Prefill GravitForms

/**
 * Prefill Gravity Forms
 */
function bis_init_prefill_gf_fields() {
    global $post;

    if ( ! empty( $post->ID ) ) {

        $post_meta = get_post_meta( $post->ID );

        $post_meta_keys = array_keys( $post_meta );

        if ( is_array( $post_meta_keys ) ) {
            foreach ( $post_meta_keys as $meta_key ) {
                if ( preg_match( '/^prefill_gf_(.*)/', $meta_key, $matches ) ) {
                    $gf_field_parameter = $matches[1];

                    add_filter( 'gform_field_value_' . $gf_field_parameter, 'bis_prefill_gf_fields', 10, 2 );
                }
            }
        }
    }
}
add_action( 'wp', 'bis_init_prefill_gf_fields' );

function bis_prefill_gf_fields( $value, $field ) {
    global $post;

    if ( ! empty( $field->inputName ) && ! empty( $post->ID ) ) {
        $value = get_post_meta( $post->ID, 'prefill_gf_' . $field->inputName, true );
    }


    return $value;
}