Function computeVisibleRange

computeVisibleRange<T>(
    items: readonly T[],
    itemHeight: ItemHeightSpec<T>,
    scrollTop: number,
    viewportHeight: number,
    overscan: number,
): VisibleRangeResult
Compute visible item range with overscan.

Algorithm:
- Fixed height: O(1) direct calculation via division
- Variable height: O(n) cumulative offset array + binary search
Type Parameters
- T
Parameters
- items: readonly T[]
  The full list of items
- itemHeight: ItemHeightSpec<T>
  Fixed height or height function
- scrollTop: number
  Current scroll position in pixels/cells
- viewportHeight: number
  Visible viewport height in pixels/cells
- overscan: number
  Number of items to render outside viewport
Returns VisibleRangeResult
Visible range with item offsets
- Defined in core/src/widgets/virtualList.ts:123