dominant-baseline - SVG: Scalable Vector Graphics 编辑

The dominant-baseline attribute specifies the dominant baseline, which is the baseline used to align the box’s text and inline-level contents. It also indicates the default alignment baseline of any boxes participating in baseline alignment in the box’s alignment context.

It is used to determine or re-determine a scaled-baseline-table. A scaled-baseline-table is a compound value with three components:

1. a baseline-identifier for the dominant-baseline,
2. a baseline-table, and
3. a baseline-table font-size.

Some values of the property re-determine all three values. Others only re-establish the baseline-table font-size. When the initial value, auto, would give an undesired result, this property can be used to explicitly set the desired scaled-baseline-table.

If there is no baseline table in the nominal font, or if the baseline table lacks an entry for the desired baseline, then the browser may use heuristics to determine the position of the desired baseline.

Note: As a presentation attribute, dominant-baseline can be used as a CSS property. See css dominant-baseline for further information.

As a presentation attribute, it can be applied to any element but it only has effect on the text content elements, including: <altGlyph>, <text>, <textPath>, <tref>, and <tspan>

html, body, svg {
  height: 100%;
}

text {
  font: bold 14px Verdana, Helvetica, Arial, sans-serif;
}

<svg viewBox="0 0 200 120" xmlns="http://www.w3.org/2000/svg">
    <path d="M20,20 L180,20 M20,50 L180,50 M20,80 L180,80" stroke="grey" />

    <text dominant-baseline="auto" x="30" y="20">Auto</text>
    <text dominant-baseline="middle" x="30" y="50">Middle</text>
    <text dominant-baseline="hanging" x="30" y="80">Hanging</text>
</svg>

Usage notes

auto

If this property occurs on a <text> element, then the computed value depends on the value of the writing-mode attribute.

If the writing-mode is horizontal, then the value of the dominant-baseline component is alphabetic. Otherwise, if the writing-mode is vertical, then the value of the dominant-baseline component is central. 

If this property occurs on a <tspan>, <tref>, <altGlyph>, or <textPath> element, then the dominant-baseline and the baseline-table components remain the same as those of the parent text content element.

If the computed baseline-shift value actually shifts the baseline, then the baseline-table font-size component is set to the value of the font-size attribute on the element on which the dominant-baseline attribute occurs, otherwise the baseline-table font-size remains the same as that of the element.

If there is no parent text content element, the scaled-baseline-table value is constructed as above for <text> elements.

use-script

The dominant-baseline and the baseline-table components are set by determining the predominant script of the character data content. The writing-mode, whether horizontal or vertical, is used to select the appropriate set of baseline-tables and the dominant baseline is used to select the baseline-table that corresponds to that baseline. The baseline-table font-size component is set to the value of the font-size attribute on the element on which the dominant-baseline attribute occurs.

no-change

The dominant-baseline, the baseline-table, and the baseline-table font-size remain the same as that of the parent text content element.

reset-size

The dominant-baseline and the baseline-table remain the same, but the baseline-table font-size is changed to the value of the font-size attribute on this element. This re-scales the baseline-table for the current font-size.

ideographic

The baseline-identifier for the dominant-baseline is set to be ideographic, the derived baseline-table is constructed using the ideographic baseline-table in the font, and the baseline-table font-size is changed to the value of the font-size attribute on this element.

alphabetic

The baseline-identifier for the dominant-baseline is set to be alphabetic, the derived baseline-table is constructed using the alphabetic baseline-table in the font, and the baseline-table font-size is changed to the value of the font-size attribute on this element.

hanging

The baseline-identifier for the dominant-baseline is set to be hanging, the derived baseline-table is constructed using the hanging baseline-table in the font, and the baseline-table font-size is changed to the value of the font-size attribute on this element.

mathematical

The baseline-identifier for the dominant-baseline is set to be mathematical, the derived baseline-table is constructed using the mathematical baseline-table in the font, and the baseline-table font-size is changed to the value of the font-size attribute on this element.

central

The baseline-identifier for the dominant-baseline is set to be central. The derived baseline-table is constructed from the defined baselines in a baseline-table in the font. That font baseline-table is chosen using the following priority order of baseline-table names: ideographic, alphabetic, hanging, mathematical. The baseline-table font-size is changed to the value of the font-size attribute on this element.

middle

The baseline-identifier for the dominant-baseline is set to be middle. The derived baseline-table is constructed from the defined baselines in a baseline-table in the font. That font baseline-table is chosen using the following priority order of baseline-table names: alphabetic, ideographic, hanging, mathematical. The baseline-table font-size is changed to the value of the font-size attribute on this element.

text-after-edge

The baseline-identifier for the dominant-baseline is set to be text-after-edge. The derived baseline-table is constructed from the defined baselines in a baseline-table in the font. The choice of which font baseline-table to use from the baseline-tables in the font is browser dependent. The baseline-table font-size is changed to the value of the font-size attribute on this element.

text-before-edge

The baseline-identifier for the dominant-baseline is set to be text-before-edge. The derived baseline-table is constructed from the defined baselines in a baseline-table in the font. The choice of which baseline-table to use from the baseline-tables in the font is browser dependent. The baseline-table font-size is changed to the value of the font-size attribute on this element.

text-top

This value uses the top of the em box as the baseline.

Example

SVG

<svg width="400" height="300" viewBox="0 0 300 300"
    xmlns="http://www.w3.org/2000/svg">

  <!-- Materialization of anchors -->
  <path d="M60,20 L60,270
           M30,20 L400,20
           M30,70 L400,70
           M30,120 L400,120
           M30,170 L400,170
           M30,220 L400,220
           M30,270 L400,270" stroke="grey" />

    <!-- Anchors in action -->
    <text dominant-baseline="auto" x="70" y="20">auto</text>
    <text dominant-baseline="middle" x="70" y="70">middle</text>
    <text dominant-baseline="hanging" x="70" y="170">hanging</text>
    <text dominant-baseline="mathematical" x="70" y="220">mathematical</text>
    <text dominant-baseline="text-top" x="70" y="270">text-top</text>

  <!-- Materialization of anchors -->
  <circle cx="60" cy="20" r="3" fill="red" />
  <circle cx="60" cy="70" r="3" fill="red" />
  <circle cx="60" cy="120" r="3" fill="red" />
  <circle cx="60" cy="170" r="3" fill="red" />
  <circle cx="60" cy="220" r="3" fill="red" />
  <circle cx="60" cy="270" r="3" fill="red" />

  <style><![CDATA[
  text {
    font: bold 30px Verdana, Helvetica, Arial, sans-serif;
  }
  ]]></style>
</svg>

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• css dominant-baseline