Really understand the @font face rules in the context of CSS3

As soon as many people mention the @font face rules, they will involuntarily say "Oh~~" in their hearts: "I know this, it can be used to generate custom character icons!" This is true, but the problem is that many people think that Generating small character icons is the whole of the @font face rule. It is actually just one of the functions. If you really understand the @font face rule, you will find that the @font face rule can actually do a lot of things, especially if we do not consider IE7 and IE8. browser case.

1. The essence of @font face is the variable

Although it is said that the real variable var appeared in the new world of CSS3 (see this article: "Understanding CSS/CSS3 native variable var"), in fact, in the CSS world, things that are essentially variables have already appeared, @font The face rule is one of them. @font face is essentially a variable that defines a font or font set. This variable is not just a simple custom font, but also includes font renaming, default font style settings, etc.

The awareness of this "variable" is very important, and it helps us unleash the potential of @font face, making our CSS code more streamlined and easier to maintain.

Before getting into the topic, we first need to have a general view of the @font face rules.

The CSS properties supported by @font face rules are: font-family, src, font-weight, font-style, unicode-range, font-variant, font-stretch, font-feature-settings. For example:

@font-face {
  font-family: 'example';
  src: url(example.ttf);
  font-style: normal;
  font-weight: normal;
  unicode-range: U+0025-00FF;
  font-variant: small-caps;
  font-stretch: expanded;
  font-feature-settings："liga1" on;
}

There are quite a lot of attributes, and for some attributes, it is probably because he knows you but you don’t know him. But from a practical point of view, some attributes do not need to be studied in detail, such as font-variant, font-stretch, and font-feature-settings. why? Because according to my experience, these three attributes feel more like they are designed for English, so if there is no business need, you can put them aside first.

Okay, now, do you feel that the pressure is much lessened all of a sudden? The only customizable attributes we need to care about are the following:

@font-face {
  font-family: 'example';
  src: url(example.ttf);
  font-style: normal;
  font-weight: normal;
  unicode-range: U+0025-00FF;
}

It is estimated that some friends will be wondering what the font-style, font-weight and unicode-range attributes in the @font-face rules are used for, especially font-style and font-weight, which seem to be specially used to make soy sauce. In fact, every attribute here is not an ordinary person, but a person with a story.

Before introducing each attribute, it is necessary to solemnly declare that there will be a large number of cases, all based on local fonts, and IE7 and IE8 browsers do not support local fonts, so the title of this article is "In the context of CSS3...", for this reason, please be careful. If your project also needs to be compatible with IE8, as this article introduces, these good things may need to be considered.

2. Detailed introduction to commonly used CSS properties of @font face

Let’s introduce them one by one:

​ 1. font-family

The font-family here can be regarded as a font variable, and the name can be very arbitrary, such as a dollar sign '$', for example:

@font-face {
  font-family: '$';
  src: local("Microsoft Yahei");
}

At this time, for ordinary HTML elements, if you set the font-family attribute value to '$', the font representation will become "Microsoft Yahei" (if this font is available locally).

Even in non-IE browsers, you can directly use pure spaces ' ', but one thing you need to pay attention to is that when using these weird characters or spaces, you must add quotation marks.

Although you can say that your variable names can be arbitrary, there is a type of name that cannot be set casually, which is the font name that originally exists in the system, such as the following code:

@font-face {
  font-family: 'Microsoft Yahei';
  src: local(SimSun);
}

From then on, the font "Microsoft Yahei" became "Songti". Of course, sometimes we may need this kind of coverage. For example, if a new design manager comes, he dislikes "Microsoft Yahei" the most in his life, and hopes to change to other fonts. At this time, we can use this variable coverage to easily Easily complete font changes for the entire site.

　2. src

src means calling a font file, which can be a local font file (supported by IE9+) or an online address (there may be cross-domain restrictions).

This article mainly focuses on the application of local font files.

Function 1: Font file name abbreviation

Many websites now use the "Microsoft Yahei" font, but the name of "Microsoft Yahei" is a bit long:

.font {
    font-family: 'Microsoft Yahei';
}

If your little hand shakes, you might spell it wrong, and you have to add quotation marks and spaces, which is really troublesome. At this point we can use @font face rules to simplify, which makes it easier to remember and write faster:

@font-face {
  font-family: YH;
  src: local("Microsoft Yahei");
}

When using it directly:

.font {
    font-family: YH;
}

How clean, how refreshing, and how comfortable it feels!

src also supports multiple local font addresses to appear at the same time. Hey, this simplified CSS code is not just a font name, but a large number of font names. For example, a website uses a large number of font-family attribute values ​​similar to the following:

body {
    font-family: PingFangSC-Regular,HelveticaNeue-Light,'Helvetica Neue Light','Microsoft YaHei',sans-serif;
}
.xxxx {
    font-family: PingFangSC-Regular,HelveticaNeue-Light,'Helvetica Neue Light','Microsoft YaHei',sans-serif;
}

　　虽然说，实现的时候，借助了Sass, Less之类工具让字体名称们成为了变量，写代码的时候好像也没怎么吃力，但是最终生成的CSS其实是比较啰嗦，如果我们走本质上就是变量的@font face，是不是不仅开发简单，代码也简单了，如下处理：

@font-face {
  font-family: BASE;
  src: local("HelveticaNeue-Light"), local("Helvetica Neue Light"),  local("PingFang SC"), local("Microsoft YaHei"), local(sans-serif);
}

　　于是我们用字体的时候直接：

body {
    font-family: BASE;
}
.xxxx {
    font-family: BASE;
}

　　看语义又好，代码又简单，实用又方便，超级使用的小技巧。

　　当然，local本地作用还不止这些。

　　业界有个名为“字蛛”的中文字体处理工具，可以提取页面中使用的特殊中文字体并生成新的体积更小的自定义字体。我们可以在这个基础上更进一步，举个例子：

　　一些特殊的标题设计师就是喜欢用“方正粗雅宋”这个字体（已经购得版权），但是很显然，这么帅气的字体，几乎很少有用户安装的，所以实际开发的时候，全都是通过工具而生成一个全新的精简版的“方正粗雅宋”字体文件，再通过src属性url()方法外链这个字体文件。

　　很棒的方案，但还不够完美，为什么呢？虽然安装“方正粗雅宋”这个字体的用户并不多，但并不表示没有用户使用之。试想一下，假如有用户安装了这个字体，结果你在网页呈现的时候，还要再去外链一个额外的文件地址，岂不是白白的浪费？既浪费流量，体验又不一定好，如果字体文件加载慢，会看到文字“变形”的过程，显然是不友好的。

　　我们可以借助@font face规则中的local实现代码和体验上的进一步的提升，如下：

@font-face {
  font-family: FZCYS;
  src: local("FZYaSongS-B-GB"), 
       url("FZCYS.woff2"),  
       url("FZCYS.woff"),
       url("FZCYS.ttf");
}

　　于是乎，那些安装了“方正粗雅宋”这个字体的用户，就没有任何字体文件请求。加载更快了，用户体验上升了，还省了流量，如此百益无一害的事情，还不妥妥的用起来。

　　3. font-style

　　在Chrome浏览器下，@font face规则设置font-style:italic可以让文字倾斜，但是这并不是其作用所在。

　　@font face规则中的font-style和font-weight类似，都是用来设置对应字体样式或自重下该使用什么字体。因为有些字体可能会有专门的斜体字，注意这个斜体字，并不是让文字的形状倾斜，而是专门设计的倾斜的字体，很多细节会跟物理上的请求不一样。于是，我在CSS代码中使用font-style:italic的时候，就会调用这个对应字体，如下示意：

@font-face {
  font-family: 'I';
  font-style: normal;
  src: local('FZYaoti');
}
@font-face {
  font-family: 'I';
  font-style: italic;
  src: local('FZShuTi');
}

　　由于专门的斜体字不太好找，所以我使用“方正姚体”和“方正舒体”代替做示意。上面CSS代码我解读一下：制定一个字体，名叫'I'，当文字样式正常的时候，字体表现使用“方正姚体”，当文字设置了font-style:italic的时候，字体表现为“方正舒体”。

　　好，现在假设有下面这样的CSS和HTML：

.i {
  font-family: I;
}

<p><i class="i">类名是i，标签是i</i></p>
<p><span class="i">类名是i, 标签是span</span></p>

　　请问最终的表现是怎样的？

　　由于标签天然font-style:italic，因此理论上，上面一行文字表现为“方正舒体”，下面一行为“方正姚体”，最终结果是如何呢？

　　当当当当，完全符合，如下截图：

　　这下大家应该明白，@font face规则中的font-style是干嘛用的了吧。

　　4. font-weight

　　font-weight和font-style类似，不过是定义了不同字重使用不同字体，对于中午而言，这个要比font-style适用性强很多。我这里就有一个非常具有代表性的例子，版权字体“汉仪旗黑”自重非常丰富，但是这个字体不像“思源黑体”，天然可以根据font-weight属性值加载对应的字体文件，怎么办呢？很简单，使用@font face规则重新定义一下即可，例如下面的CSS代码：

@font-face {
  font-family: 'QH';
  font-weight: 400;
  src: local('HYQihei 40S');
}
@font-face {
  font-family: 'QH';
  font-weight: 500;
  src: local('HYQihei 50S');
}
@font-face {
  font-family: 'QH';
  font-weight: 600;
  src: local('HYQihei 60S');
}

　　解读一下就是，是一个全新的字体，名为'QH'，当字重font-weight为400的时候，使用“汉仪旗黑 40S”字重字体，为500的时候，使用“汉仪旗黑 50S”字重字体，为600的时候，使用“汉仪旗黑 60S”字重字体。

　　于是乎，当我们应用如下的CSS和HTML代码的时候：

.hy-40s,
.hy-50s,
.hy-60s {
  font-family: 'QH';
}
.hy-40s {
  font-weight: 400;
}
.hy-50s {
  font-weight: 500;
}
.hy-60s {
  font-weight: 600;
}

<ul>
  <li class="hy-40s">汉仪旗黑40s</li>
  <li class="hy-50s">汉仪旗黑50s</li>
  <li class="hy-60s">汉仪旗黑60s</li>
</ul>

　　我们就可以看到，文字粗细错落有致的效果，如下截图：

　　如果用在网页开发中，必定会让我们的界面更加的细腻，设计更加的精致，视觉更加的愉悦。

　　5. unicode-range

　　unicode-range的作用是可以让特定的字符或者字符片段使用特定的字体。举个例子，下图是文字应用了“微软雅黑”字体后的效果：

　　但是，这两个“引号”左右间隙不均，方向不明，实在是看着不爽，此时我们就专门指定这两个“引号”使用其他字体，如下CSS：

@font-face {
  font-family: BASE;
  src: local("Microsoft Yahei");
}
@font-face {
  font-family: quote;
  src: local('SimSun');    
  unicode-range: U+201c, U+201d;
}
.font {
    font-family: quote, BASE;
}

　　然后效果就变成这样子了：