l7hammerjs/src/recognizers/pinch.js

A javascript library for multi-touch gestures

import AttrRecognizer from './attribute';
import { TOUCH_ACTION_NONE } from '../touchactionjs/touchaction-Consts';
import { STATE_BEGAN } from '../recognizerjs/recognizer-consts';

/**
 * @private
 * Pinch
 * Recognized when two or more pointers are moving toward (zoom-in) or away from each other (zoom-out).
 * @constructor
 * @extends AttrRecognizer
 */
export default class PinchRecognizer extends AttrRecognizer {
  constructor() {
    super(...arguments);
  }

  getTouchAction() {
    return [TOUCH_ACTION_NONE];
  }

  attrTest(input) {
    return super.attrTest(input) &&
        (Math.abs(input.scale - 1) > this.options.threshold || this.state & STATE_BEGAN);
  }

  emit(input) {
    if (input.scale !== 1) {
      let inOut = input.scale < 1 ? 'in' : 'out';
      input.additionalEvent = this.options.event + inOut;
    }
    super.emit(input);
  }
}

PinchRecognizer.prototype.defaults = {
  event: 'pinch',
  threshold: 0,
  pointers: 2
};