ScalingLazyColumnDefaults

fun scalingParams(
    edgeScale: Float = 0.7f,
    edgeAlpha: Float = 0.5f,
    minElementHeight: Float = 0.2f,
    maxElementHeight: Float = 0.6f,
    minTransitionArea: Float = 0.35f,
    maxTransitionArea: Float = 0.55f,
    scaleInterpolator: Easing = CubicBezierEasing(0.3f, 0f, 0.7f, 1f),
    viewportVerticalOffsetResolver: (Constraints) -> Int = { (it.maxHeight / 20f).toInt() }
): ScalingParams

Creates a ScalingParams that represents the scaling and alpha properties for a ScalingLazyColumn.

Items in the ScalingLazyColumn have scaling and alpha effects applied to them depending on their position in the viewport. The closer to the edge (top or bottom) of the viewport that they are the greater the down scaling and transparency that is applied. Note that scaling and transparency effects are applied from the center of the viewport (full size and normal transparency) towards the edge (items can be smaller and more transparent).

Deciding how much scaling and alpha to apply is based on the position and size of the item and on a series of properties that are used to determine the transition area for each item.

The transition area is defined by the edge of the screen and a transition line which is calculated for each item in the list. The items transition line is based upon its size with the potential for larger list items to start their transition earlier (closer to the center) than smaller items.

minTransitionArea and maxTransitionArea are both in the range 0f..1f and are the fraction of the distance between the edge of the viewport and the center of the viewport. E.g. a value of 0.2f for minTransitionArea and 0.75f for maxTransitionArea determines that all transition lines will fall between 1/5th (20%) and 3/4s (75%) of the distance between the viewport edge and center.

The size of the each item is used to determine where within the transition area range minTransitionArea..maxTransitionArea the actual transition line will be. minElementHeight and maxElementHeight are used along with the item height (as a fraction of the viewport height in the range 0f..1f) to find the transition line. So if the items size is 0.25f (25%) of way between minElementSize..maxElementSize then the transition line will be 0.25f (25%) of the way between minTransitionArea..maxTransitionArea.

A list item smaller than minElementHeight is rounded up to minElementHeight and larger than maxElementHeight is rounded down to maxElementHeight. Whereabouts the items height sits between minElementHeight..maxElementHeight is then used to determine where the transition line sits between minTransitionArea..maxTransition area.

If an item is smaller than or equal to minElementSize its transition line with be at minTransitionArea and if it is larger than or equal to maxElementSize its transition line will be at maxTransitionArea.

For example, if we take the default values for minTransitionArea = 0.2f and maxTransitionArea = 0.6f and minElementSize = 0.2f and maxElementSize= 0.8f then an item with a height of 0.4f (40%) of the viewport height is one third of way between minElementSize and maxElementSize, (0.4f - 0.2f) / (0.8f - 0.2f) = 0.33f. So its transition line would be one third of way between 0.2f and 0.6f, transition line = 0.2f + (0.6f - 0.2f) * 0.33f = 0.33f.

Once the position of the transition line is established we now have a transition area for the item, e.g. in the example above the item will start/finish its transitions when it is 0.33f (33%) of the distance from the edge of the viewport and will start/finish its transitions at the viewport edge.

The scaleInterpolator is used to determine how much of the scaling and alpha to apply as the item transits through the transition area.

The edge of the item furthest from the edge of the screen is used as a scaling trigger point for each item.

@Composable
fun snapFlingBehavior(
    state: ScalingLazyListState,
    snapOffset: Dp = 0.dp,
    decay: DecayAnimationSpec<Float> = exponentialDecay()
): FlingBehavior

Create and remember a FlingBehavior that will represent natural fling curve with snap to central item as the fling decays.