perspective-origin
==================

CSS 属性 **`perspective-origin`** 指定了观察者的位置，用作 `perspective` 属性的消失点。

尝试一下
----

语法
--


```css
/\* One-value syntax \*/
perspective-origin: x-position;

/\* Two-value syntax \*/
perspective-origin: x-position y-position;

/\* When both x-position and y-position are keywords,
 the following is also valid \*/
perspective-origin: y-position x-position;

/\* Global values \*/
perspective-origin: inherit;
perspective-origin: initial;
perspective-origin: unset;
```

### 值

*x-position*

指定*消失点*的横坐标，其值有以下形式：

* `<length-percentage>` 长度值或相对于元素宽度的百分比值，可为负值。
* `left`, 关键字，0 值的简记。
* `center`, 关键字，50% 的简记。
* `right`, 关键字，100% 的简记。

*y-position*

指定*消失点*的纵坐标，其值有以下形式：

* `<length-percentage>` 长度值或相对于元素高度的百分比值，可为负值。
* `top`, 关键字，0 值的简记。
* `center`, 关键字，50% 的简记。
* `bottom`, 关键字，100% 的简记。

### 形式语法
```

perspective-origin =   
  <position>    
  
<position> =   
  [ left | center | right | top | bottom | <length-percentage> ]  |  
  [ left | center | right ] && [ top | center | bottom ]  |  
  [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ]  |  
  [ [ left | right ] <length-percentage> ] && [ [ top | bottom ] <length-percentage> ]    
  
<length-percentage> =   
  <length>      |  
  <percentage>    
  
```

示例
--

### 修改 perspective origin

这个例子展示了带有常用 `perspective-origin` 值的立方体。

#### 结果

#### HTML


```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


```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;
}
```

规范
--

| Specification |
| --- |
| CSS Transforms Module Level 2 # perspective-origin-property |

|  |  |
| --- | --- |
| 初始值 | `50% 50%` |
| 适用元素 | transformable elements |
| 是否是继承属性 | 否 |
| Percentages | refer to the size of bounding box |
| 计算值 | for `length` the absolute value, otherwise a percentage |
| Animation type | simple list of length, percentage, or calc |

浏览器兼容性
------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

参见
--

* Using CSS Transforms