ResponderTouchHistoryStore.js — react Source File

Source Code

/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

import {isStartish, isMoveish, isEndish} from './ResponderTopLevelEventTypes';

/**
 * Tracks the position and time of each active touch by `touch.identifier`. We
 * should typically only see IDs in the range of 1-20 because IDs get recycled
 * when touches end and start again.
 */
type TouchRecord = {
  touchActive: boolean,
  startPageX: number,
  startPageY: number,
  startTimeStamp: number,
  currentPageX: number,
  currentPageY: number,
  currentTimeStamp: number,
  previousPageX: number,
  previousPageY: number,
  previousTimeStamp: number,
};

const MAX_TOUCH_BANK = 20;
const touchBank: Array<TouchRecord> = [];
const touchHistory = {
  touchBank,
  numberActiveTouches: 0,
  // If there is only one active touch, we remember its location. This prevents
  // us having to loop through all of the touches all the time in the most
  // common case.
  indexOfSingleActiveTouch: -1,
  mostRecentTimeStamp: 0,
};

type Touch = {
  identifier: ?number,
  pageX: number,
  pageY: number,
  timestamp: number,
  ...
};
type TouchEvent = {
  changedTouches: Array<Touch>,
  touches: Array<Touch>,
  ...
};

function timestampForTouch(touch: Touch): number {
  // The legacy internal implementation provides "timeStamp", which has been
  // renamed to "timestamp". Let both work for now while we iron it out
  // TODO (evv): rename timeStamp to timestamp in internal code
  return (touch: any).timeStamp || touch.timestamp;
}
// ... (178 more lines)