Default font metrics overriding:
-the 'ascent-override', 'descent-override' and 'line-gap-override' descriptors
+the 'ascent-override', 'descent-override', 'line-gap-override', and 'advance-override' descriptors
Name: ascent-override
@@ -168,9 +168,18 @@ For: @font-face
Initial: normal
-The 'ascent-override', 'descent-override' and 'line-gap-override' descriptors define the
+
+Name: advance-override
+Value: normal | <>
+For: @font-face
+Initial: normal
+
+
+The 'ascent-override', 'descent-override', and 'line-gap-override' descriptors define the
ascent metric, descent metric and
-line gap metric of the font, respectively.
+line gap metric of the font, respectively. The 'advance-override'
+descriptor adjusts the tracking between adjacent
+typographic character units.
When the descriptor value is 'normal', the corresponding metric value is obtained from the
font file directly.
@@ -178,9 +187,55 @@ font file directly.
Note: User agents may draw data from different places from the font file as the metric values,
which results in different text layouts.
-When the descriptor value is a percentage, the corresponding metric value is resolved as the
+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 the 'advance-override' descriptor, when the descriptor value is a percentage, the
+advance from one typographic character unit to the next is multiplied by the percentage.
+
+Note: Using the 'ascent-override', 'descent-override', and 'line-grap-override' descriptors can
+achieve a similar effect as specifying a percentage for 'line-height' property. Also, using the
+'advance-override' has a similar effect as using the 'letter-spacing' property. However,
+contrary to 'letter-spacing', 'advance-override' scales the spacing, rather than adding a
+constant to the spacing.
+
+Note: 'ascent-override', 'descent-override', 'line-gap-override', and 'advance-override'
+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.
+
+
+ Consider the following content:
+
+
+@font-face {
+ font-family: "MyHelvetica";
+ src: local("Helvetica");
+}
+...
+<div style="font: 96px 'MyHelvetica';">Ha</div>
+
+ This image shows each glyph's local origin, and the natural advance between them:
+
+
+
+ In this example, the natural advance is 69.328125 pixels.
+
+ However, if we modify the content as such:
+
+ The rendering will look like this:
+
+
+
+ In this example, the used advance between the glyphs is 69.328125 pixels * 1.4 = 97.059375 pixels.
+
+
The percentage is resolved against different font sizes for different elements.
@@ -220,14 +275,16 @@ given percentage multiplied by the used font size. Negative values are invalid a
ascent-override: 125%;
descent-override: 25%;
line-gap-override: 0%;
+ advance-override: 109%;
}
<div style="font-family: cool-web-font, fallback-to-local">Title goes here</div>
<img src="https://example.com/largeimage" alt="A large image that you don't want to shift">
- The image will not be vertically shifted when the user agent finishes loading and
- switches to use the web font.
+ The image will not be shifted as much when the user agent finishes loading and
+ switches to use the web font (assuming the override values are similar to the web font's
+ natural metrics).
diff --git a/css-fonts-5/images/Helvetica Natural Advance.png b/css-fonts-5/images/Helvetica Natural Advance.png
new file mode 100644
index 000000000000..89a2d81b0944
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diff --git a/css-fonts-5/images/Helvetica Overridden Advance.png b/css-fonts-5/images/Helvetica Overridden Advance.png
new file mode 100644
index 000000000000..6598ac870c82
Binary files /dev/null and b/css-fonts-5/images/Helvetica Overridden Advance.png differ
+ 
+