![]() ![]() The first period is the font block period.Similar to the existing font timeout behaviors that some browsers implement, font-display segments the lifetime of a font download into three major periods: However, you can tell modern browsers how you want them to behave by using font-display. In the post Avoid invisible text during font loading you can see that default browser behavior is not consistent. You still need to consider how browsers behave when rendering text that uses a font-family which is not yet available. While preloading makes it more likely that a WebFont will be available when a page's content is rendered, it offers no guarantees. Using will trigger a request for the WebFont early in the critical rendering path, without having to wait for the CSSOM to be created. If there's a high probability that your page will need a specific WebFont hosted at a URL you know in advance, you can take advantage of resource prioritization. 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.īy preloading WebFonts and using font-display to control how browsers behave with unavailable fonts, you can prevent blank pages and layout shifts due to font loading. After the font is available, the browser paints the text pixels.If the font is not yet available, the browser may not render any text pixels.The browser performs layout and paints content to the screen.Font requests are dispatched after the render tree indicates which font variants are needed to render the specified text on the page. ![]() The browser constructs the CSSOM after all of the CSS content is received and combines it with the DOM tree to construct the render tree. ![]() The browser discovers CSS, JS, and other resources and dispatches requests.The browser begins parsing the HTML response and constructing the DOM.The browser requests the HTML document.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 browser must construct the render tree, which is dependent on the DOM and CSSOM trees, before it knows which font resources it needs to render the text. Lazy loading of fonts carries an important hidden implication that may delay text rendering. However, if you're not careful, it can also create a performance bottleneck in the critical rendering path and delay text rendering. 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. For example unicode subsets, and distinct style variants. ![]() To address the problem of large files containing all variants, the CSS rule is specifically designed to allow you to split the font family into a collection of resources. In this post you will find out how to optimize loading of WebFonts so visitors only download what they will use.
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