react-native-flip/example/node_modules/react-native-web/dist/cjs/vendor/react-native/VirtualizeUtils/index.js

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/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * 
 * @format
 */
'use strict';

exports.__esModule = true;
exports.computeWindowedRenderLimits = computeWindowedRenderLimits;
exports.elementsThatOverlapOffsets = elementsThatOverlapOffsets;
exports.newRangeCount = newRangeCount;
exports.default = void 0;

var _invariant = _interopRequireDefault(require("fbjs/lib/invariant"));

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

/**
 * Used to find the indices of the frames that overlap the given offsets. Useful for finding the
 * items that bound different windows of content, such as the visible area or the buffered overscan
 * area.
 */
function elementsThatOverlapOffsets(offsets, itemCount, getFrameMetrics) {
  var out = [];
  var outLength = 0;

  for (var ii = 0; ii < itemCount; ii++) {
    var frame = getFrameMetrics(ii);
    var trailingOffset = frame.offset + frame.length;

    for (var kk = 0; kk < offsets.length; kk++) {
      if (out[kk] == null && trailingOffset >= offsets[kk]) {
        out[kk] = ii;
        outLength++;

        if (kk === offsets.length - 1) {
          (0, _invariant.default)(outLength === offsets.length, 'bad offsets input, should be in increasing order: %s', JSON.stringify(offsets));
          return out;
        }
      }
    }
  }

  return out;
}
/**
 * Computes the number of elements in the `next` range that are new compared to the `prev` range.
 * Handy for calculating how many new items will be rendered when the render window changes so we
 * can restrict the number of new items render at once so that content can appear on the screen
 * faster.
 */


function newRangeCount(prev, next) {
  return next.last - next.first + 1 - Math.max(0, 1 + Math.min(next.last, prev.last) - Math.max(next.first, prev.first));
}
/**
 * Custom logic for determining which items should be rendered given the current frame and scroll
 * metrics, as well as the previous render state. The algorithm may evolve over time, but generally
 * prioritizes the visible area first, then expands that with overscan regions ahead and behind,
 * biased in the direction of scroll.
 */


function computeWindowedRenderLimits(props, prev, getFrameMetricsApprox, scrollMetrics) {
  var data = props.data,
      getItemCount = props.getItemCount,
      maxToRenderPerBatch = props.maxToRenderPerBatch,
      windowSize = props.windowSize;
  var itemCount = getItemCount(data);

  if (itemCount === 0) {
    return prev;
  }

  var offset = scrollMetrics.offset,
      velocity = scrollMetrics.velocity,
      visibleLength = scrollMetrics.visibleLength; // Start with visible area, then compute maximum overscan region by expanding from there, biased
  // in the direction of scroll. Total overscan area is capped, which should cap memory consumption
  // too.

  var visibleBegin = Math.max(0, offset);
  var visibleEnd = visibleBegin + visibleLength;
  var overscanLength = (windowSize - 1) * visibleLength; // Considering velocity seems to introduce more churn than it's worth.

  var leadFactor = 0.5; // Math.max(0, Math.min(1, velocity / 25 + 0.5));

  var fillPreference = velocity > 1 ? 'after' : velocity < -1 ? 'before' : 'none';
  var overscanBegin = Math.max(0, visibleBegin - (1 - leadFactor) * overscanLength);
  var overscanEnd = Math.max(0, visibleEnd + leadFactor * overscanLength);
  var lastItemOffset = getFrameMetricsApprox(itemCount - 1).offset;

  if (lastItemOffset < overscanBegin) {
    // Entire list is before our overscan window
    return {
      first: Math.max(0, itemCount - 1 - maxToRenderPerBatch),
      last: itemCount - 1
    };
  } // Find the indices that correspond to the items at the render boundaries we're targeting.


  var _elementsThatOverlapO = elementsThatOverlapOffsets([overscanBegin, visibleBegin, visibleEnd, overscanEnd], props.getItemCount(props.data), getFrameMetricsApprox),
      overscanFirst = _elementsThatOverlapO[0],
      first = _elementsThatOverlapO[1],
      last = _elementsThatOverlapO[2],
      overscanLast = _elementsThatOverlapO[3];

  overscanFirst = overscanFirst == null ? 0 : overscanFirst;
  first = first == null ? Math.max(0, overscanFirst) : first;
  overscanLast = overscanLast == null ? itemCount - 1 : overscanLast;
  last = last == null ? Math.min(overscanLast, first + maxToRenderPerBatch - 1) : last;
  var visible = {
    first: first,
    last: last
  }; // We want to limit the number of new cells we're rendering per batch so that we can fill the
  // content on the screen quickly. If we rendered the entire overscan window at once, the user
  // could be staring at white space for a long time waiting for a bunch of offscreen content to
  // render.

  var newCellCount = newRangeCount(prev, visible);

  while (true) {
    if (first <= overscanFirst && last >= overscanLast) {
      // If we fill the entire overscan range, we're done.
      break;
    }

    var maxNewCells = newCellCount >= maxToRenderPerBatch;
    var firstWillAddMore = first <= prev.first || first > prev.last;
    var firstShouldIncrement = first > overscanFirst && (!maxNewCells || !firstWillAddMore);
    var lastWillAddMore = last >= prev.last || last < prev.first;
    var lastShouldIncrement = last < overscanLast && (!maxNewCells || !lastWillAddMore);

    if (maxNewCells && !firstShouldIncrement && !lastShouldIncrement) {
      // We only want to stop if we've hit maxNewCells AND we cannot increment first or last
      // without rendering new items. This let's us preserve as many already rendered items as
      // possible, reducing render churn and keeping the rendered overscan range as large as
      // possible.
      break;
    }

    if (firstShouldIncrement && !(fillPreference === 'after' && lastShouldIncrement && lastWillAddMore)) {
      if (firstWillAddMore) {
        newCellCount++;
      }

      first--;
    }

    if (lastShouldIncrement && !(fillPreference === 'before' && firstShouldIncrement && firstWillAddMore)) {
      if (lastWillAddMore) {
        newCellCount++;
      }

      last++;
    }
  }

  if (!(last >= first && first >= 0 && last < itemCount && first >= overscanFirst && last <= overscanLast && first <= visible.first && last >= visible.last)) {
    throw new Error('Bad window calculation ' + JSON.stringify({
      first: first,
      last: last,
      itemCount: itemCount,
      overscanFirst: overscanFirst,
      overscanLast: overscanLast,
      visible: visible
    }));
  }

  return {
    first: first,
    last: last
  };
}

var VirtualizeUtils = {
  computeWindowedRenderLimits: computeWindowedRenderLimits,
  elementsThatOverlapOffsets: elementsThatOverlapOffsets,
  newRangeCount: newRangeCount
};
var _default = VirtualizeUtils;
exports.default = _default;