Merge pull request w3c#6108 from litherum/size-adjust

svgeesus · web-flow · commit 137c54b62568 · 2021-03-17T15:51:05.000-04:00
[css-fonts-5] Add size-adjust @font-face descriptor
diff --git a/css-fonts-5/Overview.bs b/css-fonts-5/Overview.bs
@@ -145,7 +145,7 @@ Issue(5892):
 
 <h3 id="font-metrics-override-desc">
 Default font metrics overriding:
-the 'ascent-override', 'descent-override', and 'line-gap-override' descriptors</h3>
+the 'ascent-override', 'descent-override', 'line-gap-override', and 'size-adjust' descriptors</h3>
 
 <pre class='descdef'>
 Name: ascent-override
@@ -168,24 +168,49 @@ For: @font-face
 Initial: normal
 </pre>
 
+<pre class='descdef'>
+Name: size-adjust
+Value: normal | <<percentage>>
+For: @font-face
+Initial: normal
+</pre>
+
 The 'ascent-override', 'descent-override', and 'line-gap-override' descriptors define the
 <a spec="CSS-INLINE-3">ascent metric</a>, <a spec="CSS-INLINE-3">descent metric</a> and
-<a spec="CSS-INLINE-3">line gap metric</a> of the font, respectively.
+<a spec="CSS-INLINE-3">line gap metric</a> of the font, respectively. The `size-adjust`
+descriptor defines a scalar by which glyph outlines and metrics from this font are multiplied.
 
 When the descriptor value is 'normal', the corresponding metric value is obtained as-if the
 descriptor was absent from the <code>@font-face</code> block.
 
-Note: User agents may draw data from different places from the font file as the metric values,
+Note: User agents may gather data from different places from the font file as the metric values,
 which results in different text layouts.
 
 For the 'ascent-override', 'descent-override' and 'line-gap-override' descriptors, when the
 descriptor value is a percentage, the corresponding metric value is resolved as the
 given percentage multiplied by the used font size. Negative values are invalid at parse time.
 
+For 'size-adjust', when the descriptor value is a percentage, all metrics values of this font,
+including glyph advance sizes, are resolved as the given percentage multiplied by the used font
+size. When glyphs are visibly drawn, the visual size of the glyphs is also multiplied by the
+percentage.
+
+None of these descriptors affect the calculation of
+<a href="https://drafts.csswg.org/css-values-4/#font-relative-lengths">Font-relative Lengths</a>.
+None of these descriptors affect the behavior of any of the values of 'line-height' other than
+'normal'. The behavior of <code>line-height: normal</code> may be affected by all of these
+descriptors. 'size-adjust' does not affect the computed font size of any element.
+
+When 'size-adjust' is applied in conjunction with 'ascent-override', 'descent-override',
+or 'line-gap-override' in the same @font-face block, the relevant metrics are multiplied by both
+percentages.
+
 Note: Using the 'ascent-override', 'descent-override', and 'line-gap-override' descriptors can
-achieve a similar effect as specifying a percentage for 'line-height' property.
+achieve a similar effect as specifying a percentage for 'line-height' property. Using the
+'size-adjust' descriptor can achieve a similar effect as specifying a percentage for the
+'font-size' property.
 
-Note: 'ascent-override', 'descent-override', and 'line-gap-override'
+Note: 'ascent-override', 'descent-override', 'line-gap-override', and 'size-adjust'
 are applied per-font rather than per-element. Multiple fonts may be used
 within an individual element e.g. for characters not supported by the primary font.
 
@@ -228,6 +253,7 @@ within an individual element e.g. for characters not supported by the primary fo
   ascent-override: 125%;
   descent-override: 25%;
   line-gap-override: 0%;
+  size-adjust: 96%;
 }
 
 &lt;div style="font-family: cool-web-font, fallback-to-local"&gt;Title goes here&lt;/div&gt;
