Scrollbar doesn't reach end on first drag with LazyColumn with variable height items

[m-sasha]

When the items in a LazyColumn are of varying sizes, it's possible for the scrollbar thumb to not reach the start/end of its area on the first drag gesture.

Reproducer:

fun main() = application {
    Window(
        onCloseRequest = ::exitApplication,
        state = rememberWindowState(width = 300.dp, height = 380.dp)
    ) {
        LazyScrollable()
    }
}

@Composable
private fun LazyScrollable() {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .background(color = Color.White)
    ) {
        val state = rememberLazyListState()
        val heights = List(4){ 200.dp } + List(10){ 50.dp }

        LazyColumn(
            modifier = Modifier.fillMaxSize(),
            state = state,
        ) {
            items(heights.size) { x ->
                TextBox("Item #$x", x, heights[x])
            }
        }

        VerticalScrollbar(
            modifier = Modifier
                .align(Alignment.CenterEnd)
                .fillMaxHeight(),
            adapter = rememberScrollbarAdapter(
                scrollState = state,
            ),
        )
    }
}

@Composable
fun TextBox(text: String = "Item", index: Int, height: Dp) {
    Box(
        modifier = Modifier
            .height(height)
            .fillMaxWidth()
            .background(
                color = Color(
                    red = (index * 50).mod(255),
                    green = (index * 100).mod(255),
                    blue = (index * 150).mod(255),
                    alpha = 128
                )
            ),
        contentAlignment = Alignment.CenterStart
    ) {
        Text(text = text)
    }
}

Screen.Recording.2023-01-29.at.14.27.53.mp4

[okushnikov]

Please check the following ticket on YouTrack for follow-ups to this issue. GitHub issues will be closed in the coming weeks.