Reduce FOUT with font preloading

[julioest]

Problem

Fonts from boostlook.css load late, causing a flash of unstyled text (FOUT) on page load for libraries that use the Antora UI bundle

Solution

Add tags in the HTML to start fetching fonts early, before CSS parsing.

Changes

• Added head-fonts.hbs partial with:
  • preconnect and dns-prefetch to https://cppalliance.org for faster DNS/TLS
  • Preload links for:
    • NotoSansDisplay.ttf (normal)
    • NotoSansDisplay-Italic.ttf (italic)
    • NotoSansMono.ttf (monospace)
• Included head-fonts partial in head.hbs before stylesheets

Impact

• Fonts start loading earlier in the page lifecycle
• Reduced FOUT
• Better perceived performance
• No changes to CSS or JavaScript

Testing

• Tested on macOS (Chrome, Firefox, Safari) with boost.url library and site docs. Fonts load correctly with proper style variants across all browsers.

[cppalliance-bot]

An automated preview of the documentation is available at https://545.site-docs.prtest2.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2025-11-19 23:28:41 UTC

[sdarwin]

@julioest this PR is adding "preload" on three NotoSans fonts. In the preview https://545.site-docs.prtest2.cppalliance.org/index.html -> View Source -> the "preload" is included in the source. So the modification is there, right? Nevertheless I still get FOUT in the browser. Do you?
You're welcome to merge this. If you believe it's correct.

[sdarwin]

• notosans.woff2 continues to 404. Twice.
• site.webmanifest 404's once.
• This solution is creating a dependency on the cppalliance.org website. That's alright in the short term but longer term the doc build process, using antora, should generate standalone, self-sufficient doc builds that embed the required files, and aren't contacting cppalliance.org. If possible.

Are all these "notosans" fonts the primary main fonts? If they were 404ing before, does that mean they weren't displayed? In that case, are they needed?

[julioest]

This solution is creating a dependency on the cppalliance.org website. That's alright in the short term but longer term the doc build process, using antora, should generate standalone, self-sufficient doc builds that embed the required files, and aren't contacting cppalliance.org. If possible.

100% agreed! This PR in boostlook #545 checks for the antora-bundled font path first.

notosans.woff2 continues to 404. Twice.

It's failing because there's no /static/font/notosans.woff2 (website-v2's font path)