BottomSheetScreen.kt

    /**
     * Returns a [Shape] for BottomSheet's current [sheetState].
     * @return gradually un-rounding/rounding shape when [sheetState] is changing to [ModalBottomSheetValue.Expanded] or [ModalBottomSheetValue.HalfExpanded].
     */
    @Composable
    internal fun shape(
        sheetState: ModalBottomSheetState,
        radius: Dp = 16.0.dp,
    ): Shape {
        val offsetFraction by remember {
            derivedStateOf {
                val isExpanding = sheetState.progress.to == ModalBottomSheetValue.Expanded
                val isShrinking = sheetState.progress.from == ModalBottomSheetValue.Expanded && sheetState.progress.to == ModalBottomSheetValue.HalfExpanded
                when {
                    isExpanding -> 1 - sheetState.progress.fraction
                    isShrinking -> sheetState.progress.fraction * 3 // shrink faster than expanding
                    else -> 1.0f
                }.coerceAtMost(1.0f)
            }
        }
        return RoundedCornerShape(
            topStart = radius * offsetFraction,
            topEnd = radius * offsetFraction,
        )
    }

@Composable
fun rememberBottomSheetStickyFooterOffset(sheetState: ModalBottomSheetState): State<Float> {
    val stickyFooterOffset = remember {
        derivedStateOf {
            val isHiding = sheetState.progress.from == ModalBottomSheetValue.HalfExpanded && sheetState.progress.to == ModalBottomSheetValue.Hidden
            when {
                // sheet is hiding, slowly start hiding the sticky footer too
                isHiding -> -(sheetState.offset.value / (1 + sheetState.progress.fraction))
                // otherwise, the footer should have a negative offset to appear sticky as the sheet moves
                else -> -(sheetState.offset.value)
            }
        }
    }
    return stickyFooterOffset
}