Source

File: wp-includes/formatting.php

function wp_staticize_emoji( $text ) {
	if ( false === strpos( $text, '&#x' ) ) {
		if ( ( function_exists( 'mb_check_encoding' ) && mb_check_encoding( $text, 'ASCII' ) ) || ! preg_match( '/[^\x00-\x7F]/', $text ) ) {
			// The text doesn't contain anything that might be emoji, so we can return early.
			return $text;
		} else {
			$encoded_text = wp_encode_emoji( $text );
			if ( $encoded_text === $text ) {
				return $encoded_text;
			}

			$text = $encoded_text;
		}
	}

	$emoji = _wp_emoji_list( 'entities' );

	// Quickly narrow down the list of emoji that might be in the text and need replacing.
	$possible_emoji = array();
	foreach ( $emoji as $emojum ) {
		if ( false !== strpos( $text, $emojum ) ) {
			$possible_emoji[ $emojum ] = html_entity_decode( $emojum );
		}
	}

	if ( ! $possible_emoji ) {
		return $text;
	}

	/** This filter is documented in wp-includes/formatting.php */
	$cdn_url = apply_filters( 'emoji_url', 'https://s.w.org/images/core/emoji/13.0.0/72x72/' );

	/** This filter is documented in wp-includes/formatting.php */
	$ext = apply_filters( 'emoji_ext', '.png' );

	$output = '';
	/*
	 * HTML loop taken from smiley function, which was taken from texturize function.
	 * It'll never be consolidated.
	 *
	 * First, capture the tags as well as in between.
	 */
	$textarr = preg_split( '/(<.*>)/U', $text, -1, PREG_SPLIT_DELIM_CAPTURE );
	$stop    = count( $textarr );

	// Ignore processing of specific tags.
	$tags_to_ignore       = 'code|pre|style|script|textarea';
	$ignore_block_element = '';

	for ( $i = 0; $i < $stop; $i++ ) {
		$content = $textarr[ $i ];

		// If we're in an ignore block, wait until we find its closing tag.
		if ( '' === $ignore_block_element && preg_match( '/^<(' . $tags_to_ignore . ')>/', $content, $matches ) ) {
			$ignore_block_element = $matches[1];
		}

		// If it's not a tag and not in ignore block.
		if ( '' === $ignore_block_element && strlen( $content ) > 0 && '<' !== $content[0] && false !== strpos( $content, '&#x' ) ) {
			foreach ( $possible_emoji as $emojum => $emoji_char ) {
				if ( false === strpos( $content, $emojum ) ) {
					continue;
				}

				$file = str_replace( ';&#x', '-', $emojum );
				$file = str_replace( array( '&#x', ';' ), '', $file );

				$entity = sprintf( '<img src="%s" alt="%s" class="wp-smiley" style="height: 1em; max-height: 1em;" />', $cdn_url . $file . $ext, $emoji_char );

				$content = str_replace( $emojum, $entity, $content );
			}
		}

		// Did we exit ignore block?
		if ( '' !== $ignore_block_element && '</' . $ignore_block_element . '>' === $content ) {
			$ignore_block_element = '';
		}

		$output .= $content;
	}

	// Finally, remove any stray U+FE0F characters.
	$output = str_replace( '&#xfe0f;', '', $output );

	return $output;
}