Add snapIndex lambda parameter

[chrisbanes]

This block which returns the index which the apps wishes to snap to. The block is provided with the SnapperLayoutInfo and the index which Snapper has determined is the correct target index. Callers can override this value as they see fit.

A common use case could be rounding up/down to achieve groupings of items, which was the intention of #12.

A very simple version could look this this:

val GroupSize = 3

flingBehavior = rememberSnapperFlingBehavior(
    lazyListState = lazyListState,
    snapIndex = { layout, targetIndex ->
        val mod = targetIndex % GroupSize
        if (mod > (GroupSize / 2)) {
            // Round up towards infinity
            GroupSize + targetIndex - mod
        } else {
            // Round down towards zero
            targetIndex - mod
        }
    }
),

You could also look at the layout.currentItem to determine the fling direction to influence which direction to round.

[ghost]

Can you, please, explain more about flingDirection?
For me it looks impossible to calculate fling direction without additional input.
For case with 3 items: I can be on 6th item and scroll to the start of the 5th, then lift the finger. Or I can be on 3rd item, scroll to the end of the 4th (start of the 5th), then lift the finger. Current item will return same object for those cases, as far as I tested. (with offset near 0). However I may want to use different calculations to continue gesture (because it's in the middle)

[chrisbanes]

Can you, please, explain more about flingDirection? For me it looks impossible to calculate fling direction without additional input.

You can determine that by: val flingForward = targetIndex > layout.currentItem.index

[ghost]

Thanks, I reached behavior I wanted to 👍