Mapping touch points to rings on stage.

Touch mapping

/**
  * Map the ring nearest to touch point
  * @param {number} id      touch point id
  * @param {number} x       touch point x
  * @param {number} y       touch point y
  */

function mapNearestRing(id, x, y) {
	var minDistance = 1000000;
	var nearestRing = null;
	var SNAPPING_DISTANCE = 70;

	for (var i = 0, numRings = rings.length; i < numRings; i++) {
		var ring = rings[i];
 		var dx = x - ring.x;
 		var dy = y - ring.y;
 		var distance = Math.sqrt(dx * dx + dy * dy);

 		if (distance < minDistance) {
 			minDistance = distance;

 			if (distance <= SNAPPING_DISTANCE) {
 				nearestRing = ring;
 			}
		}
	}
	
	if (nearestRing != null) {
		return nearestRing;
	}
}