TextLayoutResult#getLineForOffset is too slow

[sunny-chung]

Describe the problem
TextLayoutResult#getLineForOffset is too slow. I looked at source code, linear search is performed in the class SkiaParagraph. It can be optimized by using binary search.

Affected platforms

• Desktop
  I only tried on Desktop.

If the problem is Android-only, report it in the Jetpack Compose tracker

Versions

• Kotlin version: 1.8.0
• Compose Multiplatform version: 1.5.11
• OS version(s) (required for Desktop and iOS issues): macOS 14.0 Beta
• OS architecture (x86 or arm64): arm64
• JDK (for desktop issues): 17

Sample code

@Composable
fun App() {
    val text = remember { "Super long text\n".repeat(10000) }
    val scrollState = rememberScrollState()

    Box {
        BasicTextField(
            value = text,
            onValueChange = {},
            onTextLayout = { textLayoutResult ->
                val lineOffsets = listOf(0) + "\n".toRegex().findAll(text).map { it.range.endInclusive + 1 }
                val lineTops = lineOffsets.map { textLayoutResult.getLineTop(textLayoutResult.getLineForOffset(it)) }
                println("Done. ${lineTops.size}")
            },
            modifier = Modifier.fillMaxSize().verticalScroll(scrollState),
        )
        VerticalScrollbar(
            modifier = Modifier.align(Alignment.CenterEnd),
            adapter = rememberScrollbarAdapter(scrollState),
        )
    }
}

Reproduction steps

1. Run the app
2. Hangs until some minutes later

Video
N/A

Profiling data
N/A

Additional information
I was implementing line number display and text folding for a TextField. As #3866 is not available yet, I try an alternative using TextLayoutResult#getLineForOffset. Unfortunately, it only works for small number of lines. I wonder if there is a feasible workaround at this moment.

[m-sasha]

Thanks, I'll fix it.

[okushnikov]

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