All synthesized variants are generated from a single weight font. As you can see, there's a noticeable difference in the results. The details of how to generate the bold and oblique variants are not specified. Therefore, the results vary from browser to browser, and are highly dependent on the font. A "full" webfont that includes all stylistic variants, which you may not need, plus all the glyphs, which may go unused, can easily result in a multi-megabyte download. To address this, the font-face CSS rule is specifically designed to allow you to split the font family into a collection of resources: unicode subsets, distinct style variants, and so on.
Given these declarations, the browser figures out the required subsets and variants and downloads the minimal set required to render the text, which is very convenient. However, if you're not careful, it can also create a performance bottleneck in the critical rendering path and delay text rendering. Lazy loading of fonts carries an important hidden implication that may delay text rendering: the browser must construct the render tree , which is dependent on the DOM and CSSOM trees, before it knows which font resources it needs in order to render the text.
As a result, font requests are delayed well after other critical resources, and the browser may be blocked from rendering text until the resource is fetched. The "race" between the first paint of page content, which can be done shortly after the render tree is built, and the request for the font resource is what creates the "blank text problem" where the browser might render page layout but omits any text. You need to use preload in conjunction with an appropriate CSS font-face definition in order to instruct the browser what do to with a given Webfont URL.
But every browser that supports preloading also supports WOFF2, so that's always the format that you should preload. While preloading makes it more likely that a Webfont will be available when a page's content is rendered, it offers no guarantees. You still need to consider how browsers behave when rendering text that uses a font-family which is not yet available. Most browsers implement a maximum timeout that they'll wait for a Webfont to download, after which a fallback font will be used.
Unfortunately, browsers differ on implementation:. To ensure consistency moving forward, the CSS Working Group has proposed a new font-face descriptor, font-display , and a corresponding property for controlling how a downloadable font renders before it is loaded. Similar to the existing font timeout behaviors that some browsers implement today, font-display segments the lifetime of a font download into three major periods:.
Understanding these periods means you can use font-display to decide how your font should render depending on whether or when it was downloaded. To work with the font-display property, add it your font-face rules:. Most browsers currently have a default strategy similar to block.
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In other words, the browser draws "invisible" text at first if the font is not loaded, but swaps the font face in as soon as it loads. To do this the browser creates an anonymous font face with metrics similar to the selected font but with all glyphs containing no "ink. Similar to block , this value should only be used when rendering text in a particular font is important for the page, but rendering in any font will still get a correct message across.
Writing python scripts to change fonts in FontForge
Similar to fallback , this is a good choice for when the downloading font is more of a "nice to have" but not critical to the experience. The optional value leaves it up to the browser to decide whether to initiate the font download, which it may choose not to do or it may do it as a low priority depending on what it thinks would be best for the user.
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The Font Loading API provides a scripting interface to define and manipulate CSS font faces, track their download progress, and override their default lazyload behavior. For example, if you're sure that a particular font variant is required, you can define it and tell the browser to initiate an immediate fetch of the font resource:.
Further, because you can check the font status via the check method and track its download progress, you can also define a custom strategy for rendering text on your pages:. Best of all, you can also mix and match the above strategies for different content on the page. For example, you can delay text rendering on some sections until the font is available, use a fallback font, and then re-render after the font download has finished, specify different timeouts, and so on.
Font resources are, typically, static resources that don't see frequent updates. As a result, they are ideally suited for a long max-age expiry - ensure that you specify both a conditional ETag header , and an optimal Cache-Control policy for all font resources. If your web application uses a service worker , serving font resources with a cache-first strategy is appropriate for most use cases. You should not store fonts using localStorage or IndexedDB ; each of those has its own set of performance issues. The browser's HTTP cache provides the best and most robust mechanism to deliver font resources to the browser.
Contrary to popular belief, the use of webfonts doesn't need to delay page rendering or have a negative impact on other performance metrics. The well-optimized use of fonts can deliver a much better overall user experience: great branding, improved readability, usability, and searchability, all while delivering a scalable multi-resolution solution that adapts well to all screen formats and resolutions.
Don't be afraid to use webfonts. That said, a naive implementation may incur large downloads and unnecessary delays. You need to help the browser by optimizing the font assets themselves and how they are fetched and used on your pages. Lighthouse can help automate the process of making sure that you're following web font optimization best practices. Lighthouse is an auditing tool built by the Chrome DevTools team.
You tell Lighthouse what URL to audit, and then it runs a bunch of tests on the page, and gives you a report of what the page is doing well, and how it can improve.
UNICODE SLAVONIC FONT MANIFESTO
The following audits can help you make sure that your pages are continuing to follow web font optimization best practices over time:. Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4. For details, see the Google Developers Site Policies.
Each time you enter a character it goes into the device's memory and, of course, ultimately ends up on the display or stored in a file. The order in which characters are entered and stored by your device, or written to a text file, is called the logical order. For simple text written in left-to-right languages e. However, for right-to-left languages, such as Arabic, the order in which the characters are displayed or rendered for reading is reversed: the display visual order is not the same as the logical order.
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I'd be interested to know if this is indeed not the case. However, I'll assume this principle is broadly correct. If you look at the charts you'll see that the range to 06FF contains the isolated versions of each character; i. So, looking at this from, say, LuaTeX's viewpoint, how is it that the series of isolated forms of Arabic characters sitting in a TeX file in logical order can be transformed into typeset Arabic in proper visual display order?
The answer is that the incoming stream of bytes representing Arabic text has to be "transformed" or "shaped" into the correct series of glyphs. Just for the moment, assume that you are using the LuaTeX engine but with the plain TeX macro package: you have no other "packages" loaded but you have setup a font which has Arabic glyphs.
All the font will do is allow you to display the characters that LuaTeX sees within its input stream. If you enter some Arabic text into a TeX file, what do you think will happen? Without any additional help or support to process the incoming Arabic text LuaTeX will simply output what is gets: a series of isolated glyphs in logical not display order:. What's happening is that the text editor itself is applying a shaping engine to the Arabic text in order to render it according to the rules of Arabic text processing and typography: you can think of this as a layer of software which sits between the underlying text and the screen display: transforming characters to glyphs.
The key point is that the core LuaTeX engine does not provide a "shaping engine": i.
The LuaTeX engine needs some help and those rules have to be provided or implemented through packages, plug-ins or through Lua code such as the ConTeXt package provides. Without this additional help LuaTeX will simply render the raw, logical order, text stream of isolated non-joined characters.
Incidentally, the text editor here is BabelPad which uses the Windows shaping engine called Uniscribe , which provides a set of "operating system services" for rendering complex scripts. Because Arabic is a cursive script, with letters that change shape according to position in a word and adjacent characters the "context" , part of the job of a "shaping engine" is to perform "contextual analysis": looking at each character and working out which glyph should be used, i. If you look the Unicode code charts for Arabic Presentation Forms-B you'll see that this Unicode range contains the joining forms of Arabic characters; and one way to perform contextual analysis involves mapping input characters i.
After the contextual analysis is complete the next step is to apply an additional layer of shaping to ensure that certain ligatures are produced such as lam alef. In addition, you then apply more advanced typographic features defined within the particular OpenType font you are using: such as accurate vowel placement, cursive positioning and so forth. This latter stage is often referred to as OpenType shaping. The key point is that OpenType font technology is designed to encapsulate advanced typographic rules within the font files themselves, using so-called OpenType tables: creating so-called "intelligent fonts".
You can think of these tables as containing an extensive set of "rules" which can be applied to a series of input glyphs in order to achieve a specific typographic objective. This is actually a fairly large and complex topic, which I'll cover in a future post "features" and "lookups". Despite OpenType font technology supporting advanced typography, you should note that the creators of specific fonts choose which features they want to support: some fonts are packed with advanced features, others may contain just a few basic rules.
In short, OpenType fonts vary enormously so you should never assume "all fonts are created equal", they are not. You pass it a Unicode string and call various functions to "drive" the application of the OpenType tables contained within the font. Of course, your font needs to support or provide the feature you are asking for but libotf has a way to "ask" the font "Do you support this feature? We've covered a lot of ground so, hopefully, the following screenshots might help to clarify the ideas presented above. These screenshots are also from BabelPad which has the ability to switch off the shaping engine to let you see the raw characters in logical order before any contextual analysis or shaping is applied.
The first screenshot shows the raw text in logical order before any shaping has been applied. This is the text that would be entered at the keyboard and saved into a TeX file. The following screenshot is the result of applying the Windows system shaping engine called Uniscribe. Of course, different operating systems have their own system services to perform complex shaping but the tasks are essentially the same: process the input text to render the display version, through the application of rules contained in the OpenType font.
One more screenshot, this time from a great little tool that I found on this excellent site.
The top section of the screenshot shows the fully shaped i. Note carefully that the text stream is in logical order see the highlighted character and that the text is stored using the Unicode range to 06FF. First, make sure you have unzipped the product before installing. Please also note that you need to install the font before using it! Occasionally, fonts may generate an error when you install it in Fontbook on a Mac.
Fontbook actually has a built-in validation tool that it runs when you install a font, and sometimes it can be picky. Sometimes an error may be generated simply because the font is already installed in your system! Other times, heavily distressed fonts in particular may generate the error due to the fact that they are memory-intensive to use and might bog down your system.
It does NOT mean that the font contains malware or anything that will harm your system. Typically these fonts are safe to install without any corrections of the error, and you will probably never notice any issues when you use the font. Some OpenType fonts have a lot of extra features, such as alternates, ligatures, and swashes.