Gesture detection: Implementing Swipe, Pinch/Stretch and Rotate gestures

gistfile1.js

// Define constant values
var MIN_ROTATION = 20;
var MIN_SCALE = .3;
var MIN_SWIPE_DISTANCE = 50;

// Define variables 
var rotation, scale, recognized, translationX, translationY;

/**
 *  Reset gesture 
 */
function resetGesture(event) {
  rotation = 0;
  scale = 1;
  translationX = translationY = 0;
  recognized = false;
}

/**
 *  Detect gesture
 */
function detectGesture(event) {
  // Disable built-in inertia
  if (event.detail == event.MSGESTURE_FLAG_INERTIA) {
    return;
  }

  // Update total values
  rotation += event.rotation * 180 / Math.PI;
  scale *= event.scale;
  translationX += event.translationX;
  translationY += event.translationY;

  // Try to detect a gesture when not recognized
  if (!recognized) {

    // Gesture direction
    var direction;

    // Check for horizontal swipe
    if (Math.abs(translationX) > MIN_SWIPE_DISTANCE) {
      recognized = true;
      // Check direction
      direction = translationX < 0 ? 'left' : 'right';
      console.log('Horizontal swipe: ', direction);
    // Check for vertical swipe
    } else if (Math.abs(translationY) > MIN_SWIPE_DISTANCE) {
      recognized = true;
      // Check direction
      direction = translationY < 0 ? 'up' : 'down'
      console.log('Vertical swipe: ', direction);
    }

    // Check for rotation
    if (Math.abs(rotation) >= MIN_ROTATION) {
      recognized = true;
      console.log('Rotate: ', rotation < 0 ? 'left' : 'right');
    // Check for Pinch/Stretch
    } else if (Math.abs(scale - 1) > MIN_SCALE) {
      recognized = true;
      console.log('Scale: ', scale > 1 ? 'stretch' : 'pinch');
    }
  }
}