viewBox

viewBox 属性允许指定一个给定的一组图形伸展以适应特定的容器元素。

viewBox 属性的值是一个包含 4 个参数的列表 min-x, min-y, width and height，以空格或者逗号分隔开，在用户空间中指定一个矩形区域映射到给定的元素，查看属性preserveAspectRatio。

不允许宽度和高度为负值，0 则禁用元素的呈现。

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示例

html,
body,
svg {
  height: 100%;
  vertical-align: top;
}
svg:not(:root) {
  display: inline-block;
}

html
<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <!--
  with relative unit such as percentage, the visual size
  of the square looks unchanged regardless of the viewBox
  -->
  <rect x="0" y="0" width="100%" height="100%" />

  <!--
  with a large viewBox the circle looks small
  as it is using user units for the r attribute:
  4 resolved against 100 as set in the viewBox
  -->
  <circle cx="50%" cy="50%" r="4" fill="white" />
</svg>

<svg viewBox="0 0 10 10" xmlns="http://www.w3.org/2000/svg">
  <!--
  with relative unit such as percentage, the visual size
  of the square looks unchanged regardless of the viewBox
  -->
  <rect x="0" y="0" width="100%" height="100%" />

  <!--
  with a small viewBox the circle looks large
  as it is using user units for the r attribute:
  4 resolved against 10 as set in the viewBox
  -->
  <circle cx="50%" cy="50%" r="4" fill="white" />
</svg>

<svg viewBox="-5 -5 10 10" xmlns="http://www.w3.org/2000/svg">
  <!--
  The point of coordinate 0,0 is now in the center of the viewport,
  and 100% is still resolve to a width or height of 10 user units so
  the rectangle looks shifted to the bottom/right corner of the viewport
  -->
  <rect x="0" y="0" width="100%" height="100%" />

  <!--
  With the point of coordinate 0,0 in the center of the viewport the
  value 50% is resolve to 5 which means the center of the circle is
  in the bottom/right corner of the viewport.
  -->
  <circle cx="50%" cy="50%" r="4" fill="white" />
</svg>

这个属性会受到 preserveAspectRatio 的影响。

备注：width 或者 height 的值，小于或等于 0 的情况下，这个元素将不会被渲染出来。

有 <marker>, <pattern>, <svg>, <symbol>, 和 <view> 等五个 svg 元素可以有这个属性。