PositionFocusedItemInLazyLayout.kt

// Copyright 2024 Google LLC.
// SPDX-License-Identifier: Apache-2.0

@OptIn(ExperimentalFoundationApi::class)
@Composable
fun PositionFocusedItemInLazyLayout(
    parentFraction: Float = 0.3f,
    childFraction: Float = 0f,
    content: @Composable () -> Unit,
) {
    // This bring-into-view spec pivots around the center of the scrollable container
    val bringIntoViewSpec = remember(parentFraction, childFraction) {
        object : BringIntoViewSpec {
            override fun calculateScrollDistance(
                // Initial position of item requesting focus
                offset: Float,
                // Size of item requesting focus
                size: Float,
                // Size of the lazy container
                containerSize: Float
            ): Float {
                val childSmallerThanParent = size <= containerSize
                val initialTargetForLeadingEdge =
                    parentFraction * containerSize - (childFraction * size)
                val spaceAvailableToShowItem = containerSize - initialTargetForLeadingEdge

                val targetForLeadingEdge =
                    if (childSmallerThanParent && spaceAvailableToShowItem < size) {
                        containerSize - size
                    } else {
                        initialTargetForLeadingEdge
                    }

                return offset - targetForLeadingEdge
            }
        }
    }

    // LocalBringIntoViewSpec will apply to all scrollables in the hierarchy
    CompositionLocalProvider(
        LocalBringIntoViewSpec provides bringIntoViewSpec,
        content = content,
    )
}

// To implement, provide a LazyRow as the PositionFocusedItemInLazyLayout's content
PositionFocusedItemInLazyLayout(parentFraction = 0.5f) {
    LazyRow {}
}

Will that be added to tv-foundation once TvLazyLists are removed?

@pflammertsma I used this snippet to document migration from TvLazyLists to LazyLists https://medium.com/@dejwidh/lazylist-pivotoffset-without-tvlazylist-7ad24fe439ab. I hope it's fine.

Hi Dawid, well observed; we are in the process of bringing scrollable containers back into componse-foundation and this code snippet replaces the pivotOffset parameter.

I will have more to share once we are closer to updating the TV libraries.

Hi Dawid, is @OptIn(ExperimentalFoundationApi::class) causes any performance issue ?