Gets an array of IDs of hidden meta boxes.

function get_hidden_meta_boxes( $screen ) {
	if ( is_string( $screen ) ) {
		$screen = convert_to_screen( $screen );
	}

	$hidden = get_user_option( "metaboxhidden_{$screen->id}" );

	$use_defaults = ! is_array( $hidden );

	// Hide slug boxes by default.
	if ( $use_defaults ) {
		$hidden = array();

		if ( 'post' === $screen->base ) {
			if ( in_array( $screen->post_type, array( 'post', 'page', 'attachment' ), true ) ) {
				$hidden = array( 'slugdiv', 'trackbacksdiv', 'postcustom', 'postexcerpt', 'commentstatusdiv', 'commentsdiv', 'authordiv', 'revisionsdiv' );
			} else {
				$hidden = array( 'slugdiv' );
			}
		}

		/**
		 * Filters the default list of hidden meta boxes.
		 *
		 * @since 3.1.0
		 *
		 * @param string[]  $hidden An array of IDs of meta boxes hidden by default.
		 * @param WP_Screen $screen WP_Screen object of the current screen.
		 */
		$hidden = apply_filters( 'default_hidden_meta_boxes', $hidden, $screen );
	}

	/**
	 * Filters the list of hidden meta boxes.
	 *
	 * @since 3.3.0
	 *
	 * @param string[]  $hidden       An array of IDs of hidden meta boxes.
	 * @param WP_Screen $screen       WP_Screen object of the current screen.
	 * @param bool      $use_defaults Whether to show the default meta boxes.
	 *                                Default true.
	 */
	return apply_filters( 'hidden_meta_boxes', $hidden, $screen, $use_defaults );
}