org/files/12539/Screen%20Shot%202016-02-16%20at%2015.53.54.png">

适用于三维的属性

在三维空间中使用 CSS 变形会稍微复杂一点。你必须先设置一个透视点(perspective)以便配置 3D 空间,再去定义 2D 元素在空间中的行为。

透视

首先需要设置的属性是透视值(perspective)。透视正是三维空间的立体感的源泉。元素与观察者之间的距离越远,他们就越小。

Setting perspective

This example shows a cube with the perspective set at different positions. How quick the cube shrinks is defined by the perspective property. The smaller its value is, the deeper the perspective is.

Result

HTML

The HTML below creates four copies of the same box, with the perspective set at different values.

<table>
  <tbody>
    <tr>
      <th><code>perspective: 250px;</code>
      </th>
      <th><code>perspective: 350px;</code>
      </th>
    </tr>
    <tr>
      <td>
        <div class="container">
          <div class="cube pers250">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pers350">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
    </tr>
    <tr>
      <th><code>perspective: 500px;</code>
      </th>
      <th><code>perspective: 650px;</code>
      </th>
    </tr>
    <tr>
      <td>
        <div class="container">
          <div class="cube pers500">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pers650">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
    </tr>
  </tbody>
</table>
CSS

The CSS establishes classes that can be used to set the perspective to different distances. It also includes classes for the container box and the cube itself, as well as each of its faces.

/* Shorthand classes for different perspective values */
.pers250 {
  perspective: 250px;
}

.pers350 {
  perspective: 350px;
}

.pers500 {
  perspective: 500px;
}

.pers650 {
  perspective: 650px;
}

/* Define the container div, the cube div, and a generic face */
.container {
  width: 200px;
  height: 200px;
  margin: 75px 0 0 75px;
  border: none;
}

.cube {
  width: 100%;
  height: 100%;
  backface-visibility: visible;
  perspective-origin: 150% 150%;
  transform-style: preserve-3d;
}

.face {
  display: block;
  position: absolute;
  width: 100px;
  height: 100px;
  border: none;
  line-height: 100px;
  font-family: sans-serif;
  font-size: 60px;
  color: white;
  text-align: center;
}

/* Define each face based on direction */
.front {
  background: rgba(0, 0, 0, 0.3);
  transform: translateZ(50px);
}

.back {
  background: rgba(0, 255, 0, 1);
  color: black;
  transform: rotateY(180deg) translateZ(50px);
}

.right {
  background: rgba(196, 0, 0, 0.7);
  transform: rotateY(90deg) translateZ(50px);
}

.left {
  background: rgba(0, 0, 196, 0.7);
  transform: rotateY(-90deg) translateZ(50px);
}

.top {
  background: rgba(196, 196, 0, 0.7);
  transform: rotateX(90deg) translateZ(50px);
}

.bottom {
  background: rgba(196, 0, 196, 0.7);
  transform: rotateX(-90deg) translateZ(50px);
}

/* Make the table a little nicer */
th, p, td {
  background-color: #EEEEEE;
  padding: 10px;
  font-family: sans-serif;
  text-align: left;
}

第二个需要设置的是观察者的位置,可通过 perspective-origin 属性来设置。默认透视值中,为观察者被置于中心,但是这并不总是适当的。

Changing the perspective origin

This example shows cubes with popular perspective-origin values.

Result

HTML
<table>
  <tbody>
    <tr>
      <th>
        <code>perspective-origin: top left;</code>
      </th>
      <th>
        <code>perspective-origin: top;</code>
      </th>
      <th>
        <code>perspective-origin: top right;</code>
      </th>
    </tr>
    <tr>
      <td>
        <div class="container">
          <div class="cube potl">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube potm">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube potr">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
    </tr>
    <tr>
      <th>
        <code>perspective-origin: left;</code>
      </th>
      <th>
        <code>perspective-origin: 50% 50%;</code>
      </th>
      <th>
        <code>perspective-origin: right;</code>
      </th>
    </tr>
    <tr>
      <td>
        <div class="container">
          <div class="cube poml">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pomm">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pomr">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
    </tr>
    <tr>
      <th>
        <code>perspective-origin: bottom left;</code>
      </th>
      <th>
        <code>perspective-origin: bottom;</code>
      </th>
      <th>
        <code>perspective-origin: bottom right;</code>
      </th>
    </tr>
    <tr>
      <td>
        <div class="container">
          <div class="cube pobl">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pobm">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
      <td>
        <div class="container">
          <div class="cube pobr">
            <div class="face front">1</div>
            <div class="face back">2</div>
            <div class="face right">3</div>
            <div class="face left">4</div>
            <div class="face top">5</div>
            <div class="face bottom">6</div>
          </div>
        </div>
      </td>
    </tr>
  </tbody>
</table>
CSS
/* Shorthand classes for perspective-origin values */
.potl {
  perspective-origin: top left;
  -webkit-perspective-origin: top left;
}

.potm {
  perspective-origin: top;
  -webkit-perspective-origin: top;
}

.potr {
  perspective-origin: top right;
  -webkit-perspective-origin: top right;
}

.poml {
  perspective-origin: left;
  -webkit-perspective-origin: left;
}

.pomm {
  perspective-origin: 50% 50%;
  -webkit-perspective-origin: 50% 50%;
}

.pomr {
  perspective-origin: right;
  -webkit-perspective-origin: right;
}

.pobl {
  perspective-origin: bottom left;
  -webkit-perspective-origin: bottom left;
}

.pobm {
  perspective-origin: bottom;
  -webkit-perspective-origin: bottom;
}

.pobr {
  perspective-origin: bottom right;
  -webkit-perspective-origin: bottom right;
}

/* Define the container div, the cube div, and a generic face */
.container {
  width: 100px;
  height: 100px;
  margin: 24px;
  border: none;
}

.cube {
  width: 100%;
  height: 100%;
  backface-visibility: visible;
  perspective: 300px;
  transform-style: preserve-3d;
  -webkit-backface-visibility: visible;
  -webkit-perspective: 300px;
  -webkit-transform-style: preserve-3d;
}

.face {
  display: block;
  position: absolute;
  width: 100px;
  height: 100px;
  border: none;
  line-height: 100px;
  font-family: sans-serif;
  font-size: 60px;
  color: white;
  text-align: center;
}

/* Define each face based on direction */
.front {
  background: rgba(0, 0, 0, 0.3);
  transform: translateZ(50px);
  -webkit-transform: translateZ(50px);
}

.back {
  background: rgba(0, 255, 0, 1);
  color: black;
  transform: rotateY(180deg) translateZ(50px);
  -webkit-transform: rotateY(180deg) translateZ(50px);
}

.right {
  background: rgba(196, 0, 0, 0.7);
  transform: rotateY(90deg) translateZ(50px);
  -webkit-transform: rotateY(90deg) translateZ(50px);
}

.left {
  background: rgba(0, 0, 196, 0.7);
  transform: rotateY(-90deg) translateZ(50px);
  -webkit-transform: rotateY(-90deg) translateZ(50px);
}

.top {
  background: rgba(196, 196, 0, 0.7);
  transform: rotateX(90deg) translateZ(50px);
  -webkit-transform: rotateX(90deg) translateZ(50px)
}

.bottom {
  background: rgba(196, 0, 196, 0.7);
  transform: rotateX(-90deg) translateZ(50px);
  -webkit-transform: rotateX(-90deg) translateZ(50px);
}

/* Make the table a little nicer */
th, p, td {
  background-color: #EEEEEE;
  padding: 10px;
  font-family: sans-serif;
  text-align: left;
}

完成这些之后,你就可以折腾被置于三维空间之中的元素了。

参见

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