{"ast":null,"code":"var _interopRequireDefault=require(\"@babel/runtime/helpers/interopRequireDefault\");Object.defineProperty(exports,\"__esModule\",{value:true});exports.computeWindowedRenderLimits=computeWindowedRenderLimits;exports.elementsThatOverlapOffsets=elementsThatOverlapOffsets;exports.newRangeCount=newRangeCount;exports.default=void 0;var _invariant=_interopRequireDefault(require(\"fbjs/lib/invariant\"));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;}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));}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;var visibleBegin=Math.max(0,offset);var visibleEnd=visibleBegin+visibleLength;var overscanLength=(windowSize-1)*visibleLength;var leadFactor=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){return{first:Math.max(0,itemCount-1-maxToRenderPerBatch),last:itemCount-1};}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};var newCellCount=newRangeCount(prev,visible);while(true){if(first<=overscanFirst&&last>=overscanLast){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){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 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* Copyright (c) 2015-present, Facebook, Inc.\n *\n * This source code is licensed under the MIT license found in the\n * LICENSE file in the root directory of this source tree.\n *\n * \n * @format\n */\nimport invariant from 'fbjs/lib/invariant';\n/**\n * Used to find the indices of the frames that overlap the given offsets. Useful for finding the\n * items that bound different windows of content, such as the visible area or the buffered overscan\n * area.\n */\n\nfunction elementsThatOverlapOffsets(offsets, itemCount, getFrameMetrics) {\n  var out = [];\n  var outLength = 0;\n\n  for (var ii = 0; ii < itemCount; ii++) {\n    var frame = getFrameMetrics(ii);\n    var trailingOffset = frame.offset + frame.length;\n\n    for (var kk = 0; kk < offsets.length; kk++) {\n      if (out[kk] == null && trailingOffset >= offsets[kk]) {\n        out[kk] = ii;\n        outLength++;\n\n        if (kk === offsets.length - 1) {\n          invariant(outLength === offsets.length, 'bad offsets input, should be in increasing order: %s', JSON.stringify(offsets));\n          return out;\n        }\n      }\n    }\n  }\n\n  return out;\n}\n/**\n * Computes the number of elements in the `next` range that are new compared to the `prev` range.\n * Handy for calculating how many new items will be rendered when the render window changes so we\n * can restrict the number of new items render at once so that content can appear on the screen\n * faster.\n */\n\n\nfunction newRangeCount(prev, next) {\n  return next.last - next.first + 1 - Math.max(0, 1 + Math.min(next.last, prev.last) - Math.max(next.first, prev.first));\n}\n/**\n * Custom logic for determining which items should be rendered given the current frame and scroll\n * metrics, as well as the previous render state. The algorithm may evolve over time, but generally\n * prioritizes the visible area first, then expands that with overscan regions ahead and behind,\n * biased in the direction of scroll.\n */\n\n\nfunction computeWindowedRenderLimits(props, prev, getFrameMetricsApprox, scrollMetrics) {\n  var data = props.data,\n      getItemCount = props.getItemCount,\n      maxToRenderPerBatch = props.maxToRenderPerBatch,\n      windowSize = props.windowSize;\n  var itemCount = getItemCount(data);\n\n  if (itemCount === 0) {\n    return prev;\n  }\n\n  var offset = scrollMetrics.offset,\n      velocity = scrollMetrics.velocity,\n      visibleLength = scrollMetrics.visibleLength; // Start with visible area, then compute maximum overscan region by expanding from there, biased\n  // in the direction of scroll. 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Math.max(0, overscanFirst) : first;\n  overscanLast = overscanLast == null ? itemCount - 1 : overscanLast;\n  last = last == null ? Math.min(overscanLast, first + maxToRenderPerBatch - 1) : last;\n  var visible = {\n    first: first,\n    last: last\n  }; // We want to limit the number of new cells we're rendering per batch so that we can fill the\n  // content on the screen quickly. If we rendered the entire overscan window at once, the user\n  // could be staring at white space for a long time waiting for a bunch of offscreen content to\n  // render.\n\n  var newCellCount = newRangeCount(prev, visible);\n\n  while (true) {\n    if (first <= overscanFirst && last >= overscanLast) {\n      // If we fill the entire overscan range, we're done.\n      break;\n    }\n\n    var maxNewCells = newCellCount >= maxToRenderPerBatch;\n    var firstWillAddMore = first <= prev.first || first > prev.last;\n    var firstShouldIncrement = first > overscanFirst && (!maxNewCells || !firstWillAddMore);\n    var lastWillAddMore = last >= prev.last || last < prev.first;\n    var lastShouldIncrement = last < overscanLast && (!maxNewCells || !lastWillAddMore);\n\n    if (maxNewCells && !firstShouldIncrement && !lastShouldIncrement) {\n      // We only want to stop if we've hit maxNewCells AND we cannot increment first or last\n      // without rendering new items. This let's us preserve as many already rendered items as\n      // possible, reducing render churn and keeping the rendered overscan range as large as\n      // possible.\n      break;\n    }\n\n    if (firstShouldIncrement && !(fillPreference === 'after' && lastShouldIncrement && lastWillAddMore)) {\n      if (firstWillAddMore) {\n        newCellCount++;\n      }\n\n      first--;\n    }\n\n    if (lastShouldIncrement && !(fillPreference === 'before' && firstShouldIncrement && firstWillAddMore)) {\n      if (lastWillAddMore) {\n        newCellCount++;\n      }\n\n      last++;\n    }\n  }\n\n  if (!(last >= first && first >= 0 && last < itemCount && first >= overscanFirst && last <= overscanLast && first <= visible.first && last >= visible.last)) {\n    throw new Error('Bad window calculation ' + JSON.stringify({\n      first: first,\n      last: last,\n      itemCount: itemCount,\n      overscanFirst: overscanFirst,\n      overscanLast: overscanLast,\n      visible: visible\n    }));\n  }\n\n  return {\n    first: first,\n    last: last\n  };\n}\n\nexport { computeWindowedRenderLimits, elementsThatOverlapOffsets, newRangeCount };\nvar VirtualizeUtils = {\n  computeWindowedRenderLimits: computeWindowedRenderLimits,\n  elementsThatOverlapOffsets: elementsThatOverlapOffsets,\n  newRangeCount: newRangeCount\n};\nexport default VirtualizeUtils;"]},"metadata":{},"sourceType":"script"}