changeset
[css-fonts] rework font-kerning description
Thu, 30 May 2013 11:39:14 +0900
- author
- John Daggett <jdaggett@mozilla.com>
- date
- Thu, 30 May 2013 11:39:14 +0900
- changeset 8276
- bf52664a49ae
- parent 8275
- a660aaa61034
- child 8277
- a09de2f3e565
[css-fonts] rework font-kerning description
| css-fonts/Fonts.html | file | annotate | diff | comparison | revisions |
1.1 --- a/css-fonts/Fonts.html Wed May 29 13:36:16 2013 -0700 1.2 +++ b/css-fonts/Fonts.html Thu May 30 11:39:14 2013 +0900 1.3 @@ -1630,7 +1630,8 @@ 1.4 whether it is substituted or not. Values have the following meanings: 1.5 1.6 <dl> 1.7 - <dt><strong>none</strong> 1.8 + <dt><a href="#font-variant-ligatures-none-value"><strong>none</strong></a> 1.9 + 1.10 1.11 <dd>Do not preserve the font's x-height. 1.12 1.13 @@ -2058,8 +2059,9 @@ 1.14 If ‘<a href="#weight"><code class=property>weight</code></a>’ is not 1.15 specified, user agents must not synthesize bold faces and if ‘<code 1.16 class=property>style</code>’ is not specified user agents must not 1.17 - synthesize italic faces. A value of ‘<code class=property>none</code>’ 1.18 - disallows all synthetic faces. 1.19 + synthesize italic faces. A value of ‘<a 1.20 + href="#font-variant-ligatures-none-value"><code 1.21 + class=property>none</code></a>’ disallows all synthetic faces. 1.22 1.23 <div class=example> 1.24 <p>The style rule below disables the use of synthetically obliqued Arabic:</p> 1.25 @@ -3474,28 +3476,44 @@ 1.26 1.27 <p>Kerning is the contextual adjustment of inter-glyph spacing. This 1.28 property controls metric kerning, kerning that utilizes adjustment data 1.29 - contained in the font. The value ‘<a href="#normal2"><code 1.30 - class=property>normal</code></a>’ implies that kerning is applied while 1.31 - the value ‘<code class=property>none</code>’ implies that kerning is 1.32 - not applied when rendering text. If the value is ‘<code 1.33 - class=property>auto</code>’, a user agent is free to choose whether 1.34 - kerning is enabled or not by default and to vary that default based on the 1.35 - underlying text script. 1.36 + contained in the font. 1.37 + 1.38 + <dl> 1.39 + <dt>auto 1.40 + 1.41 + <dd>Specifies that kerning is applied at the discretion of the user agent 1.42 + 1.43 + <dt>normal 1.44 + 1.45 + <dd>Specifies that kerning is applied 1.46 + 1.47 + <dt>none 1.48 + 1.49 + <dd>Specifies that kerning is not applied 1.50 + </dl> 1.51 1.52 <p>For fonts that do not include kerning data this property will have no 1.53 visible effect. When rendering with OpenType fonts, the <a 1.54 href="#OPENTYPE" rel=biblioentry>[OPENTYPE]<!--{{!OPENTYPE}}--></a> 1.55 specification suggests that kerning be enabled by default. When kerning is 1.56 enabled, the OpenType <span class=tag>kern</span> feature is enabled (for 1.57 - vertical text runs the <span class=tag>vkrn</span> feature is enabled). 1.58 - User agents must also support fonts that only support kerning via data 1.59 - contained in a ‘<code class=property>kern</code>’ font table, as 1.60 - detailed in the OpenType specification. Authors may prefer to disable 1.61 - kerning in situations where performance is more important than precise 1.62 - appearance. If the ‘<code class=property>letter-spacing</code>’ 1.63 - property is defined, kerning adjustments are considered part of the 1.64 - default spacing, letter spacing adjustments are made after kerning has 1.65 - been applied.</p> 1.66 + vertical text runs the <span class=tag>vkrn</span> feature is enabled 1.67 + instead). User agents must also support fonts that only support kerning 1.68 + via data contained in a <span class=tag>kern</span> font table, as 1.69 + detailed in the OpenType specification. If the ‘<code 1.70 + class=property>letter-spacing</code>’ property is defined, kerning 1.71 + adjustments are considered part of the default spacing and letter spacing 1.72 + adjustments are made after kerning has been applied. 1.73 + 1.74 + <p>When set to ‘<code class=property>auto</code>’, user agents can 1.75 + determine whether to apply kerning or not based on a number of factors: 1.76 + text size, script, or other factors that influence text processing speed. 1.77 + Authors who want proper kerning should use ‘<a href="#normal2"><code 1.78 + class=property>normal</code></a>’ to explicitly enable kerning. 1.79 + Likewise, some authors may prefer to disable kerning in situations where 1.80 + performance is more important than precise appearance. However, in 1.81 + well-designed modern implementations the use of kerning generally does not 1.82 + have a large impact on text rendering speed.</p> 1.83 <!-- prop: font-variant-ligatures --> 1.84 1.85 <h3 id=font-variant-ligatures-prop><span class=secno>6.4 </span>Ligatures: 1.86 @@ -3559,15 +3577,7 @@ 1.87 </table> 1.88 1.89 <p>Ligatures and contextual forms are ways of combining glyphs to produce 1.90 - more harmonized forms. A value of ‘<a href="#normal2"><code 1.91 - class=property>normal</code></a>’ implies that common default features 1.92 - are enabled, <a href="#font-feature-resolution">as described in detail in 1.93 - the next section</a>. For OpenType fonts, common ligatures and contextual 1.94 - forms are on by default, discretionary and historical ligatures are not. A 1.95 - value of ‘<code class=property>none</code>’ implies that all types of 1.96 - ligatures and contextual forms covered by this property are explicitly 1.97 - disabled. In situations where ligatures are not considered necessary, this 1.98 - may improve the speed of text rendering. 1.99 + more harmonized forms. 1.100 1.101 <pre 1.102 class=prod><dfn id=common-lig-values><var><common-lig-values></var></dfn> = [ <a href="#common-ligatures">common-ligatures</a> | <a href="#no-common-ligatures">no-common-ligatures</a> ]</pre> 1.103 @@ -3584,6 +3594,22 @@ 1.104 <p>Individual values have the following meanings: 1.105 1.106 <dl> 1.107 + <dt><dfn id=font-variant-ligatures-normal-value 1.108 + title="font-variant-ligatures normal value">normal</dfn> 1.109 + 1.110 + <dd>A value of ‘<a href="#normal2"><code 1.111 + class=property>normal</code></a>’ specifies that common default 1.112 + features are enabled, <a href="#font-feature-resolution">as described in 1.113 + detail in the next section</a>. For OpenType fonts, common ligatures and 1.114 + contextual forms are on by default, discretionary and historical 1.115 + ligatures are not. 1.116 + 1.117 + <dt><dfn id=font-variant-ligatures-none-value>none</dfn> 1.118 + 1.119 + <dd>Specifies that all types of ligatures and contextual forms covered by 1.120 + this property are explicitly disabled. In situations where ligatures are 1.121 + not considered necessary, this may improve the speed of text rendering. 1.122 + 1.123 <dt><dfn id=common-ligatures>common-ligatures</dfn> 1.124 1.125 <dd>Enables display of common ligatures (OpenType features: <span 1.126 @@ -3649,8 +3675,9 @@ 1.127 </dl> 1.128 1.129 <p>Required ligatures, needed for correctly rendering complex scripts, are 1.130 - not affected by the settings above, including ‘<code 1.131 - class=property>none</code>’ (OpenType feature: <span 1.132 + not affected by the settings above, including ‘<a 1.133 + href="#font-variant-ligatures-none-value"><code 1.134 + class=property>none</code></a>’ (OpenType feature: <span 1.135 class=tag>rlig</span>).</p> 1.136 <!-- prop: font-variant-position --> 1.137 1.138 @@ -3723,7 +3750,7 @@ 1.139 class=property>super</code>’ imply the appropriate variant glyph is 1.140 displayed when available in the font (OpenType features: <span 1.141 class=tag>subs, sups</span>). A value of ‘<a href="#normal2"><code 1.142 - class=property>normal</code></a>’ implies neither of these alternate 1.143 + class=property>normal</code></a>’ specifies neither of these alternate 1.144 glyphs are substituted. 1.145 1.146 <p>Because of the semantic nature of subscripts and superscripts, when the 1.147 @@ -4923,12 +4950,14 @@ 1.148 1.149 <p>The value ‘<a href="#normal2"><code 1.150 class=property>normal</code></a>’ resets all other font feature 1.151 - properties to their inital value. The ‘<code 1.152 - class=property>none</code>’ value sets ‘<a 1.153 + properties to their inital value. The ‘<a 1.154 + href="#font-variant-ligatures-none-value"><code 1.155 + class=property>none</code></a>’ value sets ‘<a 1.156 href="#propdef-font-variant-ligatures"><code 1.157 - class=property>font-variant-ligatures</code></a>’ to ‘<code 1.158 - class=property>none</code>’ and resets all other font feature properties 1.159 - to their initial value. Like other shorthands, using ‘<a 1.160 + class=property>font-variant-ligatures</code></a>’ to ‘<a 1.161 + href="#font-variant-ligatures-none-value"><code 1.162 + class=property>none</code></a>’ and resets all other font feature 1.163 + properties to their initial value. Like other shorthands, using ‘<a 1.164 href="#propdef-font-variant"><code 1.165 class=property>font-variant</code></a>’ resets unspecified font-variant 1.166 subproperties to their initial values. It does not reset the values of 1.167 @@ -5133,13 +5162,14 @@ 1.168 </table> 1.169 1.170 <p>The value of ‘<a href="#normal2"><code 1.171 - class=property>normal</code></a>’ implies that when rendering with 1.172 - OpenType fonts the language of the document is used to infer the OpenType 1.173 - language system, used to select language specific features when rendering. 1.174 - The value of the <string> is a single three-letter OpenType <a 1.175 + class=property>normal</code></a>’ specifies that when rendering with 1.176 + OpenType fonts the content language of the element is used to infer the 1.177 + OpenType language system. The value of the <string> is a single 1.178 + three-letter OpenType <a 1.179 href="http://www.microsoft.com/typography/otspec/languagetags.htm">language 1.180 system tag</a>, defined in the layout tag registry of the OpenType 1.181 - specification. 1.182 + specification. It indicates the OpenType language system to be used 1.183 + instead of the language system implied by the language of the element. 1.184 1.185 <div class=example> 1.186 <p>The <a href="http://www.un.org/en/documents/udhr/index.shtml">Universal 1.187 @@ -5479,25 +5509,25 @@ 1.188 <p>Specifically, font family name data is handled differently across 1.189 platforms. For TrueType and OpenType fonts these names are contained in 1.190 the ‘<code class=property>name</code>’ table, in name records with 1.191 - name ID 1. Mulitple names can be stored for different locales but 1.192 + name ID 1. Mulitple names can be stored for different locales, but 1.193 Microsoft recommends fonts always include at least a US English version of 1.194 the name. On Windows, Microsoft made the decision for backwards 1.195 compatibility to limit this family name to a maximum of four faces; for 1.196 larger groupings the "preferred family" (name ID 16) or "WWS family" (name 1.197 ID 21) can be used. Other platforms such as OSX don't have this 1.198 - limitation, the family name is used to define all possible groupings. 1.199 + limitation, so the family name is used to define all possible groupings. 1.200 1.201 <p>Other name table data provides names used to uniquely identify a 1.202 specific face within a family. The full font name (name ID 4) and the 1.203 - Postscript name (name ID 6) describe a single face uniquely. The bold face 1.204 - of the Gill Sans family has a fullname of "Gill Sans Bold" and a 1.205 - Postscript name of "GillSans-Bold". There can be multiple localized 1.206 - versions of the fullname for a given face but the Postscript name is 1.207 + Postscript name (name ID 6) describe a single face uniquely. For example, 1.208 + the bold face of the Gill Sans family has a fullname of "Gill Sans Bold" 1.209 + and a Postscript name of "GillSans-Bold". There can be multiple localized 1.210 + versions of the fullname for a given face, but the Postscript name is 1.211 always a unique name made from a limited set of ASCII characters. 1.212 1.213 <p>On various platforms, different names are used to search for a font. For 1.214 example, with the Windows GDI CreateIndirectFont API, either a family or 1.215 - fullname can be used to lookup a face while on Mac OS X the 1.216 + fullname can be used to lookup a face, while on Mac OS X the 1.217 CTFontCreateWithName API call is used to lookup a given face using the 1.218 fullname and Postscript name. Under Linux, the fontconfig API allows fonts 1.219 to be searched using any of these names. In situations where platform 1.220 @@ -6139,6 +6169,10 @@ 1.221 <li>font-variant-ligatures, <a href="#propdef-font-variant-ligatures" 1.222 title=font-variant-ligatures><strong>6.4</strong></a> 1.223 1.224 + <li>font-variant-ligatures normal value, <a 1.225 + href="#font-variant-ligatures-normal-value" title="font-variant-ligatures 1.226 + normal value"><strong>6.4</strong></a> 1.227 + 1.228 <li>font-variant-numeric, <a href="#propdef-font-variant-numeric" 1.229 title=font-variant-numeric><strong>6.7</strong></a> 1.230 1.231 @@ -6204,6 +6238,9 @@ 1.232 <li>no-historical-ligatures, <a href="#no-historical-ligatures" 1.233 title=no-historical-ligatures><strong>6.4</strong></a> 1.234 1.235 + <li>none, <a href="#font-variant-ligatures-none-value" 1.236 + title=none><strong>6.4</strong></a> 1.237 + 1.238 <li>normal, <a href="#normal" title=normal><strong>6.6</strong></a>, <a 1.239 href="#normal0" title=normal><strong>6.7</strong></a>, <a href="#normal1" 1.240 title=normal><strong>6.8</strong></a>, <a href="#normal2"
