vscroll/dist/esm2015/processes/preClip.js

Virtual scroll engine

import { BaseProcessFactory, CommonProcess, ProcessStatus } from './misc/index';
import { Direction } from '../inputs/index';
export default class PreClip extends BaseProcessFactory(CommonProcess.preClip) {
  static run(scroller) {
    PreClip.prepareClip(scroller);
    scroller.workflow.call({
      process: PreClip.process,
      status: ProcessStatus.next,
      payload: {
        doClip: scroller.state.clip.doClip
      }
    });
  }
  static prepareClip(scroller) {
    const { fetch, clip } = scroller.state;
    if (PreClip.shouldNotClip(scroller)) {
      return;
    }
    const firstIndex = fetch.first.indexBuffer;
    const lastIndex = fetch.last.indexBuffer;
    scroller.logger.log(() => `looking for ${fetch.direction ? 'anti-' + fetch.direction + ' ' : ''}items ` +
      `that are out of [${firstIndex}..${lastIndex}] range`);
    if (PreClip.isBackward(scroller, firstIndex)) {
      PreClip.prepareClipByDirection(scroller, Direction.backward, firstIndex);
    }
    if (PreClip.isForward(scroller, lastIndex)) {
      PreClip.prepareClipByDirection(scroller, Direction.forward, lastIndex);
    }
    if (!clip.doClip) {
      scroller.logger.log('skipping clip [no items to clip]');
    }
    return;
  }
  static shouldNotClip(scroller) {
    const { settings, buffer, state } = scroller;
    if (settings.infinite && !state.clip.force) {
      scroller.logger.log('skipping clip [infinite mode]');
      return true;
    }
    if (!buffer.size) {
      scroller.logger.log('skipping clip [empty buffer]');
      return true;
    }
    if (state.cycle.isInitial) {
      scroller.logger.log('skipping clip [initial cycle]');
      return true;
    }
    return false;
  }
  static isBackward(scroller, firstIndex) {
    const { buffer, state } = scroller;
    const { clip, fetch } = state;
    if (clip.force) {
      return clip.forceBackward;
    }
    if (fetch.direction !== Direction.backward) {
      if (firstIndex - 1 >= buffer.absMinIndex) {
        return true;
      }
    }
    return false;
  }
  static isForward(scroller, lastIndex) {
    const { buffer, state } = scroller;
    const { clip, fetch } = state;
    if (clip.force) {
      return clip.forceForward;
    }
    if (fetch.direction !== Direction.forward) {
      if (lastIndex + 1 <= buffer.absMaxIndex) {
        return true;
      }
    }
    return false;
  }
  static prepareClipByDirection(scroller, direction, edgeIndex) {
    const forward = direction === Direction.forward;
    scroller.buffer.items.forEach(item => {
      if ((!forward && item.$index < edgeIndex) || (forward && item.$index > edgeIndex)) {
        item.toRemove = true;
        item.removeDirection = direction;
        scroller.state.clip.doClip = true;
      }
    });
  }
}
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