Toolbar: optimization: add 64px crop size for the site icon

[fushar]

Trac ticket: https://core.trac.wordpress.org/ticket/65668

What

A follow-up to #11781 (site icon in the admin bar). The toolbar builds a 2x srcset for retina displays:

wordpress-develop/src/wp-includes/admin-bar.php

Lines 397 to 404 in d792cbd

	$site_icon_url = get_site_icon_url( 32 );
	$site_icon_url_2x = get_site_icon_url( 64 );
	$srcset = ( $site_icon_url_2x && $site_icon_url !== $site_icon_url_2x ) ? sprintf( ' srcset="%s 2x"', esc_url( $site_icon_url_2x ) ) : '';
	$site_icon = sprintf(
	'<img class="site-icon" src="%s"%s alt="" width="20" height="20" />',
	esc_url( $site_icon_url ),
	$srcset
	);

But WP_Site_Icon only generates crops at 270, 192, 180, 32. There is no 64px crop:

wordpress-develop/src/wp-admin/includes/class-wp-site-icon.php

Lines 46 to 64 in d792cbd

	270,
	/*
	* App icon for Android/Chrome.
	*
	* @link https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android
	* @link https://developer.chrome.com/multidevice/android/installtohomescreen
	*/
	192,
	/*
	* App icons up to iPhone 6 Plus.
	*
	* See https://developer.apple.com/library/prerelease/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html
	*/
	180,
	// Our regular Favicon.
	32,

So the get_site_icon_url( 64 ) call finds no exact match and falls back to get the first larger size than 64, which is the default thumbnail size (150 x 150). This is too large to serve a 20x20 (or 28x28 in mobile) site icon in the admin bar.

This PR simply adds a new 64 entry to it. With this, browsers can download much smaller image file in retina displays.

Note

This only affects NEW site icon uploads. Existing icons unfortunately won't get the new crop size until it's reuploaded.

This will also benefit the post embeds as it also calls get_site_icon_url( 64 ):

wordpress-develop/src/wp-includes/embed.php

Line 1242 in d792cbd

$site_icon_url_2x = get_site_icon_url( 64, $fallback_icon_url );

Testing

1. Go to Settings -> General.
2. Upload a site icon.
3. Save.
4. Go to wp-admin / frontend.
5. Inspect the site icon element.
6. Verify you get the 64x64 crop. Before this, you get 150x150

See the difference in the image file sizes:

Before	After

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Opus 4.8
Used for: brainstorming and code generation; reviewed by me.

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props fushar.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.