thing2.js

private fun startAnimate() {
    compositeDisposable.add(Observable
        .interval(0, 1, TimeUnit.SECONDS)
        .flatMap {
            return@flatMap Observable
                .interval(0, 100, TimeUnit.MILLISECONDS)
                .take(image.size.toLong())
        }
        .map { it.toInt() }
        .doAfterNext { if (it == (image.size - 1)) control *= -1 }
        .map { if (control == 1) it else image.size - 1 - it }
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe { showImage(it) })
}