Function computeVirtualScrollRenderPolicy

src/hooks/useVirtualScroll.ts:344–388

({
  start,
  end,
  deferredStart,
  deferredEnd,
  pendingDelta,
  isSticky,
  brokeSticky = false,
  isRangeSettling = false,
  offsets,
  viewportHeight,
  listOrigin,
  itemCount,
  scrollTop,
  maxMountedItems = MAX_MOUNTED_ITEMS,
}: VirtualScrollRenderPolicyInput)

}

export function computeVirtualScrollRenderPolicy({
  start,
  end,
  deferredStart,
  deferredEnd,
  pendingDelta,
  isSticky,
  brokeSticky = false,
  isRangeSettling = false,
  offsets,
  viewportHeight,
  listOrigin,
  itemCount,
  scrollTop,
  maxMountedItems = MAX_MOUNTED_ITEMS,
}: VirtualScrollRenderPolicyInput): VirtualScrollRenderPolicy {
  let effStart = start < deferredStart ? deferredStart : start
  let effEnd = end > deferredEnd ? deferredEnd : end

  if (effStart > effEnd || isSticky || brokeSticky) {
    effStart = start
    effEnd = end
  }

  if (pendingDelta > 0) {
    effEnd = end
  }

  if (effEnd - effStart > maxMountedItems) {
    const mid = (offsets[effStart]! + offsets[effEnd]!) / 2
    if (scrollTop - listOrigin < mid) {
      effEnd = effStart + maxMountedItems
    } else {
      effStart = effEnd - maxMountedItems
    }
  }

  const clampEnabled =
    !isSticky && !isRangeSettling && viewportHeight > 0 && scrollTop >= 0

  return {
    range: [effStart, effEnd],
    clampEnabled,
  }
}

export function computeVirtualScrollClampBounds({
  clampEnabled,