AlignmentLine

import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.layout.HorizontalAlignmentLine
import androidx.compose.ui.layout.Layout

// Create a horizontal alignment line. Note it is not common for alignment lines to be created
// in the scope of one composable, since they are usually used across more than one function.
// We use ::min as merging strategy, which means that the parent will have the minimum of
// the values of the alignment line, when this is inherited from more than one child.
val exampleLine = remember { HorizontalAlignmentLine(::min) }

// A layout with a fixed size, and a given position for the exampleLine alignment line.
@Composable
fun LineProviderLayout(exampleLinePosition: Int) {
    val size: Int = 20
    Layout({}) { _, _ -> layout(size, size, mapOf(exampleLine to exampleLinePosition)) {} }
}

Layout({
    LineProviderLayout(exampleLinePosition = 5)
    LineProviderLayout(exampleLinePosition = 10)
}) { measurables, constraints ->
    val placeables = measurables.map { it.measure(constraints) }
    // placeables[0][line] will be 5
    // placeables[1][line] will be 10
    layout(constraints.maxWidth, constraints.maxHeight) {
        placeables[0].place(0, 3)
        placeables[1].place(constraints.maxWidth / 2, 0)
    }
}
// Note that if the parent of this Layout (the parent of AlignmentLineSample) was able to
// query its position of exampleLine (assuming this was in a shared scope), its position would
// be 8. This is because the Layout positioned its first child at 3 from the top,
// and because of the ::min merging strategy the position of exampleLine will be
// min(5 + 3, 10 + 0).