animation_compose.kt

fun Modifier.animatePlacement(): Modifier = composed {
    val scope = rememberCoroutineScope()
    var targetOffset by remember { mutableStateOf(IntOffset.Zero) }
    var animatable by remember {
        mutableStateOf<Animatable<IntOffset, AnimationVector2D>?>(null)
    }
    this
        // 🔥 onPlaced should be before offset Modifier
        .onPlaced {
            // Calculate the position in the parent layout
            targetOffset = it
                .positionInParent()
                .round()
        }
        .offset {
            // Animate to the new target offset when alignment changes.
            val anim = animatable ?: Animatable(targetOffset, IntOffset.VectorConverter).also {
                animatable = it
            }

            if (anim.targetValue != targetOffset) {
                scope.launch {
                    anim.animateTo(targetOffset, spring(stiffness = Spring.StiffnessMediumLow))
                }
            }
            // Offset the child in the opposite direction to the targetOffset, and slowly catch
            // up to zero offset via an animation to achieve an overall animated movement.
            animatable?.let { it.value - targetOffset } ?: IntOffset.Zero
        }
}