private fun loadData() {
  ...
  App.books = makeGrid(bookModels)
}

val offsets = listOf(
    Pair(-1.5f, -1.5f), Pair(-0.5f, -1.5f), Pair(0.5f, -1.5f), Pair(1.5f, -1.5f),
    Pair(-1.5f, -0.5f), Pair(-0.5f, -0.5f), Pair(0.5f, -0.5f), Pair(1.5f, -0.5f),
    Pair(-1.5f, 0.5f), Pair(-0.5f, 0.5f), Pair(0.5f, 0.5f), Pair(1.5f, 0.5f),
    Pair(-1.5f, 1.5f), Pair(-0.5f, 1.5f), Pair(0.5f, 1.5f), Pair(1.5f, 1.5f)
)

fun makeGrid(data: List<BookModel>): MutableList<ARBook> {
    val res = mutableListOf<ARBook>()
    var x: Float
    var z: Float
    var zLayer = 0
    var i = 0

    val elevationMap = MutableList(16) { 0f }

    for (book in data) {
        x = offsets[i].first * (paperbackWidth + 0.03f)
        z = offsets[i].second * (paperbackHeight + 0.03f)

        res.add(
            ARBook(
                makeSize(book.pages),
                Vector3(x, elevationMap[i], z),
                makeAngle(),
                book.cover
            )
        )

        elevationMap[i] += res[res.size - 1].size.y

        if (i == 15) {
            zLayer++
            i = 0
        } else {
            i++
        }
    }
    return res
}