Test plugin for Gutenberg PR #80385: toggles the wp_generate_animated_image_subsizes filter from Settings > Media

animated-gif-subsizes-toggle.php

<?php
/**
 * Toggle animated sub-size generation for animated images.
 *
 * @wordpress-plugin
 * Plugin Name: Animated Sub-sizes Toggle
 * Description: Adds a Settings > Media checkbox that turns the wp_generate_animated_image_subsizes filter on or off, for testing Gutenberg PR #80385.
 * Plugin URI:  https://github.com/WordPress/gutenberg/pull/80385
 * Version:     1.0.0
 * Author:      Adam Silverstein
 * License:     Apache License 2.0
 * License URI: https://www.apache.org/licenses/LICENSE-2.0
 */

defined( 'ABSPATH' ) || exit;

const AGST_OPTION = 'agst_generate_animated_image_subsizes';

/**
 * Returns the filter to the value stored by the Settings > Media checkbox.
 *
 * @param bool $enabled Whether animated sub-sizes should be generated.
 * @return bool Filtered value.
 */
function agst_filter_animated_subsizes( $enabled ) {
	return (bool) get_option( AGST_OPTION, false );
}
add_filter( 'wp_generate_animated_image_subsizes', 'agst_filter_animated_subsizes' );

/**
 * Registers the setting and its field on Settings > Media.
 */
function agst_register_setting() {
	register_setting(
		'media',
		AGST_OPTION,
		array(
			'type'              => 'boolean',
			'sanitize_callback' => 'rest_sanitize_boolean',
			'default'           => false,
			'show_in_rest'      => false,
		)
	);

	add_settings_field(
		AGST_OPTION,
		'Animated sub-sizes',
		'agst_render_field',
		'media',
		'default'
	);
}
add_action( 'admin_init', 'agst_register_setting' );

/**
 * Renders the checkbox.
 */
function agst_render_field() {
	$enabled = (bool) get_option( AGST_OPTION, false );
	?>
	<label for="<?php echo esc_attr( AGST_OPTION ); ?>">
		<input
			type="checkbox"
			name="<?php echo esc_attr( AGST_OPTION ); ?>"
			id="<?php echo esc_attr( AGST_OPTION ); ?>"
			value="1"
			<?php checked( $enabled ); ?>
		/>
		Keep animation in uncropped sub-sizes of animated images
	</label>
	<p class="description">
		Sets the <code>wp_generate_animated_image_subsizes</code> filter. Cropped sizes such as the thumbnail are always taken from the first frame. Reload the editor after changing this.
	</p>
	<?php
}

/**
 * Shows the current state in the admin bar, so the editor page itself says which mode is live.
 *
 * @param WP_Admin_Bar $admin_bar Admin bar instance.
 */
function agst_admin_bar_indicator( $admin_bar ) {
	if ( ! current_user_can( 'upload_files' ) ) {
		return;
	}

	$enabled = (bool) apply_filters( 'wp_generate_animated_image_subsizes', false );

	$admin_bar->add_node(
		array(
			'id'    => 'agst-indicator',
			'title' => $enabled ? 'Animated sub-sizes: ON' : 'Animated sub-sizes: OFF',
			'href'  => admin_url( 'options-media.php' ),
			'meta'  => array( 'title' => 'Toggle on Settings > Media' ),
		)
	);
}
add_action( 'admin_bar_menu', 'agst_admin_bar_indicator', 100 );

Sharing the toggle plugin I used while testing WordPress/gutenberg#80385, in case it helps anyone else who wants to try that PR.

Claude wrote the plugin and these notes, forwarding them along:

The PR makes animated sub-sizes opt-in behind a new wp_generate_animated_image_subsizes filter. Rather than editing a file to flip that filter, this plugin puts a checkbox at Settings > Media, so one site can be tested both ways without a redeploy. The admin bar shows Animated sub-sizes: ON or OFF, so the editor page itself says which mode is live.

To install it, use the Download ZIP button above and upload the zip at Plugins > Add New > Upload Plugin. The plugin folder winds up named after the gist id, which is harmless.

Testing steps:

1. Leave the toggle off, which is the default, and upload an animated GIF. The sub-sizes should all be static.
2. Tick the box on Settings > Media, reload the editor, then upload again. Uncropped sub-sizes should now animate.

Worth using a source wider than 1024px so medium, medium_large, and large are all generated - a smaller GIF only yields one uncropped size, which makes for a thin test. The thumbnail stays static either way, since cropped sizes are always taken from the first frame.

Note that this only applies to uploads that go through client-side media processing. Uploads taking the server-side path still produce static sub-sizes, since core has no animated resize support.